A driving circuit and an edge modulation circuit thereof
By using a full-bridge circuit unit to excite and demagnetize the isolation transformer, and utilizing the freewheeling current of the switching diode to achieve active demagnetization, the problems of insufficient driving capability and slow demagnetization speed in the prior art are solved, thereby improving the driving capability and reliability of the switching power supply and supporting the application of high-power semiconductors.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- MORNSUN GUANGZHOU SCI & TECH
- Filing Date
- 2022-11-14
- Publication Date
- 2026-06-02
AI Technical Summary
Existing transformer-isolated drives suffer from insufficient driving capability, large size, high cost, and poor reliability in high-frequency, high-power, and small-size switching power supplies. In particular, when transmitting high-power signals, they are prone to causing sudden voltage changes in the secondary capacitor, which can damage the power switching transistors.
A full-bridge circuit unit is used to excite and demagnetize the isolation transformer. Active demagnetization is achieved by controlling the on and off of each switch on the full-bridge circuit unit, thereby improving the driving capability. Demagnetization is also achieved by using the freewheeling current of the body diodes of the switch tubes, thus avoiding the problem of slow demagnetization speed in traditional methods.
It improves the demagnetization speed of isolation transformers, enhances driving capability, supports the driving of high-power semiconductors, and achieves active demagnetization without adding components, avoiding the risk of transformers exceeding specifications due to continuous increase in excitation current.
Smart Images
Figure CN115694150B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of switching power supplies, and in particular to a drive circuit and its edge modulation circuit for use in switching power supplies. Background Technology
[0002] Compared to linear power supplies, switching power supplies are characterized by their small size, high efficiency, high power, and strong anti-interference capabilities, and are widely used in automotive, photovoltaic, industrial control, medical, and handheld devices. With continuous technological iteration, switching power supplies are developing towards higher frequencies, higher power, and smaller size. MOSFETs and insulated gate bipolar transistors (IGBTs) have superior performance at higher frequencies and are therefore used as power switching devices in the power stage of switching power supplies. As we all know, each power switching device requires a driving circuit. Switching power supplies have different topologies in different applications, and the position of the power switching device in different topologies determines the driving method. Currently, there are two driving methods for power switching devices: non-isolated direct drive and isolated floating ground drive.
[0003] There are three existing types of isolated drivers: bootstrap drivers, transformer-isolated drivers, and drivers that combine power and load power. Bootstrap drivers are the ideal driving solution for bridge topologies, but due to their isolation voltage withstand capability, they can only be used in conventional applications. They cannot be used directly for applications exceeding 1kV or non-bridge topologies, which limits their application. Drivers that combine power and load power are costly and bulky, suitable for high-power drives where size and cost are not critical. Transformer-isolated drivers are a solution applicable to all scenarios and offer a relatively balanced cost and size. Traditional transformer-isolated drivers use an asymmetrical half-bridge architecture with capacitors on both the primary and secondary sides. Because the transformer is constantly in a state of excitation and demagnetization when transmitting duty cycle signals, the inductance must be increased to reduce the excitation current and thus reduce losses. This results in a larger size. In addition, when the transmitted duty cycle is too large or a sudden change occurs, the secondary capacitor voltage cannot change abruptly, leading to a continuous high level at the output that can damage the power switch. Solving this problem requires adding a secondary capacitor discharge circuit, further increasing cost and size.
[0004] To address the issues of size, cost, and reliability associated with traditional transformer-isolated drives, Chinese invention patent CN113193735A proposes a novel control method and circuit. (Reference...) Figure 1The method modulates the rising edge of the input signal into a fixed-width positive pulse and the falling edge into a fixed-width negative pulse using an edge modulation circuit. While the input signal is continuously high, an energy replenishment circuit generates multiple consecutive positive pulses at a certain period. These pulses are then transmitted to the secondary side via an isolation transformer. The secondary side circuit demodulates the first corresponding positive pulse into the rising edge of the secondary-side drive and the first corresponding negative pulse into the falling edge of the secondary-side drive. The continuous positive pulses replenish the energy of the driven power transistor to maintain the voltage required for conduction, thus restoring the input signal and solving the problem of continuous conduction. The width and period of the continuous positive and negative pulses can be adjusted as needed. This method also improves the problem of insufficient drive voltage during low-frequency startup.
[0005] However, this solution has the following limitations:
[0006] The key factor affecting the driving capability of the above scheme is the pulse width ratio. The higher the pulse width ratio, the more energy is transferred and the stronger the driving capability. The pulse width ratio refers to the proportion of the pulse duration to the entire switching cycle.
[0007] According to the modulation principle, reference Figure 2 , Figure 2 The edge modulation circuit 100 shown is Figure 1 The internal block diagram of the edge modulation circuit in the central region shows the excitation process as follows: Taking a positive pulse as an example, when the upper switch Sa of the first bridge arm and the lower switch Sd of the second bridge arm are turned on, the input voltage V... gs When applied to both ends of the primary side of the transformer, the transformer is energized; the current flows out from the positive terminal of the power supply, passes sequentially through the upper switch Sa of the first bridge arm, the primary winding of the transformer, and the lower switch Sd of the second bridge arm, before returning to the negative terminal of the power supply.
[0008] Excitation current calculation: In the formula, L is the magnetizing inductance of the isolation transformer, ΔI1 is the magnetizing current, Δt1 is the magnetizing time, and V gs This is the input voltage.
[0009] After the pulse ends, the lower switch Sd of the second bridge arm remains in the on state when the input signal is high. After the narrow pulse ends, the upper switch Sa of the first bridge arm turns off. According to the modulation logic, the upper switch Sa and the lower switch Sb of the first bridge arm are complementary. The lower switch Sb of the first bridge arm turns on, the transformer is demagnetized, and the current flows out from the lower end of the primary winding of the transformer, passes through the lower switch Sd of the second bridge arm and the lower switch Sb of the first bridge arm in sequence, and then returns to the upper end of the primary winding of the transformer.
[0010] Demagnetizing current calculation: In the formula, L is the magnetizing inductance of the isolation transformer, ΔI2 is the demagnetizing current, Δt2 is the demagnetizing time, and V R This is the demagnetizing voltage.
