TWI817321B - Multi-mode hybrid control DC-DC power conversion circuit and control method - Google Patents

Abstract

A multi-mode hybrid controlled DC-DC power conversion circuit includes a switching power converter and a microcontroller. The switching power converter includes a transformer and a switching switch. The microcontroller converts power according to the switching power supply. Set multiple feedback voltage thresholds for the input voltage of the converter, and determine the relationship between the feedback voltage of the switching power converter and each of the feedback voltage thresholds, so as to execute a frequency conversion control mode based on the judgment results. Fixed frequency control mode or one-hop period control mode; the microcontroller outputs a driving signal to the switch, and the microcontroller adjusts the frequency of the driving signal according to the executed mode, so that the switching power converter can easily Load to full load to obtain the best efficiency curve.

Description

Multi-mode hybrid control DC-DC power conversion circuit and control method

The present invention relates to a DC-to-DC power conversion circuit, and in particular to a multi-mode hybrid control DC-to-DC power conversion circuit and control method.

A conventional DC-DC power conversion circuit includes a switching power converter and a microcontroller. Among them, a flyback power converter is a circuit architecture of the switching power converter. The flyback power converter The power output end of the converter is used to connect a load. The flyback power converter basically includes a transformer. The primary winding of the transformer is connected in series with a transistor. The transistor is usually a metal oxide semi-field effect transistor (MOSFET). The microcontroller and its control loop are connected to the power input terminal, the power output terminal of the switching power converter and the gate of the transistor.

Thereby, using the microcontroller to control, the input voltage and feedback voltage of the switching power converter can be detected to determine the load amount of the load connected to the switching power converter, and generate a signal based on the load amount. A driving signal (PWM) is given to the transistor, and the transistor implements an ON/OFF action mode according to the driving signal.

Generally speaking, the microcontroller implements a quasi-resonant control mode (QR mode). The function of the quasi-resonant mode is that when the detected load is lower, the frequency of the driving signal is higher. However, the load has various forms, including at least heavy load and light load. For example, when the load is full, the frequency of the driving signal can be 120kHz; but when the load is reduced to a light load (such as full load) 30%), the frequency of the driving signal may be increased to 400kHz. It can be seen that when the load is light load or lower, or even no-load, the frequency of the drive signal will be maintained at a higher frequency, causing the drive switch to perform on/off switching at a higher frequency, resulting in high Frequency noise, high-frequency switching losses and electromagnetic interference on circuit board lines and other issues.

In view of this, the main purpose of the present invention is to provide a multi-mode hybrid control DC-DC power conversion circuit and control method, in order to improve the performance of the conventional DC-DC power conversion circuit when the load is in the quasi-resonant control mode (QR mode). The load is light load or lower, resulting in problems such as high-frequency noise, high-frequency switching loss and electromagnetic interference on the circuit board lines.

The multi-mode hybrid controlled DC-DC power conversion circuit of the present invention includes: A switching power converter containing: a transformer; and A switch is connected in series to the primary winding of the transformer and has a control terminal; and A microcontroller is connected to the control terminal of the switching power converter and the switching switch. The microcontroller sets a plurality of feedback voltage thresholds according to the input voltage of the switching power converter, and determines the conversion of the switching power supply. The relationship between a feedback voltage of the device and each feedback voltage threshold is used to execute a variable frequency control mode, a constant frequency control mode or a skip cycle control mode according to the judgment result; the microcontroller outputs a driving signal to the switch, and correspondingly adjust the frequency of the driving signal according to the executed frequency conversion control mode, the fixed frequency control mode or the skip cycle control mode.

The control method of the multi-mode hybrid control DC-DC power conversion circuit of the present invention is executed by a microcontroller, and the microcontroller is connected to a switching power converter and a switch. The control method includes the following steps: (a) detecting an input voltage and a feedback voltage of the switching power converter; (b) setting multiple feedback voltage thresholds based on the input voltage of the switching power converter; (c) Determine the relationship between the feedback voltage of the switching power converter and each feedback voltage threshold; and (d) Execute a frequency conversion control mode, a constant frequency control mode or a skip cycle control mode according to the judgment result of step (c), in which the microcontroller outputs a drive signal to the switch, and executes the frequency conversion control mode according to the executed frequency conversion control mode. The control mode, the fixed frequency control mode or the skip cycle control mode correspondingly adjusts the frequency of the driving signal.

According to the multi-mode hybrid control DC-DC power conversion circuit and control method of the present invention, the so-called multi-mode includes, for example, the frequency conversion control mode, the fixed frequency control mode and the skip cycle control mode, and the microcontroller monitors the switching in real time The input voltage and feedback voltage of the switching power converter, where the feedback voltage of the switching power converter can reflect the load of a load connected to the DC-DC power conversion circuit, the microcontroller sets the These feedback voltage thresholds are used as judgment reference values for evaluating the load.

