A drive control circuit and a drive control method thereof
By combining the full-bridge unit and the demagnetizing unit, the demagnetizing voltage is increased and the demagnetizing process is optimized, thus solving the problems of insufficient driving capability and slow demagnetizing speed in transformer-isolated drives, and realizing efficient driving of high-power MOSFETs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- MORNSUN GUANGZHOU SCI & TECH
- Filing Date
- 2022-06-25
- Publication Date
- 2026-05-12
AI Technical Summary
Existing transformer-isolated drives suffer from insufficient driving capability, slow demagnetization speed, and large cost and size, especially when driving high-power MOSFETs.
It adopts a full-bridge unit and demagnetizing unit structure, and increases the demagnetizing voltage and optimizes the demagnetizing process by combining diodes and switching transistors, thereby improving the excitation and demagnetizing speed and enhancing the driving capability.
It improves the demagnetization speed and driving capability of isolation transformers, supports the driving of high-power MOSFETs, reduces startup time and energy replenishment pulse density, and lowers cost and size.
Smart Images
Figure CN115149815B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of switching power supplies, and in particular to a drive control circuit and drive control method using transformer isolation. 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 application CN113193735A proposes a novel drive control method and circuit. (Reference...) Figure 1The rising edge of the input signal is modulated into a fixed-width positive pulse by the edge modulation circuit in the drive control circuit, and the falling edge of the input signal is modulated into a fixed-width negative pulse. When the input signal is continuously high, multiple consecutive positive pulses are generated at a certain period by the energy replenishment circuit. These pulses are then transmitted to the secondary side through the 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 are used to replenish energy to the driven power transistor to maintain the voltage required for conduction, thereby 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. At the same time, this scheme 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 2 100 in Figure 1 The internal block diagram of the edge modulation circuit shows the excitation process as follows: Taking a positive pulse as an example, when the upper transistor Sa of the first bridge arm and the lower transistor Sd of the second bridge arm are turned on, the input voltage V... gs When applied to both ends of the primary winding of the transformer, the transformer is energized; the current flows out from the positive terminal of the power supply, passes sequentially through the upper tube Sa of the first bridge arm, the primary winding of the transformer, and the lower tube Sd of the second bridge arm, before returning to the negative terminal of the power supply.
[0008] Excitation current calculation: Where ΔI1 represents the increment of excitation current, V gs Represents the input power supply voltage;
[0009] After the pulse ends, the lower transistor Sd of the second bridge arm remains on when the input signal is high. After the narrow pulse ends, the upper transistor Sa of the first bridge arm turns off. According to the modulation logic, the upper transistor Sa and the lower transistor Sb of the first bridge arm are complementary. When the lower transistor 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 transistor Sd of the second bridge arm and the lower transistor 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: Where ΔI2 represents the demagnetizing current increment, V R This represents the reverse voltage (i.e., demagnetizing voltage) across the primary winding of the isolation transformer during the demagnetizing stage.
[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 conduction impedance of the first bridge arm lower transistor Sb, the conduction impedance of the second bridge arm lower transistor Sd, and the line 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 solution suffers from insufficient driving capability when driving high-power MOSFETs.
[0014] To address the problems existing in the aforementioned drive control circuit, those skilled in the art have proposed a new drive control circuit, referencing... Figure 4 When the PWM signal input to the control circuit is high, the edge modulation circuit in the drive control circuit modulates the rising edge of the PWM signal into a positive pulse with a fixed pulse width. Under the condition that the PWM signal is continuously high, multiple consecutive positive pulses are generated at a certain period. During each positive pulse, the control switches S6 and S7 are turned on, and the switches S5 and S8 are turned off, thus completing the transformer excitation. After each positive pulse ends, the demagnetization stage begins. By controlling the switch S2 to turn on, the current flows out from the opposite end of the transformer primary winding, passes through diode D15, switch S4, switch S2 and diode D14 in sequence, and returns to the same end of the transformer primary winding, thus completing the transformer demagnetization.
[0015] Similarly, when the PWM signal is low, the edge modulation circuit modulates the falling edge of the PWM signal into a negative pulse with a fixed pulse width. While the PWM signal is continuously high, it generates multiple consecutive negative pulses at a certain period. During each negative pulse, switches S5 and S8 are turned on, while switches S6 and S7 are turned off, completing transformer excitation. After each negative pulse, the demagnetization stage begins. By turning on switch S3, current flows from the same-name terminal of the transformer's primary winding, sequentially through switch S1, diode D12, diode D10, and switch S3, returning to the opposite-name terminal of the transformer's primary winding, completing transformer demagnetization. A schematic diagram of the excitation and demagnetization currents of this edge modulation circuit is shown below. Figure 5 .
