An isolated drive control circuit and drive control method

Abstract

The application relates to the technical field of isolation driving, in particular to an isolation driving control circuit and a driving control method suitable for high power, which comprises an edge modulation circuit and an isolation transformer, the edge modulation circuit comprises a control circuit, a driving circuit, an input filter circuit, a full-bridge circuit and a demagnetization circuit; the control circuit is connected with the full-bridge circuit through the driving circuit, the input filter circuit and the full-bridge circuit are connected in parallel with the input end of a power supply, the input filter circuit comprises two series-connected capacitor filter circuits, one end of the demagnetization circuit is connected with the middle point of the series connection of the two capacitor filter circuits, the other end of the demagnetization circuit is connected with the middle point of one bridge arm of the full-bridge circuit, and the demagnetization circuit is used for increasing the demagnetization voltage of the isolation transformer in the demagnetization process of the isolation transformer. The isolation driving control circuit can increase the demagnetization voltage and effectively reduce the loss of the demagnetization circuit.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of isolated drive, in particular to an isolated drive control circuit and a driving control method suitable for high power. BACKGROUND

[0002] Compared with linear power supply, switching power supply has the characteristics of small size, high efficiency and large power, and is widely used in the fields of automobile, photovoltaic, industrial control, medical treatment and handheld device. With the continuous iteration of technology, switching power supply is developing towards high frequency, high power and small size. MOSFET and insulated gate bipolar transistor (IGBT) have superior performance at high frequency, and are used as power switching devices in switching power supply as power stage. As we all know, each power switching device needs a driving circuit. Switching power supply has different topological structures in different applications. The position of the power switching device in different topological structures determines the driving mode. At present, there are two ways to drive the power switching device, one is non-isolated direct drive, and the other is isolated floating ground drive.

[0003] There are three kinds of existing isolated drive, bootstrap drive, transformer isolated drive and drive power combined driver. Bootstrap drive is the most ideal drive scheme applied to bridge topology, but it is limited by its own isolation voltage and can only be applied to conventional occasions. It cannot be directly used for applications exceeding 1kV or non-bridge topology, which has certain limitations. The scheme of drive power combined driver has high cost and large size, and is suitable for high power drive and occasions which are not sensitive to size and cost. Transformer isolated drive is a kind of scheme which is suitable for all scenes and has a relatively moderate cost and size. The traditional transformer isolated drive adopts asymmetric half-bridge structure, and the primary and secondary sides are both placed with capacitors. Since the transformer is always in the state of excitation and demagnetization when transmitting the duty cycle signal, the inductance must be increased to reduce the excitation current and thus reduce the loss. The disadvantage is that the size is relatively large. In addition, when the transmitted duty cycle is too large or changes suddenly, the output end will be damaged due to the problem that the voltage of the secondary side capacitor cannot change suddenly, resulting in continuous high level of the power switching tube. To solve this problem, the secondary side capacitor discharge circuit needs to be increased, which further increases the cost and size.

[0004] In order to solve the problems of traditional transformer isolated drive in size, cost and driving capacity, a new control method and circuit are proposed in Chinese invention application No. CN113193735A entitled "a driving control method and circuit", as shown in Figure 1The rising edge of the input PWM signal is modulated into a positive pulse with a fixed pulse width by the edge modulation circuit, the falling edge of the input signal is modulated into a negative pulse with a fixed pulse width, and when the input signal is a continuous high level, a plurality of continuous positive pulses are generated at a certain period by the energy supplement circuit, then the corresponding first positive pulse is demodulated into the rising edge of the secondary side drive by the secondary side circuit, and the corresponding first negative pulse is demodulated into the falling edge of the secondary side drive, the continuous positive pulse is used to supplement the energy required for the driven power tube to maintain conduction, thereby restoring the input signal and solving the problem of continuous conduction, and the width and period of the continuous positive pulse and the continuous negative pulse are adjusted as required; meanwhile, the scheme also improves the problem of insufficient drive voltage when starting at low frequency. However, the scheme has the following limitations:

[0005] 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 transmitted, and the stronger the driving capability, wherein the pulse width ratio refers to the proportion of the pulse duration to the entire switching period.

[0006] According to the modulation principle, the excitation process of the above scheme is as follows: taking the positive pulse as an example, when the first bridge arm upper tube Sa and the second bridge arm lower tube Sd are turned on, the input voltage V gs is applied to the two ends of the primary side of the transformer, the transformer is excited, and the current flows out from the positive electrode of the power supply, passes through the first bridge arm upper tube Sa, the primary side winding of the transformer, and the second bridge arm lower tube Sd in turn, and then returns to the negative electrode of the power supply.

[0007] Excitation current calculation: Where ΔI1 represents the excitation current increment, V gs represents the input power supply voltage;

[0008] After the pulse ends, the second bridge arm lower tube Sd is always in the on state when the input signal is high, and after the narrow pulse ends, the first bridge arm upper tube Sa is turned off, according to the modulation logic, the first bridge arm upper tube Sa and the first bridge arm lower tube Sb are in a complementary relationship, the first bridge arm lower tube Sb is turned on, the transformer is demagnetized, and the current flows out from the lower end of the primary side winding of the transformer, passes through the second bridge arm lower tube Sd and the first bridge arm lower tube Sb in turn, and then returns to the upper end of the primary side winding of the transformer.