[0011] Demagnetizing voltage V R Determined by the loop current and line impedance, the demagnetizing voltage V decreases as the loop current decreases. R The line impedance decreases synchronously, including the on-resistance of the MOSFET (Switch) and the circuit impedance, thereby reducing the demagnetizing voltage V. R It is much smaller than the excitation voltage.
[0012] In other words, the demagnetization stage of the transformer in the above scheme mainly relies on the on-state voltage drop of the two MOSFETs and the line impedance for demagnetization, resulting in a relatively slow demagnetization speed. The excitation current of the above method is illustrated as follows: Figure 3 As shown, using the above scheme to increase the driving power and further increase the pulse width ratio, while keeping the pulse width unchanged, the pulse density is increased and the pulse interval time is reduced. The amplitude of the single energy replenishment pulse excitation process is greater than the amplitude of the demagnetization process, the excitation current continues to rise, and the transformer is at risk of exceeding specifications.
[0013] Furthermore, the above-mentioned solution suffers from insufficient driving capability when driving high-power semiconductor transistors. Summary of the Invention
[0014] To address the shortcomings of existing technologies, this invention provides a driving circuit and its edge modulation circuit, which are applied to switching power supplies. The circuit uses a full-bridge circuit unit to excite and demagnetize the isolation transformer. By controlling the on and off states of each switch transistor on the full-bridge circuit unit, active demagnetization is achieved, improving the driving capability and supporting the driving of high-power semiconductors.
[0015] One objective of this invention is to provide a driving circuit, including a power input, an edge modulation circuit, and an isolation transformer, and further including a demodulation module. The power input includes a positive power input and a power input ground. The isolation transformer includes a first input terminal, a second input terminal, and an output port. The edge modulation circuit includes a full-bridge circuit unit, which includes a bridge arm one and a bridge arm two. Switch S1 and switch S2 are disposed on bridge arm one, and switch S3 and switch S4 are disposed on bridge arm two. The first terminal of switch S1 in bridge arm one is connected to the positive power input, and the second terminal of switch S1 is connected to the first input terminal of the isolation transformer. The first terminal of switch S2 in bridge arm one is connected to the first input terminal of the isolation transformer, and the second terminal of switch S2 is connected to the power input ground. The power input is connected to the source input ground. The first terminal of the switch S3 of the second bridge arm is connected to the positive power input, and the second terminal of the switch S3 is connected to the second input terminal of the isolation transformer. The first terminal of the switch S4 of the second bridge arm is connected to the second input terminal of the isolation transformer, and the second terminal of the switch S4 is connected to the power input ground. The third terminal of the switch S1 is connected to the first pulse drive circuit, the third terminal of the switch S2 is connected to the second pulse drive circuit, the third terminal of the switch S3 is connected to the third pulse drive circuit, and the third terminal of the switch S4 is connected to the fourth pulse drive circuit. The demodulation module is connected to the output port of the isolation transformer, and the output terminal of the demodulation module is connected to the power semiconductor. It is used to demodulate and amplify the signal generated by the edge modulation circuit to drive the power semiconductor.
[0016] The drive circuit performs the following process:
[0017] Excitation process: During each pulse generated by the edge modulation circuit, the isolation transformer is energized by driving the four switching transistors of the full-bridge circuit unit to turn on or off;
[0018] Demagnetization process: After each pulse ends, the isolation transformer is demagnetized by forming a freewheeling circuit with the lower bridge arm switch S2 and switch S4 of the full-bridge circuit unit.
[0019] The present invention also has the following preferred designs:
[0020] The present invention also includes a control circuit, wherein a first input terminal of the control circuit is connected to the positive power input, a second input terminal of the control circuit is connected to the input signal PWM, a third input terminal of the control circuit is connected to the power input ground, and the four output terminals of the control circuit are connected one-to-one with the input terminals of the first pulse drive circuit, the second pulse drive circuit, the third pulse drive circuit, and the fourth pulse drive circuit, to achieve:
[0021] When the input signal PWM is high: the control circuit modulates the input signal PWM into four types of pulses, which are then input to the corresponding pulse drive circuits to control the switching transistors S1 and S4 to turn on, and the switching transistors S2 and S3 to turn off. The edge modulation circuit generates a positive pulse, and the input voltage is applied to both ends of the primary winding of the isolation transformer. The current flows out from the positive terminal of the power supply, passes through the switching transistor S1, the primary winding of the isolation transformer, and the switching transistor S4 in sequence, and then flows into the negative terminal of the power supply, completing the excitation process of the isolation transformer. After each pulse ends, the control circuit controls the switching transistor S4 to turn on, and the switching transistors S1, S2, and S3 are all turned off. The current flows out from the opposite end of the primary winding of the isolation transformer, passes through the body diodes of the switching transistors S4 and S2 in sequence, and returns to the same end of the primary winding of the isolation transformer, completing the demagnetization process of the isolation transformer. The above excitation and demagnetization processes are repeated until the input signal PWM switches to low level.
[0022] When the input signal PWM is low: the control circuit modulates the input signal PWM into four types of pulses, which are then input to the corresponding pulse drive circuits to control the switching transistors S2 and S3 to turn on, and the switching transistors S1 and S4 to turn off. The edge modulation circuit generates a positive pulse, and the input voltage is applied to both ends of the primary winding of the isolation transformer. Current flows out from the positive terminal of the power supply and sequentially flows through the switching transistor S3, the primary winding of the isolation transformer, and the switching transistor S2 into the negative terminal of the power supply, completing the excitation process of the isolation transformer. After each pulse ends, the control circuit controls the switching transistor S2 to turn on, and the switching transistors S1, S3, and S4 are all turned off. Current flows out from the same-name terminal of the primary winding of the isolation transformer and sequentially flows through the body diodes of the switching transistors S2 and S4 back to the opposite-name terminal of the primary winding of the isolation transformer, completing the demagnetization process of the isolation transformer. The above excitation and demagnetization processes are repeated until the input signal PWM switches to a high level.