When the microcontroller determines that the load is heavy load, the variable frequency control mode is executed; when the microcontroller determines that the load is light load or lower, the fixed frequency control mode or the cycle skip control mode is executed. In the fixed frequency control mode or the skip cycle control mode, the frequency of the driving signal is maintained at a constant value without increasing as the load becomes lighter. In this way, the load is effectively improved when the load is light or light as described in the prior art. It reduces the problems caused by high-frequency noise, high-frequency switching losses and electromagnetic interference on the circuit board lines, and allows the switching power converter to obtain the best efficiency curve from light load to full load.

The multi-mode hybrid controlled DC-DC power conversion circuit of the present invention includes a switching power converter and a microcontroller (MCU), or may further include an active clamping circuit, wherein the switching power converter is based on a Taking a flyback power converter as an example, it should be noted that the working principle of the flyback power converter is not a feature of the present invention and is only briefly described without going into detail.

Please refer to FIG. 1 , the switching power converter 10 includes a transformer 20 , a switching switch Q1 and an output circuit 30 . The primary winding 21 and the secondary winding 22 of the transformer 20 are not grounded together. A first end of the primary winding 21 is connected to the power input end 11 of the switching power converter 10 for receiving a DC input voltage V _I , the switch Q1 is connected in series to the primary winding 21 and has a control terminal. In the embodiment of the present invention, the switch Q1 can be a transistor, such as a metal oxide semi-field effect transistor (MOSFET), and its gate The switch Q1 is connected in series with the primary winding 21 through this connection structure. The output circuit 30 is connected to the secondary winding 22 and includes a power output terminal 12 for connecting to a load. The power output terminal 12 provides an output voltage V _O to the load. A signal input terminal of the microcontroller 40 is connected to the switching power converter 10 , and a signal output terminal of the microcontroller 40 is connected to the control terminal of the switch Q1 . The microcontroller 40 can output a driving signal S1 to The switch Q1 is used to control the operation (ie, on/off) of the switch Q1. The drive signal S1 can be a pulse width modulation (PWM) signal, and the microcontroller 40 can set and adjust the drive signal. The pulse width and frequency of the signal.

In the embodiment of the present invention, a first signal input terminal of the microcontroller 40 is connected to the power output terminal 12 of the switching power converter 10 through an isolated feedback circuit 50 to receive a signal from the isolated feedback circuit 50 Feedback voltage V _FB , the feedback voltage V _FB can reflect the output voltage V _O of the switching power converter 10 , that is, when the switching power converter 10 is connected to a load, the feedback voltage V _FB The size can reflect the load provided by the load, such as full load, heavy load, light load, very light load or no load. It should be noted that using an isolated feedback circuit 50 to obtain the feedback voltage V _FB to detect the load is common knowledge in the field of power circuit technology. The working principle of the isolated feedback circuit 50 is not a feature of the present invention. Without going into details, the detailed circuit of the isolation feedback circuit 50 can be referred to FIG. 2. The isolation feedback circuit 50 basically includes an optical coupler 51. The optical coupler 51 includes two input terminals, a first An output terminal and a second output terminal, the two input terminals are respectively connected to the power output terminal 12 of the switching power converter 10, the first output terminal is connected to a voltage source Vcc and the first signal of the microcontroller 40 The input terminal allows the microcontroller 40 to receive the feedback voltage V _FB from the isolated feedback circuit 50 . The second output terminal of the optocoupler 51 is grounded, where the voltage source Vcc can be taken from the The primary side winding 21, for example, the primary side winding 21 can be coupled to an auxiliary winding (not shown in the figure) or connected to a voltage dividing circuit (not shown in the figure), and the optical coupler 51 is connected to the auxiliary winding or the A voltage divider circuit is used to obtain the voltage source Vcc.

The microcontroller 40 stores a plurality of feedback voltage thresholds. These feedback voltage thresholds are adjustable preset values. These feedback voltage thresholds are used as judgment reference values for evaluating the load capacity of the load. The microcontroller 40 determines the relationship between the feedback voltage V _FB and each feedback voltage threshold, and executes one of a plurality of feedback control modes according to the determination result. The implemented feedback control mode adjusts the pulse width and/or frequency of the drive signal S1 output to the switch Q1 accordingly.

