TWI626821B - Flyback power converter circuit with active clamping and zero voltage switching and conversion control circuit thereof - Google Patents

Abstract

A flyback power conversion circuit includes: a transformer including a primary-side winding coupled to an input power source, and a secondary-side winding coupled to an output node, wherein the input power source includes an input voltage A primary switch coupled to the primary winding to switch the input power so that the secondary winding generates an output power at the output node, where the output power includes an output voltage; a clamp The circuit includes: an auxiliary switch and an auxiliary capacitor connected in series with the auxiliary switch to form an auxiliary branch, and the auxiliary branch is connected in parallel with the primary winding; and a conversion control circuit, according to a current-related signal, the At least one of the input voltage and the output voltage adjusts the on-time of the auxiliary switch so that the primary-side switch is switched to zero voltage when it is on.

Description

Flyback power conversion circuit with active clamping and zero voltage switching and conversion control circuit therein

The invention relates to a flyback power conversion circuit, in particular to a flyback power conversion circuit with active clamping and zero voltage switching. The present invention also relates to a switching control circuit used in a flyback type.

FIG. 1 illustrates a prior art flyback power conversion circuit with active clamping (flyback power conversion circuit 1). The flyback power conversion circuit 1 is used to convert an input voltage into an output. The voltage, which includes an auxiliary switch S2 and an auxiliary capacitor Cr, forms an active clamping branch, which is turned on when the primary switch S1 is not conducting, so that the leakage inductance Lr and the excitation inductance Lm of the primary winding The energy stored when the primary switch S1 is turned on can be discharged through this branch and stored in the auxiliary capacitor Cr. In addition, before the primary switch S1 is turned on, the energy stored in the auxiliary capacitor Cr can be discharged. To discharge the parasitic capacitance Coss of the primary switch S1, so that the primary switch S1 is turned on for Zero Voltage Switching (ZVS). In the prior art, the switching of the primary switch S1 and the auxiliary switch S2 is substantially mutual. Is inverted.

The disadvantage of the prior art shown in FIG. 1 is that, because the switching of the primary switch S1 and the auxiliary switch S2 is substantially opposite to each other, the on-time of the auxiliary switch S2 may be too long, resulting in a large surround current. (circulation current), further causing power loss.

FIG. 2 shows a waveform diagram of another type of prior art flyback power conversion circuit with active clamping. This prior art is similar to the prior art shown in FIG. 1 except that the difference is in the auxiliary switch S2. The on-time TON2 is a fixed on-time.

The disadvantage of the prior art shown in FIG. 2 is that, since the on-time TON2 of the auxiliary switch S2 is a fixed on-time, the on-time TON2 of the auxiliary switch S2 may be insufficient in applications such as a high input voltage VI. The charge in the parasitic capacitance Coss of the primary-side switch S1 is completely discharged, so that the primary-side switch S1 cannot achieve zero-voltage switching, which further causes power loss.

Compared with the prior art of FIGS. 1 and 2, the present invention can adjust the on-time TON2 of the auxiliary switch S2 to ensure that the primary switch S1 can achieve zero voltage switching, thereby reducing power loss and improving power conversion efficiency.

According to one aspect, the present invention provides a flyback power conversion circuit, including: a transformer including a primary winding, coupled to an input power source, and a secondary winding, coupled to an output Node, where the input power includes an input voltage and an input current; a primary-side switch is coupled to the primary-side winding to switch the primary-side winding to convert the input power, so that the secondary-side winding is The output node generates an output power source, where the output power source includes an output voltage and an output current; a clamp circuit includes: an auxiliary switch and an auxiliary capacitor, which are connected in series with the auxiliary switch to form an auxiliary branch, and Keisuke The auxiliary branch is connected in parallel with the primary winding; and a conversion control circuit for generating a primary switch control signal and an auxiliary switch control signal for controlling the primary switch and the auxiliary switch, respectively, and converting the input Power to generate the output power, wherein the auxiliary switch and the primary-side switch are non-complementary switching; the conversion control circuit includes: an auxiliary switch control circuit for adjusting the on-time of the auxiliary switch according to at least one of the following: The current-related signal, the input voltage, and the output voltage make the voltage difference between a current input terminal and a current output terminal of the primary-side switch to be substantially zero when the primary-side switch is turned on, thereby achieving zero-voltage switching; wherein the current-related signal is related to At least one of the following: the output current, the on-current of the primary-side switch, and the current of the primary-side winding; and a signal-sensing circuit for sensing the current-related signal, the input voltage, or the output voltage .

In a preferred embodiment, the on-time of the auxiliary switch increases with at least one of the following: the current-related signal represents a decrease in the peak current of one of the primary switches, an increase in the input voltage, and an increase in the output voltage, so that Turning on a magnetizing current of a magnetizing inductor of the primary winding and discharging a parasitic capacitor of the primary switch makes the primary voltage switch to zero voltage switching.

In a preferred embodiment, the auxiliary switch control circuit includes: a threshold value generating circuit for generating a voltage threshold value according to a difference between a reference voltage and the current-related signal; a ramp signal generating circuit for generating a voltage signal according to a A reference current and the auxiliary switch control signal to generate a ramp signal; a comparison circuit that compares the ramp signal with the voltage threshold to generate a comparison result; and a logic circuit based on the comparison result and an auxiliary switch activation signal and The auxiliary switch control signal is generated to control the auxiliary switch, so that the on-time of the auxiliary switch increases as the current-related signal represents a decrease in the peak current of the primary-side switch; The switching control circuit generates the auxiliary switch activation signal according to a preset clock signal or a feedback signal.

