TWI666861B - Control circuit for reducing power loss of llc resonant converter during light-load or no-load operation - Google Patents

Abstract

The conventional technology cannot efficiently solve the switching loss of the LLC series resonant converter when it is operated at light load and no load; in view of this, the present invention proposes a control that can effectively reduce the light load and no load loss of the LLC resonant converter. The circuit is only composed of a signal detection unit and a controller unit. The signal detection unit is used to detect the primary current from the transformer unit of the LLC resonant converter, and then convert the primary current into a reference voltage signal. In this way, according to a level change of the reference voltage signal, the controller unit can appropriately reduce at least one control signal of the power switching unit for input to the LLC resonant converter based on a duty cycle reduction ratio. Duty cycle, thereby reducing the power loss of the LLC resonant converter operating under light load and no-load operation, and simultaneously reducing the operating temperature of the power switching unit.

Description

Control circuit for reducing light-load and no-load losses of LLC resonant converter

The present invention relates to the technical field of electronic circuits, and in particular to a control circuit capable of effectively reducing switching losses of an LLC resonant converter operating at light or no load.

Switching-mode power supply (SMPS) technology has been widely used in the manufacture of power supplies for various motors and electronic products. In addition, as electronic products develop toward the trend of thinness, lightness, and shortness, the power density of the switching power converter must be increased by increasing the switching frequency to effectively reduce the mechanism size of the switching power converter. Unfortunately, it has been found in practice that although the switching frequency can be increased to allow the switching power converter to carry small magnetic components and capacitors, it has instead increased the switching loss of the power switching element and caused the switching power converter to be susceptible to electromagnetic interference.

In view of this, an LLC resonant converter with the characteristics of Zero Voltage Switching (ZVS) and Zero Current Switching (ZCS) was proposed. Please refer to FIG. 1, which is a circuit diagram of a conventional LLC series resonant converter. As shown in FIG. 1, the conventional LLC series resonant converter 2 ′ includes: a power switch unit 23 ′, a resonance unit 24 ′, a transformer unit 25 ′, and an output rectification unit coupled to a DC power source V _DC ′. 26 ', and a low-pass filtering unit 27'. It is worth noting that a closed-loop control module 1 'is connected between the output terminal of the LLC series resonant converter 2' and the power switching unit 23 '. Furthermore, it can be known from FIG. 1 that the closed-loop control module 1 ′ mainly includes a signal detection unit 11 ′, a controller unit 12 ′, and a driving unit 13 ′.

In order to control the LLC series resonant converter 2 'to provide stable output to the load 3', the closed-loop control module 1 'alternately and correspondingly inputs a first control signal and a second control signal according to the output current and / or output voltage to A first power switch and a second power switch inside the power switch unit 23 '. It is worth noting that there is an interval between the two control signals, which is called dead time. Moreover, when the LLC series resonant converter 2 'operates at light load, the closed-loop control module 1' usually stabilizes the output current / voltage of the LLC series resonant converter 2 'by increasing the switching frequency of the power switching unit 23'; however, When the power switching unit 23 'performs high-frequency switching, the output voltage of the LLC series resonant converter 2' will be affected by the stray capacitance effect and increase. Therefore, in order to solve the switching loss caused by the operation of the LLC series resonant converter 2 'at light load or no load, some scholars and power converter manufacturers have proposed several improvement methods.

The first method is to add a dummy load to reduce the stray capacitance effect when the LLC series resonant converter 2 'is operated at light load or no load. Unfortunately, the additional load not only reduces the conversion efficiency of the LLC series resonant converter 2 ', but also causes the overall volume of the LLC series resonant converter 2' to increase. On the other hand, the second method is to install a burst mode controller on the primary side of the transformer unit 25 'to control the LLC series resonant converter 2' under light load to operate in the burst mode. mode. It is worth noting that through a special design, a periodic control signal includes both long idle periods and high-frequency switching periods, so that the power switch enters the OFF state during the long idle time. And performing high-frequency switching close to a fixed frequency in the high-frequency switching interval. Through such a special design, the "average switching frequency" of the power switch is reasonably reduced, and the switching loss can be effectively reduced.