In embodiments of the present invention, the feedback control modes include a variable frequency control mode, a constant frequency control mode and a pulse skipping mode (PSM). When the load is full or heavy, the microcontroller 40 executes the frequency conversion control mode. As the name suggests, the microcontroller 40 causes the frequency of the drive signal S1 to change with the load. Generally speaking, with the The lower the load, the higher the frequency of the driving signal S1. Conversely, as the load increases, the frequency of the driving signal S1 becomes lower. This is also common knowledge in the field of power circuit technology. For example, The frequency conversion control mode may be a quasi-resonant frequency conversion control mode (Quasi-Resonant mode, QR mode). When the load is light load, the microcontroller 40 executes the fixed frequency control mode. As the name suggests, the microcontroller 40 makes the frequency of the driving signal S1 a fixed frequency. When the load of the load is extremely light or no-load, the microcontroller 40 executes the cycle skipping control mode, so that the frequency of the driving signal S1 changes alternately between "zero" and "non-zero", and "non-zero" changes alternately. The frequency of "zero" refers to the fixed frequency of the fixed frequency control mode, which will be explained later. In the frequency conversion control mode, when the load of the load is full load, the frequency of the drive signal S1 is defined as a full load frequency, which is, for example, about 120 kHz; in the fixed frequency control mode and the skip cycle control mode , the frequency of the driving signal S1 is more than half of the full load frequency.

A second signal input terminal of the microcontroller 40 can detect the input voltage _VI of the switching power converter 10. Taking FIG. 1 as an example, the second signal input terminal of the microcontroller 40 can detect The voltage circuit 13 is connected to the power input terminal 11 of the switching power converter 10 to detect the input voltage V _I . The microcontroller 40 sets the feedback voltage thresholds according to the input voltage _VI of the switching power converter 10 . In embodiments of the present invention, the feedback voltage thresholds include a first feedback voltage threshold V _LL and a second feedback voltage threshold V _SK , and V _LL is greater than V _SK . When the microcontroller 40 determines that the feedback voltage V _FB is greater than the first feedback voltage threshold V _LL , the microcontroller 40 executes the frequency conversion control mode to correspond to the load being full load or heavy load; when the microcontroller 40 The microcontroller 40 determines that the feedback voltage V _FB is less than or equal to the first feedback voltage threshold V _LL and is greater than the second feedback voltage threshold V _SK , and the microcontroller 40 executes the fixed frequency control mode, The corresponding load is light load; when the microcontroller 40 determines that the feedback voltage V _FB is less than or equal to the second feedback voltage threshold V _SK , the microcontroller 40 executes the cycle skip control mode to The corresponding load capacity is extremely light load or no load.

The circuit architecture and functions of the switching power converter 10 and the microcontroller 40 have been described above. The multi-mode hybrid control method executed by the microcontroller 40 will be described below with the help of waveform diagrams. The flow chart of the control method can be referred to FIG. 3.

Step S01: Detect the input voltage V _I and the feedback voltage V _FB of the switching power converter 10 . As mentioned above, the microcontroller 40 can detect the input voltage V _I of the switching power converter 10 through the voltage dividing circuit 13 and receive the feedback voltage V _FB through the isolation feedback circuit 50 . The feedback voltage V _FB reflects the output voltage V _O of the switching power converter 10 , and the output voltage V _O reflects the load capacity of the connected load. Therefore, the feedback voltage V _FB can be used to detect the load capacity of the load. .

Step S02: Set multiple feedback voltage thresholds according to the input voltage _VI of the switching power converter 10. As mentioned above, the feedback voltage thresholds include the first feedback voltage threshold V _LL and the second feedback voltage threshold V _SK , and V _LL is greater than V _SK . In the embodiment of the present invention, the microcontroller 40 stores a plurality of feedback voltage threshold reference values, a first proportional value R1 and a second proportional value R2. The feedback voltage threshold reference values respectively correspond to the switching formula. For different input voltage V _I of the power converter 10, the first proportional value is greater than the second proportional value, that is, R1 is greater than R2. For example, the first proportional value can be 55%, and the second proportional value can be 10 %, but not limited to this. The microcontroller 40 selects one of the feedback voltage threshold reference values corresponding to the input voltage _VI of the switching power converter 10, and then multiplies the selected feedback voltage threshold reference value by the first proportional value. The first feedback voltage threshold value V _LL is set, that is, V _LL = the selected feedback voltage threshold reference value × R1, and the selected feedback voltage threshold reference value is multiplied by the second proportional value. This is the second feedback voltage threshold value V _SK , that is, V _SK = selected feedback voltage threshold reference value × R2. The following table records an example, but is not limited to this example. That is to say, when the microcontroller 40 detects that the input voltage V _I of the switching power converter 10 is 9V, the feedback voltage of 2.32V is selected. The threshold reference value is used for calculating the first feedback voltage threshold V _LL and the second feedback voltage threshold V _SK , and so on.