[0016] However, this drive control circuit has the following limitations:
[0017] 1. To ensure that the transformer excitation current is less than or equal to the demagnetizing current, the increase in excitation current during the energy replenishment pulse must be less than or equal to the decrease in demagnetizing current during the demagnetizing phase. After the first pulse, subsequent energy replenishment pulses and pulse intervals must meet the following conditions:
[0018]
[0019] In other words, the current change during the demagnetization stage must be greater than the current change during the excitation stage to avoid exceeding the transformer's specifications. The demagnetization voltage V of the transformer in the aforementioned drive control circuit... R It consists of the forward voltage drop of two switching transistors (the forward voltage drop of the switching transistors is very small, usually tens of millivolts), the forward voltage drop of two diodes, and the voltage drop across the line impedance. Compared with patent application CN113193735A, it adds about 1.2V of the forward voltage drop of two diodes, but the demagnetizing voltage is still relatively small. When the parasitic parameters of the driven power switching transistors are large, if the driving voltage is to remain constant, the edge modulation circuit needs to generate a denser energy replenishment signal. According to the above formula, the demagnetizing voltage needs to be further increased.
[0020] 2. The above-mentioned drive control circuit increases the demagnetizing voltage by connecting a diode in series in the demagnetizing circuit and relying on the forward voltage drop of the diode. The loss generated during the demagnetizing stage is relatively large. Summary of the Invention
[0021] The present invention aims to solve at least one of the problems in the prior art, and provides a drive control circuit and drive control method that can improve the high current drive capability, increase the demagnetizing voltage of the isolation transformer, and maintain the normally open function of the power switching device to keep it continuously conducting.
[0022] The technical solution adopted in this invention is as follows:
[0023] A first aspect: A drive control circuit is provided, the drive control circuit including an edge modulation circuit and an isolation transformer connected to the edge modulation circuit, wherein the edge modulation circuit includes a control circuit, a drive circuit and a full-bridge unit, the full-bridge unit having a switch S1, a switch S2, a switch S3 and a switch S4, the source of switch S1 is connected to the drain of switch S2 and the first end of the primary winding of the isolation transformer, the source of switch S3 is connected to the drain of switch S4 and the second end of the primary winding of the isolation transformer, the drain of switch S1 and the drain of switch S3 are connected to the positive terminal of the power supply, and the source of switch S2 and the source of switch S4 are connected to the negative terminal of the power supply. The edge modulation circuit also includes a first demagnetizing unit and a second demagnetizing unit.
[0024] The first demagnetizing unit includes diode D2, switch S2, switch S4 and switch S6. Diode D2 and switch S6 are connected in series and then in parallel to the drain and gate of switch S4.
[0025] The second demagnetizing unit includes diode D1, switch S2, switch S4 and switch S5. Diode D1 and switch S5 are connected in series and then in parallel to the drain and gate of switch S2.
[0026] Preferably, the anode of diode D2 is connected to the drain of switching transistor S4 and the first end of the primary winding of the isolation transformer, respectively; the cathode of diode D2 is connected to the drain of switching transistor S6; and the source of switching transistor S6 is connected to the gate of switching transistor S4. The drain of switching transistor S2 is connected to the second end of the primary winding of the isolation transformer, and the source of switching transistor S2 is connected to the negative terminal of the power supply.
[0027] The anode of diode D1 is connected to the drain of switch S2 and the second end of the primary winding of the isolation transformer. The cathode of diode D1 is connected to the drain of switch S5. The source of switch S5 is connected to the gate of switch S2. The drain of switch S4 is connected to the first end of the primary winding of the isolation transformer.
[0028] Preferably, the first demagnetizing unit is used to demagnetize the isolation transformer when the PWM signal input to the control circuit is high. The demagnetizing process specifically includes: the switch S6 is turned on, and the demagnetizing current flows out from the first end of the primary winding of the isolation transformer. It first passes through the diode D2, the switch S6, the gate-source parasitic capacitance of the switch S4 and the body diode of the switch S2, and then returns to the second end of the primary winding of the isolation transformer to charge the gate-source parasitic capacitance of the switch S4. When the gate voltage of the switch S4 reaches its conduction threshold, the switch S4 is turned on. Then the demagnetizing current flows out from the first end of the primary winding of the isolation transformer, passes through the body diodes of the switch S4 and the switch S2 in sequence, and returns to the second end of the primary winding of the isolation transformer.
[0029] The second demagnetizing switch is used to demagnetize the isolation transformer when the PWM signal input to the control circuit is low. The demagnetizing process specifically includes: the switch S5 is turned on, and the demagnetizing current flows out from the second end of the primary winding of the isolation transformer. It first passes through diode D1, switch S5, the gate-source parasitic capacitance of switch S2 and the body diode of switch S4, and then returns to the first end of the primary winding of the isolation transformer to charge the gate-source parasitic capacitance of switch S2. When the gate voltage of switch S2 reaches its conduction threshold, switch S2 is turned on. Then the demagnetizing current flows out from the second end of the primary winding of the isolation transformer, passes through the body diodes of switch S2 and switch S4 in sequence, and then returns to the first end of the primary winding of the isolation transformer.
[0030] Preferably, the drive control circuit further includes resistors R1 and R2; one end of resistor R2 is connected to the gate of switch S4, and the other end is connected to the source of switch S4; one end of resistor R1 is connected to the gate of switch S2, and the other end is connected to the source of switch S2.