[0009] Demagnetization current calculation: Where ΔI2 represents the demagnetization current increment, V R represents the reverse voltage between the primary side windings of the isolation transformer in the demagnetization stage (i.e. demagnetization voltage).

[0010] The demagnetization voltage V R is determined by the loop current and the line impedance, and decreases with the decrease of the loop current. RSynchronization reduction, line impedance includes MOS Sb conduction impedance, MOS Sd conduction impedance and line impedance, so that the demagnetizing voltage V R Far less than the excitation voltage.

[0011] That is, the demagnetization phase of the transformer in the above scheme is after each pulse, and the demagnetization phase of the transformer mainly relies on the conduction voltage drop of the two MOS tubes to demagnetize, and the demagnetization speed is relatively slow. At the same time, due to the lack of energy feedback, this part of the loss will reduce the efficiency. The excitation current of the above method is shown in Figure 2 Due to the passive demagnetization of the conduction voltage drop of the two MOS tubes and the line impedance, the demagnetizing current drops slowly, and if the driving power is increased by using the above scheme to further increase the pulse density under the condition that the pulse width is unchanged, the pulse interval time is small, the excitation current continues to rise, and the transformer has the risk of saturation and overspecification.

[0012] Furthermore, when driving a high-power MOS tube, the above scheme has the problem of insufficient driving capacity.

[0013] In order to solve the problems existing in the above driving control method, another isolation driving control circuit is proposed by those skilled in the art, as shown in Figure 3 When the input PWM signal is high, the rising edge of the input PWM signal is modulated into a fixed pulse width positive pulse by the edge modulation circuit, and there are continuous positive pulses with a certain period under the condition that the input signal is continuously high. And at the end of each positive pulse entering the demagnetization phase, by controlling the conduction of switch tube S2 and switch tube S4, the transformer primary current flows through diode D15, switch tube S4, switch tube S2 and diode D14, and the demagnetization process is carried out through the line impedance and the conduction voltage drop of the two switch tubes, as well as the conduction voltage drop of the two additional diodes. Similarly, when the input PWM signal is low, the falling edge of the input PWM signal is modulated into a fixed pulse width negative pulse by the edge modulation circuit, and there are continuous negative pulses with a certain period under the condition that the input signal is continuously low. And at the end of each negative pulse entering the demagnetization phase, by controlling the conduction of switch tube S1 and switch tube S3, the transformer primary current flows through switch tube S1, diode D12, diode D9 and switch tube S3, and the demagnetization process is carried out through the line impedance, the conduction voltage drop of the two switch tubes, and the conduction voltage drop of the two additional diodes. The excitation current waveform of the above isolation driving control circuit is shown in Figure 4 However, this scheme has the following limitations:

[0014] In order to ensure that the transformer current peak value does not continuously rise, the part of the energy supplement pulse excitation current increase should be less than or equal to the part of the demagnetization current decrease in the demagnetization stage. After the end of the first pulse, the subsequent energy supplement pulse and pulse interval need to meet the following conditions:

[0015]

[0016] That is, the current change amount generated in the demagnetization stage should be greater than the current change amount generated in the excitation stage, so as not to exceed the specification of the transformer. According to the above formula, the greater the demagnetization voltage V R , the smaller the demagnetization time Δt2, and the more intensive the energy supplement pulse interval for excitation, and the higher the driven load power. Although the above patent adds the conduction voltage drop of two diodes to the line impedance and the conduction voltage drop of two switching tubes to increase the demagnetization voltage V R in the demagnetization process, the voltage drop of the two diodes is about 1.2V. If a higher power load is to be driven, the energy supplement interval must be more intensive, and the demagnetization voltage V R must be further increased. At the same time, the voltage drop and freewheeling current generated by the diode and the conduction impedance will cause loss during demagnetization, which is also an inherent disadvantage of this demagnetization method.

[0017] In summary, the current isolation drive circuit modulation control method has two main problems to be solved: the first is how to increase the demagnetization voltage, and the second is how to reduce the demagnetization circuit loss. Currently, there is no drive control circuit that can combine these two characteristics. SUMMARY

[0018] The present application aims to solve at least one of the problems in the prior art, and provides an isolation drive control circuit and a drive control method that can increase the demagnetization voltage and effectively reduce the demagnetization circuit loss.

[0019] In a first aspect, an isolation drive control circuit is provided, which includes an edge modulation circuit and an isolation transformer. The edge modulation circuit includes a control circuit, a drive circuit, an input filter circuit, a full-bridge circuit, and a demagnetization circuit. The control circuit is connected to the full-bridge circuit through the drive circuit. The input filter circuit and the full-bridge circuit are connected in parallel to the input end of the power supply. The input filter circuit includes two series-connected capacitor filter circuits. One end of the demagnetization circuit is connected to the middle point of the series connection of the two capacitor filter circuits. The other end of the demagnetization circuit is connected to the middle point of one bridge arm of the full-bridge circuit. The demagnetization circuit is used to increase the demagnetization voltage of the isolation transformer during the demagnetization process of the isolation transformer.

