JP4244283B2 - DC / DC converter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a DC / DC converter that performs a step-up operation by turning on and off a switching transistor by PWM (Pulse-Width Modulation) control, and in particular, suppresses a change in the maximum duty ratio of a pulse, The present invention relates to a technique suitable for avoiding a malfunction at the time of charging.
[0002]
[Prior art]
In the DC / DC converter, in order to perform an operation of outputting after adjusting the supplied voltage by changing the ratio of the ON / OFF period of the switching transistor, the detection voltage obtained by dividing the output voltage from the reference voltage is changed. Comparing the output voltage of the error amplifier that amplifies the difference, the upper limit of the duty ratio of the switching transistor and the voltage value that determines the soft start time, whichever is lower, and the sawtooth voltage Thus, a PWM control technique for switching control of the switching transistor is used.
[0003]
FIG. 13 is an explanatory diagram showing a basic configuration example of a boosting operation portion of a chopper type boosting switching regulator in a conventional DC / DC converter.
[0004]
In this chopper type step-up switching regulator, when the switching transistor NMOS is turned on by the PWM-controlled pulse EXT, a switch current flows from the input voltage VIN to the coil Coil, and energy is accumulated in the coil. When the transistor NMOS is turned off, the energy stored in the coil Coil is superimposed on the input voltage VIN, rectified by the diode Diode, and then the output is smoothed by the capacitor COUT to perform the boosting operation.
[0005]
In particular, in a step-up PWM switching regulator, a dead time control voltage (DTC voltage) is set for limiting the duty ratio of an output pulse in order to determine the maximum pulse width.
[0006]
FIG. 14 is a circuit diagram showing a first configuration example of a conventional DC / DC converter, FIG. 15 is a circuit diagram showing a second configuration example of the conventional DC / DC converter, and FIG. FIG. 17 is a circuit diagram showing a fourth configuration example of a conventional DC / DC converter, and FIG. 18 shows a maximum generated by the conventional DC / DC converter. It is explanatory drawing which shows the state of the dispersion | variation in a duty.
[0007]
The DC / DC converter shown in FIG. 14 is a typical step-up DC / DC converter configuration, and the feedback voltage VFB obtained by dividing the output voltage by the resistors Ra and Rb is compared with the reference voltage (Vref) by the amplifier Aa. By comparing the output with the triangular wave generated by the triangular wave generation circuit 12 and the DTC voltage including the soft start function generated by the reference voltage 11 and the resistors Rc and Rd and the capacitor Cb by the comparator Ab, the duty width To control.
[0008]
The pulse EXT whose duty width is controlled is output to the switching transistor Ta via the logic element La.
[0009]
Here, the specification can be adjusted externally by connecting a capacitor Cb for soft start setting to the terminal SS.
[0010]
On the other hand, in the DC / DC converter shown in FIG. 15, each component is the same as the DC / DC converter shown in FIG. 14, but the maximum duty and soft start time are increased by providing a reference voltage terminal outside. The configuration can be set.
[0011]
FIG. 16 shows a configuration example of a two-output type DC / DC converter having an inverting function. Switching terminals EXT (1), EXT (2) and an amplifier feedback terminal are provided on the boosting and inverting sides, respectively. There are VFB (1), VFB (2), soft start time setting terminals SS (1), (2), an output terminal (VREFOUT) as a reference voltage on the inverting side, and each maximum duty is an internal resistance Rc, Set by Rd, Re, Rf.
[0012]
The DC / DC converter shown in FIG. 17 includes the same components as the DC / DC converter shown in FIG. 16, but external resistors Rc, Rd, Re, Rf via external terminals DTC (1) and (2). And capacitors Cb and Cc are connected, and the maximum duty and soft start time can be set from the outside.
[0013]
However, in these conventional DC / DC converters, since the triangular wave generation circuit 12 and the duty ratio limiting circuit are not synchronized, the maximum duty setting as a result is caused by variations in the set voltage value due to temperature changes, trimming, etc. Not only the limitation but also the variation of the maximum duty as shown in FIG.
[0014]
As countermeasures against such problems, conventionally, for example, a maximum duty setting circuit as described in JP-A-2000-217340 is provided, or a triangular wave is set up as described in JP-A-11-214971. A circuit that uses the downlink for duty setting has been proposed. However, these circuits require a separate setting circuit, which increases the cost.