In a preferred embodiment, the conversion control circuit further includes a mode operation circuit for controlling the primary-side switch according to at least one of the input voltage, the output voltage, the input current, and the output current. The switching frequency enables the flyback power conversion circuit to operate in a discontinuous conduction mode (DCM) or a quasi-resonant mode (QRM).

In a preferred embodiment, the conversion control circuit further includes a mode operation circuit that determines a switching frequency of the primary-side switch according to the input voltage, the input current, the output voltage, or the output current, and the The switching frequency has an upper limit frequency and a lower limit frequency.

In a preferred embodiment, the auxiliary switch control circuit triggers the auxiliary switch to turn on according to an auxiliary switch start signal; wherein the conversion control circuit generates the auxiliary switch according to a preset clock signal or a feedback signal. A start signal; wherein the switching control circuit further includes a sequence circuit for triggering the primary switch to be turned on after the auxiliary switch becomes non-conducting and after an auxiliary dead time according to a signal related to the auxiliary switch; The switch related signal is the auxiliary switch control signal or its related signal.

In a preferred embodiment, the sequence circuit includes: a dead time control circuit for generating a dead time control signal according to the auxiliary switch related signal to determine the auxiliary dead time, so that the primary switch and the auxiliary The switches are non-conducting during the auxiliary dead time; a primary-side switch timing control circuit is used to generate the primary-side switch control signal according to the dead-time control signal and a primary-side switch time control signal, where the The dead time control signal triggers the primary switch control signal to turn the primary switch on, and the primary switch time control signal triggers the primary switch control signal to turn the primary switch to non-conductive And a primary switch time control circuit for generating the primary switch control signal according to the dead time control signal to determine the on time of the primary switch.

In a preferred embodiment, the sequence circuit includes: a first timing control circuit for generating the auxiliary switch control signal according to the auxiliary switch start signal and a first time control signal, wherein the auxiliary switch start signal Triggering the auxiliary switch control signal to turn the auxiliary switch on, and the first time control signal triggering the auxiliary switch control signal to turn the auxiliary switch to non-conducting; a first time control circuit for starting according to the auxiliary switch Generating a first time control signal to determine the on-time of the auxiliary switch; a second time control circuit for generating a second time control signal to determine the auxiliary dead time according to the first time control signal So that both the primary switch and the auxiliary switch are non-conducting during the auxiliary dead time; a second timing control circuit is used to generate the primary switch control according to the second time control signal and a third time control signal Signal, wherein the second time control signal triggers the primary switch control signal to turn the primary switch into And the third time control signal triggers the primary side switch control signal to make the primary side switch non-conducting; a third time control circuit for generating the third time control signal according to the second time control signal To determine the on-time of the primary switch.

In a preferred embodiment, the on-time of the primary-side switch is controlled by a primary-side feedback path or a secondary-side feedback path.

In another aspect, the present invention also provides a conversion control circuit for controlling a flyback power conversion circuit. The flyback power conversion circuit includes: a transformer including a primary winding, coupled to An input power source and a secondary winding are coupled to an output node, where the input power source includes an input voltage and an input current; a primary-side switch is coupled to the primary-side winding to switch the primary Side winding to convert the input power and make the The secondary winding generates an output power at the output node, wherein the output power includes an output voltage and an output current; a clamping circuit includes: an auxiliary switch, and an auxiliary capacitor in series with the auxiliary switch to form an An auxiliary branch, and the auxiliary branch is connected in parallel with the primary winding; the conversion control circuit is used to generate a primary switch control signal and an auxiliary switch control signal, which are respectively used to control the primary switch and the auxiliary switch, The input power is converted to generate the output power, wherein the auxiliary switch and the primary-side switch are non-complementary switching; the conversion control circuit includes: an auxiliary switch control circuit for adjusting the auxiliary switch according to at least one of the following On-time: a current-related signal, the input voltage and the output voltage such that when the primary switch is turned on, the voltage difference between a current input terminal and a current output terminal is substantially equal to zero voltage switching; where the current The relevant signal is related to at least one of the following: the output current, the conduction of the primary switch , And the primary winding current; and a signal sensing circuit for sensing the current signal related to the input voltage or the output voltage.

According to another aspect, the present invention also provides a flyback power conversion circuit, including: a transformer including a primary-side winding, coupled to an input power source, and a secondary-side winding, coupled to a An output node, where the input power includes an input voltage and an input current; a primary-side switch is coupled to the primary-side winding to switch the primary-side winding to convert the input power, so that the secondary-side winding An output power is generated at the output node, wherein the output power includes an output voltage and an output current; a clamp circuit includes: an auxiliary switch and an auxiliary capacitor, which are connected in series with the auxiliary switch to form an auxiliary branch, And the auxiliary branch is connected in parallel with the primary winding; and a conversion control circuit for generating a primary switch control signal and an auxiliary switch control signal according to a feedback signal for controlling the primary switch and The auxiliary switch to convert the input power to generate the output power; wherein the conversion control circuit includes: a sequence circuit for A trigger signal to start the auxiliary switch guide The auxiliary switch is turned on, and the primary switch is triggered to be turned on after the auxiliary switch becomes non-conducting and after an auxiliary dead time, so that when the primary switch is turned on, the voltage difference between a current input terminal and a current output terminal It is approximately 0, and achieves zero voltage switching. The switching control circuit generates the auxiliary switch activation signal according to a preset clock signal or the feedback signal.