[0020] Preferably, the demagnetizing circuit comprises two switch tubes connected in series, and the two switch tubes of the demagnetizing circuit are connected between the middle point of the two series-connected capacitor filter circuits and the middle point of one bridge arm of the full-bridge circuit.

[0021] Preferably, the two switch tubes of the demagnetizing circuit are switch tube S5 and switch tube S7, respectively, and the switch tube S5 and the switch tube S7 are connected in common source, the drain of the switch tube S5 is connected to the middle point of the two series-connected capacitor filter circuits, and the drain of the switch tube S7 is connected to the middle point of one bridge arm of the full-bridge circuit.

[0022] Preferably, the two switch tubes of the demagnetizing circuit are switch tube S5 and switch tube S7, respectively, and the switch tube S5 and the switch tube S7 are connected in common drain, the source of the switch tube S5 is connected to the middle point of the two series-connected capacitor filter circuits, and the source of the switch tube S7 is connected to the middle point of one bridge arm of the full-bridge circuit.

[0023] Preferably, the isolation driving control circuit further comprises a second demagnetizing circuit, and the second demagnetizing circuit comprises two other switch tubes connected in series, and the two switch tubes of the second demagnetizing circuit are connected between the middle point of the two series-connected capacitor filter circuits and the middle point of the other bridge arm of the full-bridge circuit.

[0024] Preferably, the edge modulation circuit further comprises a resistance circuit, and the resistance circuit comprises a resistor R1 and a resistor R2, the resistor R1 is connected in parallel to one capacitor filter circuit, and the resistor R2 is connected in parallel to the other capacitor filter circuit.

[0025] Preferably, the two switch tubes in the demagnetizing circuit are both unidirectional switch tubes, and are both enhancement-mode NMOS tubes.

[0026] In a second aspect, a driving control method is provided for use in an isolation driving control circuit, the isolation driving control circuit comprising an edge modulation circuit and an isolation transformer, the edge modulation circuit comprising a control circuit, a driving circuit, an input filter circuit, a full-bridge circuit, and a demagnetizing circuit; the control circuit is connected to the full-bridge circuit through the driving circuit, the input filter circuit and the full-bridge circuit are connected in parallel to the input end of a power supply, the input filter circuit comprises two series-connected capacitor filter circuits, one end of the demagnetizing circuit is connected to the middle point of the two series-connected capacitor filter circuits, and the other end of the demagnetizing circuit is connected to the middle point of one bridge arm of the full-bridge circuit.

[0027] The control method comprises the following steps:

[0028] The excitation step: during the generation of each pulse in the edge modulation circuit, the isolation transformer is excited through the full-bridge circuit;

[0029] The demagnetizing step: after each pulse, the isolation transformer is demagnetized by increasing the demagnetizing voltage through the demagnetizing circuit.

[0030] Preferably, the full-bridge circuit comprises switch S1, switch S2, switch S3 and switch S4; the demagnetization circuit comprises switch S5 and switch S7 connected in series;

[0031] When the PWM signal input to the control circuit is high, the demagnetization step sequentially comprises a fast demagnetization step and a slow demagnetization step; in the fast demagnetization step, switch S3, switch S5 and switch S7 are controlled to be turned on; in the slow demagnetization step, switch S5 and switch S7 are controlled to be turned off and switch S1 and switch S3 are controlled to be turned on.

[0032] When the PWM signal input to the control circuit is low, the demagnetization step sequentially comprises a fast demagnetization step and a slow demagnetization step; in the fast demagnetization step, switch S4, switch S5 and switch S7 are controlled to be turned on; in the slow demagnetization step, switch S5 and switch S7 are controlled to be turned off and switch S2 and switch S4 are controlled to be turned on.

[0033] Preferably, the full-bridge circuit comprises switch S1, switch S2, switch S3 and switch S4; the demagnetization circuit comprises a first demagnetization circuit and a second demagnetization circuit, wherein the first demagnetization circuit comprises switch S5 and switch S7, and the second demagnetization circuit comprises switch S6 and switch S8;

[0034] When the PWM signal input to the control circuit is high, the demagnetization step sequentially comprises a first fast demagnetization step, a first slow demagnetization step, a second fast demagnetization step and a second slow demagnetization step.

[0035] In the first fast demagnetization step, switch S3, switch S5 and switch S7 are controlled to be turned on.

[0036] In the first slow demagnetization step, switch S5 and switch S7 are controlled to be turned off and switch S1 and switch S3 are controlled to be turned on.

[0037] In the second fast demagnetization step, switch S6, switch S8 and switch S2 are controlled to be turned on.

[0038] In the second slow demagnetization step, switch S6 and switch S8 are controlled to be turned off and switch S4 and switch S2 are controlled to be turned on.