[0031] The second aspect: providing a driving control method for the above-mentioned driving control circuit, including:
[0032] When the PWM signal input to the control circuit is high, the isolation transformer is demagnetized by the first demagnetizing unit; when the PWM signal input to the control circuit is low, the isolation transformer is demagnetized by the second demagnetizing unit.
[0033] Preferably, the demagnetization of the isolation transformer by the first demagnetization unit specifically includes two stages:
[0034] First stage: Switch S6 is turned on and switch S2 is turned off. The demagnetizing current flowing from the first end of the primary winding of the isolation transformer charges the gate-source parasitic capacitance of switch S4 through diode D2 and switch S6.
[0035] Second stage: When the voltage of the gate-source parasitic capacitance of switch S4 reaches the conduction threshold of switch S4, switch S4 is turned on, and the demagnetizing current flows out from the first end of the primary winding of the isolation transformer, passes through the body diodes of switch S4 and switch S2 in sequence, and returns to the second end of the primary winding of the isolation transformer.
[0036] Preferably, the isolation transformer is demagnetized by the second demagnetizing unit, which specifically includes two stages:
[0037] First stage: Switch S5 is turned on and switch S4 is turned off. The demagnetizing current flowing from the second end of the primary winding of the isolation transformer charges the gate-source parasitic capacitance of switch S2 through diode D1 and switch S5.
[0038] Second stage: When the voltage of the gate-source parasitic capacitance of switch S2 reaches the conduction threshold of switch S2, switch S2 is turned on, and the demagnetizing current flows out from the second end of the primary winding of the isolation transformer, passes through the body diodes of switch S2 and switch S4 in sequence, and returns to the first end of the primary winding of the isolation transformer.
[0039] Third aspect: A drive control circuit is provided, the drive control circuit including an edge modulation circuit and an isolation transformer connected to the edge modulation circuit, wherein the edge modulation circuit includes a control circuit, a drive circuit and a full-bridge unit; wherein the full-bridge unit has a switch S1, a switch S2, a switch S3 and a switch S4, the source of switch S3 is connected to the drain of switch S4 and the first end of the primary winding of the isolation transformer, the source of switch S1 is connected to the drain of switch S2 and the second end of the primary winding of the isolation transformer, the drain of switch S1 and the drain of switch S3 are connected to the positive terminal of the power supply, and the source of switch S2 and the source of switch S4 are connected to the negative terminal of the power supply. The edge modulation circuit also includes a first demagnetizing unit and a second demagnetizing unit.
[0040] The first demagnetizing unit includes diode D2, switch S6, switch S4, switch S10, and switch S2. Diode D2 and switch S6 are connected in series and then in parallel to the drain and gate of switch S4. The drain of switch S10 is connected to the gate of switch S4, and the source of switch S10 is connected to the source of switch S4.
[0041] The second demagnetizing unit includes diode D1, switch S5, switch S2, switch S8 and switch S4. Diode D1 and switch S5 are connected in series and then in parallel to the drain and gate of switch S2. The drain of switch S8 is connected to the gate of switch S2, and the source of switch S8 is connected to the source of switch S2.
[0042] Preferably, the drive control circuit further includes a switch S7 and a switch S9. The drain of switch S7 is connected to the positive terminal of the power supply, and the source of switch S7 is connected to the gate of switch S2. The drain of switch S9 is connected to the positive terminal of the power supply, and the source of switch S9 is connected to the gate of switch S4.
[0043] The working principle of this invention will be described in detail in specific embodiments. Compared with the prior art, this invention has the following beneficial effects:
[0044] 1) By using a full-bridge unit and a demagnetizing unit to excite and demagnetize the isolation transformer, the demagnetizing voltage of the isolation transformer is increased by the on-state voltage drop of the clamping switch in the demagnetizing unit, thereby improving the demagnetizing speed of the isolation transformer.
[0045] 2) The larger the demagnetizing voltage, the shorter the demagnetizing time required, which results in a higher energy replenishment pulse density, thereby significantly improving the driving capability, supporting the driving of high-power MOSFETs, and improving the startup speed. Attached Figure Description
[0046] Figure 1 This is a schematic diagram of the main structure of an existing pulse magnetic isolation drive circuit;
[0047] Figure 2 This is a schematic diagram of the main structure of an existing pulse magnetic isolation drive edge modulation circuit;
[0048] Figure 3 This is a schematic diagram of the input PWM signal, modulation signal, and excitation current of an existing pulse magnetic isolation drive;
[0049] Figure 4 This is a schematic diagram of the main structure of an existing pulse magnetic isolation drive edge modulation circuit;
[0050] Figure 5 This is a schematic diagram of the input PWM signal, modulation signal, and excitation current of an existing pulse magnetic isolation drive;
[0051] Figure 6 This is a schematic diagram of the drive control circuit of the first embodiment of the present invention;
[0052] Figure 7 This is a schematic diagram of the input PWM signal, modulation signal, and excitation current in the first embodiment of the present invention;
[0053] Figure 8 This is a schematic diagram of the drive control circuit according to the second embodiment of the present invention. Detailed implementation method:
[0054] The accompanying drawings are for illustrative purposes only and should not be construed as limiting the invention. To better illustrate the following embodiments, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions; it is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.