In a preferred embodiment, the sequence circuit includes: a first timing control circuit for generating the auxiliary switch control signal according to the auxiliary switch start signal and a first time control signal, wherein the auxiliary switch start signal Triggering the auxiliary switch control signal to turn the auxiliary switch on, and the first time control signal triggering the auxiliary switch control signal to turn the auxiliary switch to non-conducting; a first time control circuit for starting according to the auxiliary switch Generating a first time control signal to determine the on-time of the auxiliary switch; a second time control circuit for generating a second time control signal to determine the auxiliary dead time according to the first time control signal So that both the primary switch and the auxiliary switch are non-conducting during the auxiliary dead time; a second timing control circuit is used to generate the primary switch control according to the second time control signal and a third time control signal Signal, wherein the second time control signal triggers the primary switch control signal to turn the primary switch into And the third time control signal triggers the primary side switch control signal to make the primary side switch non-conducting; a third time control circuit for generating the third time control signal according to the second time control signal To determine the on-time of the primary switch.

Detailed descriptions will be provided below through specific embodiments to make it easier to understand the purpose, technical content, features and effects of the present invention.

1,3‧‧‧Flyback power conversion circuit

10‧‧‧Transformer

20‧‧‧Clamp circuit

30‧‧‧ Conversion control circuit

31‧‧‧Auxiliary switch control circuit

311‧‧‧threshold value generating circuit

312‧‧‧Slope signal generating circuit

313‧‧‧Logic Circuit

50‧‧‧Signal sensing circuit

Coss‧‧‧parasitic capacitance

CI‧‧‧Integral Capacitor

CP‧‧‧ comparison circuit

CPO‧‧‧ Comparison Results

Cr‧‧‧ auxiliary capacitor

FB‧‧‧ feedback signal

IIN‧‧‧Input current

Im‧‧‧Excitation current

IOUT‧‧‧Output current

Ipk‧‧‧Primary winding peak current

IP‧‧‧Primary winding current

ISEN‧‧‧Current related signals

Lr‧‧‧Leakage

Lm‧‧‧ Excitation Inductance

n‧‧‧winding ratio

OUT‧‧‧output node

S1‧‧‧Primary side switch

S1C‧‧‧Primary switch control signal

S2‧‧‧Auxiliary switch

S2C‧‧‧Auxiliary switch control signal

S2CR‧‧‧Auxiliary switch related signals

S2S‧‧‧ auxiliary switch start signal

SWI‧‧‧Integration Switch

TD‧‧‧Auxiliary idle time

TON1‧‧‧on time

TON2‧‧‧on time

VI‧‧‧Input voltage

VO‧‧‧Output voltage

VS‧‧‧Slope signal

VTH‧‧‧Voltage Threshold

W1‧‧‧ primary winding

W2‧‧‧Secondary winding

Figure 1 shows a schematic diagram of a prior art flyback power conversion circuit with active clamping.

Figure 2 shows a waveform diagram of a prior art flyback power conversion circuit with active clamping.

FIG. 3 is a schematic diagram of an embodiment of a flyback power conversion circuit with active clamping and zero voltage switching according to the present invention.

FIG. 4A is a schematic diagram of a specific embodiment of a conversion control circuit in the flyback power conversion circuit with active clamping and zero voltage switching according to the present invention.

FIG. 4B is a schematic diagram of a specific embodiment of an auxiliary switch control circuit in the flyback power conversion circuit with active clamping and zero voltage switching according to the present invention.

FIG. 4C is a schematic diagram of a specific embodiment of an auxiliary switch control circuit in the flyback power conversion circuit with active clamping and zero voltage switching according to the present invention.

FIG. 4D shows a waveform diagram corresponding to the embodiment of FIG. 4C.

FIG. 5A is a schematic diagram of a specific embodiment of a conversion control circuit in a flyback power conversion circuit with active clamping and zero voltage switching according to the present invention.

FIG. 5B is a schematic diagram of a specific embodiment of the conversion control circuit in the flyback power conversion circuit with active clamping and zero voltage switching according to the present invention.

FIG. 5C is a schematic diagram of a specific embodiment of a sequence circuit in the flyback power conversion circuit with active clamping and zero voltage switching according to the present invention.

FIG. 5D is a schematic diagram of a specific embodiment of a conversion control circuit in the flyback power conversion circuit with active clamping and zero voltage switching according to the present invention.

FIG. 5E is a schematic diagram of a specific embodiment of a sequence circuit in the flyback power conversion circuit with active clamping and zero voltage switching according to the present invention.

Fig. 6A shows a schematic diagram of operation modes corresponding to Figs. 5A and 5B.

Fig. 6B shows the operation mode diagram corresponding to Figs. 5A and 5B.

Fig. 6C shows the operation waveform diagram of the flyback power conversion circuit corresponding to Figs. 5A-5C.

The drawings in the present invention are schematic, and are mainly intended to represent the coupling relationship between various circuits and the relationship between signal waveforms. As for the circuits, signal waveforms and frequencies, they are not drawn to scale.

Please refer to FIG. 3, which shows an embodiment of the flyback power conversion circuit with active clamping and zero voltage switching according to the present invention (flyback power conversion circuit 3). The flyback power conversion circuit 3 includes The transformer 10, the primary-side switch S1, the clamp circuit 20, and the switching control circuit 30. The transformer 10 includes a primary-side winding W1 coupled to an input power source, and a secondary-side winding W2 coupled to an output node OUT. The input power source includes an input voltage VI and an input current IIN. The primary-side switch S1 is coupled to the primary-side winding W1 to switch the primary-side winding W1 to convert the input power, and the secondary-side winding W2 generates an output power at the output node OUT to supply the load 40. The output power includes The output voltage VO and an output current IOUT.