[0039] The working principle of the present application will be analyzed in detail in the specific implementation mode, and the present application has the following beneficial effects compared with the prior art:

[0040] 1) By adopting full-bridge circuit and multi-increased series capacitor, demagnetizing circuit excitation and demagnetization of the primary side of the isolation transformer, the demagnetizing voltage is greatly improved, the demagnetizing speed of the primary side of the isolation transformer is improved, the energy supplement pulse modulation density is improved, the driving capacity is greatly improved, and the driving of high-power MOS tube is supported;

[0041] 2) By continuous charging and discharging of capacitors C1 and C2, the demagnetizing energy can be fed back, so as to reduce the demagnetizing loss and improve the efficiency;

[0042] 3) By setting resistors R1 and R2, the demagnetizing voltage can be flexibly adjusted. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 is a schematic diagram of the pulse modulation control circuit of the existing pulse magnetic isolation driving technology;

[0044] Figure 2 is a schematic diagram of the energy supplement pulse modulation density and excitation current of the existing pulse magnetic isolation driving technology;

[0045] Figure 3 is a schematic diagram of the pulse modulation control circuit of the existing pulse magnetic isolation driving technology;

[0046] Figure 4 is a schematic diagram of the energy supplement pulse modulation density and excitation current of the existing pulse magnetic isolation driving technology;

[0047] Figure 5 is a schematic diagram of the isolation driving control circuit of the first embodiment of the present application;

[0048] Figure 6 is a schematic diagram of the energy supplement pulse modulation density and excitation current of the pulse magnetic isolation driving technology of the first embodiment of the present application;

[0049] Figure 7 is a schematic diagram of the isolation driving control circuit of the second embodiment of the present application;

[0050] Figure 8 is a schematic diagram of the isolation driving control circuit of the third embodiment of the present application;

[0051] Figure 9 is a schematic diagram of the isolation driving control circuit of the fourth embodiment of the present application. DETAILED DESCRIPTION

[0052] The drawings of the present application are only used for illustrative explanation, and cannot be understood as a limitation of the present application. In order to better illustrate the following embodiments, some components in the drawings may be omitted, enlarged or reduced, and cannot represent the size of the actual product; for those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings can be omitted.

[0053] First Embodiment

[0054] In this embodiment, a drive control method is provided, applied to an isolated drive control circuit with edge modulation circuitry, such as... Figure 5 As shown, the edge modulation circuit includes an input filter circuit composed of two capacitor filter circuits, a resistor circuit, a control circuit, a drive circuit, a full-bridge circuit, and a demagnetizing circuit. The first input terminal of the control circuit is connected to the positive terminal of the power supply, the second input terminal is connected to the PWM signal, the third input terminal is connected to the negative terminal of the power supply, and the output terminal is connected to the input terminal of the drive circuit. The output terminal of the drive circuit is connected to the control input terminal of the full-bridge circuit and the control input terminal of the demagnetizing circuit, respectively. The first terminal of the full-bridge circuit is connected to the positive terminal of the power supply, the second terminal is connected to the same-name terminal of the primary winding of the isolation transformer, the third terminal is connected to the negative terminal of the power supply, and the fourth terminal is connected to the opposite-name terminal of the primary winding of the isolation transformer. The first terminal of the demagnetizing circuit is connected to the midpoint of the series connection of the two capacitor filter circuits, and the second terminal is connected to the midpoint of one arm of the full-bridge circuit.

[0055] The isolated drive control method includes the following steps:

[0056] Excitation steps: During each pulse generated by the edge modulation circuit, the isolation transformer is energized through the full-bridge circuit;

[0057] Demagnetization step: After each pulse ends, the isolation transformer is demagnetized by increasing the demagnetizing voltage through the demagnetizing circuit.

[0058] Please refer to Figure 5The edge modulation circuit includes a first control circuit, a second control circuit, a third control circuit, a fourth control circuit and a fifth control circuit; the driving circuit includes a first driving circuit, a second driving circuit, a third driving circuit, a fourth driving circuit and a fifth driving circuit; the full-bridge circuit includes a switch tube S1, a switch tube S2, a switch tube S3 and a switch tube S4; the demagnetizing circuit includes a switch tube S5 and a switch tube S7; the input filter circuit is composed of two capacitor filter circuits, wherein the first capacitor filter circuit is composed of a capacitor C1, and the second capacitor filter circuit is composed of a capacitor C2; the resistor circuit is composed of a resistor R1 and a resistor R2; the output end of the first control circuit is connected with the input end of the first driving circuit, the output end of the second control circuit is connected with the input end of the second driving circuit, the output end of the third control circuit is connected with the input end of the third driving circuit, the output end of the fourth control circuit is connected with the input end of the fourth driving circuit, and the output end of the fifth control circuit is connected with the input end of the fifth driving circuit; the output end of the first driving circuit is connected with the gate of the switch tube S1; the output end of the second driving circuit is connected with the gate of the switch tube S2; the output end of the third driving circuit is connected with the gate of the switch tube S3; the output end of the fourth driving circuit is connected with the gate of the switch tube S4; and the output end of the fifth driving circuit is connected with the gate of the switch tube S5 and the gate of the switch tube S7.