[0055] First Embodiment
[0056] Please refer to Figure 6 In this embodiment, a drive control circuit with an edge modulation circuit and an isolation transformer is provided, wherein the edge modulation circuit includes a control circuit, a drive circuit, a full-bridge unit, a first demagnetizing unit, and a second demagnetizing unit.
[0057] The first input terminal of the control circuit is used to connect to the positive terminal of the power supply, the second input terminal is used to connect to the PWM signal, the third input terminal is used to connect to the negative terminal of the power supply, and the output terminal is connected to the input terminal of the drive circuit. The control circuit is used to control the conduction and cutoff of the full-bridge unit, the first demagnetizing unit, and the second demagnetizing unit according to the PWM signal.
[0058] The output of the drive circuit is connected to the control input of the full-bridge unit, the control input of the first demagnetizing unit, and the control input of the second demagnetizing unit, respectively. The drive circuit is used to amplify the control signal output by the control circuit to control the conduction and cutoff of the full-bridge unit and the demagnetizing unit.
[0059] Specifically, the driving circuit includes a first driving circuit, a second driving circuit, a third driving circuit, a fourth driving circuit, a fifth driving circuit, and a sixth driving circuit; the first output terminal of the control circuit is connected to the input terminal of the first driving circuit, the second output terminal is connected to the input terminal of the second driving circuit, the third output terminal is connected to the input terminal of the third driving circuit, the fourth output terminal is connected to the input terminal of the fourth driving circuit, the fifth output terminal is connected to the input terminal of the fifth driving circuit, and the sixth output terminal is connected to the input terminal of the sixth driving circuit; the output terminal of the first driving circuit is connected to the gate of the switching transistor S1; the output terminal of the second driving circuit is connected to the gate of the switching transistor S2; the output terminal of the third driving circuit is connected to the gate of the switching transistor S3; the output terminal of the fourth driving circuit is connected to the gate of the switching transistor S4; the output terminal of the fifth driving circuit is connected to the gate of the switching transistor S5; and the output terminal of the sixth driving circuit is connected to the gate of the switching transistor S6.
[0060] The first end of the full-bridge unit is used to connect to the positive terminal of the power supply, the second end is used to connect to the same-name terminal of the primary winding of the isolation transformer (i.e., the second end of the primary winding), the third end is used to connect to the negative terminal of the power supply, and the fourth end is used to connect to the opposite-name terminal of the primary winding of the isolation transformer (i.e., the first end of the primary winding). The full-bridge unit is used to generate several pulses to excite the isolation transformer.
[0061] Specifically, the full-bridge unit includes switching transistors S1, S2, S3, and S4; the drains of switching transistors S1 and S3 serve as the first terminal of the full-bridge unit for connection to the positive terminal of the power supply; the source of switching transistor S1 and the drain of switching transistor S2 serve as the second terminal of the full-bridge unit for connection to the same-name terminal of the primary winding of the isolation transformer; the source of switching transistor S2 and the source of switching transistor S4 serve as the third terminal of the full-bridge unit for connection to the negative terminal of the power supply; and the drain of switching transistor S4 and the source of switching transistor S3 serve as the fourth terminal of the full-bridge unit for connection to the opposite-name terminal of the primary winding of the isolation transformer.
[0062] The first demagnetizing unit includes diode D2, switch S6, switch S4 and switch S2; diode D2 and switch S6 are connected in series and then in parallel to the drain and gate of switch S4.
[0063] Specifically, the anode of diode D2 is connected to the drain of switch S4 as the first terminal of the first demagnetizing unit, the cathode of diode D2 is connected to the drain of switch S6, the source of switch S6 is connected to the gate of switch S4, one end of resistor R2 is connected to the gate of switch S4, and the other end is connected to the source of switch S2, the source of switch S4 and the negative terminal of the power supply as the second terminal of the first demagnetizing unit. The drain of switch S2 is connected to the same-name terminal of the primary winding of the isolation transformer as the third terminal of the first demagnetizing unit.
[0064] The first demagnetizing unit includes diode D2, switch S2, switch S4 and switch S6. The second demagnetizing unit includes diode D1, switch S2, switch S4 and switch S5. Diode D1 and switch S5 are connected in series and then in parallel to the drain and gate of switch S2.
[0065] Specifically, the anode of diode D1 is connected to the drain of switch S2 as the first terminal of the second demagnetizing unit, the cathode of diode D1 is connected to the drain of switch S5, the source of switch S5 is connected to the gate of switch S2, one end of resistor R1 is connected to the gate of switch S2, and the other end is connected to the source of switch S2, the source of switch S4 and the negative terminal of the power supply as the second terminal of the second demagnetizing unit. The drain of switch S4 is connected to the opposite terminal of the primary winding of the isolation transformer as the third terminal of the second demagnetizing unit.