[0023] The control circuit of the present invention includes a signal generator, a phase shift circuit, a delay matching circuit, a NAND gate, an OR gate, a first AND gate, a second AND gate, a third AND gate, a first NOT gate, and a second NOT gate. The input terminals of the phase shift circuit, the first input terminal of the NAND gate, and the delay matching circuit serve as the second input terminals of the control circuit for connecting to the input signal PWM. The output terminal of the signal generator is connected to the second input terminal of the NAND gate and the first input terminal of the OR gate, respectively. The output terminal of the phase shift circuit is connected to the second input terminal of the OR gate. The output terminal of the delay matching circuit is connected to the input terminal of the first NOT gate. The output terminal of the NAND gate is connected to the first input terminal of the first AND gate. The output terminal of the OR gate is connected to the second input terminal of the first AND gate. The output of the first AND gate is connected to the input of the second NOT gate and the first input of the second AND gate, respectively. The output of the first NOT gate is connected to the second input of the second AND gate. The output of the second NOT gate is connected to the first input of the third AND gate. The output of the delay matching circuit is also connected to the second input of the third AND gate. The output of the third AND gate serves as the first output of the control circuit and is connected to the first pulse drive circuit. The output of the first NOT gate also serves as the second output of the control circuit and is connected to the second pulse drive circuit. The output of the second AND gate serves as the third output of the control circuit and is connected to the third pulse drive circuit. The output of the delay matching circuit also serves as the fourth output of the control circuit and is connected to the fourth pulse drive circuit.
[0024] The process by which the control circuit of the present invention modulates the input signal into four types of pulses using PWM is as follows:
[0025] When the input signal PWM is high: the phase shift circuit outputs a high level, with a phase difference of Ta from the input signal PWM; the output signal PWM1 of the first output terminal of the control circuit is a continuous positive narrow pulse, wherein the first positive narrow pulse output by the first output terminal of the control circuit is the phase difference Ta between the phase shift circuit and the input signal PWM; the frequency and pulse width of the remaining positive narrow pulses are consistent with the output signal of the signal generator; the output signal PWM3 of the third output terminal of the control circuit is low.
[0026] When the input signal PWM is low: the phase shift circuit outputs a low level, with a phase difference of Ta from the input signal PWM; the output signal PWM1 of the first output terminal of the control circuit is low; and the output signal PWM3 of the third output terminal of the control circuit is a continuous positive narrow pulse. The first positive narrow pulse output by the third output terminal of the control circuit is the phase difference Ta between the phase shift circuit and the input signal PWM. The frequency and pulse width of the remaining positive narrow pulses are consistent with the output signal of the signal generator.
[0027] The signal generator produces a pulse signal with a fixed frequency and pulse width of Tb and a frequency of Fb.
[0028] The delay time of the delay matching circuit is set to 0, so that the output signal PWM4 of the fourth output terminal of the control circuit is the same as the input signal PWM, and the output signal PWM2 of the second output terminal of the control circuit is complementary to the output signal PWM4 of the fourth output terminal of the control circuit.
[0029] In this invention, the switching transistors S1 and S3 are MOSFETs, and the switching transistors S2 and S4 are N-channel MOSFETs.
[0030] As a feasible implementation, the first terminal of each of the switching transistors S1, S2, S3 and S4 is the drain, the second terminal is the source, and the third terminal is the gate. The first input terminal of the isolation transformer is the same-name terminal of the primary winding, and the second input terminal of the isolation transformer is the opposite-name terminal of the primary winding.
[0031] The demodulation module of the present invention includes an energy storage circuit, a demodulation circuit, and an amplification circuit. The energy storage circuit is used to store the energy of the pulses transmitted from the primary side to the secondary side of the isolation transformer to power subsequent circuits. The demodulation circuit is used to demodulate the pulses transmitted from the primary side to the secondary side of the isolation transformer into a drive signal that is the same as the input signal PWM. The amplification circuit is used to amplify the drive signal demodulated by the demodulation circuit.
[0032] The output port of the isolation transformer of the present invention includes a terminal of the same name as the secondary winding of the isolation transformer and a terminal of the opposite name as the secondary winding. The first input terminal of the demodulation circuit is connected to the terminal of the same name as the secondary winding of the isolation transformer, the second input terminal of the demodulation circuit is connected to the terminal of the opposite name as the secondary winding of the isolation transformer, the third input terminal of the demodulation circuit is connected to the first output terminal of the energy storage circuit, the first output terminal of the demodulation circuit is connected to the second input terminal of the amplifier circuit, and the second output terminal of the demodulation circuit is grounded. The first input terminal of the energy storage circuit is connected to the terminal of the same name as the secondary winding of the isolation transformer, the second input terminal of the energy storage circuit is connected to the terminal of the opposite name as the secondary winding of the isolation transformer, the first output terminal of the energy storage circuit is also connected to the first input terminal of the amplifier circuit, and the second output terminal of the energy storage circuit is grounded. The first output terminal of the amplifier circuit is used to connect to the drain of the power semiconductor, and the second output terminal of the amplifier circuit is grounded and also connected to the source of the power semiconductor, for amplifying the driving signal demodulated by the demodulation circuit to drive the power semiconductor.
[0033] A second objective of this invention is to provide an edge modulation circuit for the drive circuit of the aforementioned switching power supply, comprising a control circuit and a full-bridge circuit unit. The full-bridge circuit unit includes a bridge arm one and a bridge arm two. Switch S1 and switch S2 are mounted on bridge arm one, and switch S3 and switch S4 are mounted on bridge arm two. The first terminal of switch S1 in bridge arm one is connected to the positive power input, and the second terminal of switch S1 is used to connect to the same-name terminal of the primary winding of the isolation transformer. The first terminal of switch S2 in bridge arm one is used to connect to the same-name terminal of the primary winding of the isolation transformer, and the second terminal of switch S2 is connected to the power input ground. The first terminal of switch S3 in bridge arm two is connected to the positive power input, and the second terminal of switch S3 is used to connect to the opposite-name terminal of the primary winding of the isolation transformer. The first terminal of switch S4 in bridge arm two is used to connect to the... The second terminal of the switching transistor S4 is connected to the power input ground, the third terminal of the switching transistor S1 is connected to the first pulse drive circuit, the third terminal of the switching transistor S2 is connected to the second pulse drive circuit, the third terminal of the switching transistor S3 is connected to the third pulse drive circuit, and the third terminal of the switching transistor S4 is connected to the fourth pulse drive circuit. The first input terminal of the control circuit is connected to the positive power input, the second input terminal of the control circuit is connected to the input signal PWM, and the third input terminal of the control circuit is connected to the power input ground. The four output terminals of the control circuit are connected one-to-one with the input terminals of the first, second, third, and fourth pulse drive circuits. The control circuit modulates the input signal PWM into four types of pulses to drive the four switching transistors to turn on and off.