Switching power converter input voltage Feedback voltage threshold reference value 9V 2.32V 24V 2.09V 36V 1.81V

In principle, the feedback voltage threshold reference value, the first proportional value R1 and the second proportional value R2 are designed for the purpose of more optimized light load efficiency and low no-load power consumption to determine the microcontroller 40 The timing to enter the fixed frequency control mode and the skip cycle control mode. In the embodiment of the present invention, through the setting of the first proportional value R1, the fixed frequency control mode is implemented when the load capacity of the load is half load (ie: half of the full load), so that the frequency of the drive signal S1 is More than half of the full load frequency.

Step S03: Determine the relationship between the feedback voltage V _FB of the switching power converter 10 and the feedback voltage thresholds. In the embodiment of the present invention, the microcontroller 40 successively determines the voltage magnitude between the feedback voltage V _FB and the first feedback voltage threshold V _LL and the second feedback voltage threshold V _SK . Explain later.

Step S04: Execute a variable frequency control mode, a constant frequency control mode or a skip period control mode according to the judgment result of step S03, in which the microcontroller 40 outputs a driving signal S1 to the switch Q1, and executes the control mode according to the executed The variable frequency control mode, the fixed frequency control mode or the skip cycle control mode correspondingly adjusts the voltage, pulse width and/or frequency of the driving signal S1. The waveforms of the output current I _O and the output voltage V _O , the feedback voltage V _FB and the driving signal S1 of the switching power converter 10 can be referred to FIG. 4A to FIG. 4D , wherein FIG. 4A shows the switching power converter. The waveform of the output current I _O of 10, the output current I _O is a maximum current at time t0 and decreases with time, so starting from time t0, it can show full load, heavy load, light load, extremely light load and empty load in sequence. The amount of load carried.

In step S03, the microcontroller 40 determines whether the feedback voltage V _FB is less than or equal to the first feedback voltage threshold V _LL (step S031). If it is determined to be no in step S031, it proceeds to step S04 to execute the frequency conversion. The control mode causes the frequency of the drive signal S1 to change with the load of the load. If it is determined to be yes in step S031, the microcontroller 40 further determines whether the feedback voltage V _FB is less than or equal to the second feedback voltage threshold V _SK (step S032). If it is determined to be no in step S032, step S032 is entered. S04 is to execute the fixed frequency control mode so that the frequency of the driving signal S1 is a fixed frequency.

If it is determined to be yes in step S032, the microcontroller 40 enters step S04 to execute the cycle skip control mode. In the cycle skip control mode, the microcontroller 40 determines whether the feedback voltage V _FB rebounds and is greater than or equal to The second feedback voltage threshold V _SK (step S041); if the determination in step S041 is yes, the microcontroller 40 executes the fixed frequency control mode to make the frequency of the driving signal S1 the fixed frequency and then returns to Step S031; If the determination in step S041 is negative, the microcontroller 40 stops outputting the driving signal S1 to the switch Q1.

Based on Figures 4A to 4D, the microcontroller 40 determines that V _FB ≦ V _LL at time t1 and enters the fixed frequency control mode. That is to say, time t0 to t1 represents that the load is full load or heavy load. Therefore, the microcontroller 40 executes the frequency conversion control mode from time t0 to t1, and it can be seen that the output current I _O of the switching power converter 10 from time t0 to t1 is relatively high and the output voltage V _O is relatively stable. The microcontroller 40 determines that V _FB ≦ V _SK at time t2 and enters the cycle skip control mode. That is to say, time t1 to t2 represents that the load is light load, and it can be seen that the microcontroller 40 starts from the frequency conversion control mode. After the mode enters the fixed frequency control mode, the frequency of the driving signal S1 is reduced. Time t2 to t4 represents that the load is extremely light load or no load, so the microcontroller 40 executes the cycle skip control mode at time t2 to t4, wherein the microcontroller 40 determines V _FB at time t2 to t3 ≦V _SK and stop outputting the driving signal S1 (ie: 0V and the frequency is 0 Hz). At time t3, it is determined that V _FB ≧V _SK and the fixed frequency control mode is executed, so that the frequency of the driving signal S1 is at Between time t2 and t4, there is an alternating change of "zero" and "non-zero".

The waveform fluctuation phenomenon of the output voltage V _O of the switching power converter 10 from time t2 to t4 is a phenomenon of the skip cycle control mode. With reference to FIG. 2 and FIG. 4A to 4D, when the driving signal S1 starts temporarily from time t2 is 0V, the output voltage V _O of the switching power converter 10 begins to decrease, and the feedback voltage V _FB received by the microcontroller 40 from the isolation feedback circuit 50 increases (based on the first signal of the optocoupler 51 The voltage source Vcc) connected to the output terminal, as time progresses, the microcontroller 40 determines that V _FB ≧V _SK at time t3 and executes the fixed frequency control mode, so it outputs the fixed frequency control mode from time t3 to t4 The driving signal S1 is given to the switching switch Q1, the output voltage V _O of the switching power converter 10 begins to increase, and the feedback voltage V _FB received by the microcontroller 40 from the isolation feedback circuit 50 decreases. After time t4, and by analogy, the microcontroller 40 can again determine that V _FB ≦ V _SK and stop outputting the driving signal S1, and repeat the cycle, so that the frequency of the driving signal S1 appears "zero" in the skip cycle control mode. ” and “non-zero” alternately.