[0066] To prevent the peak current of the isolation transformer from continuously rising, 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, subsequent energy replenishment pulses and pulse intervals must meet the following conditions:
[0067] Where ΔI1 represents the increment of the excitation current, V gs V represents the input voltage, ΔI2 represents the demagnetizing current increment. R The reverse voltage across the primary winding of the isolation transformer during the demagnetizing stage (defined as the demagnetizing voltage).
[0068] From the above formula, we can see that the input voltage V gs Determined by system parameters, this cannot be optimized. The primary-side magnetizing inductance synchronously affects both the magnetizing and demagnetizing currents, making optimization impossible. The only way to optimize this is by extending the demagnetizing time or increasing the demagnetizing voltage. Firstly, extending the demagnetizing time sufficiently prevents the current from rising during the energy replenishment phase. Secondly, increasing the demagnetizing 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] In this embodiment, the drive control method of the drive control circuit includes the following steps:
[0070] Excitation steps: During each pulse generated by the edge modulation circuit, the isolation transformer is energized through the full-bridge unit;
[0071] Demagnetization step: After each pulse ends, the isolation transformer is demagnetized by either the first demagnetization unit or the second demagnetization unit;
[0072] In the demagnetization step, when the PWM signal input to the control circuit is high, the isolation transformer is demagnetized by the first demagnetization unit; when the PWM signal input to the control circuit is low, the isolation transformer is demagnetized by the second demagnetization unit.
[0073] The specific principle of the drive control method in this embodiment is as follows:
[0074] refer to Figure 7 , Figure 7 The display shows the waveforms of the PWM signal input to the control circuit, the modulation signal waveform (i.e., the output waveform of the edge modulation circuit), and the excitation current of the isolation transformer.
[0075] When the PWM signal is at a high level, the control method in this embodiment includes an excitation process and a demagnetization process, which will be described in detail below.
[0076] The edge modulation circuit modulates the rising edge of the input PWM signal into a positive pulse of fixed pulse width (corresponding to...). Figure 7 The circuit generates multiple consecutive positive pulses at a certain period while the input PWM signal is continuously high. When the input PWM signal is high, the control circuit controls switch S6 to turn on via the sixth drive circuit. During each generated positive pulse, the control circuit controls switches S1 and S4 to turn on via the first and fourth drive circuits, while switches S2 and S3 are turned off. The edge modulation circuit generates a positive pulse, and the input voltage V... gs When 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.
[0077] After the above excitation process, because the input PWM signal is continuously high, the demagnetizing voltage V across the primary winding of the isolation transformer increases after each excitation pulse. RThe demagnetizing current is the sum of the forward voltage drop of diode D2, the forward threshold voltage of switch S4, and the forward voltage drop of the body diode of switch S2. This current is used to quickly demagnetize the isolation transformer. The demagnetizing current flows out from the opposite-named terminal of the primary winding of the isolation transformer, passes through diode D2 and switch S6, clamps the voltage drop of switch S4 to the sum of the forward threshold voltage of switch S4 and the forward voltage drop of diode D2, and then returns to the same-named terminal of the primary winding of the isolation transformer through switch S4 and the body diode of switch S2, thus completing the demagnetizing process of the isolation transformer.
[0078] Even when the input PWM signal is low, the process still includes excitation and demagnetization, which will be described in detail below.
[0079] The edge modulation circuit modulates the falling edge of the input PWM signal into a negative pulse of fixed pulse width, and generates multiple consecutive negative pulses at a certain period while the input PWM signal is continuously low. When the input PWM signal is low, the control circuit controls switch S5 to conduct via the fifth drive circuit. During each generated negative pulse, the control circuit controls switches S2 and S3 to conduct via the second and third drive circuits, while switches S1 and S4 are de-energized. The edge modulation circuit generates the negative pulse, and the input voltage V... gs The current is applied in reverse 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 switch S3, the primary winding of the isolation transformer, and the switch S2 in sequence, and then flows into the negative terminal of the power supply, completing the reverse excitation process of the isolation transformer.
[0080] After the above reverse excitation process, because the input PWM signal is in a continuous low-level state, after each reverse excitation pulse, the demagnetizing voltage across the isolation transformer is the sum of the forward voltage drop of diode D1, the forward threshold voltage of switch S2, and the forward voltage drop of the body diode of switch S4. This rapidly demagnetizes the transformer. The demagnetizing current flows out from the same-name terminal of the primary winding of the isolation transformer, passes through diode D1 and switch S5, clamps the voltage drop of switch S2 to the sum of the forward threshold voltage of switch S2 and the forward voltage drop of diode D1, and then returns to the opposite-name terminal of the primary winding of the isolation transformer through the body diodes of switch S2 and switch S4, completing the demagnetizing process of the isolation transformer.
[0081] Based on the demagnetizing principle of the isolation transformer described above, the demagnetizing voltage V R Determined by the forward voltage drop of the two diodes, the turn-on threshold voltage of the switching transistor, the loop current, and the line impedance, even as the current decreases, the demagnetizing voltage V... R There will be no significant attenuation.