Please continue to refer to FIG. 3, the clamp circuit 20 includes an auxiliary switch S2 and an auxiliary capacitor Cr, which are connected in series with the auxiliary switch S2 to form an auxiliary branch. As shown in the figure, the auxiliary branch is connected in parallel with the primary winding W1. The conversion control circuit 30 is configured to generate a primary-side switch control signal S1C and an auxiliary switch control signal S2C according to a feedback signal FB, and is used to control the primary-side switch S1 and the auxiliary switch S2, respectively, and convert input power to generate output power. Among them, the auxiliary switch S2 is turned on for a period of time when the primary switch S1 is not turned on, so that the leakage inductance Lr of the primary winding W1 and The energy stored in the excitation inductance Lm when the primary switch S1 is turned on can be discharged through the auxiliary branch and stored in the auxiliary capacitor Cr. In addition, before the primary switch S1 is turned on, it can be stored in the auxiliary The energy in the capacitor Cr discharges the parasitic capacitance Coss of the primary-side switch S1, so that when the primary-side switch S1 is turned on, it is switched to zero voltage.

According to the present invention, the switching control circuit 30 adjusts the on-time TON2 of the auxiliary switch S2 according to at least one of the following: a current-related signal ISEN, an input voltage VI, and an output voltage VO, so that when the primary switch S1 is turned on, its current input terminal The voltage difference between PHASE and the current output terminal (coupled to a current sensing resistor RCS in this embodiment, or to the primary ground point in other embodiments) (VDS1 in the figure) is approximately 0. Zero voltage switching is achieved; the current-related signal ISEN is related to at least one of the following: the output current IOUT, the on-current IDS1 of the primary switch, and the current IP of the primary winding W1. In one embodiment, the current The relevant signal ISEN can be obtained by sensing the VDS1 of the primary switch S1, the on-current IDS1 of the primary switch S1, or the cross-voltage VCS of the current sensing resistor RCS.

It should be noted that the aforementioned feedback signal FB may be related to, for example, the output voltage VO or the output current IOUT, that is, the feedback signal FB is generated through a secondary-side feedback path. In one embodiment, the feedback signal FB may be borrowed. A feedback sensing circuit 50 converts the output voltage VO or the output current IOUT to generate a feedback signal FB. In an embodiment, the feedback signal FB may be related to the primary winding current IP or the primary-side voltage (eg, VDS1), that is, the feedback signal FB is generated through a primary-side feedback path, and thereby, Determine the on-time TON1 of the primary switch S1.

It should be noted that in the Discontinuous Conduction Mode (DCM) or Quasi Resonant Mode (QRM), if the primary switch S1 is to achieve zero voltage switching, it is stored in the leakage of the primary winding. The energy of the inductance Lr (leakage inductance) and the magnetizing inductance Lm (magnetizing inductance) and the charge energy stored by the parasitic capacitance Coss must meet the following inequality:

among them

Substitute Eq.1 into Eq.2 and solve it:

Among them, Ipk refers to the peak current of the primary winding current IP, Im refers to the magnetizing current of the magnetizing inductance Lm, and n refers to the winding ratio of the primary winding W1 to the secondary winding W2.

For example, when the input voltage VI is large, the energy of the leakage inductance Lr of the primary winding stored in the auxiliary capacitor Cr may not be enough for the parasitic capacitance Coss of the primary switch S1 to be completely before the primary switch S1 is turned on. Discharge. In this case, the primary switch S1 cannot achieve zero voltage switching. Therefore, the energy of the excitation inductance Lm stored in the primary winding can be adjusted by the on-time TON2 of the auxiliary switch S2 to enable the clamping circuit. 20 can completely discharge the parasitic capacitance Coss of the primary switch S1, so that the primary switch S1 can achieve zero voltage switching. According to the present invention, the on-time TON2 of the auxiliary switch S2 can be increased with at least one of the following: when the current-related signal ISEN represents the peak current Ipk of the primary-side switch S1 decreases, or when the input voltage VI increases, or when the output When the voltage VO increases, it can be known from the above equation (Eq.1-3) that by controlling the on time TON2 of the auxiliary switch S2, the exciting current Im of the magnetizing inductance Lm (magnetizing inductance) of the primary winding W1 can be conducted, and the The parasitic capacitor Coss of the primary-side switch S1 is discharged, so that when the primary-side switch S1 is turned on, it is switched to zero voltage.

In addition, it should be noted that since the excitation current Im of the excitation inductance Lm of the primary winding W1 is adjusted by adjusting the on-time TON2 as described above, it has a significant effect under DCM or QRM. Therefore, in an embodiment In the conversion control circuit 30, the switching frequency of the primary switch S1 can be controlled according to at least one of the input voltage VI, the output voltage VO, the input current IIN, and the output current IOUT, so that the flyback power conversion circuit operates in DCM or QRM. Then, the above-mentioned zero voltage switching is achieved.

Please refer to FIG. 4A, which shows a specific embodiment of the conversion control circuit (the conversion control circuit 30) in the flyback power conversion circuit of the present invention. The conversion control circuit 30 includes an auxiliary switch control circuit 31 and a signal sensing circuit. 33. The signal sensing circuit 33 is used to sense at least one of the current-related signal ISEN, the input voltage VI and the output voltage VO, and the auxiliary switch control circuit 31 is used to generate the auxiliary switch control according to the output of the signal sensing circuit 33 The signal S2C adjusts the on-time TON2 of the auxiliary switch S2 so that the primary-side switch S1 is switched to zero voltage when it is on.