Please refer to Figures 1 and 2. The active clamping circuit 60 in the present invention is connected to the primary winding 21 of the transformer 20. The active clamping circuit 60 can be a self-excited active clamping circuit and includes a clamp switch Q2. , a first capacitor C1, a second capacitor C2, a resistor R, and may further include a diode D. From the perspective of the circuit architecture of the flyback power converter, the clamp switch Q2 can be a high-side switch, and the switching switch Q1 can be a low-side switch.

One end of the clamp switch Q2 is connected to one end of the first capacitor C1 , and the other end of the first capacitor C1 is connected to the first end of the primary winding 21 of the transformer 20 and the power input end 11 of the switching power converter 10 ; The other end of the clamp switch Q2 is connected to one end of the second capacitor C2, and the other end of the second capacitor C2 is connected to the second end of the primary winding 21 of the transformer 20 and one end of the switch Q1, so that the The clamp switch Q2 is connected in series between the first capacitor C1 and the second capacitor C2; in addition, the clamp switch Q2 also has a control terminal. In the embodiment of the present invention, the clamp switch Q2 is a transistor, such as a metal oxide semi-field effect transistor (MOSFET). Its gate serves as the control terminal, its drain is connected to the first capacitor C1, and its source The second capacitor C2 is connected, and there is a parasitic capacitance C3 between its gate and source.

One end of the resistor R is connected to the control end of the clamp switch Q2, and the other end of the resistor R is connected to the second end of the primary winding 21 of the transformer 20 and one end of the switch Q1. The anode of the diode D is connected to the control end of the clamp switch Q2, and the cathode of the diode D2 is connected to the second end of the primary winding 21 of the transformer 20 and one end of the switch Q1, that is to say, the The resistor R is connected across the anode and cathode of the diode D.

The active clamping circuit 60 is applied in a current critical mode, hereinafter referred to as BCM mode (Boundary Current Mode). Please refer to Figures 5A to 5H for its related voltage waveforms. The vertical axis of each waveform diagram indicates the voltage value (V), and the horizontal axis represents time; the circuit operation of the active clamping circuit 60 will be further described below.

T0 period: In the BCM mode, the voltage V _P of the primary side winding 21 of the transformer 20 gradually drops to 0V, the voltage V _C2 across the second capacitor C2 also drops to 0V, and the voltage of the parasitic capacitor C3 passes through the diode. Body D is quickly discharged to 0V, causing the gate voltage of the clamp switch Q2 to be lower than the conduction critical voltage (Vgs-th). The clamp switch Q2 turns to the closed state (OFF). At this time, the switch Q1 The drain-source voltage V _Q1-DS gradually drops from the original high level to 0V along with Vp. The gate voltage V _Q1-G of the switch Q1 starts to send a high-level signal. The control of the switch Q1 The mode also achieves zero voltage switching (ZVS).

Period T1: The switch Q1 is turned on, that is, the switch Q1 is about to switch from the original off state (OFF) to the on state (ON), and the voltage Vp of the primary winding 21 of the transformer 20 rises from 0V to V _I .

Period T2: When the gate voltage V _Q1-G of the switch Q1 decreases to a low level (ie, the low level of the PWM signal), the switch Q1 becomes closed (OFF). Because the switch Q1 changes from the on state to the off state, a reverse voltage is generated on the primary winding 21 of the transformer 20, so the primary winding voltage _VP shown in FIG. 5H shows a negative value. As shown in Figure 6, the voltage V _P charges the second capacitor C2 and the first capacitor C1 through the body diode of the clamp switch Q2. The second capacitor C2 and the first capacitor C1 During charging, the spike generated by the leakage inductance of the transformer 20 will also be absorbed. At this time, the second capacitor C2 and the first capacitor C1 will gradually charge to a steady state. The drain of the clamp switch Q2 -The source voltage V _Q2-DS is also because the body diode is turned on first and drops to about the forward voltage (VF) of the body diode before the driving signal is given, as shown in the waveform diagram marked with S. The second capacitor C2 will also charge the parasitic capacitor C3 through the resistor R during the charging process. When the voltage of the parasitic capacitor C3 reaches the conduction threshold voltage (Vgs-th) of the clamp switch Q2, the clamp switch Q2 That is, it turns into a conductive state to achieve zero voltage switching (ZVS) and absorb surges. Among them, the resistor R serves as a delay element. During charging, the gate voltage V _Q2-G of the clamp switch Q2 is controlled by the delay time determined by the resistor R and the parasitic capacitance C3. The conduction critical voltage (Vgs-th) is reached only when the drain-source voltage V _Q2-DS drops to approximately the forward voltage (VF) of the body diode, allowing the clamp switch Q2 to The drive control meets the requirements of zero voltage switching.