[0015]
[Problems to be solved by the invention]
The problem to be solved is that the conventional technique cannot suppress the duty variation caused by the temperature change and the variation of the set voltage value without adding a new circuit.
[0016]
An object of the present invention is to solve these problems of the prior art and improve the performance of a DC / DC converter at low cost and in a space-saving manner.
[0017]
[Means for Solving the Problems]
In order to achieve the above object, the present invention is a DC / DC converter that boosts an input voltage by turning on and off a switching element by a PWM-controlled pulse, and outputs an output voltage from a divided reference voltage. An amplifier that amplifies the difference between them, a triangular wave circuit that generates a sawtooth signal, a DTC generation circuit that generates a signal used for setting an upper limit value of a pulse duty ratio and setting a soft start time, and DTC generation A PWM control circuit for generating a pulse for controlling on / off of the switching element by inputting a signal from the circuit, a sawtooth signal from the triangular wave circuit, and an output signal from the amplifier, and each circuit connected to the triangular wave circuit and the DTC generation circuit And a reference voltage source for supplying a reference voltage. Further, the DTC generation circuit is characterized by having a resistor for setting a duty so that the resistance can be adjusted to the outside. Further, the triangular wave circuit is started up earlier than the DTC generation circuit, and the generation of abnormal pulses when the power supply voltage is turned on is prevented. Further, it is a multi-output type DC / DC converter that requires a rising sequence.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0019]
FIG. 1 is a block diagram showing a first configuration example of a DC / DC converter according to the present invention, FIG. 2 is an explanatory diagram showing a change in maximum duty in the DC / DC converter in FIG. 1, and FIG. FIG. 2 is an explanatory diagram showing an operation example of the DC / DC converter in FIG. 1.
[0020]
The DC / DC converter shown in FIG. 1 generates a triangular wave and an amplifier 3a that amplifies and outputs a feedback voltage VFB and a reference voltage (Vref) in comparison with the DC / DC converter shown in FIG. Comparator 3c, 3d, RS latch 7, constant current power supplies 8a, 8b, inverter 9, capacitor 10b and a DTC generation circuit for generating a DTC signal including a soft start function The voltage source 1, resistors 2d and 2e and capacitor 10a, the comparator 3b as a PWM generation circuit for controlling the duty width by comparing the output of the amplifier 3a with the DTC voltage including the triangular wave and the soft start function, and this The output of the pulse EXT whose duty width is controlled is connected to a low voltage malfunction prevention signal ( It has a logic element 6 which controls on the basis of the VLO signal), outside of the IC by placing the capacitor 10a of the soft-start configuration has a specification that can be externally adjusted.
[0021]
A feature of the DC / DC converter shown in FIG. 1 is that a voltage (VH, VL) for determining an upper limit value and a lower limit value of a triangular wave and a voltage for determining a DTC voltage are divided by a resistance divided from the same reference voltage source 1 ( Since the resistors 2a, 2b, and 2c) are used, the triangular wave and the maximum duty are synchronized with each other, and variation in the maximum duty can be prevented as shown in FIG.
[0022]
In this example, the DTC level has a configuration in which the resistance division ratio can be freely changed by trimming or the like.
[0023]
By the way, in general, in a DC / DC converter, a UVLO release delay signal having a certain delay is used as a circuit start signal in order to prevent a malfunction caused by a UVLO release signal. By this UVLO release delay signal, the switching transistor 5 connected to the DTC voltage is turned off, so that the voltage gradually rises and performs a soft start function, and then becomes a voltage value that determines the maximum duty.
[0024]
Such an operation is shown in FIG. Here, since the reference voltage for determining the upper and lower limits of the triangular wave is not controlled by the UVLO release signal, it rises from before the UVLO release signal. On the other hand, the DTC voltage rises after the UVLO release delay signal and becomes a voltage value that determines the maximum duty after the soft start period.
[0025]
FIG. 4 is a block diagram showing a second configuration example of the DC / DC converter according to the present invention, FIG. 5 is an explanatory diagram showing an operation example of the DC / DC converter in FIG. 1, and FIG. FIG. 7 is a block diagram illustrating a third configuration example of the DC / DC converter according to FIG. 7, and FIG. 7 is an explanatory diagram illustrating an operation example of the DC / DC converter in FIG.