Please refer to FIG. 4B, which shows a specific embodiment of the auxiliary switch control circuit (auxiliary switch control circuit 31) in the flyback power conversion circuit of the present invention. The auxiliary switch control circuit 31 includes a threshold value generating circuit 311 and a ramp signal. The generating circuit 312, the comparison circuit CP, and the logic circuit 313. The threshold value generating circuit 311 is configured to generate a voltage threshold value VTH according to a difference between a reference voltage VREF and a current-related signal ISEN. In one embodiment, the voltage threshold value VTH and the current-related signal ISEN are approximately inversely related; a ramp signal is generated The circuit 312 is used to generate a ramp signal VS according to a reference current IREF and the auxiliary switch control signal S2C; the comparison circuit CP compares the ramp signal VS with a voltage threshold VTH to generate a comparison result CPO; the logic circuit 313 is based on the comparison result CPO and An auxiliary switch starts the signal S2S to generate an auxiliary switch control signal S2C, which is used to control the auxiliary switch S2, so that the on-time TON2 of the auxiliary switch S2 follows the current-related signal ISEN indicates that the peak current of the primary switch S1 decreases and increases to achieve the zero-voltage switching of the primary switch S1.

In one embodiment, the conversion control circuit 30 may generate an auxiliary switch activation signal S2S according to a preset clock signal CK, and in one embodiment, the conversion control circuit 30 may generate a feedback signal FB and / or a current-related signal. ISEN generates the auxiliary switch start signal S2S. For example, when the flyback power conversion circuit operates at a fixed frequency, the preset clock signal CK can be generated by an internal oscillator, and when the flyback power conversion circuit operates at, for example, But it is not limited to pulse frequency modulation (PFM) and other control methods. The auxiliary switch start signal S2S can be generated according to the feedback signal FB.

FIG. 4C shows a specific embodiment of the auxiliary switch control circuit (auxiliary switch control circuit 31) in the flyback power conversion circuit of the present invention. The threshold value generation circuit 311 includes a transconductance amplifier circuit GM and a signal conversion resistor R1. The voltage threshold VTH is generated according to the difference between a reference voltage VREF and a current-related signal ISEN, where VTH = VREF-gm * R1 * ISEN, and gm is the transconductance of the transconductance amplifier circuit GM. The ramp signal generating circuit 312 generates a ramp signal VS according to a reference current IREF and an auxiliary switch control signal S2C to control an integrating capacitor CI and an integrating switch SWI, and determines the conduction of the auxiliary switch S2 by comparing the ramp signal VS with a voltage threshold VTH. The length of time TON2. Please also refer to FIG. 4D, which is a waveform diagram corresponding to the embodiment of FIG. 4C. In this embodiment, the voltage threshold VTH and the current-related signal ISEN have an inverse relationship, so that the on-time TON2 of the auxiliary switch S2 follows The current-related signal ISEN indicates that the peak current of the primary-side switch S1 decreases and increases (or vice versa) to achieve the zero-current switching of the aforementioned primary-side switch S1.

Please refer to FIG. 5A, which shows a specific embodiment of the conversion control circuit (conversion control circuit 30) in the flyback power conversion circuit of the present invention. In one embodiment, the auxiliary switch control circuit 30 may further include a Mode operation circuit 34, please refer to Figs. 6A and 6B at the same time. The mode operation circuit 34 is used according to the input voltage VI, input current IIN, output voltage VO, or output current IOUT (that is, corresponding to the output in Figures 6A and 6B or Input power) to determine the switching frequency of the primary switch S1 (such as, but not limited to, the operating frequency of the start signal S2S by controlling the auxiliary switch), and the switching frequency has an upper limit frequency Fmax and a lower limit frequency Fmin, making the invention The flyback power conversion circuit can operate in different operating modes such as, but not limited to, fixed frequency or non-constant frequency pulse width modulation (PWM), PFM, QRM, or burst mode (Burst Mode).

It should be noted that, as in the embodiment shown in FIG. 5A, the mode operation circuit 34 can also be used to control the switching of the primary switch S1 according to at least one of the input voltage VI, the output voltage VO, the input current IIN, and the output current IOUT. The frequency enables the flyback power conversion circuit to operate in the discontinuous conduction mode (DCM) or quasi-resonant mode QRM as described above, thereby achieving the aforementioned zero-voltage switching.

Please refer to FIG. 5B. In an embodiment, the conversion control circuit 30 may include a sequence circuit (sequence circuit 32) for triggering the auxiliary switch S2 to be turned on according to the auxiliary switch start signal S2S, and the auxiliary switch S2 is turned off. After being turned on, after an auxiliary dead time TD, the primary switch S1 is turned on.

In terms of a point of view, according to the present invention, the operation of the aforementioned sequential circuit enables the primary switch S1 to be turned on before the auxiliary switch S2 is turned on, and after the turn-on time TON2 of the auxiliary switch S2 is turned on, an auxiliary The dead time TD is to ensure zero voltage switching when the primary switch S1 is turned on.