However, the second method still has the following disadvantages: When the power switch unit 23 'is operated in the burst mode according to the control of the burst mode controller, the LLC series resonant converter 2' will simultaneously generate audio frequency. Noise pollution. In addition, the third method is to use a closed-loop control module 1 'to variable-frequency (VF) and phase-shift (Phase-shift, PS) control; conceivably, in order to achieve the third method, the controller unit 12 'must include multiple circuit chips at the same time, so the circuit complexity and circuit cost of the closed-loop control module 1' are increased.

From the above description, it can be known that currently there is no ideal improvement solution that can efficiently solve the problems arising from the operation of the LLC series resonant converter at light load and no load; in view of this, the inventor of this case has made great efforts to study Invention, and finally developed a control circuit for reducing the light-load and no-load losses of the LLC resonant converter.

In view of the foregoing, it is pointed out that the conventional technology cannot efficiently solve the problems arising from the operation of the LLC series resonant converter at light load and no load. The main purpose of the present invention is to provide a light load and no load that can reduce the LLC resonant converter. A kind of control circuit for loss, which is only composed of a signal detection unit and a controller unit. The signal detection unit is used to detect the primary current from the transformer unit of the LLC resonant converter, and then convert the primary current into a reference voltage signal. In this way, according to a level change of the reference voltage signal, the controller unit can appropriately reduce at least one control signal of the power switching unit for input to the LLC resonant converter based on a duty cycle reduction ratio. Duty cycle, thereby reducing the power loss of the LLC resonant converter operating under light load and no-load operation, and simultaneously reducing the operating temperature of the power switching unit.

In order to achieve the above-mentioned main purpose of the present invention, the inventor of the present case provides an embodiment of the control circuit, which is applied to an LLC resonant converter, wherein the LLC resonant converter includes at least: a power switching unit, a resonant unit A transformer unit, an output rectifier unit, and a low-pass filter unit; and the control circuit includes: a signal detection unit electrically connected to the primary side of the transformer unit to detect a current Sampling a signal and correspondingly outputting a reference voltage signal; and a controller unit electrically connected to the signal detection unit to receive the reference voltage signal; and the controller unit outputs at least one control signal to the power A switching unit; wherein, according to a level change of the reference voltage signal, the controller unit appropriately reduces the duty cycle of the control signal based on a first ratio, and the first ratio is The ratio of a light load duty cycle to a base duty cycle.

In order to more clearly describe a control circuit (hereinafter referred to as "control circuit") for reducing the light-load and no-load losses of the LLC resonant converter proposed by the present invention, the preferred implementation of the present invention will be described in detail below with reference to the drawings. example.

First embodiment

Please also refer to FIG. 2, which is a circuit block diagram of an LLC resonant converter including a control circuit of the present invention. As shown in FIG. 2, the LLC resonant converter 2 generally includes: a power switching unit 23, a resonance unit 24, a transformer unit 25, at least one output rectification unit 26, and at least one low voltage coupled to a _DC power source V _DC . The pass filter unit 27, wherein the power switch unit 23 controls the resonance unit 24 and the transformer unit 25 to transfer energy. The control circuit 1 proposed in the present invention is provided in the LLC resonant converter 2 and is used to output a first control signal and a second control signal to the power switch unit correspondingly according to the load condition of the LLC resonant converter 2. twenty three. Please refer to FIG. 3 at the same time, which shows a circuit architecture diagram of a first embodiment of a control circuit of the present invention. As shown in FIGS. 2 and 3, the control circuit 1 mainly includes a signal detection unit 11 and a controller unit 12.

In particular, in the present invention, the signal detection unit 11 is constituted by a current converter 111, a full-wave rectification unit 112, and a current-voltage conversion unit 113. The current transformer 111 is electrically connected to the primary side of the transformer unit 25 to detect the primary current, and further reduces the primary current to a current sampling signal according to a reduction ratio (for example, 1: 100). In addition, the full-wave rectifier unit 112 is electrically connected to the current converter 111 for performing a full-wave rectification process on the current sampling signal detected by the current converter 111. Finally, the current-voltage conversion unit 113 electrically connected to the full-wave rectification unit 112 is used to convert the current sampling signal that completes the full-wave rectification process into a reference voltage signal V _REF . In addition, the simplest embodiment of the current-voltage conversion unit 113 is a resistor group.