[0034] The beneficial effects of this invention are as follows:
[0035] 1) By using a full-bridge circuit unit to excite and demagnetize the isolation transformer and by using the switching diode for freewheeling, the demagnetization speed of the isolation transformer is improved, the driving capability is enhanced, and the driving of high-power semiconductors is supported.
[0036] 2) Achieve active demagnetization without adding any components. Attached Figure Description
[0037] Figure 1 This is a schematic diagram of the main structure of existing pulse magnetic isolation drive technology circuits;
[0038] Figure 2 This is a schematic diagram of the main structure of the edge modulation circuit in the existing pulse magnetic isolation drive technology;
[0039] Figure 3 This is a schematic diagram of the energy replenishment density and excitation current of existing pulse magnetic isolation drive technology;
[0040] Figure 4 This is a schematic diagram of a transformer isolation drive circuit according to an embodiment of the present invention;
[0041] Figure 5 This is a schematic diagram of the main structure of the edge modulation circuit according to an embodiment of the present invention;
[0042] Figure 6 This is a schematic diagram of the control circuit of the edge modulation circuit in an embodiment of the present invention;
[0043] Figure 7 These are control waveform diagrams and process waveform diagrams of the edge modulation circuit according to an embodiment of the present invention;
[0044] Explanation of reference numerals in the attached figures:
[0045] 1. Edge modulation circuit, 2. Isolation transformer, 3. Energy storage circuit, 4. Demodulation circuit, 5. Amplification circuit, 6. Power semiconductor, 7. NAND gate, 8. OR gate, 9. First AND gate, 10. First NOT gate, 11. Second NOT gate, 12. Second AND gate, 13. Third AND gate. Detailed Implementation
[0046] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and embodiments, so that those skilled in the art can better understand and implement the technical solution of the present invention.
[0047] Example 1
[0048] like Figures 4 to 7As shown, a driving circuit for a switching power supply includes a power input, an edge modulation circuit 1, an isolation transformer 2, and a demodulation module. The power input includes a positive power input and a power input ground (GND). The isolation transformer 2 includes a first input terminal, a second input terminal, and an output port. The edge modulation circuit 2 includes a full-bridge circuit unit, comprising a bridge arm 1 and a bridge arm 2. Switch S1 and switch S2 are mounted on bridge arm 1, and switch S3 and switch S4 are mounted on bridge arm 2. The first terminal of switch S1 in bridge arm 1 is connected to the positive power input, and the second terminal of switch S1 is connected to the first input terminal of the isolation transformer 2. The first terminal of switch S2 in bridge arm 1 is connected to the first input terminal of the isolation transformer 2, and the second terminal of switch S2 is connected to the power input... The first terminal of the switching transistor S3 in bridge arm two is connected to the positive input of the power supply, and the second terminal of the switching transistor S3 is connected to the second input terminal of the isolation transformer 2. The first terminal of the switching transistor S4 in bridge arm two is connected to the second input terminal of the isolation transformer 2, and the second terminal of the switching transistor S4 is connected to the power supply input ground GND. The third terminal of the switching transistor S1 is connected to the first pulse drive circuit, the third terminal of the switching transistor S2 is connected to the second pulse drive circuit, the third terminal of the switching transistor S3 is connected to the third pulse drive circuit, and the third terminal of the switching transistor S4 is connected to the fourth pulse drive circuit. The demodulation module is connected to the output port of the isolation transformer 2, and the output terminal of the demodulation module is connected to the power semiconductor 6. It is used to demodulate and amplify the signal generated by the edge modulation circuit to drive the power semiconductor 6.
[0049] This invention is based on Chinese Patent CN113193735A and further improves upon it. The basic working principle can be found in the existing content of that patent. The specific improvements of this invention are described in detail below.
[0050] The driving circuit of the present invention performs the following process:
[0051] Excitation process: During each pulse generated by the edge modulation circuit, the isolation transformer is energized by driving the four switching transistors of the full-bridge circuit unit to turn on or off;
[0052] Demagnetization process: After each pulse ends, the isolation transformer 2 is demagnetized by the freewheeling circuit formed by the switching transistors S2 and S4 of the lower bridge arm of the full-bridge circuit unit and the isolation transformer 2.
[0053] As a preferred embodiment:
[0054] like Figure 5As shown, it also includes a control circuit. The first input terminal of the control circuit is connected to the positive power input, the second input terminal is connected to the input signal PWM, the third input terminal is connected to the power input ground GND, and the four output terminals of the control circuit (the four output signals are PWM1, PWM2, PWM3, and PWM4) are connected one-to-one with the input terminals of the first pulse drive circuit, the second pulse drive circuit, the third pulse drive circuit, and the fourth pulse drive circuit to achieve:
[0055] When the input signal PWM is high: the control circuit modulates the input signal PWM into four types of pulses, which are then input to the corresponding pulse drive circuits to control the switching transistors S1 and S4 to turn on, and the switching transistors S2 and S3 to turn off. The edge modulation circuit 1 generates a positive pulse, and the input voltage is applied to both ends of the primary winding of the isolation transformer 2. The current flows out from the positive terminal of the power supply, passes through the switching transistor S1, the primary winding of the isolation transformer 2, and the switching transistor S4 in sequence, and then flows into the negative terminal of the power supply, i.e., the power input ground GND, completing the excitation process of the isolation transformer 2. After each pulse ends, the control circuit controls the switching transistor S4 to turn on, and the switching transistors S1, S2, and S3 are all turned off. The current flows out from the opposite end of the primary winding of the isolation transformer 2, passes through the body diodes of the switching transistors S4 and S2 in sequence, and returns to the same end of the primary winding of the isolation transformer 2, completing the demagnetization process of the isolation transformer 2.