[0082] In this embodiment, the isolation transformer is demagnetized by the first demagnetizing unit. During the demagnetizing process, the demagnetizing current passes through diode D2 and switch S6 to clamp the on-state voltage drop of switch S4, so that the on-state voltage drop of switch S4 is approximately equal to the sum of the on-state threshold voltage of switch S4 and the on-state voltage drop of diode D2. Compared with the prior art, this greatly increases the on-state voltage drop of switch S4.
[0083] Taking the demagnetizing phase of the positive pulse as an example, the line impedance is the circuit's own line impedance. The sum of the forward voltage drops of diode D2 and the body diode of switch S2 is approximately 1.2V, and the on-threshold voltage of switch S4 is approximately 1.5V. Therefore, the sum of the forward voltage drops of diode D2 and the body diode of switch S2 plus the on-threshold voltage of switch S4 reaches 2.7V. It is evident that the drive control circuit and control method of this invention can effectively improve the demagnetizing voltage, reduce the energy replenishment interval, increase the energy replenishment pulse density, and increase the drive power.
[0084] Second Embodiment
[0085] In this embodiment, an isolated drive control method is provided, applied to a drive control circuit with an edge modulation circuit and an isolation transformer, such as... Figure 8 As shown, the edge modulation circuit includes a control circuit, a drive circuit, a full-bridge unit, and a demagnetizing circuit.
[0086] The difference from the first embodiment is that the components of the first demagnetizing unit and the second demagnetizing unit are different in this embodiment. The first demagnetizing unit includes diode D2, switch S6, switch S4, switch S10 and switch S2, and the second demagnetizing unit includes diode D1, switch S5, switch S2, switch S8 and switch S4; in addition, switch S7 and switch S9 are added.
[0087] The first output terminal of the control circuit is connected to the input terminal of the first drive circuit; the second output terminal of the control circuit is connected to the input terminal of the second drive circuit; the third output terminal of the control circuit is connected to the input terminal of the third drive circuit; the fourth output terminal of the control circuit is connected to the input terminal of the fourth drive circuit; the fifth output terminal of the control circuit is connected to the input terminal of the fifth drive circuit; and the sixth output terminal of the control circuit is connected to the input terminal of the sixth drive circuit. The output terminal of the first drive circuit is connected to the gates of switching transistors S1 and S9; the output terminal of the second drive circuit is connected to the gate of switching transistor S8; the output terminal of the third drive circuit is connected to the gates of switching transistors S3 and S7; the output terminal of the fourth drive circuit is connected to the gate of switching transistor S10; the output terminal of the fifth drive circuit is connected to the gate of switching transistor S5; and the output terminal of the sixth drive circuit is connected to the gate of switching transistor S6.
[0088] The drains of switching transistors S1 and S3 serve as the first terminal of the full-bridge unit, connected to the positive terminal of the power supply; the source of switching transistor S1 and the drain of switching transistor S2 serve as the second terminal of the full-bridge unit, connected to the same-name terminal of the primary winding of the isolation transformer; the source of switching transistors S2, S4, S8, and S10 serve as the third terminal of the full-bridge unit, connected to the negative terminal of the power supply; and the drains of switching transistors S4 and S3 serve as the fourth terminal of the full-bridge unit, connected to the opposite-name terminal of the primary winding of the isolation transformer.
[0089] The anode of diode D2 is connected to the drain of switch S4 as the first terminal of the first demagnetizing unit. The cathode of diode D2 is connected to the drain of switch S6. The source of switch S6 is connected to the gate of switch S4. The drain of switch S10 is connected to the gate of switch S4. The source of switch S10 is connected to the source of switch S2, the source of switch S4, and the negative terminal of the power supply as the second terminal of the first demagnetizing unit. The drain of switch S2 is connected to the same-name terminal of the primary winding of the isolation transformer as the third terminal of the first demagnetizing unit. The anode of diode D1 is connected to the drain of switch S2 as the first terminal of the second demagnetizing unit. The cathode of diode D1 is connected to the drain of switch S5. The source of switch S5 is connected to the gate of switch S2. The drain of switch S8 is connected to the gate of switch S2. The source of switch S8 is connected to the source of switch S2, the source of switch S4, and the negative terminal of the power supply as the second terminal of the second demagnetizing unit. The drain of switch S4 is connected to the opposite terminal of the primary winding of the isolation transformer as the third terminal of the second demagnetizing unit.
[0090] The specific principle of the control method in this embodiment is similar to that of the first embodiment, but with the addition of some control circuitry. When the input PWM is high, the control circuit controls the switching transistors S1 and S9 to turn on through the first driving circuit, and controls the switching transistor S6 to turn on through the sixth driving circuit, while switching transistors S2 and S3 are turned off. After switching transistor S9 turns on, the power supply charges the gate capacitor of switching transistor S4 through switching transistor S9, controlling switching transistor S4 to turn on. The edge modulation circuit generates a positive pulse, and the input voltage V... gs When 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.