Period T3: In the BCM mode, the voltage V _P of the primary winding 21 of the transformer 20 will gradually drop to zero, and the voltage V _C2 across the second capacitor C2 will also drop to 0V. The voltage of the parasitic capacitor C3 passes through the two The pole body D is quickly discharged to 0V (see Figure 7), causing the gate voltage V _Q2-G of the clamp switch Q2 to be lower than the conduction critical voltage (Vgs-th), and the clamp switch Q2 turns to the closed state. (OFF), because the clamp switch Q2 can be turned off quickly, the switching loss of the clamp switch Q2 can be reduced, and the drain-source voltage V _Q1-DS of the switch Q1 gradually drops from the original high level to 0V. , repeat the actions in the T0 period.

T4 period: At this time, the switch Q1 is turned on, as shown in Figure 7, and the action of the T1 period is repeated.

In a preferred embodiment, in order to minimize the on-resistance (R _DS ) and the lowest loss when the clamp switch Q2 is turned on, the gate of the clamp switch Q2 should be maintained at a more ideal driving voltage value, which is about A better value is about 10V. The sum of the voltages of the first capacitor C1 and the second capacitor C2 (V _C1 + V _C2 ) is approximately equal to the voltage of the primary winding 21 when releasing energy (that is, _VP is the reverse voltage). The _VP voltage at this time The value is related to the number of turns N _P of the primary side winding 21 and the number of turns N _S of the secondary side winding 22 of the transformer 20 , that is, V _P =[(N _S /N _P )×V _O ]. When actually designing a power conversion device, due to different input/output requirements, V _P is limited by the turns ratio and cannot approach the optimal value of 10V. Therefore, the present invention can select an appropriate value of the second capacitor C2, so that After the first capacitor C1 and the second capacitor C2 divide the voltage, a voltage close to the optimal value of 10V is obtained on the second capacitor C2, so that the gate of the clamp switch Q2 has a better driving voltage value. , to achieve a more ideal driving effect.

To sum up, the present invention has the following effects:

1. The microcontroller 40 monitors the input voltage V _I and the feedback voltage V _FB of the switching power converter 10 in real time. The feedback voltage V _FB can reflect the load. The microcontroller 40 implements multi-mode hybrid control. The so-called multi-mode includes, for example, the variable frequency control mode, the fixed frequency control mode and the cycle skipping control mode to achieve power conversion characteristics that optimize the efficiency curve.

For example, when the load connected to the present invention is fully loaded or heavily loaded, the microcontroller 40 executes the frequency conversion control mode. As the load becomes lighter, the frequency of the driving signal S1 output to the switch Q1 becomes higher. In order to avoid high-frequency noise caused by the high-frequency switching of the switch Q1 during light load, extremely light load or no load, , switching loss and electromagnetic interference on the circuit board circuit, the microcontroller 40 can instantly switch to the fixed frequency control mode, and also instantly switch to the cycle skip control mode when the load is extremely light or no load, causing the driver to The frequency of the signal S1 is maintained at a constant value without increasing, thereby optimizing the power conversion efficiency and effectively improving the aforementioned problems of high-frequency noise, switching loss, and electromagnetic interference on the circuit board lines.

2. Through the arrangement of the active clamp circuit 60, it does not need to add an additional drive circuit, and can control the on/off of the clamp switch Q2 according to the polarity of the voltage _VP of the primary winding 21. The active clamp circuit 60 can not only achieve the function of absorbing surges, but also enable the gate of the clamp switch Q2 to obtain an ideal driving voltage by appropriately selecting the second capacitor C2. When turned on, it presents a smaller on-resistance (R _DS ) and reduces losses.