[0026]
The DC / DC converter shown in FIG. 4 is composed of the same components as the DC / DC converter shown in FIG. 1, but the specifications are such that the resistors 2d and 2e are placed outside the IC together with the capacitor 10a for soft start setting and can be adjusted externally. It has become.
[0027]
As described above, the maximum duty and soft start time can be freely adjusted outside by providing the reference voltage terminal outside.
[0028]
Further, the reference voltage source is configured to be controlled by the UVLO release delay signal, and this makes it possible to prevent a malfunction by lowering the reference voltage when the voltage is low.
[0029]
In the operation of the DC / DC converter having such a configuration, as shown in FIG. 5, both the triangular wave and the DTC voltage rise after the rise of the UVLO release delay signal.
[0030]
The pulse surrounded by a broken line in FIG. 5 is generated when the level of the triangular wave and the level of DTC are near zero when the UVLO release delay signal rises, and is caused by a comparator offset or the like.
[0031]
This is not a problem with the step-up single output DC / DC converter shown in FIG. 1 and FIG. 4, but when a sequence operation is required for output in the multi-output DC / DC converter shown in FIG. Is a problem.
[0032]
As shown in FIGS. 4 and 5, the DC / DC converter shown in FIG. 6 has a configuration that prevents the generation of a pulse at the time of a UVLO release delay signal that occurs at the same time, and the configuration of the DC / DC conversion in FIG. On the other hand, a UVLO release signal is used as a control signal for the reference voltage source 1.
[0033]
That is, as shown in FIG. 7, the triangular wave signal controlled by the UVLO release signal starts to rise simultaneously with the UVLO release, and when the UVLO release delay signal that activates the DTC voltage is input, the level of the triangular wave is relative to GND (ground). The voltage is enough for the comparator to compare. Thereby, it is possible to prevent the pulse output when the UVLO release delay signal is input as seen in the example of FIG.
[0034]
Next, an example of a multi-output type DC / DC converter will be described with reference to FIGS.
[0035]
FIG. 8 is a block diagram showing a fourth configuration example of a DC / DC converter according to the present invention, FIG. 9 is an explanatory diagram showing an operation example of the DC / DC converter in FIG. 8, and FIG. FIG. 11 is a block diagram showing a fifth configuration example of the DC / DC converter according to FIG. 11, FIG. 11 is an explanatory diagram showing an operation example of the DC / DC converter in FIG. 10, and FIG. 12 is a DC / DC converter according to the present invention. It is a block diagram which shows the 6th structural example.
[0036]
The DC / DC converter shown in FIG. 8 includes the same components as those of the conventional multi-output type DC / DC converter shown in FIG. 16, and on the boost side, an amplifier A1, a comparator A3, resistors R3 and R4, and a switching transistor T1. , A logic element L1 is provided, and on the inversion side, an amplifier A2, a comparator A4, resistors R5 and R6, a switching transistor T2, a logic element L2, and an inversion side reference voltage amplifier A5, transistors T3 and T4, a resistor R7 , R8 are provided.
[0037]
The DC / DC converter shown in FIG. 8 is different from the conventional multi-output type DC / DC converter shown in FIG. 16 in that the reference voltage (VREFOUT) signal of the inverted voltage (VOUT2) is supplied to the amplifier A5 and the transistor. It is controlled by the UVLO release signal via T3, T4 and resistors R7, R8, and the DTC voltage having the soft start function is reset by the UVLO release delay signal via the transistor T1.
[0038]
As a result, as shown in FIG. 9, when the UVLO release signal is input, the DTC (1) and (2) voltages can be kept at the GND level, and erroneous pulses can be prevented.
[0039]
In the DC / DC converter of FIG. 8, the maximum duty lower limit value (VH, VL) of the triangular wave is determined from the reference voltage circuit 11 that determines the DTC (1), (2) voltage, thereby preventing variations in the maximum duty. Yes.
