A soft switching circuit based on resonant voltage detection

Abstract

The present invention discloses a soft switching circuit based on resonant voltage detection, which relates to the field of soft switching technology. The circuit comprises: a resonant sampling circuit connected to the drain and source ends of a switching field effect transistor, sampling the sinusoidal resonant voltage wave generated by the voltage changes at the drain and source ends; a comparator circuit for generating corresponding high / low level signals based on the magnitude of the sinusoidal resonant voltage and a preset voltage; a drive control circuit for generating corresponding timing signals based on the received high / low level signals; and a control chip for estimating the target time and performing soft switching control based on each timing signal. Based on the principle of sinusoidal wave symmetry, the present invention uses three time points to predict in advance the time point when the resonant voltage returns to the high point comparison voltage, thereby estimating the zero crossing point of the resonant voltage, i.e., the moment when the terminal voltage is minimum, for soft switching control, further reducing switching losses.

Description

Technical Field

[0001] The present invention relates to the technical field of soft switching, and in particular to a soft switching circuit based on resonant voltage detection. Background Art

[0002] To reduce switching losses, converters often employ soft switching. Soft switching involves reducing the terminal voltage of a switching device to a very low value near zero through a resonant circuit before turning it on. This reduces voltage and current overlap during the switching process, thereby reducing switching losses. To achieve soft switching, it is necessary to detect the moment when the voltage of the switching device resonates to zero before turning it on. Traditional terminal voltage detection circuits for switching devices compare the terminal voltage with a set reference value and immediately send a drive signal to the switching device when the terminal voltage falls below a voltage threshold. However, this detection method has a certain hysteresis, making it difficult to perform soft switching in a timely manner when the voltage crosses zero, resulting in some switching device losses. Summary of the Invention

[0003] In order to further reduce the loss of switching devices and improve the accuracy of soft switching, the present invention proposes a soft switching circuit based on resonant voltage detection. The switching device is a switching field effect transistor, including:

[0004] The resonant sampling circuit is connected to the drain and source ends of the switching field effect transistor and is used to sample the sinusoidal resonant voltage wave generated by the voltage change between the drain and source ends when the switching field effect transistor switches from the off state to the on state;

[0005] a comparator circuit configured to output a first high-level signal and a second high-level signal respectively when the sinusoidal resonant voltage is in a rising state and is higher than a first preset voltage and a second preset voltage, and to output a second low-level signal and a first low-level signal respectively when the sinusoidal resonant voltage is in a falling state and is lower than the second preset voltage and the first preset voltage;

[0006] a drive control circuit, configured to output a first timing signal upon receiving a first high-level signal, output a second timing signal upon receiving a second high-level signal, output a third timing signal upon receiving a second low-level signal, and output a fourth timing signal upon receiving a first low-level signal;

[0007] a control chip, configured to estimate a target time for receiving the fourth timing signal based on the time at which the first timing signal, the second timing signal, and the fourth timing signal are received, obtain a zero-crossing time point of the sinusoidal resonant voltage based on a preset delay when the target time is reached, and output a drive signal;

[0008] The driver is used to control the field effect tube to conduct when receiving a driving signal.

[0009] Furthermore, the resonant circuit includes an RC circuit consisting of a first capacitor and a third resistor connected in series, wherein:

[0010] The capacitor end of the RC circuit is connected to the drain of the switching field effect transistor through the first resistor, and the resistor end of the RC circuit is connected to the source of the switching field effect transistor; the second resistor is connected in parallel to both ends of the first capacitor, and the second capacitor is connected in parallel to both ends of the third resistor.

[0011] Furthermore, the first resistor is a current limiting resistor, used to limit the current input to the RC circuit; the second resistor is a discharge resistor, used to release the energy storage voltage of the first capacitor; the second capacitor is a high-frequency filter capacitor, used to filter out high-frequency signals in the sinusoidal resonant voltage wave.

[0012] Furthermore, the comparator circuit includes a first comparator and a second comparator connected to each other at the negative input terminal, wherein:

[0013] The negative input terminals of the first comparator and the second comparator are connected between the first capacitor and the third resistor in series, and are used to receive a sinusoidal resonant voltage wave; the positive input terminal of the first comparator is connected to a first preset voltage, and the output terminal of the first comparator is used to output a first high-level signal or a first low-level signal; the positive input terminal of the second comparator is connected to a second preset voltage, and the output terminal of the second comparator is used to output a second high-level signal or a second low-level signal.