10: Switching power converter 11: Power input terminal 12: Power output terminal 13: Voltage dividing circuit 20: Transformer 21: Primary side winding 22: Secondary side winding 30: Output circuit 40: Microcontroller 50: Isolated return Feeding circuit 51: Optocoupler 60: Active clamping circuit Q1: Switch Q2: Clamp switch C1: First capacitor C2: Second capacitor C3: Parasitic capacitance R: Resistor D: Diode V _I : Input voltage V _O : Output voltage Vcc: Voltage source V _FB : Feedback voltage V _LL : First feedback voltage threshold V _SK : Second feedback voltage threshold V _P : Voltage of primary winding I _O : Output current S1: Drive signal

Figure 1: Circuit schematic diagram (1) of an embodiment of a multi-mode hybrid controlled DC-DC power conversion circuit of the present invention. Figure 2: Circuit schematic diagram (2) of an embodiment of the multi-mode hybrid controlled DC-DC power conversion circuit of the present invention. Figure 3: Schematic flow chart of the control method of the present invention. Figure 4A: In an embodiment of the present invention, the output current I _O waveform diagram of the switching power converter. Figure 4B: Waveform diagram of feedback voltage V _FB in the embodiment of the present invention. Figure 4C: Waveform diagram of the driving signal S1 in the embodiment of the present invention. Figure 4D: Waveform diagram of the output voltage V _O of the switching power converter in an embodiment of the present invention. Figure 5A: Detailed waveform diagram of the output voltage V _O of the switching power converter in an embodiment of the present invention. Figure 5B: In the embodiment of the present invention, the waveform diagram of voltage V _C2 across the second capacitor C2. Figure 5C: In the embodiment of the present invention, the waveform diagram of voltage V _C1 across the first capacitor C1. Figure 5D: In the embodiment of the present invention, the voltage V _{Q 2 -DS} waveform diagram between the drain and the source of the clamp switch Q2. Figure 5E: In the embodiment of the present invention, the voltage V _Q2-G waveform between the gate and the source of the clamp switch Q2. Figure 5F: In the embodiment of the present invention, the voltage V _Q1-DS between the drain and the source of the switch Q1 is a waveform diagram. Figure 5G: In the embodiment of the present invention, the gate voltage V _Q1-G waveform diagram of the switch Q1. Figure 5H: In the embodiment of the present invention, the voltage V _P waveform between the two ends of the primary winding of the transformer. Figure 6: In the embodiment of the present invention, the circuit operation diagram is shown when the switch Q1 is turned off and the clamp switch Q2 is turned on. Figure 7 is a schematic diagram of the circuit operation when the switch Q1 is turned on and the clamp switch Q2 is turned off in the embodiment of the present invention.

10: Switching power converter 11: Power input terminal 12: Power output terminal 13: Voltage dividing circuit 20: Transformer 21: Primary side winding 22: Secondary side winding 30: Output circuit 40: Microcontroller 50: Isolated return Feed circuit 60: Active clamping circuit V _I : Input voltage V _O : Output voltage V _FB : Feedback voltage V _P : Voltage of primary winding I _O : Output current S1: Drive signal Q1: Switch

Claims (10)