Continue to refer to FIG. 2 and FIG. 3. In the present invention, the controller unit 12 is electrically connected to the signal detection unit 11 to receive the reference voltage signal V _REF . In this way, according to a level change of the received reference voltage signal V _REF , the controller unit 12 can appropriately reduce the duty cycle of the control signal based on a first ratio, thereby reducing the LLC The losses derived from the resonant converter 2 operating at light or no load. Conversely, when the LLC resonant converter 2 is operating at a normal load, the controller unit 12 appropriately adjusts the duty cycle of the control signal based on a second ratio, thereby enabling the LLC resonant converter 2 to provide a stable output. .

In order to explain more clearly how the control circuit 1 of the present invention achieves the effect of reducing light-load / no-load loss by reducing the duty cycle of the control signal, it will be explained in detail below with the assistance of experimental data. Please refer to FIG. 4, which is a graph showing the level of the reference voltage signal versus the duty cycle. It is worth noting that the graph contains 4 intervals (I, II, III, IV), and the meaning of each interval is arranged in the following table (1). According to Table (1) and FIG. 4, when the LLC resonant converter 2 is operated at a normal load (that is, non-light-load operation), the level of the reference voltage signal V _REF is higher than or equal to 180 mV. Therefore, when the level of the reference voltage signal V _REF is less than 180mV, it means that the LLC resonant converter 2 enters light load operation, and the controller unit 12 will immediately reduce the duty cycle of the control signal from 45% to 42% The reduction ratio of the duty cycle is 93.3%. Table 1)

In this test experiment, 42% was considered a light load duty cycle. It is worth noting that, in an ideal state, the controller unit 12 outputs a control signal with a basic duty cycle of 50% to the power switching unit 23, so that the LLC resonant converter 2 operating at a normal load provides a stable output to the rear-end load 3 . However, considering that the precision of the controller unit 12 and the sensitivity of other electronic components mounted on the LLC resonant converter 2 are all different, the experimental example of the present invention uses 45% as the basic duty cycle. Simply put, with the difference in the circuit composition of LLC resonant converter 2, the basic duty cycle will not be a fixed value, it may be between 45% and 50%; similarly, with the LLC resonant converter The difference in the circuit composition of 2 will not be a fixed value for the light load duty cycle, but it must be smaller than the basic duty cycle. Therefore, the present invention specifically makes the duty cycle adjustment ratio (ie, the first ratio) between 88% and 99%.

In particular, the controller unit 12 can at least determine that the LLC resonant converter 2 is operating at full load and / or light load through the reference voltage signal V _REF provided by the signal detection unit 11. The so-called light load can be less than 70% of the full load (Full Load). In addition, it is worth mentioning that the LLC resonant converter 2 operates in a fixed frequency mode during the experiment; and when the controller unit 12 detects that the LLC resonant converter 2 is operating at light load, it immediately follows the first ratio The duty cycle of the control signal is adjusted to a so-called light load duty cycle.

The following table (2) describes the power loss of the LLC resonant converter 2 with the control circuit 1 of the present invention under light load operation and the temperature of the power switching unit 23 thereof. As shown in Table (2), when the LLC resonant converter 2 enters light load operation and the duty cycle of the control signal of the power switching unit 23 is 45% (ie, the basic duty cycle set by the experimental example), the power switching unit The operating temperature of 23 sharply rises to 100 ^o C; at this time, the power consumption of the LLC resonant converter 2 due to the switching loss of the power switching unit 23 is 19.8W. It is worth noting that after the controller unit 12 reduces the duty cycle of the control signal to 42% (that is, the light duty cycle), the operating temperature of the power switch unit 23 is greatly reduced from 100 ^o C to 40. ^o C, meanwhile, the power loss of LLC resonant converter 2 has also decreased from 19.8W to 9.2W. Therefore, experimental data confirm that the control circuit 1 of the present invention can effectively reduce the light-load and no-load losses of the LLC resonant converter 2. Table 2)