[0014] Furthermore, the drive control circuit includes a first drive field effect transistor and a second drive field effect transistor, wherein:

[0015] The gate of the first driving field effect transistor is connected to the output end of the first comparator, the drain of the first driving field effect transistor outputs the first timing signal or the fourth timing signal and is connected to the driving voltage through the fourth resistor, and the source of the first driving field effect transistor is connected to the source of the switch field effect transistor;

[0016] The gate of the second driving field effect transistor is connected to the output end of the second comparator, the drain of the second driving field effect transistor outputs the second timing signal or the third timing signal, and is connected to the driving voltage through the fifth resistor, and the source of the second driving field effect transistor is connected to the source of the switching field effect transistor.

[0017] Furthermore, a voltage protection circuit is included for limiting the amplitude of the output voltage of the resonant sampling circuit, including:

[0018] The first diode and the second diode are connected in series, and the connection point of the first diode and the second diode is connected to the sinusoidal resonant voltage wave, wherein the cathode of the first diode is connected to the anode of the driving voltage, and the anode of the second diode is connected to the cathode of the driving voltage.

[0019] Furthermore, the target time is obtained by the following formula:

[0020] t4=t2+t3-t1

[0021] Wherein, t4 is the target time, t3 is the reception time of the third timing signal, t2 is the reception time of the second timing signal, and t1 is the reception time of the first timing signal.

[0022] Compared with the prior art, the present invention has at least the following beneficial effects:

[0023] (1) The soft switching circuit based on resonant voltage detection described in the present invention senses the terminal voltage change of the switching device through an RC circuit and generates a resonant voltage wave with a sinusoidal characteristic. When the current limiting resistor is small, by setting two comparison voltages, while detecting the dynamic change of the terminal voltage, the time point when the voltage drops to the corresponding voltage and the time point when it rises back to the low comparison voltage are obtained. Based on the principle of sine wave symmetry, the time point when the voltage rises back to the high comparison voltage is estimated in advance through the three time points, thereby achieving the estimated resonant voltage zero crossing point, that is, the time when the terminal voltage is minimum, to perform soft switching control, thereby further reducing switching losses;

[0024] (2) It can adaptively adjust the zero-crossing time according to the fluctuation of the mains voltage frequency, so it is more adaptable and not affected by fluctuations. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A modular schematic diagram of a soft switching circuit based on resonant voltage detection;

[0026] Figure 2 Schematic diagram of circuit connection of soft switching circuit;

[0027] Figure 3 Schematic diagram of voltage fluctuation. DETAILED DESCRIPTION

[0028] The following are specific embodiments of the present invention and the accompanying drawings to further describe the technical solutions of the present invention, but the present invention is not limited to these embodiments.

[0029] Example 1

[0030] In order to accurately perform soft switching when the voltage at the switching device terminal reaches the minimum value and reduce switching losses, such as Figure 1 As shown, the present invention proposes a soft switching circuit based on resonant voltage detection, wherein the switching device is a switching field effect transistor, including:

[0031] The resonant sampling circuit is connected to the drain and source ends of the switching field effect transistor and is used to sample the sinusoidal resonant voltage wave generated by the voltage change between the drain and source ends when the switching field effect transistor switches from the off state to the on state;

[0032] a comparator circuit configured to output a first high-level signal and a second high-level signal respectively when the sinusoidal resonant voltage is in a rising state and is higher than a first preset voltage and a second preset voltage, and to output a second low-level signal and a first low-level signal respectively when the sinusoidal resonant voltage is in a falling state and is lower than the second preset voltage and the first preset voltage;

[0033] a drive control circuit, configured to output a first timing signal upon receiving a first high-level signal, output a second timing signal upon receiving a second high-level signal, output a third timing signal upon receiving a second low-level signal, and output a fourth timing signal upon receiving a first low-level signal;

[0034] a control chip, configured to estimate a target time for receiving the fourth timing signal based on the time at which the first timing signal, the second timing signal, and the fourth timing signal are received, obtain a zero-crossing time point of the sinusoidal resonant voltage based on a preset delay when the target time is reached, and output a drive signal;

[0035] The driver is used to control the field effect tube to conduct when receiving a driving signal.