[0059] The drain of the switch tube S1 and the drain of the switch tube S3 are used as the first end of the full-bridge circuit to be connected with the positive pole of the power supply; the source of the switch tube S1 and the drain of the switch tube S2 are used as the second end of the full-bridge circuit to be connected with the same-named end of the primary winding of the isolation transformer T1; the source of the switch tube S2 and the source of the switch tube S4 are used as the third end of the full-bridge circuit to be connected with the negative pole of the power supply; the drain of the switch tube S4 and the source of the switch tube S3 are used as the fourth end of the full-bridge circuit to be connected with the different-named end of the primary winding of the isolation transformer; the resistor R1 and the resistor R2 are connected in series between the positive pole and the negative pole of the power supply; the capacitor C1 and the capacitor C2 are connected in parallel on the resistor R1 and the resistor R2 respectively; the source of the switch tube S5 and the source of the switch tube S7 are connected; the drain of the switch tube S5 is connected with the middle point of the series connection of the two capacitor filter circuits as the first end of the demagnetizing circuit, and the drain of the switch tube S7 is used as the second end of the demagnetizing circuit to be connected with the middle point of one bridge arm of the full-bridge circuit.

[0060] In order to ensure that the current peak value of the isolation transformer does not continuously rise, the part of the energy supplement pulse exciting current that increases should be less than or equal to the part of the demagnetizing current that decreases in the demagnetizing stage. After the end of the first pulse, the subsequent energy supplement pulse and pulse interval need to meet the following conditions:

[0061] Where ΔI1 represents the increment of the exciting current, V gs represents the input power supply voltage, ΔI2 represents the increment of the demagnetizing current, VR The reverse voltage across the primary winding of the isolation transformer in the demagnetization phase.

[0062] That is, the current increment generated in the demagnetization phase is greater than the current increment generated in the excitation phase, so as not to exceed the specifications of the transformer. According to the above formula, the demagnetization voltage V R is greater, the required demagnetization time is smaller, and the interval of the energy supplement pulse for excitation can be more intensive, and the driven load power is higher.

[0063] When R1=R2, the demagnetization voltage V R of the present application is half of the input power voltage, while the demagnetization voltage of the prior art circuit is usually equal to the sum of the voltage drops of two diodes (corresponding Figure 3 to the voltage drops of diode D15 and diode S14) and the loop impedance voltage drop, about 1.5V. It can be seen that, compared with the demagnetization voltage of the prior art circuit, the demagnetization voltage V R of the present application is greatly improved, and thus a higher power load can be driven.

[0064] The specific principle of the control method of the present embodiment is as follows:

[0065] Reference Figure 6 , Figure 6 is shown. In the state that the PWM signal is a continuous high level, the control method of the present embodiment includes an excitation process and a demagnetization process, which are described in detail below.

[0066] The rising edge of the input PWM signal is modulated into a fixed-width positive pulse by the edge modulation circuit (corresponding to the positive pulse of the modulation signal in Figure 6 ). And in the state that the input PWM signal is a continuous high level, a plurality of continuous positive pulses are generated at a certain period. During the generation of the first positive pulse, the control circuit controls the switch S1 and the switch S4 to be turned on and the switch S2 and the switch S3 to be turned off through the first driving circuit and the fourth driving circuit. When the edge modulation circuit generates a positive pulse, the input power voltage Vgs is applied to the two ends of the primary winding of the isolation transformer, and the current flows out from the positive electrode of the input power, passes through the switch S1, the primary winding of the isolation transformer, and the switch S4 in turn, and then flows into the negative electrode of the input power, thereby completing the excitation process of the isolation transformer. In the excitation process, the excitation current rises.

[0067] After the excitation process, since the input PWM signal is still in the state of continuous high level, the demagnetization process is carried out. The control principle of the demagnetization process is as follows: first, after the first positive pulse is fired (i.e. after the excitation process), the control circuit controls the switch S3, the switch S5 and the switch S7 to be turned on through the third driving circuit and the fifth driving circuit, the voltage at the non-identical end of the primary winding of the isolation transformer is the input power supply voltage Vgs, and the voltage at the identical end of the primary winding of the isolation transformer is the voltage of the capacitor C2, which is equivalent to the voltage drop V C1 across the capacitor C1. The voltage drop V C2 is reversely added to the two ends of the primary winding of the isolation transformer, and the fast demagnetization of the isolation transformer is carried out. Then, the control circuit controls the switch S5 and the switch S7 to be turned off through the fifth driving circuit, and controls the switch S1 and the switch S3 to be turned on through the first driving circuit and the third driving circuit. The current flows out from the non-identical end of the primary winding of the isolation transformer, passes through the switch S3 and the switch S1 in turn, and returns to the identical end of the primary winding of the isolation transformer, so that the slow demagnetization of the isolation transformer is carried out, and the capacitor C1 is charged at the same time. Such a cycle is repeated to complete the whole excitation and demagnetization process when the input PWM signal is in the state of high level.

[0068] When the input PWM signal is in the state of continuous low level, the excitation process and the demagnetization process are also included, which will be described in detail below.