Continue to refer to FIG. 5, which is a graph showing the level of the reference voltage signal versus the duty cycle. It is worth noting that the graph contains 4 intervals (I ', II', III ', IV'), and the meaning of each interval is arranged in the following table (3). According to Table (3) and FIG. 5, when the LLC resonant converter 2 is operated at no load, the level of the reference voltage signal V _REF will be lower than 40mV, and the duty cycle is set to 0 at this time. In addition, when the level of the reference voltage signal V _REF is greater than or equal to 40mV, it means that the LLC resonant converter 2 enters light load operation, and the controller unit 12 will immediately increase the duty cycle of the control signal from 0 to 42%. . It is worth noting that when the level of the reference voltage signal V _REF is greater than or equal to 450mV, it means that the LLC resonant converter 2 enters normal load operation, and the controller unit 12 will immediately adjust the duty cycle of the control signal from 42% It is increased to 45%, and the duty cycle is adjusted to 107%. Similarly, as the circuit composition of the LLC resonant converter 2 is different, the increase ratio (that is, the second ratio) of the duty ratio is between 102% and 112%. table 3)

Second embodiment

Please refer to FIG. 6, which shows a circuit architecture diagram of a second embodiment of the control circuit of the present invention. Comparing FIG. 3 with FIG. 6, it can be known that by adding an isolation transformer unit 13 to the first embodiment of the control circuit 1 of the present invention, a second embodiment of the control circuit 1 can be obtained. As shown in FIG. 6, the isolation transformer unit 13 is electrically connected between the controller unit 12 and the power switch unit 23 to protect the controller unit 12 and prevent the controller unit 12 from being caused by a DC power source V _DC . damage.

Third embodiment

Please continue to refer to FIG. 7, which shows a circuit architecture diagram of a third embodiment of the control circuit of the present invention. Comparing FIG. 6 with FIG. 7, it can be known that the LLC resonant converter 2 in the third embodiment has multiple outputs. The specific implementation method is to make the winding group of the transformer unit 25 include a main winding group and a plurality of times. (Sub) winding group. In addition, as shown in FIG. 7, each sub-winding group of the transformer unit 25 is connected to a set of output rectifying units 26 and a set of low-pass filtering units 27. It is worth noting that based on the transformer unit 25 being modularized, the output rectification unit 26 and the low-pass filtering unit 27 may also be modularized together with the electrical connector used to connect the load 3. In addition, a module of the output rectifying unit 26, the low-pass filtering unit 27, and an electrical connector for connecting the load 3 is referred to as a power module. In particular, the application through the power module helps to improve the convenience of the LLC resonant converter 2 in increasing / decreasing the output channel. In addition, between the low-pass filter unit 27 and the load 3, a DC / DC converter line, such as Buck, Boost, or Buck / Boost, may be added to obtain a stable output of the LLC resonant converter 2. The load 3 may be an LED.

In this way, the above-mentioned system has completely and clearly explained a control circuit for reducing light-load and no-load losses of the LLC resonant converter disclosed by the present invention; and through the above, we can know that the present system has the following advantages:

(1) The conventional technology cannot efficiently solve the problems arising from the operation of the LLC series resonant converter at light load and no-load; in view of this, the present invention proposes to effectively reduce the light load and empty of the LLC resonant converter 2. A control circuit for load loss, which is only composed of a signal detection unit 11 and a controller unit 12. The signal detection unit 11 is configured to detect a primary current from the transformer unit 25 of the LLC resonant converter 2, and then convert the primary current into a reference voltage signal V _REF . In this way, according to a level change of the reference voltage signal V _REF , the controller unit 12 can appropriately reduce the power of the power switch unit 23 for input to the LLC resonant converter 2 based on a duty cycle reduction ratio. At least one duty cycle of the control signal, thereby reducing the power loss of the LLC resonant converter 2 under light or no-load operation and reducing the operating temperature of the power switching unit 23.

(2) On the other hand, except that the controller unit 12 belongs to a microcircuit chip, the present invention only composes the circuit unit of the control circuit 1 with basic electronic parts; therefore, compared to the closed-loop control circuit used in the conventional technology, it includes multiple The microcircuit chip and the control circuit 1 of the present invention show the advantages of simple topology and low manufacturing cost.

It must be emphasized that the above detailed description is a specific description of the feasible embodiment of the present invention, but this embodiment is not intended to limit the patent scope of the present invention, and any equivalent implementation or change without departing from the technical spirit of the present invention, All should be included in the patent scope of this case.