[0036] Considering that the voltage frequency of the mains electricity may fluctuate to a certain extent and cannot always maintain the same frequency, if the traditional comparison of the terminal voltage with the set reference value is used for soft switching control, there may be a certain deviation. Therefore, in order to reduce the resulting estimation deviation and further improve the adaptability of the soft switching control, the present invention proposes another soft switching determination method, which is based on the advance prediction of the zero-crossing point of the induced sinusoidal resonant voltage. Assuming that the voltage frequency at both ends of the switching device is a cosine wave, then the corresponding sine wave is formed by the change of the induced terminal voltage, and the zero-crossing moment of the rising section of the sine wave is the lowest voltage point of the cosine wave. Therefore, as long as the zero-crossing moment of the sine wave is predicted, precise soft switching control of the switching device can be achieved.

[0037] In the present invention, the induced voltage (that is, the cosine voltage wave generated based on the sinusoidal resonant voltage wave) is generated by the RC circuit in the resonant sampling circuit. Specifically, Figure 2 As shown, the RC circuit consists of a first capacitor C1 and a third resistor R3 connected in series, where:

[0038] The capacitor end of the RC circuit is connected to the drain of the switching field effect transistor (connected through pin 1) through the first resistor R1, and the resistor end of the RC circuit is connected to the source of the switching field effect transistor (connected through pin 2); the second resistor R2 is connected in parallel to both ends of the first capacitor, and the second capacitor C2 is connected in parallel to both ends of the third resistor.

[0039] Among them, the first resistor is a current-limiting resistor, which is used to limit the current flowing into the RC circuit to avoid breakdown of electronic components caused by excessive current; the RC circuit is used to generate an induced voltage based on the voltage changes at the drain and source ends of the switching field-effect transistor; the second capacitor is used to filter out high-frequency signals in the voltage signal, so that the induced sinusoidal resonant voltage wave will not lead to incorrect judgment of the time point due to irregular fluctuations; and the second resistor in parallel is used to release the energy stored in the first capacitor, and together with the third resistor, divide the voltage to ensure steady-state voltage division.

[0040] After the sinusoidal resonant voltage is generated by induction, the voltage magnitude is judged by the comparator circuit. Specifically, Figure 2 As shown, it includes a first comparator U1 and a second comparator U2 connected to each other at the negative input terminals, wherein:

[0041] The negative input terminals of the first comparator and the second comparator are connected between the first capacitor and the third resistor in series, and are used to receive a sinusoidal resonant voltage wave; the positive input terminal of the first comparator is connected to a first preset voltage V1, and the output terminal of the first comparator is used to output a first high-level signal or a first low-level signal; the positive input terminal of the second comparator is connected to a second preset voltage V2, and the output terminal of the second comparator is used to output a second high-level signal or a second low-level signal.

[0042] The generated high / low level signal is received by the subsequent drive control circuit, such as Figure 2 As shown, the drive control circuit includes a first drive field effect transistor S1 and a second drive field effect transistor S2, wherein:

[0043] The gate of the first driving field effect transistor is connected to the output end of the first comparator, the drain of the first driving field effect transistor outputs the first timing signal or the fourth timing signal (output through pin 3), and is connected to the driving voltage VCC through the fourth resistor R4, and the source of the first driving field effect transistor is connected to the source of the switch field effect transistor;

[0044] The gate of the second driving field effect transistor is connected to the output end of the second comparator, the drain of the second driving field effect transistor outputs the second timing signal or the third timing signal (output through pin 4), and is connected to the driving voltage VCC through the fifth resistor R5, and the source of the second driving field effect transistor is connected to the source of the switching field effect transistor.

[0045] At the same time, in order to limit the amplitude of the output voltage of the resonant sampling circuit to avoid exceeding the input range of the comparator, a voltage protection circuit is also included, which contains:

[0046] The first diode D1 and the second diode D2 are connected in series at the beginning and the end, and the connection between the first diode and the second diode is connected to the sinusoidal resonant voltage wave, wherein the cathode of the first diode is connected to the positive electrode of the driving voltage VCC+, and the anode of the second diode is connected to the negative electrode of the driving voltage VCC-.