A multi-mode hybrid controlled DC-DC power conversion circuit includes: a switching power converter, including: a transformer; and a switching switch connected in series to the primary side winding of the transformer and having a control end; and a microcontroller The microcontroller is connected to the switching power converter and the control terminal of the switching switch, and stores a plurality of feedback voltage threshold reference values and a plurality of proportional values; the microcontroller detects an input voltage of the switching power converter, Select one of the feedback voltage threshold reference values corresponding to the input voltage of the switching power converter, multiply the selected feedback voltage threshold reference value by the plurality of proportional values, and set them respectively as evaluation load values. Determine multiple feedback voltage thresholds of the reference value, and determine the magnitude relationship between a feedback voltage of the switching power converter and each of the feedback voltage thresholds, so as to execute a frequency conversion control mode based on the judgment results. A fixed frequency control mode or a skip cycle control mode; the microcontroller outputs a drive signal to the switch, and adjusts the drive signal according to the executed frequency control mode, the fixed frequency control mode, or the skip cycle control mode. frequency. The multi-mode hybrid controlled DC-DC power conversion circuit as described in claim 1, wherein the microcontroller is connected to the power output end of the switching power converter through an isolated feedback circuit to receive the signal from the isolated feedback circuit. Receive the feedback voltage; the microcontroller determines the relationship between the feedback voltage and the feedback voltage threshold, and executes the variable frequency control mode, the fixed frequency control mode or the cycle skipping according to the judgment result control mode. The multi-mode hybrid controlled DC-DC power conversion circuit as described in claim 2, wherein the feedback voltage thresholds include a first feedback voltage threshold and a second feedback voltage threshold, the first The feedback voltage threshold is greater than the second feedback voltage threshold; when the microcontroller determines that the feedback voltage is greater than the first feedback voltage threshold, the microcontroller executes the frequency conversion control mode so that the driver The frequency of the signal changes with the load; When the microcontroller determines that the feedback voltage is less than or equal to the first feedback voltage threshold and greater than the second feedback voltage threshold, the microcontroller executes the fixed frequency control mode so that the driving signal The frequency is a fixed frequency; when the microcontroller determines that the feedback voltage is less than or equal to the second feedback voltage threshold, the microcontroller executes the cycle skip control mode. In the cycle skip control mode, the microcontroller The controller determines whether the feedback voltage rises and is greater than or equal to the second feedback voltage threshold; if so, the microcontroller makes the frequency of the drive signal a fixed frequency; if not, the microcontroller stops outputting the drive signal. to the toggle switch. The multi-mode hybrid control DC-DC power conversion circuit as described in claim 3, wherein in the frequency conversion control mode, when the load is full load, the frequency of the drive signal is defined as a full load frequency; In the fixed frequency control mode and the skip cycle control mode, the frequency of the driving signal is more than half of the full load frequency. The multi-mode hybrid controlled DC-DC power conversion circuit as described in any one of claims 1 to 4, further includes an active clamp circuit connected to the primary winding of the transformer and including: a clamp switch connected in series Between a first capacitor and a second capacitor, the other end of the first capacitor is connected to the first end of the primary winding of the transformer, and the other end of the second capacitor is connected to the second end of the primary winding of the transformer; And a resistor, one end of which is connected to a control end of the clamp switch, and the other end is connected to the second end of the primary side winding of the transformer; one end of the switch is connected to the second end of the primary side winding of the transformer and is connected to the second end of the primary side winding of the transformer. The primary windings are connected in series. The multi-mode hybrid controlled DC-DC power conversion circuit as described in claim 5, wherein the active clamping circuit includes a diode, the anode of which is connected to the control terminal of the clamp switch, and the cathode of which is connected to the primary terminal of the transformer. The second end of the side winding. A control method for a multi-mode hybrid control DC-DC power conversion circuit is executed by a microcontroller, which is connected to a switching power converter and a switch, and stores multiple feedback voltage threshold reference values and a plurality of proportional values, the control method includes the following steps: (a) detecting an input voltage and a feedback voltage of the switching power converter; (b) selecting a phase phase with the input voltage of the switching power converter Corresponding to one of the feedback voltage threshold reference values, the selected feedback voltage threshold reference value is multiplied by the multiple proportional values to respectively set multiple feedback voltage threshold values as the judgment reference value for evaluating the load; (c) Determine the relationship between the feedback voltage of the switching power converter and each feedback voltage threshold; and (d) execute a variable frequency control mode and a constant frequency control based on the judgment result of step (c) mode or a skip cycle control mode, wherein the microcontroller outputs a drive signal to the switch, and adjusts the drive signal according to the executed frequency control mode, the fixed frequency control mode or the skip cycle control mode. frequency. As claimed in claim 7, the control method of the multi-mode hybrid control DC-DC power conversion circuit, in step (b), the feedback voltage thresholds include a first feedback voltage threshold and a second feedback voltage threshold, the first feedback voltage threshold is greater than the second feedback voltage threshold; in step (c), it further includes: (c-1) the microcontroller determines whether the feedback voltage is less than or equal to If the first feedback voltage threshold is determined to be negative in step (c-1), step (d) is entered to execute the frequency conversion control mode so that the frequency of the drive signal changes with the load; (c-2) If it is determined to be yes in step (c-1), the microcontroller determines whether the feedback voltage is less than or equal to the second feedback voltage threshold. If it is determined to be yes in step (c-2) No, go to step (d) to execute the fixed frequency control mode so that the frequency of the drive signal is a fixed frequency; (c-3) If it is determined to be yes in step (c-2), go to step (d) to execute In the skip cycle control mode, in the skip cycle control mode, the microcontroller determines whether the feedback voltage rises and is greater than or equal to the second feedback voltage threshold; if so, the microcontroller sets the frequency of the drive signal to is a fixed frequency and returns to step (c-1); if not, the microcontroller stops outputting the driving signal to the switch. The control method of a multi-mode hybrid control DC-DC power conversion circuit as described in claim 8, wherein the plurality of proportional values include a first proportional value and a second proportional value; in step (b), the micro The controller multiplies the selected feedback voltage threshold reference value by the first proportional value to set the first feedback voltage threshold value, and multiplies the selected feedback voltage threshold reference value by the second proportional value. The second feedback voltage threshold is set to a value, wherein the selected feedback voltage threshold reference value corresponds to the detected input voltage of the switching power converter. The control method of the multi-mode hybrid control DC-DC power conversion circuit as described in claim 8 or 9, wherein in the frequency conversion control mode, when the load is full load, the frequency of the drive signal is defined as a full load frequency; in the fixed frequency control mode and the skip cycle control mode, the frequency of the driving signal is more than half of the full load frequency.

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