<Invention>

2‧‧‧LLC resonant converter

23‧‧‧Power Switch Unit

V _DC ‧‧‧ DC Power Supply

24‧‧‧Resonant unit

25‧‧‧Transformer unit

26‧‧‧Output rectifier unit

27‧‧‧low-pass filter unit

1‧‧‧Control circuit

11‧‧‧Signal detection unit

12‧‧‧controller unit

111‧‧‧ specific current

112‧‧‧full wave rectifier unit

113‧‧‧Current-voltage conversion unit

14‧‧‧reference voltage generating unit

V _REF ‧‧‧ Reference voltage signal

3‧‧‧ load

I, II, III, IV‧‧‧ intervals

I ’, II’, III ’, IV’ ‧‧‧ intervals

13‧‧‧Isolation transformer unit

＜ Learning ＞

2’‧‧‧LLC series resonant converter

V _DC '‧‧‧ DC Power Supply

23’‧‧‧Power Switch Unit

24’‧‧‧ resonant unit

25’‧‧‧Transformer unit

26’‧‧‧ output rectifier unit

27’‧‧‧low-pass filter unit

1’‧‧‧closed-loop control module

11’‧‧‧Signal detection unit

12’‧‧‧controller unit

13’‧‧‧Drive unit

3’‧‧‧ load

FIG. 1 is a circuit block diagram of a conventional LLC series resonant converter; FIG. 2 is a circuit block diagram of an LLC resonant converter including a control circuit of the present invention; FIG. 3 is a control circuit of the present invention; FIG. 4 is a graph showing the level of the reference voltage signal versus the duty cycle; FIG. 5 is a graph showing the level of the reference voltage signal versus the duty cycle; FIG. 6 is a diagram showing A circuit architecture diagram of the second embodiment of the control circuit of the present invention; FIG. 7 is a circuit architecture diagram of the third embodiment of the control circuit of the present invention.

Claims (9)

A control circuit is applied to an LLC resonant converter. The LLC resonant converter includes at least a power switch unit, a resonance unit, and a transformer unit. The power switch unit controls the resonance unit and the transformer unit. Transferring energy; and the control circuit includes: a signal detection unit, including: a current ratior, which is electrically connected to the primary side of the transformer unit to detect a current sampling signal; a full wave A rectifying unit is electrically connected to the secondary side of the current converter for performing a full-wave rectification process on the current sampling signal detected by the current converter; and a current-voltage conversion unit is electrical Connected to the full-wave rectification unit for converting the current sampling signal that has completed the full-wave rectification process into a reference voltage signal; and a controller unit electrically connected to the signal detection unit to receive the reference voltage And the controller unit outputs at least one control signal to the power switch unit; wherein, according to a level change of the reference voltage signal, The controller unit appropriately adjusts the duty cycle of the control signal based on a first ratio, and the first ratio is a ratio of a light duty cycle to a basic duty cycle. The control circuit according to item 1 of the scope of patent application, wherein, according to the level change of the reference voltage signal, the controller unit appropriately raises the duty cycle of the control signal based on a second ratio, This allows the LLC resonant converter to provide a stable output when operating under normal loads; and the second ratio is a ratio of the basic duty cycle to the light load duty cycle. The control circuit according to item 2 of the scope of patent application, wherein the light duty cycle is smaller than the basic duty cycle. The control circuit according to item 2 of the scope of patent application, wherein the first ratio is between 88% and 99%, and the second ratio is between 102% and 112%. The control circuit according to item 1 of the scope of patent application further comprises: an isolation transformer unit, which is electrically connected between the controller unit and the power switch unit. The control circuit according to item 1 of the scope of patent application, wherein the LLC resonant converter works in a fixed frequency mode. The control circuit according to item 1 of the scope of patent application, wherein, through the reference voltage signal provided by the signal detection unit, the controller unit can at least determine that the LLC resonant converter is operating at full load and / or light load The light load is less than 70% of the full load. The control circuit according to item 1 of the scope of patent application, wherein the LLC resonant converter can be connected to a plurality of output rectifying units. The control circuit according to item 8 of the scope of patent application, wherein the transformer unit has a main winding group and a plurality of secondary winding groups, and each secondary winding group is connected to a set of output rectifying units.