[0069] The falling edge of the input PWM signal is modulated into a negative pulse with a fixed pulse width (the negative pulse of the modulation signal in Figure 6 corresponding to the falling edge of the input PWM signal) by the edge modulation circuit, and a plurality of continuous negative pulses are generated at a certain period. During the first negative pulse, the second driving circuit and the third driving circuit control the switch S2 and the switch S3 to be turned on, and the switch S1 and the switch S4 to be turned off. When the edge modulation circuit generates the negative pulse, the input power supply voltage Vgs is reversely added to the two ends of the primary winding of the isolation transformer, the current flows out from the positive electrode of the power supply, passes through the switch S3, the primary winding of the isolation transformer and the switch S2 in turn, and flows into the negative electrode of the power supply, so that the reverse excitation process of the isolation transformer is completed.

[0070] After the reverse excitation process, since the input PWM signal is in the state of continuous low level, the demagnetization process is carried out. The control principle of the demagnetization process is as follows: first, after the first negative pulse is fired (i.e. after the reverse excitation process), the control circuit controls the switch S5, the switch S7 and the switch S4 to be turned on through the fifth driving circuit and the fourth driving circuit, the identical end of the primary winding of the isolation transformer is the voltage of the capacitor C2, and the non-identical end of the primary winding of the isolation transformer is the negative electrode of the power supply. It is equivalent to the voltage drop V C2The control circuit controls the switch tube S5 and the switch tube S7 to be turned off and controls the switch tube S2 and the switch tube S4 to be turned on through the fifth driving circuit and the fourth driving circuit, the current flows out from the same name end of the primary winding of the isolation transformer, sequentially passes through the switch tube S2 and the switch tube S4, and returns to the different name end of the primary winding of the isolation transformer, so as to perform the slow demagnetization of the isolation transformer and charge the capacitor C2. The above cycle is repeated to complete the whole magnetization and demagnetization process when the input PWM signal is at the low level.

[0071] In the embodiment, when the PWM signal is at the high level, the demagnetization voltage V R is calculated by the formula V R = Vgs * R1 / (R1+R2); when the PWM signal is at the low level, the demagnetization voltage V R is calculated by the formula V R = Vgs * R2 / (R1+R2). Generally, R1=R2, that is, the demagnetization voltage V R is half of the input power voltage Vgs.

[0072] According to the above demagnetization principle, the demagnetization voltage V R is determined by the loop current, the line impedance and the input power voltage Vgs. The input power voltage Vgs does not change, even if the pressure drop on the conduction impedance decreases with the decrease of the current, the attenuation of the demagnetization voltage V R can be ignored. In the embodiment, the isolation transformer is demagnetized by the demagnetization circuit. Taking the input power voltage 12V and the positive pulse demagnetization process as an example, the line impedance includes the conduction impedance of the switch tube S5, the conduction impedance of the switch tube S7 and the conduction impedance of the switch tube S3 during the demagnetization. The demagnetization voltage V R is the pressure drop on the line impedance plus the voltage division of the input power voltage Vgs, which is about 6V, so as to greatly improve the demagnetization voltage, reduce the energy supplement interval, improve the energy supplement pulse modulation density and improve the driving power. At the same time, the energy generated by the demagnetization circuit is fed back to the capacitor C1 and the capacitor C2, so as to reduce the demagnetization loss.

[0073] Second embodiment

[0074] In the embodiment, an isolation driving control method is provided, which is applied to an isolation driving control circuit with an edge modulation circuit, such as Figure 7As shown in the figure, wherein the edge modulation circuit includes input filter circuit, resistance circuit, control circuit, drive circuit, full bridge circuit and demagnetization circuit. The difference from the first embodiment is that in this embodiment, the control circuit adds a sixth control circuit, the drive circuit adds a sixth drive circuit, and contains a first demagnetization circuit and a second demagnetization circuit, wherein the first demagnetization circuit includes switch tube S5 and switch tube S7, and the second demagnetization circuit includes switch tube S6 and switch tube S8.

[0075] In this embodiment, the output end of the sixth control circuit is connected with the input end of the sixth drive circuit; the output end of the sixth drive circuit is connected with the gate of switch tube S6 and the gate of switch tube S8, and the source of switch tube S6 and the source of switch tube S8 are connected; the drain of switch tube S5 is connected with the middle point of the series connection of the two capacitor filter circuits as the first end of the first demagnetization circuit, and the drain of switch tube S7 is connected with the middle point of one bridge arm of the full bridge circuit as the second end of the first demagnetization circuit; the drain of switch tube S6 is connected with the middle point of the series connection of the two capacitor filter circuits as the first end of the second demagnetization circuit, and the drain of switch tube S8 is connected with the middle point of the other bridge arm of the full bridge circuit as the second end of the second demagnetization circuit.