[0040]
The DC / DC converter shown in FIG. 10 is different from the DC / DC converter shown in FIG. 8 in that the reference voltage for determining the DTC voltage and the upper and lower limit values (VH, VL) of the triangular wave is changed from the VREFOUT voltage to the resistors R7, 8 is a resistance division.
[0041]
With this configuration, the reference voltage circuit 11 that is desired to be provided in the DC / DC converter of FIG. 8 can be omitted. The reference voltage that determines the DTC voltage and the upper and lower limit values (VH, VL) of the triangular wave is a common output, and the effect of preventing variation in the maximum duty is maintained.
[0042]
Further, as shown in FIG. 11, since the rise of the DTC voltage is determined by the UVLO release delay signal as in the DC / DC converter of FIG. 8, when the UVLO release signal is input, DTC (1), (2 ) The voltage can be kept at the GND level, and erroneous pulse generation can be prevented.
[0043]
The DC / DC converter shown in FIG. 12 is different from the DC / DC converter shown in FIG. 10 in that the resistors R3 to R6 that determine the DTC voltage are externally adjustable. Thereby, the maximum duty can be freely determined. The operation is the same as that of the DC / DC converter of FIG. 10 shown in FIG.
[0044]
As described above with reference to FIGS. 1 to 12, in this example, the DC / DC that is output after adjusting the supplied voltage by changing the ratio of the on / off periods of the switching transistors (T5, T6). An amplifier (A1, A2) which is a converter and amplifies a difference between a detection voltage obtained by dividing an output voltage from a reference voltage and outputs the output voltage of the amplifier (A1, A2) and a switching transistor (T5) , T6), the lower voltage of the voltage value having both the upper limit value of the duty ratio and the voltage value that determines the soft start time is compared with the sawtooth voltage from the triangular wave generating circuit, and the switching transistor (T5) is compared. , T6) in a DC / DC converter including a PWM control circuit that controls switching and a low-voltage malfunction prevention function (UVLO signal). It has a configuration using a voltage that sets the upper limit value of the duty ratio.
[0045]
For example, as shown in the prior art of FIG. 14, a DC / DC converter that boosts the input voltage from the input power source VIN by turning on and off the switching transistor Ta by a PWM-controlled pulse. The amplifier Aa that amplifies and outputs the difference from the reference voltage Vref of the voltage VFB divided by Rb, the triangular wave circuit 12 that generates a sawtooth signal, the setting of the upper limit value of the duty ratio of the pulse, and the soft start time A DTC generation circuit (consisting of a reference voltage 11, a capacitor Cb, and resistors Rc and Rd) that generates a signal used for setting, a signal from the DTC generation circuit, a sawtooth signal from the triangular wave circuit 12, and an output from the amplifier Aa P composed of an amplifier Ab that generates a pulse for controlling on / off of the switching transistor Ta with a signal as an input As shown in FIG. 1, a DC / DC converter having an M control circuit is provided with a reference voltage source 1 that is connected to a triangular wave circuit 12 and a DTC generation circuit and supplies a reference voltage to each circuit. .
[0046]
In this way, the voltage that determines the upper and lower limit values of the triangular wave and the voltage that determines the maximum duty are divided from the same reference voltage source to prevent duty variation due to temperature changes and set voltage value variations. In addition, even in a multi-output DC / DC converter, it is possible to suppress variation in duty and prevent malfunction at power-on.
[0047]
As a circuit for setting the duty ratio, for example, a resistor (2d, 2e, R3 to R6) for setting the duty is configured to be adjustable externally.
[0048]
In addition, in order to prevent abnormal pulse generation when the power supply voltage is turned on, the UVLO release signal is used as the control signal of the reference voltage source 1, so that the triangular wave circuit is started up earlier than the DTC generation circuit and is controlled by the UVLO release signal. The triangular wave signal is raised at the same time as the UVLO release, and when the UVLO release delay signal that activates the DTC voltage is input, the triangular wave level is set to a voltage that the comparator can sufficiently compare to GND (ground).
[0049]
In addition, this invention is not limited to the example demonstrated using FIGS. 1-12, A various change is possible in the range which does not deviate from the summary.