[0091] After the above excitation process, because the input signal PWM is in a continuous high-level state, after each excitation pulse, the control circuit controls the switch S10 to be turned on for a short period of time through the fourth drive circuit, and turns off the switch S4. Then the current flows out from the opposite end of the primary winding of the isolation transformer, through diode D2 and switch S6, clamping the voltage drop of switch S4 to the sum of the conduction threshold voltage of switch S4 and the conduction voltage drop of diode D2. The demagnetizing voltage across the isolation transformer is the sum of the conduction voltage drop of diode D2, the conduction threshold voltage of switch S4 and the conduction voltage drop of the body diode of switch S2, which quickly demagnetizes the isolation transformer. The demagnetizing current returns to the same end of the primary winding of the isolation transformer through switch S4 and the body diode of switch S2, completing the demagnetizing process of the isolation transformer.
[0092] When the input PWM is low, the control circuit controls the switching transistors S3 and S7 to turn on via the third drive circuit, and controls the switching transistor S5 to turn on via the fifth drive circuit. Switches S1 and S4 are turned off. After switch S7 turns on, the power supply charges the gate capacitor of switch S2 through switch S7, controlling switch S2 to turn on. The edge modulation circuit generates a negative pulse, and the input voltage V... gs The current is applied in reverse 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 switch S3, the primary winding of the isolation transformer, and the switch S2 in sequence, and then flows into the negative terminal of the power supply, completing the reverse excitation process of the isolation transformer.
[0093] After the aforementioned reverse excitation process, because the input signal PWM is in a continuously low level state, after each reverse excitation pulse, the control circuit controls the switch S8 to conduct for a short period of time through the second drive circuit, turning off the switch S2. Then, the current flows out from the same-name terminal of the primary winding of the isolation transformer, through diode D1 and switch S5, clamping the voltage drop of switch S2 to the sum of the conduction threshold voltage of switch S2 and the conduction voltage drop of diode D1. The demagnetizing voltage across the isolation transformer is the sum of the conduction voltage drop of diode D1, the conduction threshold voltage of switch S2, and the conduction voltage drop of the body diode of switch S4, rapidly demagnetizing the transformer. The demagnetizing current returns to the opposite-name terminal of the primary winding of the isolation transformer through the body diodes of switch S2 and switch S4, completing the demagnetizing process of the isolation transformer.
[0094] The above are merely preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be regarded as limitations on the present invention. For those skilled in the art, several improvements and modifications can be made without departing from the spirit and scope of the present invention. Here, the embodiments will not be elaborated further. The scope of protection of the present invention should be determined by the scope defined in the claims.
Claims
1. A drive control circuit, the drive control circuit comprising an edge modulation circuit and an isolation transformer connected to the edge modulation circuit, wherein, The edge modulation circuit includes a control circuit, a drive circuit, and a full-bridge unit. The full-bridge unit has switching transistors S1, S2, S3, and S4. The source of switching transistor S1 is connected to the drain of switching transistor S2 and the first end of the primary winding of the isolation transformer. The source of switching transistor S3 is connected to the drain of switching transistor S4 and the second end of the primary winding of the isolation transformer. The drains of switching transistors S1 and S3 are connected to the positive terminal of the power supply. The sources of switching transistors S2 and S4 are connected to the negative terminal of the power supply. The edge modulation circuit further includes a first demagnetizing unit and a second demagnetizing unit. The first demagnetizing unit includes diode D2, the switch S2, the switch S4 and the switch S6. Diode D2 and switch S6 are connected in series and then connected in parallel to the drain and gate of switch S4. The second demagnetizing unit includes diode D1, the switch S2, the switch S4, and the switch S5. Diode D1 and switch S5 are connected in series and then in parallel to the drain and gate of switch S2. When the PWM signal input to the control circuit is high, the isolation transformer is demagnetized by the first demagnetizing unit; when the PWM signal input to the control circuit is low, the isolation transformer is demagnetized by the second demagnetizing unit.
2. The drive control circuit according to claim 1, characterized in that: The anode of diode D2 is connected to the drain of switch S4 and the first end of the primary winding of the isolation transformer, respectively. The cathode of diode D2 is connected to the drain of switch S6, and the source of switch S6 is connected to the gate of switch S4. The drain of switch S2 is connected to the second end of the primary winding of the isolation transformer, and the source of switch S2 is connected to the negative terminal of the power supply. The anode of diode D1 is connected to the drain of switch S2 and the second end of the primary winding of the isolation transformer. The cathode of diode D1 is connected to the drain of switch S5. The source of switch S5 is connected to the gate of switch S2. The drain of switch S4 is connected to the first end of the primary winding of the isolation transformer.