[0076] The specific principle of the control method of this embodiment is similar to that of the first embodiment, except that a second demagnetization circuit is additionally provided. When the input PWM signal is high and enters the demagnetization process, first, after the first positive pulse is fired, the control circuit controls switch tube S3 and switch tube S5 and switch tube S7 to be turned on through the third drive circuit and the fifth drive circuit, the opposite-phase end of the primary winding of the isolation transformer is the power supply voltage, and the same-phase end of the primary winding of the isolation transformer is the voltage of capacitor C2. It is equivalent to that the voltage drop V C1 is added to the two ends of the primary winding of the isolation transformer in the opposite direction, and the fast demagnetization of the isolation transformer is performed (first fast demagnetization); then, the control circuit controls switch tube S5 and switch tube S7 to be turned off through the fifth drive circuit, and controls switch tube S1 and switch tube S3 to be turned on through the first drive circuit and the third drive circuit, the current flows out from the opposite-phase end of the primary winding of the isolation transformer, passes through switch tube S3 and switch tube S1 in turn, and returns to the same-phase end of the primary winding of the isolation transformer, and the slow demagnetization of the isolation transformer is performed (first slow demagnetization), while capacitor C1 is charged; again, after the second positive pulse is fired, the control circuit controls switch tube S6, switch tube S8 and switch tube S2 to be turned on through the sixth drive circuit and the second drive circuit, the opposite-phase end of the primary winding of the isolation transformer is the voltage of capacitor C2, and the same-phase end of the primary winding of the isolation transformer is the negative electrode of the power supply. It is equivalent to that the voltage drop V C2The current is reversed and applied to both ends of the primary winding of the isolation transformer for rapid demagnetization (second rapid demagnetization). Finally, the control circuit controls the switches S6 and S8 to turn off via the sixth drive circuit and controls the switches S4 and S2 to turn on via the fourth and second drive circuits. Current flows out from the opposite end of the primary winding of the isolation transformer, passes through the switches S4 and S2 in sequence, and returns to the same end of the primary winding of the isolation transformer for slow demagnetization (second slow demagnetization). At the same time, capacitor C2 is charged. This cycle repeats, completing the entire excitation and demagnetization process when the PWM signal is high.

[0077] The principle of a low-level PWM signal is similar to that described above. During the demagnetization process, after the first negative pulse, the control circuit, through the first and sixth drive circuits, controls the switching transistors S1, S6, and S8 to conduct. The same-name terminal of the primary winding of the isolation transformer receives the power supply voltage, and the opposite-name terminal receives the voltage across capacitor C2. This is equivalent to the voltage drop V across capacitor C1. C1 The current is applied across the primary winding of the isolation transformer for rapid demagnetization. Next, the control circuit, through the sixth drive circuit, controls switches S6 and S8 to disconnect, and through the first and third drive circuits, controls switches S1 and S3 to turn on. Current flows from the same-name terminal of the primary winding of the isolation transformer, through switches S1 and S3, and back to the opposite-name terminal of the primary winding, for slow demagnetization. Simultaneously, capacitor C1 is charged. Then, after the second negative pulse, the control circuit, through the fifth and fourth drive circuits, controls switches S5, S7, and S4 to turn on. The same-name terminal of the primary winding of the isolation transformer is the voltage across capacitor C2, and the opposite-name terminal is the negative terminal of the power supply. This is equivalent to a voltage drop V across capacitor C2. C2 The current is applied to both ends of the primary winding of the isolation transformer for rapid demagnetization. Finally, the control circuit controls the switches S5 and S7 to turn off through the fifth drive circuit and controls the switches S2 and S4 to turn on through the second and fourth drive circuits. The current flows out from the same-name terminal of the primary winding of the isolation transformer, passes through the switches S2 and S4 in sequence, and returns to the opposite-name terminal of the primary winding of the isolation transformer for slow demagnetization. At the same time, capacitor C2 is charged. This cycle is repeated to complete the entire excitation and demagnetization process when the PWM signal is low.

[0078] Third Embodiment

[0079] In this embodiment, an isolated drive control method is provided, such as... Figure 8As shown, two unidirectional switch tubes in the demagnetizing circuit in the first embodiment are changed from common-source connection to common-drain connection, and the control method and specific principle are the same as those in the first embodiment.

[0080] Fourth embodiment

[0081] In the embodiment, an isolation driving control method is provided, as shown in Figure 9 As shown, two pairs of unidirectional switch tubes in the two demagnetizing circuits in the second embodiment are changed from common-source connection to common-drain connection, and the control method and specific principle are the same as those in the second embodiment.

[0082] The above is only the preferred embodiment of the present application, and it should be noted that the above preferred embodiment should not be regarded as a limitation of the present application, and for those skilled in the art, several improvements and refinements can be made without departing from the spirit and scope of the present application, which will not be described in detail here, and the protection scope of the present application should be limited by the scope defined in the claims.

Claims

1. An isolated drive control circuit comprising an edge modulation circuit and an isolation transformer, characterized by, The edge modulation circuit comprises a control circuit, a driving circuit, an input filter circuit, a full-bridge circuit and a demagnetization circuit; the control circuit is connected with the full-bridge circuit through the driving circuit; the input filter circuit and the full-bridge circuit are connected in parallel with the input end of a power supply; the input filter circuit comprises two capacitor filter circuits connected in series; one end of the demagnetization circuit is connected with the middle point of the two capacitor filter circuits connected in series; the other end of the demagnetization circuit is connected with the middle point of one bridge arm of the full-bridge circuit; the demagnetization circuit is used for increasing the demagnetization voltage of the isolation transformer during the demagnetization process of the isolation transformer; The demagnetization circuit comprises two switch tubes connected in series; the two switch tubes of the demagnetization circuit are connected between the middle point of the two capacitor filter circuits connected in series and the middle point of one bridge arm of the full-bridge circuit; The edge modulation circuit further comprises a resistance circuit; the resistance circuit comprises a resistor R1 and a resistor R2; the resistor R1 is connected in parallel with one capacitor filter circuit; the resistor R2 is connected in parallel with the other capacitor filter circuit.