[0050]
【The invention's effect】
According to the present invention, it is possible to suppress a duty variation caused by a temperature change, a set voltage value shift due to trimming or the like without adding a new circuit, and also in a multi-channel DC / DC converter. Thus, it is possible to simultaneously prevent erroneous pulses at the time of power-on that cause a sequence malfunction, and to improve the performance of the DC / DC converter at low cost and in a space-saving manner.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a first configuration example of a DC / DC converter according to the present invention.
FIG. 2 is an explanatory diagram showing a change in maximum duty in the DC / DC converter in FIG. 1;
FIG. 3 is an explanatory diagram showing an operation example of the DC / DC converter in FIG. 1;
FIG. 4 is a block diagram showing a second configuration example of the DC / DC converter according to the present invention.
FIG. 5 is an explanatory diagram showing an operation example of the DC / DC converter in FIG. 1;
FIG. 6 is a block diagram showing a third configuration example of the DC / DC converter according to the present invention.
7 is an explanatory diagram showing an operation example of the DC / DC converter in FIG. 6. FIG.
FIG. 8 is a block diagram showing a fourth configuration example of the DC / DC converter according to the present invention.
9 is an explanatory diagram showing an operation example of the DC / DC converter in FIG. 8. FIG.
FIG. 10 is a block diagram showing a fifth configuration example of the DC / DC converter according to the present invention.
11 is an explanatory diagram showing an operation example of the DC / DC converter in FIG.
FIG. 12 is a block diagram showing a sixth configuration example of the DC / DC converter according to the present invention.
FIG. 13 is an explanatory diagram showing a basic configuration example of a step-up operation portion of a chopper type step-up switching regulator in a conventional DC / DC converter.
FIG. 14 is a circuit diagram showing a first configuration example of a conventional DC / DC converter.
FIG. 15 is a circuit diagram showing a second configuration example of a conventional DC / DC converter.
FIG. 16 is a circuit diagram showing a third configuration example of a conventional DC / DC converter.
FIG. 17 is a circuit diagram showing a fourth configuration example of a conventional DC / DC converter.
FIG. 18 is an explanatory diagram showing a state of variation in maximum duty that occurs in a conventional DC / DC converter.
[Explanation of symbols]
1: Reference voltage source, 2a to 2e: Resistor, 3a: Amplifier, 3b to 3d: Comparator, 4, 4a: External of IC, 5: Switching transistor, 6: Logic element, 7: RS latch, 8a, 8b: Constant current Source: 9: Inverter, 10a, 10b: Capacitor, 11: Reference voltage circuit, 12: Triangular wave generation circuit, A1, A2, A5: Amplifier, A3-A4: Comparator, C1-C4: Capacitor, Coil (1), ( 2): Coil, D1, D2: Diode, L1, L2: Logic element, R1 to R10: Resistor, T1 to T6: Switching transistor, VIN: Input power supply, Aa, Ac, Ae: Amplifier, Ab, Ad: Comparator, Ca to Cd: capacitor, coil: coil, Da, Db: diode, La, Lb: logic element, Ra to Rj: resistor, Ta: switch on Transistor.

Claims (4)

A DC / DC converter that boosts an input voltage by turning on and off a switching element by a PWM-controlled pulse,
An amplifier that amplifies and outputs the difference from the reference voltage of the divided voltage of the output voltage;
A triangular wave circuit for generating a sawtooth signal;
A DTC generation circuit for generating a signal used for setting an upper limit value of the duty ratio of the pulse and setting a soft start time;
A PWM control circuit for generating a pulse for controlling on / off of the switching element by inputting a signal from the DTC generation circuit, a sawtooth signal from the triangular wave circuit, and an output signal from the amplifier;
And a voltage determining the DTC voltage to enter the voltage and the DTC generation circuit for determining the upper limit value and the lower limit value of the triangular wave in the triangular wave circuit, that has a supply voltage dividing circuit from the same reference voltage source divide Characteristic DC / DC converter. The DC / DC converter according to claim 1,
The DTC generation circuit includes:
A DC / DC converter characterized in that a resistor for setting a duty ratio is adjustable outside the IC . The DC / DC converter according to claim 1 or 2, wherein
A DC / DC converter comprising means for starting up the triangular wave circuit earlier than the DTC generation circuit. A DC / DC converter according to any one of claims 1 to 3 ,
A DC / DC converter characterized by being a multi- output type DC / DC converter.

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