[0056] When the input signal PWM is low: the control circuit modulates the input signal PWM into four types of pulses, which are then input to the corresponding pulse drive circuits to control the switching transistors S2 and S3 to turn on, while the switching transistors S1 and S4 are turned off. The edge modulation circuit 1 generates a positive pulse, and the input voltage is applied to both ends of the primary winding of the isolation transformer 2. The current flows out from the positive terminal of the power supply and sequentially flows through the switching transistor S3, the primary winding of the isolation transformer 2, and the switching transistor S2 into the negative terminal of the power supply, i.e., the power input ground GND, thus completing the excitation process of the isolation transformer 2. After each pulse ends, the control circuit controls the switching transistor S2 to turn on, while the switching transistors S1, S3, and S4 are all turned off. The current flows out from the same-name terminal of the primary winding of the isolation transformer 2 and sequentially flows through the body diodes of the switching transistors S2 and S4 back to the opposite-name terminal of the primary winding of the isolation transformer 2, thus completing the demagnetization process of the isolation transformer 2.
[0057] like Figure 6As shown, the control circuit includes a signal generator, a phase shift circuit, a delay matching circuit, a NAND gate 7, an OR gate 8, a first AND gate 9, a second AND gate 12, a third AND gate 13, a first NOT gate 10, and a second NOT gate 11. The input terminals of the phase shift circuit, the first input terminal of the NAND gate 7, and the delay matching circuit serve as the second input terminals of the control circuit, used to connect to the input signal PWM. The output terminal of the signal generator is connected to the second input terminal of the NAND gate 7 and the first input terminal of the OR gate 8, respectively. The output terminal of the phase shift circuit is connected to the second input terminal of the OR gate 8. The output terminal of the delay matching circuit is connected to the input terminal of the first NOT gate 10. The output terminal of the NAND gate 7 is connected to the first input terminal of the first AND gate 9. The output terminal of the OR gate 8 is connected to the second input terminal of the first AND gate 9. The output of the first AND gate 9 is connected to the input of the second NOT gate 11 and the first input of the second AND gate 12, respectively. The output of the first NOT gate 10 is connected to the second input of the second AND gate 12. The output of the second NOT gate 11 is connected to the first input of the third AND gate 13. The output of the delay matching circuit is also connected to the second input of the third AND gate 13. The output of the third AND gate 13 serves as the first output of the control circuit and is connected to the first pulse drive circuit. The output of the first NOT gate 10 serves as the second output of the control circuit and is connected to the second pulse drive circuit. The output of the second AND gate 12 serves as the third output of the control circuit and is connected to the third pulse drive circuit. The output of the delay matching circuit serves as the fourth output of the control circuit and is connected to the fourth pulse drive circuit.
[0058] The process by which the control circuit modulates the input signal into four types of pulses using PWM is as follows:
[0059] like Figure 7 The waveforms shown are the modulated control waveform and process waveform. From top to bottom, they are: input signal PWM, output signal PWM4 from the fourth output terminal of the control circuit, output signal PWM2 from the second output terminal of the control circuit, output signal of the phase shift circuit, output signal of the signal generator, output signal of NAND gate 7, output signal of OR gate 8, output signal of the first AND gate 9, output signal PWM3 from the second AND gate 10, output signal of the second NOT gate 12, and output signal PWM1 from the third AND gate 13.
[0060] When the input signal PWM is high: the phase shift circuit outputs a high level, with a phase difference of Ta from the input signal PWM; the output signal PWM1 of the first output terminal of the control circuit is a continuous positive narrow pulse, wherein the first positive narrow pulse output by the first output terminal of the control circuit is the phase difference Ta between the phase shift circuit and the input signal PWM; the frequency and pulse width of the remaining positive narrow pulses are consistent with the output signal of the signal generator; the output signal PWM3 of the third output terminal of the control circuit is low.
[0061] When the input signal PWM is low: the phase shift circuit outputs a low level, with a phase difference of Ta from the input signal PWM; the output signal of the first output terminal of the control circuit is low; and the output signal of the third output terminal of the control circuit is a continuous positive narrow pulse. The first positive narrow pulse output by the third output terminal of the control circuit is the phase difference Ta between the phase shift circuit and the input signal PWM. The frequency and pulse width of the remaining positive narrow pulses are consistent with the output signal of the signal generator.
[0062] The signal generator produces a pulse signal with a fixed frequency and pulse width of Tb and a frequency of Fb.
[0063] The delay time of the delay matching circuit is set to 0, so that the output signal PWM4 of the fourth output terminal of the control circuit is the same as the input signal PWM, and the output signal PWM2 of the second output terminal of the control circuit is complementary to the output signal PWM4 of the fourth output terminal of the control circuit.
[0064] In this embodiment, the switching transistors S1 and S3 are MOSFETs, and the switching transistors S2 and S4 are N-channel MOSFETs.
[0065] In this embodiment, the first terminal of each of the switching transistors S1, S2, S3 and S4 is the drain, the second terminal is the source, and the third terminal is the gate. The first input terminal of the isolation transformer 2 is the same-name terminal of the primary winding, and the second input terminal of the isolation transformer 2 is the opposite-name terminal of the primary winding. The specific connection method is as follows: the output terminal of the first pulse drive circuit is connected to the gate of the switching transistor S1, the output terminal of the second pulse drive circuit is connected to the gate of the switching transistor S2, the output terminal of the third pulse drive circuit is connected to the gate of the switching transistor S3, the fourth pulse drive circuit is connected to the gate of the switching transistor S4, the drain of the switching transistor S1 and the drain of the switching transistor S3 serve as the first terminal of the full-bridge circuit unit for positive connection with the power input, the source of the switching transistor S1 and the drain of the switching transistor S2 serve as the second terminal of the full-bridge circuit unit for connection with the same-name terminal of the primary winding of the isolation transformer 2, the source of the switching transistor S2 and the source of the switching transistor S4 serve as the third terminal of the full-bridge circuit unit for connection with the power input ground, and the source of the switching transistor S3 and the drain of the switching transistor S4 serve as the fourth terminal of the full-bridge circuit unit for connection with the opposite-name terminal of the primary winding of the isolation transformer 2.