Please refer to FIG. 5C, which shows a specific embodiment of the sequence circuit (sequence circuit 32) in the flyback power conversion circuit of the present invention. The sequence circuit 32 includes a first timing control circuit 321. The first timing control circuit 322, the second timing control circuit 323, the second timing control circuit 324, and the third timing control circuit 325; the first timing control circuit 321 (such as but not limited to the latch circuit as shown in the figure) is used The auxiliary switch control signal S2C is generated according to the auxiliary switch start signal S2S and the first time control signal S2T, where the auxiliary switch start signal S2S triggers the auxiliary switch control signal S2C to turn the auxiliary switch S2 on and the first time control signal S2T is triggered The auxiliary switch control signal S2C makes the auxiliary switch S2 non-conducting; the first time control circuit 322 is used to generate the first time control signal S2T according to the auxiliary switch start signal S2S to determine the on time TON2 of the auxiliary switch; the second time control The circuit 323 is configured to generate a second time control signal S2D according to the first time control signal S2T to determine the auxiliary dead time TD, so that the primary side The off S1 and the auxiliary switch S2 are not conductive during the auxiliary dead time TD; the second timing control circuit 324 (such as but not limited to the latch circuit as shown in the figure) is used to control the signal S2D and the third time according to the second time The control signal S1T generates the primary switch control signal S1C. The second time control signal S2D triggers the primary switch control signal S1C to turn the primary switch S1 on, and the third time control signal S1T triggers the primary switch control signal S1C. The primary-side switch S1 is turned off; the third time control circuit 325 is used to determine the on-time TON1 of the primary-side switch S1 according to the second time control signal S2D. In an embodiment, the third time control circuit 325 further generates a third time control signal S1T according to the feedback signal FB and / or the current-related signal ISEN. In an embodiment, the third time control circuit 325 determines the on-time TON1 of the primary switch S1 according to the feedback signal FB and / or the current-related signal ISEN.

Please refer to FIG. 5D. This embodiment is similar to the embodiment shown in FIG. 4A. The conversion control circuit 30 further includes a sequence circuit (sequence circuit 32). The sequence circuit 32 is used according to an auxiliary switch. The related signal S2CR is turned off after the auxiliary switch S2 is turned off and after a auxiliary dead time TD, the auxiliary switch related signal S2CR is the auxiliary switch control signal S2C or its related signal (for example but not It is limited to the comparison result CPO in the embodiment of FIG. 4B).

Please refer to FIG. 5E, which shows a specific embodiment of the sequence circuit corresponding to the embodiment of FIG. 5D. The sequence circuit 32 includes a dead time control circuit 323, a primary-side switching timing control circuit 324, and a primary-side switching time. Control circuit 325. The dead time control circuit 323 is used to generate a dead time control signal S2D according to the auxiliary switch related signal S2CR to determine the auxiliary dead time TD, so that the primary switch S1 and the auxiliary switch S2 are not conductive at the auxiliary dead time TD. ; The primary side switch timing control circuit 324 is used to generate the primary side switch control signal S1C according to the dead time control signal S2D and the primary side switch time control signal S1T. The dead time control signal S2D triggers the primary side switch control signal S1C to make one time. The side switch S1 is turned on, and the primary side switch time control signal S1T triggers the primary side switch control signal S1C to make the primary side switch S1 non-conductive. The primary-side switch time control circuit 325 is used to generate a primary-side switch control signal S1T according to the dead time control signal S2D to determine the on-time TON1 of the primary-side switch S1.

Please refer to Figure 6C, which shows the operation waveform diagram of the flyback power conversion circuit corresponding to Figures 5A-5E. As shown in the figure, the auxiliary switch start signal S2S triggers the auxiliary switch control signal S2C, which causes the auxiliary switch S2 to turn. Is turned on (time t1 in the figure), and the auxiliary switch S2 is turned off after the turn-on time TON2 (time t2 in the figure), and both the primary switch S1 and the auxiliary switch S2 are maintained non-conductive for a period of auxiliary dead time After TD, the primary-side switch control signal S1C is triggered, so that the primary-side switch S1 is turned on (time t3 in the figure). It should be noted that, in this embodiment, the auxiliary switch activation signal S2S is also as described above, and may be generated according to a preset clock signal CK, or a feedback signal FB and / or a current-related signal ISEN.

The present invention has been described above with reference to the preferred embodiments, but the above is only for making those skilled in the art easily understand the content of the present invention, and is not intended to limit the scope of rights of the present invention. The described embodiments are not limited to separate applications, and can be combined; for example, the "sequence circuit" can be combined with "auxiliary switch control circuit", "mode operation circuit", and "signal sensing circuit" In this case, the switching control circuit may include a logic control circuit for integrating the foregoing circuits to control the primary switch S1 or the auxiliary switch S2. In addition, in the same spirit of the present invention, those skilled in the art can think of various equivalent changes and various combinations. For example, the term "processing or calculation according to a signal or generating an output result" in the present invention is not limited to the signal itself, but also includes performing voltage-current conversion, current-voltage conversion, and / or the signal when necessary. Proportional conversion, etc., and then processed or calculated according to the converted signal to produce an output result. It can be seen that, under the same spirit of the present invention, those skilled in the art can think of various equivalent changes and various combinations, and there are many combinations, which are not listed here. Therefore, the scope of the invention should cover the above and all other equivalent variations.