[0047] Next, the transmission and generation process of each signal of the present invention is described. Figure 3 As shown, Vds is the voltage change curve of the drain and source of the switching device (that is, pin 1 and pin 2), and the dotted line V RC The resonant sampling circuit composed of R1, R2, R3, C1 and C2 outputs the sinusoidal resonant voltage wave. At time t0, the tube voltage Vds begins to drop, V RC Based on the induced potential, the voltage V RC When the voltage is lower than V1, U1 outputs the first high level signal, turning on the first driving field effect tube S1, and the output of pin 3 is low level, which is recognized by the control chip as the first timing signal. RC When the voltage is lower than V2, U2 outputs the second high level signal, turning on the second drive field effect tube S2, and the output of pin 4 is low level, which is recognized by the control chip as the second timing signal. RC When the voltage rises back up and is higher than V2, U2 outputs the second low level signal to restore the second drive field effect tube to the off state. At this time, the output of pin 4 is high level and is recognized by the control chip as the third timing signal. At time t4, the voltage V RC When it rises back and is higher than the voltage of V1, U1 outputs a first low-level signal to restore the first driving field effect transistor to the off state. At this time, the output of pin 3 is high level, which is recognized by the control chip as the fourth timing signal.

[0048] Since the sine wave is symmetrical and the timing signals are all generated based on the first preset voltage or the second preset voltage, once the reception times of the first, second, and third timing signals are obtained successively, the time point of the fourth timing signal (i.e., the target time) can be accurately predicted. The specific formula is as follows:

[0049] t4=t2+t3-t1

[0050] Wherein, t4 is the target time, t3 is the reception time of the third timing signal, t2 is the reception time of the second timing signal, and t1 is the reception time of the first timing signal.

[0051] Generally speaking, the closer V1 is to 0, the closer t4 is to t5 (the moment when Vds is at its lowest point). However, since normal tube voltage fluctuations can introduce a lot of interference signals, using V2 to compare the voltage level can distinguish whether resonance of the voltage across the switching device has been triggered. According to t2-t1=t4-t3, when t3 arrives, t4 can be estimated in advance: t4=t2+t3-t1. Since t4 and t5 are very close, the time difference can be ignored. Therefore, by estimating t4 in advance and taking into account the delay td caused by the sampling and drive circuit and drive response (also known as the preset delay), a switch drive signal can be issued at t4-td to achieve the switching device turning on at the lowest point of the resonant voltage, which is also known as soft switching of the switching device.

[0052] In summary, the soft switching circuit based on resonant voltage detection described in the present invention senses the terminal voltage change of the switching device through an RC circuit and generates a resonant voltage wave with sinusoidal characteristics. When the current limiting resistor is small, by setting two comparison voltages, while detecting the dynamic change of the terminal voltage, the time point when the voltage drops to the corresponding voltage and the time point when the voltage rises back to the low point comparison voltage are obtained. Based on the principle of sine wave symmetry, the time point when the voltage rises back to the high point comparison voltage is estimated in advance through three time points, thereby achieving the estimated resonant voltage zero crossing point, that is, the moment when the terminal voltage is minimum, to perform soft switching control, thereby further reducing switching losses. The zero crossing time can be adaptively adjusted according to the fluctuation of the mains voltage frequency, so it is more adaptable and not affected by fluctuations.

[0053] It should be noted that all directional indications in the embodiments of the present invention (such as up, down, left, right, front, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the various components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0054] In addition, in the present invention, descriptions such as "first," "second," and "one" are for descriptive purposes only and should not be understood to indicate or imply their relative importance or implicitly specify the number of the technical features indicated. Therefore, a feature specified as "first" or "second" may explicitly or implicitly include at least one of such features. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0055] In the present invention, unless otherwise specified or limited, the terms "connection" and "fixation" should be understood in a broad sense. For example, "fixation" can mean fixed connection, detachable connection, or integration; mechanical connection or electrical connection; direct connection or indirect connection through an intermediate medium; internal communication between two elements or interaction between two elements, unless otherwise specified. Those skilled in the art will be able to understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0056] In addition, the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on the fact that ordinary technicians in this field can implement it. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