[0066] To ensure that the peak current of isolation transformer 2 does not continue to rise, the increase in the energy replenishment pulse excitation current must be less than or equal to the decrease in the demagnetizing current during the demagnetizing phase. After the first pulse ends, subsequent energy replenishment pulses and pulse intervals must meet the following conditions:
[0067] Where ΔI1 is the excitation current, V gs V is the input voltage, Δt1 is the excitation time, L is the magnetizing inductance of the primary side of the isolation transformer, ΔI2 is the demagnetizing current, and V is the input voltage. R Δt2 is the demagnetizing voltage, and Δt2 is the demagnetizing time.
[0068] From the above formula, we can see that the input voltage V gs Determined by system parameters, it cannot be optimized. The primary-side magnetizing inductance L synchronously affects the magnetizing current ΔI1 and the demagnetizing current ΔI2, which also cannot be optimized. The only solution is to extend the demagnetizing time Δt2 or increase the demagnetizing voltage V. R To optimize and adjust, firstly, extend the demagnetization time Δt2 to ensure a sufficiently long demagnetization time so that the current does not rise during the energy replenishment phase; secondly, increase the demagnetization voltage V. R By increasing the demagnetizing voltage V R This can accelerate the demagnetization speed and reduce the demagnetization time Δt2, thereby increasing the energy replenishment pulse density and improving the driving power.
[0069] The specific principle of the control method described in this embodiment is as follows:
[0070] When the input PWM is high, the control circuit controls the operation of switches S1 and S4 through the first pulse drive circuit and the fourth pulse drive circuit. At this time, the output signal PWM1 at the first output terminal of the control circuit is a continuous positive narrow pulse, and the output signal PWM4 at the fourth output terminal of the control circuit is continuously high. When the output signal PWM1 is high, switch S1 is turned on, and when the output signal PWM4 is high, switch S4 is turned on. At the same time, the output signals PWM2 and PWM3 at the second and third output terminals of the control circuit are both low, and switches S2 and S3 are both turned off. At this time, the input voltage is applied to both ends of the primary winding of the isolation transformer, and the current flows out from the positive terminal of the power supply, passing through switch S1, the primary winding of the isolation transformer, and switch S4 in sequence before flowing into the negative terminal of the power supply, completing the excitation process of the isolation transformer. When the output signal PWM1 is low, switch S1 is turned off, and the output signal PWM... With the input signal PWM continuously high, switch S4 remains on, while switches S2 and S3 remain off. Current flows from the opposite-named terminal of the primary winding of the isolation transformer, passes sequentially through the body diodes of switches S4 and S2, and returns to the same-named terminal of the primary winding of the isolation transformer, completing the demagnetization process of the isolation transformer. This process repeats until the input signal PWM switches to low, turning off switches S1 and S4.
[0071] When the input signal PWM is low, the control circuit controls the operation of switches S2 and S3 through the second and third pulse drive circuits. At this time, the output signal PWM3 at the third output terminal of the control circuit is a continuous positive narrow pulse, and the output signal PWM2 at the second output terminal of the control circuit is continuously high. When the output signal PWM3 is high, switch S3 is turned on; when the output signal PWM2 is high, switch S2 is turned on. Simultaneously, the output signals PWM1 and PWM4 at the first and fourth output terminals of the control circuit are both low, and switches S1 and S4 are both turned off. At this time, current flows out from the positive terminal of the power supply, passes through switch S3, the primary winding of the isolation transformer, and switch S2 in sequence, and then flows into the negative terminal of the power supply, completing the excitation process of the isolation transformer. When the output signal PWM3 is low, switch S3 is turned off, and the output signal PWM... When the input signal PWM is continuously high, switch S2 remains on, while switches S1 and S4 remain off. Current flows from the same-name terminal of the primary winding of the isolation transformer, passes sequentially through the body diodes of switches S2 and S4, and returns to the opposite-name terminal of the primary winding of the isolation transformer, completing the demagnetization process of the isolation transformer. This process repeats until the input signal PWM switches to a high level, at which point switches S3 and S2 are turned off.
[0072] Based on the demagnetizing principle of the isolation transformer described above, the demagnetizing voltage V RThe demagnetizing voltage is determined by the on-state voltage drop of the switching transistor, the loop current, and the line impedance. In this embodiment, automatic demagnetization is achieved by using the body diode of the switching transistor to form a freewheeling current. Taking the demagnetizing stage when the input signal PWM is high as an example, after switching transistor S1 is turned off, switching transistor S4 remains on. The body diodes of switching transistors S4 and S2 are connected to the isolation transformer 2 to form a demagnetizing loop. Automatic demagnetization ends after each positive narrow pulse of the output signal PWM1. The demagnetizing voltage can be determined based on the on-state voltage drop of the switching transistor and the line impedance, which facilitates increasing the demagnetizing voltage, reducing the energy replenishment interval, increasing the energy replenishment pulse density, and increasing the drive power to support the drive of high-power semiconductors. It also avoids the risk of the excitation current continuously rising and causing the isolation transformer to exceed its specifications.
[0073] The demodulation module in this embodiment includes an energy storage circuit 3, a demodulation circuit 4, and an amplification circuit 5. The energy storage circuit 3 stores the energy of the pulses transmitted from the primary side to the secondary side of the isolation transformer 2 to power subsequent circuits. The demodulation circuit 4 demodulates the pulses transmitted from the primary side to the secondary side of the isolation transformer 2 into a drive signal identical to the input signal PWM. The amplification circuit 5 amplifies the drive signal demodulated by the demodulation circuit. For the specific working principle of this demodulation module, please refer to Chinese Patent Publication No. CN113193735A.