Claims (19)

A flyback power conversion circuit includes: a transformer including a primary-side winding coupled to an input power source, and a secondary-side winding coupled to an output node, wherein the input power source includes an input voltage And an input current; a primary-side switch coupled to the primary-side winding for switching the primary-side winding to convert the input power, so that the secondary-side winding generates an output power at the output node, where the The output power includes an output voltage and an output current; a clamp circuit includes: an auxiliary switch and an auxiliary capacitor, which are connected in series with the auxiliary switch to form an auxiliary branch, and the auxiliary branch is connected in parallel with the primary winding And a conversion control circuit for generating a primary switch control signal and an auxiliary switch control signal for controlling the primary switch and the auxiliary switch, respectively, and converting the input power to generate the output power, wherein the The auxiliary switch and the primary-side switch are non-complementary switching; the conversion control circuit includes: an auxiliary switch control circuit for rooting Adjust the on-time of the auxiliary switch by at least one of the following: a current-related signal, the input voltage, and the output voltage such that when the primary switch is on, the voltage difference between a current input terminal and a current output terminal is approximately 0, to achieve zero voltage switching; wherein the current-related signal is related to at least one of the following: the output current, the on-current of the primary switch, and the current of the primary winding; and a signal sensing circuit for sensing Measure the current-related signal, the input voltage, or the output voltage. The flyback power conversion circuit according to item 1 of the scope of patent application, wherein the on-time of the auxiliary switch increases with at least one of the following: the current-related signal represents a decrease in the peak current of one of the primary switches, and the input When the voltage is increased and the output voltage is increased, a parasitic capacitor of the primary switch is discharged by conducting a magnetizing current of a magnetizing inductor of the primary winding, so that the primary switch is turned on. Zero voltage switching. The flyback power conversion circuit according to item 1 of the scope of patent application, wherein the auxiliary switch control circuit includes: a threshold value generating circuit for generating a voltage threshold value according to a difference between a reference voltage and the current-related signal; A ramp signal generating circuit for generating a ramp signal according to a reference current and the auxiliary switch control signal; a comparison circuit for generating a comparison result by comparing the ramp signal with the voltage threshold; and a logic circuit according to The comparison result and an auxiliary switch start signal generate the auxiliary switch control signal to control the auxiliary switch, so that the on-time of the auxiliary switch increases as the current-related signal represents a decrease in the peak current of the primary switch; where The conversion control circuit generates the auxiliary switch activation signal according to a preset clock signal or a feedback signal. The flyback power conversion circuit according to item 1 of the scope of the patent application, wherein the conversion control circuit further includes a mode operation circuit for controlling the input voltage, the output voltage, the input current, and the output current. At least one of them controls the switching frequency of the primary-side switch, so that the flyback power conversion circuit operates in a discontinuous conduction mode (DCM) or a quasi-resonant mode (QRM). The flyback power conversion circuit according to item 1 of the scope of patent application, wherein the conversion control circuit circuit further includes a mode operation circuit, which is determined according to the input voltage, the input current, the output voltage, or the output current. One of the primary switches has a switching frequency, and the switching frequency has an upper limit frequency and a lower limit frequency. The flyback power conversion circuit according to item 1 of the patent application scope, wherein the auxiliary switch control circuit triggers the auxiliary switch to turn on according to an auxiliary switch start signal; wherein the conversion control circuit is based on a preset clock signal Or a feedback signal to generate the auxiliary switch start signal; wherein the changeover control circuit further includes: a sequence circuit for turning off the auxiliary switch after the auxiliary switch is turned off and after an auxiliary dead time according to a signal related to the auxiliary switch; The primary switch is triggered to be turned on, and the related signal of the auxiliary switch is the auxiliary switch control signal or its related signal. The flyback power conversion circuit according to item 6 of the patent application scope, wherein the sequence circuit includes: a dead time control circuit for generating a dead time control signal according to the auxiliary switch related signal to determine the auxiliary dead time Time, so that the primary switch and the auxiliary switch are not conductive during the auxiliary dead time; a primary switch timing control circuit is used to control the signal according to the dead time and a primary switch time control signal. Generate the primary switch control signal, wherein the dead time control signal triggers the primary switch control signal to turn the primary switch on, and the primary switch time control signal triggers the primary switch control signal to make the primary side The switch is turned off; and a primary-side switch time control circuit is used to generate the primary-side switch control signal according to the dead time control signal to determine the on-time of the primary-side switch. As in the flyback power conversion circuit described in item 1 of the scope of the patent application, the primary switch's on-time is controlled by a primary-side feedback path or a secondary-side feedback path. A conversion control circuit for controlling a flyback power conversion circuit. The flyback power conversion circuit includes: a transformer including a primary winding, coupled to an input power source, and a secondary winding. Is coupled to an output node, wherein the input power includes an input voltage and an input current; a primary switch is coupled to the primary winding to switch the primary winding to convert the input power so that the input power The secondary winding generates an output power at the output node, wherein the output power includes an output voltage and an output current; a clamping circuit includes: an auxiliary switch, and an auxiliary capacitor in series with the auxiliary switch to form an An auxiliary branch, and the auxiliary branch is connected in parallel with the primary winding; the conversion control circuit is used to generate a primary switch control signal and an auxiliary switch control signal, which are respectively used to control the primary switch and the auxiliary switch, The input power is converted to generate the output power, wherein the auxiliary switch and the primary-side switch are not complementary switching; the conversion control The circuit includes: an auxiliary switch control circuit for adjusting the on-time of the auxiliary switch according to at least one of the following: a current-related signal, the input voltage and the output voltage such that when the primary switch is turned on, a current input thereof The voltage difference between the terminal and a current output terminal is approximately 0, so that zero-voltage switching is achieved. The current-related signal is related to at least one of the following: the output current, the on-current of the primary switch, and the Current; and a signal sensing circuit for sensing