Claims

1. A soft switching circuit based on resonant voltage detection, characterized in that: The switching device is a switching field effect transistor, including: The resonant sampling circuit is connected to the drain and source ends of the switching field effect transistor and is used to sample the sinusoidal resonant voltage wave generated by the voltage change between the drain and source ends when the switching field effect transistor switches from the off state to the on state; a comparator circuit configured to output a first high-level signal and a second high-level signal respectively when the sinusoidal resonant voltage is in a rising state and is higher than a first preset voltage and a second preset voltage, and to output a second low-level signal and a first low-level signal respectively when the sinusoidal resonant voltage is in a falling state and is lower than the second preset voltage and the first preset voltage; a drive control circuit, configured to output a first timing signal upon receiving a first high-level signal, output a second timing signal upon receiving a second high-level signal, output a third timing signal upon receiving a second low-level signal, and output a fourth timing signal upon receiving a first low-level signal; a control chip, configured to estimate a target time for receiving the fourth timing signal based on the times at which the first timing signal, the second timing signal, and the third timing signal are received, obtain a zero-crossing time point of the sinusoidal resonant voltage based on a preset delay when the target time is reached, and output a drive signal; The driver is used to control the field effect tube to conduct when receiving a driving signal.

2. A soft switching circuit based on resonant voltage detection according to claim 1, characterized in that: The resonant sampling circuit includes an RC circuit consisting of a first capacitor and a third resistor connected in series, wherein: The capacitor end of the RC circuit is connected to the drain of the switching field effect transistor through the first resistor, and the resistor end of the RC circuit is connected to the source of the switching field effect transistor; the second resistor is connected in parallel to both ends of the first capacitor, and the second capacitor is connected in parallel to both ends of the third resistor.

3. A soft switching circuit based on resonant voltage detection according to claim 2, characterized in that: The first resistor is a current limiting resistor, used to limit the current input to the RC circuit; the second resistor is a discharge resistor, used to release the energy storage voltage of the first capacitor; the second capacitor is a high-frequency filter capacitor, used to filter out high-frequency signals in the sinusoidal resonant voltage wave.

4. A soft switching circuit based on resonant voltage detection according to claim 2, characterized in that: The comparator circuit includes a first comparator and a second comparator connected to each other at negative input terminals, wherein: The negative input terminals of the first comparator and the second comparator are connected between the first capacitor and the third resistor in series, and are used to receive a sinusoidal resonant voltage wave; the positive input terminal of the first comparator is connected to a first preset voltage, and the output terminal of the first comparator is used to output a first high-level signal or a first low-level signal; the positive input terminal of the second comparator is connected to a second preset voltage, and the output terminal of the second comparator is used to output a second high-level signal or a second low-level signal.

5. A soft switching circuit based on resonant voltage detection according to claim 4, characterized in that: The driving control circuit includes a first driving field effect transistor and a second driving field effect transistor, wherein: The gate of the first driving field effect transistor is connected to the output end of the first comparator, the drain of the first driving field effect transistor outputs the first timing signal or the fourth timing signal and is connected to the driving voltage through the fourth resistor, and the source of the first driving field effect transistor is connected to the source of the switch field effect transistor; The gate of the second driving field effect transistor is connected to the output end of the second comparator, the drain of the second driving field effect transistor outputs the second timing signal or the third timing signal, and is connected to the driving voltage through the fifth resistor, and the source of the second driving field effect transistor is connected to the source of the switching field effect transistor.

6. The soft switching circuit based on resonant voltage detection according to claim 1, characterized in that: The invention also includes a voltage protection circuit for limiting the amplitude of the output voltage of the resonant sampling circuit, including: The first diode and the second diode are connected in series, and the connection point of the first diode and the second diode is connected to the sinusoidal resonant voltage wave, wherein the cathode of the first diode is connected to the anode of the driving voltage, and the anode of the second diode is connected to the cathode of the driving voltage.

7. The soft switching circuit based on resonant voltage detection according to claim 1, characterized in that: The target time is obtained by the following formula: t4=t2+t3-t1 Wherein, t4 is the target time, t3 is the reception time of the third timing signal, t2 is the reception time of the second timing signal, and t1 is the reception time of the first timing signal.

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