[0074] Specifically, the first input terminal of the demodulation circuit is connected to the same-name terminal of the secondary winding of the isolation transformer 2, the second input terminal of the demodulation circuit is connected to the opposite-name terminal of the secondary winding of the isolation transformer 2, the third input terminal of the demodulation circuit is connected to the first output terminal of the energy storage circuit, the first output terminal of the demodulation circuit is connected to the second input terminal of the amplifier circuit, and the second output terminal of the demodulation circuit is grounded to SGND; the first input terminal of the energy storage circuit is connected to the same-name terminal of the secondary winding of the isolation transformer, the second input terminal of the energy storage circuit is connected to the opposite-name terminal of the secondary winding of the isolation transformer, the first output terminal of the energy storage circuit is also connected to the first input terminal of the amplifier circuit, and the second output terminal of the energy storage circuit is grounded to SGND; the first output terminal of the amplifier circuit is used to connect to the drain of the power semiconductor 6, and the second output terminal of the amplifier circuit is grounded to SGND and also connected to the source of the power semiconductor 6, for amplifying the drive signal demodulated by the demodulation circuit to drive the power semiconductor 6.
[0075] Example 2:
[0076] like Figure 5As shown, this embodiment is an edge modulation circuit 1 applied to the drive circuit in Embodiment 1, including a control circuit and a full-bridge circuit unit. The full-bridge circuit unit includes a bridge arm 1 and a bridge arm 2. Switch S1 and switch S2 are disposed on bridge arm 1, and switch S3 and switch S4 are disposed on bridge arm 2. The first terminal of switch S1 in bridge arm 1 is connected to the positive power input, and the second terminal of switch S1 is used to connect to the same-name terminal of the primary winding of the isolation transformer. The first terminal of switch S2 in bridge arm 1 is used to connect to the same-name terminal of the primary winding of the isolation transformer, and the second terminal of switch S2 is connected to the power input ground. The first terminal of switch S3 in bridge arm 2 is connected to the positive power input, and the second terminal of switch S3 is used to connect to the opposite-name terminal of the primary winding of the isolation transformer. The first terminal of switch S4 in bridge arm 2 is used to connect to the isolation transformer. The primary winding of the transformer has different terminals. The second terminal of switch S4 is connected to the power input ground. The third terminal of switch S1 is connected to the first pulse drive circuit. The third terminal of switch S2 is connected to the second pulse drive circuit. The third terminal of switch S3 is connected to the third pulse drive circuit. The third terminal of switch S4 is connected to the fourth pulse drive circuit. The first input terminal of the control circuit is connected to the positive power input. The second input terminal of the control circuit is connected to the input signal PWM. The third input terminal of the control circuit is connected to the power input ground. The four output terminals of the control circuit are connected one-to-one with the input terminals of the first, second, third, and fourth pulse drive circuits. The control circuit modulates the input signal PWM into four types of pulses to drive the four switches to turn on and off. The isolation transformer is then energized and demagnetized through a full-bridge circuit unit.
[0077] The above embodiments are merely preferred embodiments of the present invention, but should not be construed as limiting the invention. Any modifications and improvements made based on the concept of the present invention should fall within the protection scope of the present invention, and the specific protection scope is subject to the claims.
Claims
1. A driving circuit for use in a switching power supply, comprising a power input, an edge modulation circuit, and an isolation transformer, characterized in that: It also includes a demodulation module, wherein the power input includes a positive power input and a power input ground; the isolation transformer includes a first input terminal, a second input terminal, and an output port; the edge modulation circuit includes a full-bridge circuit unit, the full-bridge circuit unit includes bridge arm one and bridge arm two; bridge arm one is equipped with switching transistors S1 and S2; bridge arm two is equipped with switching transistors S3 and S4; the first terminal of switching transistor S1 in bridge arm one is connected to the positive power input, and the second terminal of switching transistor S1 is connected to the first input terminal of the isolation transformer; the first terminal of switching transistor S2 in bridge arm one is connected to the first input terminal of the isolation transformer, and the second terminal of switching transistor S2 is connected to the power input ground; the first terminal of switching transistor S3 in bridge arm two is connected to the first input terminal of the isolation transformer. The first terminal of the power input is connected to the positive terminal of the power supply, the second terminal of the switching transistor S3 is connected to the second input terminal of the isolation transformer, the first terminal of the switching transistor S4 of the second bridge arm is connected to the second input terminal of the isolation transformer, the second terminal of the switching transistor S4 is connected to the power input ground, the third terminal of the switching transistor S1 is connected to the first pulse drive circuit, the third terminal of the switching transistor S2 is connected to the second pulse drive circuit, the third terminal of the switching transistor S3 is connected to the third pulse drive circuit, the third terminal of the switching transistor S4 is connected to the fourth pulse drive circuit, the demodulation module is connected to the output port of the isolation transformer, and the output terminal of the demodulation module is connected to the power semiconductor, which is used to demodulate and amplify the signal generated by the edge modulation circuit to drive the power semiconductor; The transformer isolation drive circuit performs the following process: Excitation process: During each pulse generated by the edge modulation circuit, the isolation transformer is energized by driving the four switching transistors of the full-bridge circuit unit to turn on or off; Demagnetization process: After each pulse ends, the isolation transformer is demagnetized by forming a freewheeling circuit with the lower bridge arm switch S2 and switch S4 of the full-bridge circuit unit. It also includes a control circuit, the first input terminal of which is connected to the positive power input, the second input terminal of which is connected to the input signal PWM, the third input terminal of which is connected to the power input ground, and the four output terminals of which are connected one-to-one with the input terminals of the first pulse drive circuit, the second pulse drive circuit, the third pulse drive circuit, and the fourth pulse drive circuit, to achieve: When the input signal PWM is high: the control circuit modulates the input signal PWM into four types of pulses, which are then input to the corresponding pulse drive circuits to control the switching transistors S1 and S4 to turn on, and the switching transistors S2 and S3 to turn off. The edge modulation circuit generates a positive pulse, and the input voltage is applied to both ends of the primary winding of the isolation transformer. The current flows out from the positive terminal of the power supply, passes through the switching transistor S1, the primary winding of the isolation transformer, and the switching transistor S4 in sequence, and then flows into the negative terminal of the power supply, completing the excitation process of the isolation transformer. After each pulse ends, the control circuit controls the switching transistor S4 to turn on, and the switching transistors S1, S2, and S3 are all turned off. The current flows out from the opposite end of the primary winding of the isolation transformer, passes through the body diodes of the switching transistors S4 and S2 in sequence, and returns to the same end of the primary winding of the isolation transformer, completing the demagnetization process of the isolation transformer. The above excitation and demagnetization processes are repeated until the input signal PWM switches to low level. When the input signal PWM is low: the control circuit modulates the input signal PWM into four types of pulses, which are then input to the corresponding pulse drive circuits to control the switching transistors S2 and S3 to turn on, and the switching transistors S1 and S4 to turn off. The edge modulation circuit generates a positive pulse, and the input voltage is applied to both ends of the primary winding of the isolation transformer. Current flows out from the positive terminal of the power supply and sequentially flows through the switching transistor S3, the primary winding of the isolation transformer, and the switching transistor S2 into the negative terminal of the power supply, completing the excitation process of the isolation transformer. After each pulse ends, the control circuit controls the switching transistor S2 to turn on, and the switching transistors S1, S3, and S4 are all turned off. Current flows out from the same-name terminal of the primary winding of the isolation transformer and sequentially flows through the body diodes of the switching transistors S2 and S4 back to the opposite-name terminal of the primary winding of the isolation transformer, completing the demagnetization process of the isolation transformer. The above excitation and demagnetization processes are repeated until the input signal PWM switches to a high level.