3. The drive control circuit according to claim 2, characterized in that: The first demagnetizing unit is used to demagnetize the isolation transformer when the PWM signal input to the control circuit is high. The demagnetizing process specifically includes: the switch S6 is turned on, and the demagnetizing current flows out from the first end of the primary winding of the isolation transformer, first through the diode D2, the switch S6, the gate-source parasitic capacitance of the switch S4 and the body diode of the switch S2, and then back to the second end of the primary winding of the isolation transformer to charge the gate-source parasitic capacitance of the switch S4; when the gate voltage of the switch S4 reaches its conduction threshold, the switch S4 is turned on, and then the demagnetizing current flows out from the first end of the primary winding of the isolation transformer, passes through the body diodes of the switch S4 and the switch S2 in sequence, and returns to the second end of the primary winding of the isolation transformer; The second demagnetizing switch is used to demagnetize the isolation transformer when the PWM signal input to the control circuit is low. The demagnetizing process specifically includes: the switch S5 is turned on, and the demagnetizing current flows out from the second end of the primary winding of the isolation transformer. It first passes through the diode D1, the switch S5, the gate-source parasitic capacitance of the switch S2, and the body diode of the switch S4, and then returns to the first end of the primary winding of the isolation transformer to charge the gate-source parasitic capacitance of the switch S2. When the gate voltage of the switch S2 reaches its conduction threshold, the switch S2 is turned on. Then the demagnetizing current flows out from the second end of the primary winding of the isolation transformer, passes through the body diodes of the switch S2 and the switch S4 in sequence, and then returns to the first end of the primary winding of the isolation transformer.
4. The drive control circuit according to claim 1, characterized in that: Resistors R1 and R2 are also provided; one end of resistor R2 is connected to the gate of the switching transistor S4, and the other end is connected to the source of the switching transistor S4; one end of resistor R1 is connected to the gate of the switching transistor S2, and the other end is connected to the source of the switching transistor S2.
5. The drive control circuit according to claim 1, characterized in that: The demagnetization of the isolation transformer by the first demagnetization unit specifically includes two stages: First stage: The switch S6 is turned on and the switch S2 is turned off. The demagnetizing current flowing from the first end of the primary winding of the isolation transformer charges the gate-source parasitic capacitance of the switch S4 through the diode D2 and the switch S6. Second stage: When the voltage of the gate-source parasitic capacitance of the switch S4 reaches the conduction threshold of the switch S4, the switch S4 is turned on, and the demagnetizing current flows out from the first end of the primary winding of the isolation transformer, passes through the body diodes of the switch S4 and the switch S2 in sequence, and returns to the second end of the primary winding of the isolation transformer.
6. The drive control circuit according to claim 1, characterized in that: The isolation transformer is demagnetized by the second demagnetizing unit, which specifically includes two stages: First stage: The switch S5 is turned on and the switch S4 is turned off. The demagnetizing current flowing from the second end of the primary winding of the isolation transformer charges the gate-source parasitic capacitance of the switch S2 through the diode D1 and the switch S5. Second stage: When the voltage of the gate-source parasitic capacitance of the switch S2 reaches the conduction threshold of the switch S2, the switch S2 is turned on, and the demagnetizing current flows out from the second end of the primary winding of the isolation transformer, passes through the body diodes of the switch S2 and the switch S4 in sequence, and returns to the first end of the primary winding of the isolation transformer.
7. A drive control circuit, the drive control circuit comprising an edge modulation circuit and an isolation transformer connected to the edge modulation circuit, wherein, The edge modulation circuit includes a control circuit, a drive circuit, and a full-bridge unit; wherein, the full-bridge unit has switching transistors S1, S2, S3, and S4, the source of switching transistor S3 is connected to the drain of switching transistor S4 and the first end of the primary winding of the isolation transformer, the source of switching transistor S1 is connected to the drain of switching transistor S2 and the second end of the primary winding of the isolation transformer, the drain of switching transistor S1 and the drain of switching transistor S3 are connected to the positive terminal of the power supply, and the source of switching transistor S2 and the source of switching transistor S4 are connected to the negative terminal of the power supply. The edge modulation circuit further includes a first demagnetizing unit and a second demagnetizing unit. The first demagnetizing unit includes a diode D2, a switch S6, a switch S4, a switch S10, and a switch S2. The diode D2 and the switch S6 are connected in series and then in parallel to the drain and gate of the switch S4. The drain of the switch S10 is connected to the gate of the switch S4, and the source of the switch S10 is connected to the source of the switch S4. The second demagnetizing unit includes a diode D1, a switch S5, a switch S2, a switch S8, and a switch S4. The diode D1 and the switch S5 are connected in series and then in parallel to the drain and gate of the switch S2. The drain of the switch S8 is connected to the gate of the switch S2, and the source of the switch S8 is connected to the source of the switch S2. When the PWM signal input to the control circuit is high, the isolation transformer is demagnetized by the first demagnetizing unit; when the PWM signal input to the control circuit is low, the isolation transformer is demagnetized by the second demagnetizing unit.
8. The drive control circuit according to claim 7, characterized in that: The device also includes a switching transistor S7 and a switching transistor S9. The drain of the switching transistor S7 is connected to the positive terminal of the power supply, and the source of the switching transistor S7 is connected to the gate of the switching transistor S2. The drain of the switching transistor S9 is connected to the positive terminal of the power supply, and the source of the switching transistor S9 is connected to the gate of the switching transistor S4.