2. The isolated drive control circuit of claim 1, wherein: The two switch tubes of the demagnetization circuit are a switch tube S5 and a switch tube S7; the switch tube S5 and the switch tube S7 are connected in common source; the drain of the switch tube S5 is connected with the middle point of the two capacitor filter circuits connected in series; the drain of the switch tube S7 is connected with the middle point of one bridge arm of the full-bridge circuit.

3. The isolated drive control circuit of claim 1, wherein: The two switch tubes of the demagnetization circuit are a switch tube S5 and a switch tube S7; the switch tube S5 and the switch tube S7 are connected in common drain; the source of the switch tube S5 is connected with the middle point of the two capacitor filter circuits connected in series; the source of the switch tube S7 is connected with the middle point of one bridge arm of the full-bridge circuit.

4. The isolated drive control circuit of claim 1, wherein: A second demagnetization circuit is further provided; the second demagnetization circuit comprises two other switch tubes connected in series; the two switch tubes of the second demagnetization circuit are connected with the middle point of the two capacitor filter circuits connected in series and the middle point of the other bridge arm of the full-bridge circuit.

5. The isolated drive control circuit of claim 1, wherein: The two switch tubes of the demagnetization circuit are unidirectional switch tubes and are both enhancement mode NMOS tubes.

6. A drive control method for use in an isolated drive control circuit, the isolated drive control circuit comprising an edge modulation circuit and an isolation transformer, characterized by, The edge modulation circuit comprises a control circuit, a driving circuit, an input filter circuit, a full-bridge circuit and a demagnetization circuit; the control circuit is connected with the full-bridge circuit through the driving circuit; the input filter circuit and the full-bridge circuit are connected in parallel with the input end of a power supply; the input filter circuit comprises two capacitor filter circuits connected in series; one end of the demagnetization circuit is connected with the middle point of the two capacitor filter circuits connected in series; the other end of the demagnetization circuit is connected with the middle point of one bridge arm of the full-bridge circuit; The control method comprises the following steps: The excitation step: during the generation of each pulse of the edge modulation circuit, the isolation transformer is excited through the full-bridge circuit; The demagnetization step: after each pulse, the isolation transformer is demagnetized by increasing the demagnetization voltage through the demagnetization circuit; The full-bridge circuit comprises a switch tube S1, a switch tube S2, a switch tube S3 and a switch tube S4; the demagnetization circuit comprises a switch tube S5 and a switch tube S7 connected in series; When the PWM signal input to the control circuit is high, the demagnetization step sequentially includes a fast demagnetization step and a slow demagnetization step; in the fast demagnetization step, the switch tube S3, the switch tube S5 and the switch tube S7 are controlled to be turned on; in the slow demagnetization step, the switch tube S5 and the switch tube S7 are controlled to be turned off, and the switch tube S1 and the switch tube S3 are controlled to be turned on. When the PWM signal input to the control circuit is low, the demagnetization step sequentially includes a fast demagnetization step and a slow demagnetization step; in the fast demagnetization step, the switch tube S4, the switch tube S5 and the switch tube S7 are controlled to be turned on; in the slow demagnetization step, the switch tube S5 and the switch tube S7 are controlled to be turned off, and the switch tube S2 and the switch tube S4 are controlled to be turned on. Or the full-bridge circuit includes switch tubes S1, S2, S3 and S4; the demagnetization circuit includes a first demagnetization circuit and a second demagnetization circuit, wherein the first demagnetization circuit includes switch tubes S5 and S7, and the second demagnetization circuit includes switch tubes S6 and S8; When the PWM signal input to the control circuit is high, the demagnetization step sequentially includes a first fast demagnetization step, a first slow demagnetization step, a second fast demagnetization step, and a second slow demagnetization step. In the first fast demagnetization step, the switch tube S3, the switch tube S5 and the switch tube S7 are controlled to be turned on. In the first slow demagnetization step, the switch tube S5 and the switch tube S7 are controlled to be turned off, and the switch tube S1 and the switch tube S3 are controlled to be turned on. In the second fast demagnetization step, the switch tube S6, the switch tube S8 and the switch tube S2 are controlled to be turned on. In the second slow demagnetization step, the switch tube S6 and the switch tube S8 are controlled to be turned off, and the switch tube S4 and the switch tube S2 are controlled to be turned on.

7. The drive control method according to claim 6, characterized by: The edge modulation circuit is further provided with a resistance circuit, which includes resistors R1 and R2, the resistor R1 is connected in parallel to one of the capacitor filter circuits, and the resistor R2 is connected in parallel to the other capacitor filter circuit.

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