2. The driving circuit according to claim 1, characterized in that: The control circuit includes a signal generator, a phase shift circuit, a delay matching circuit, a NAND gate, an OR gate, a first AND gate, a second AND gate, a third AND gate, a first NOT gate, and a second NOT gate. The input terminals of the phase shift circuit, the first input terminal of the NAND gate, and the delay matching circuit serve as the second input terminals of the control circuit, used to connect to the input signal PWM. The output terminal of the signal generator is connected to the second input terminal of the NAND gate and the first input terminal of the OR gate, respectively. The output terminal of the phase shift circuit is connected to the second input terminal of the OR gate. The output terminal of the delay matching circuit is connected to the input terminal of the first NOT gate. The output terminal of the NAND gate is connected to the first input terminal of the first AND gate. The output terminal of the OR gate is connected to the second input terminal of the first AND gate. The output of the first AND gate is connected to the input of the second NOT gate and the first input of the second AND gate, respectively. The output of the first NOT gate is connected to the second input of the second AND gate. The output of the second NOT gate is connected to the first input of the third AND gate. The output of the delay matching circuit is also connected to the second input of the third AND gate. The output of the third AND gate serves as the first output of the control circuit and is connected to the first pulse drive circuit. The output of the first NOT gate also serves as the second output of the control circuit and is connected to the second pulse drive circuit. The output of the second AND gate serves as the third output of the control circuit and is connected to the third pulse drive circuit. The output of the delay matching circuit also serves as the fourth output of the control circuit and is connected to the fourth pulse drive circuit.
3. The driving circuit according to claim 2, characterized in that: The process by which the control circuit modulates the input signal into four types of pulses using PWM is as follows: When the input signal PWM is high: the phase shift circuit outputs a high level, with a phase difference of Ta between it and the input signal PWM; the output signal of the first output terminal of the control circuit is a continuous positive narrow pulse, wherein the first positive narrow pulse output by the first output terminal of the control circuit is the phase difference Ta between the phase shift circuit and the input signal PWM; the frequency and pulse width of the remaining positive narrow pulses are consistent with the output signal of the signal generator; the output signal of the third output terminal of the control circuit is low. When the input signal PWM is low: the phase shift circuit outputs a low level, with a phase difference of Ta from the input signal PWM; the output signal of the first output terminal of the control circuit is low; and the output signal of the third output terminal of the control circuit is a continuous positive narrow pulse. The first positive narrow pulse output by the third output terminal of the control circuit is the phase difference Ta between the phase shift circuit and the input signal PWM. The frequency and pulse width of the remaining positive narrow pulses are consistent with the output signal of the signal generator. The signal generator produces a pulse signal with a fixed frequency and pulse width of Tb and a frequency of Fb. The delay time of the delay matching circuit is set to 0, so that the output signal of the fourth output terminal of the control circuit is the same as the input signal PWM, and the output signal of the second output terminal of the control circuit is complementary to the output signal of the fourth output terminal of the control circuit.
4. The driving circuit according to claim 2, characterized in that: The switching transistors S1 and S3 are MOSFETs, and the switching transistors S2 and S4 are N-channel MOSFETs.
5. The driving circuit according to claim 4, characterized in that: The first terminal of each of the switching transistors S1, S2, S3 and S4 is the drain, the second terminal is the source, and the third terminal is the gate. The first input terminal of the isolation transformer is the same-name terminal of the primary winding, and the second input terminal of the isolation transformer is the opposite-name terminal of the primary winding.
6. The driving circuit according to any one of claims 1 to 5, characterized in that: The demodulation module includes an energy storage circuit, a demodulation circuit, and an amplification circuit. The energy storage circuit stores the energy of the pulses transmitted from the primary side to the secondary side of the isolation transformer to power subsequent circuits. The demodulation circuit demodulates the pulses transmitted from the primary side to the secondary side of the isolation transformer into a drive signal identical to the input signal PWM. The amplification circuit amplifies the drive signal demodulated by the demodulation circuit.
7. The driving circuit according to claim 6, characterized in that: The output port of the isolation transformer includes a terminal with the same name as the secondary winding and a terminal with the opposite name as the secondary winding. The first input terminal of the demodulation circuit is connected to the terminal with the same name as the secondary winding of the isolation transformer, the second input terminal of the demodulation circuit is connected to the terminal with the opposite name as the secondary winding of the isolation transformer, the third input terminal of the demodulation circuit is connected to the first output terminal of the energy storage circuit, the first output terminal of the demodulation circuit is connected to the second input terminal of the amplifier circuit, and the second output terminal of the demodulation circuit is grounded. The first input terminal of the energy storage circuit is connected to the terminal with the same name as the secondary winding of the isolation transformer, the second input terminal of the energy storage circuit is connected to the terminal with the opposite name as the secondary winding of the isolation transformer, the first output terminal of the energy storage circuit is also connected to the first input terminal of the amplifier circuit, and the second output terminal of the energy storage circuit is grounded. The first output terminal of the amplifier circuit is connected to the drain of the power semiconductor, and the second output terminal of the amplifier circuit is grounded and also connected to the source of the power semiconductor, for amplifying the drive signal demodulated by the demodulation circuit to drive the power semiconductor.