the current-related signal, the input voltage, or the output voltage. The conversion control circuit according to item 9 of the scope of patent application, wherein the on-time of the auxiliary switch increases with at least one of the following: the current-related signal represents a decrease in a peak current of one of the primary switches, and the input voltage increases, And the output voltage increases to conduct a magnetizing current of a magnetizing inductor of the primary winding and discharge a parasitic capacitor of the primary switch, so that the primary switch has zero voltage when conducting Switch. The conversion control circuit according to item 9 of the scope of patent application, wherein the auxiliary switch control circuit includes: a threshold value generating circuit for generating a voltage threshold value according to a difference between a reference voltage and the current-related signal; a ramp signal A generating circuit for generating a ramp signal according to a reference current and the auxiliary switch control signal; a comparison circuit for generating a comparison result by comparing the ramp signal with the voltage threshold; and a logic circuit according to the comparison result And an auxiliary switch start signal to generate the auxiliary switch control signal for controlling the auxiliary switch, so that the on-time of the auxiliary switch increases as the current-related signal represents a decrease in the peak current of the primary switch; wherein the switching control The circuit generates the auxiliary switch activation signal according to a preset clock signal or a feedback signal. The conversion control circuit according to item 9 of the scope of patent application, further comprising a mode operation circuit for controlling the primary side according to at least one of the input voltage, the output voltage, the input current, and the output current. The switching frequency of the switch enables the flyback power conversion circuit to operate in a discontinuous conduction mode (DCM) or a quasi-resonant mode (QRM). The conversion control circuit according to item 9 of the scope of patent application, further comprising: a mode operation circuit that determines a switching frequency of the primary-side switch according to the input voltage, the input current, the output voltage, or the output current, And the switching frequency has an upper limit frequency and a lower limit frequency. The switching control circuit according to item 9 of the scope of patent application, wherein the auxiliary switch control circuit triggers the auxiliary switch to turn on according to an auxiliary switch start signal; wherein the switching control circuit is based on a preset clock signal or a return signal. The start signal of the auxiliary switch is generated by the signal; the conversion control circuit further includes: a sequence circuit for triggering the turn-on of the auxiliary switch after the auxiliary switch becomes non-conducting according to the signal of the auxiliary switch; Primary side switch, wherein the auxiliary switch related signal is the auxiliary switch control signal or its related signal. The conversion control circuit according to item 14 of the scope of patent application, wherein the sequence circuit includes: a dead time control circuit for generating a dead time control signal according to the auxiliary switch related signal to determine the auxiliary dead time, so that The primary side switch and the auxiliary switch are non-conducting during the auxiliary dead time; a primary side switch timing control circuit is used to generate the primary side according to the dead time control signal and a primary side switch time control signal. Side switch control signal, wherein the dead time control signal triggers the primary side switch control signal to turn the primary switch on, and the primary side switch time control signal triggers the primary side switch control signal to turn the primary side switch to Non-conducting; and a primary switching time control circuit for generating the primary switching control signal according to the dead time control signal to determine the conducting time of the primary switching. The conversion control circuit according to item 9 of the scope of the patent application, wherein the feedback signal controls the on-time of the primary switch through a primary feedback path or a secondary feedback path. A flyback power conversion circuit includes: a transformer including a primary-side winding coupled to an input power source, and a secondary-side winding coupled to an output node, wherein the input power source includes an input voltage And an input current; a primary-side switch coupled to the primary-side winding for switching the primary-side winding to convert the input power, so that the secondary-side winding generates an output power at the output node, where the The output power includes an output voltage and an output current; a clamp circuit includes: an auxiliary switch and an auxiliary capacitor, which are connected in series with the auxiliary switch to form an auxiliary branch, and the auxiliary branch is connected in parallel with the primary winding And a conversion control circuit for generating a primary switch control signal and an auxiliary switch control signal according to a feedback signal, respectively for controlling the primary switch and the auxiliary switch, and converting the input power to generate The output power; wherein the conversion control circuit includes: a sequence circuit for triggering conduction according to an auxiliary switch start signal An auxiliary switch, and the primary switch is triggered to be turned on after the auxiliary switch becomes non-conductive and after an auxiliary dead time, so that when the primary switch is turned on, the voltage difference between a current input terminal and a current output terminal is substantially It is zero to achieve zero voltage switching; wherein the conversion control circuit generates the auxiliary switch activation signal according to a preset clock signal or the feedback signal. The flyback power conversion circuit according to item 17 of the scope of patent application, wherein the conversion control circuit further includes: a mode operation circuit, which is determined according to the input voltage, the input current, the output voltage, or the output current. The auxiliary switch activates an operating frequency of the signal, and the operating frequency has an upper limit frequency and a lower limit frequency. The flyback power conversion circuit according to item 17 of the patent application scope, wherein the sequence circuit includes: a first timing control circuit for generating the auxiliary according to the auxiliary switch start signal and a first time control signal. A switch control signal, wherein the auxiliary switch activation signal triggers the auxiliary switch control signal to turn the auxiliary switch on, and the first time control signal triggers the auxiliary switch control signal to turn the auxiliary switch to non-conduction; a first time A control circuit for generating the first time control signal according to the activation signal of the auxiliary switch to determine the on time of the auxiliary switch; a second time control circuit for generating a second time control signal according to the first time control signal Time control signal to determine the auxiliary dead time, so that the primary switch and the auxiliary switch are non-conducting during the auxiliary dead time; a second timing control circuit for controlling the signal and a third time according to the second time Time control signal to generate the primary side switch control signal, wherein the second time control signal triggers the one time A switch control signal turns the primary switch on, and the third time control signal triggers the primary switch control signal to turn the primary switch off; and a third time control circuit for controlling the The time control signal generates the third time control signal to determine the on-time of the primary switch.