Protection circuit

Abstract

The utility model relates to the technical field of absorption circuits, and discloses a protection circuit which comprises a power switch tube Q1, a first absorption unit and a second absorption unit are connected between a drain electrode and a source electrode of the power switch tube Q1, the source electrode of the power switch tube Q1 is connected with the ground, and the first absorption unit and the second absorption unit are connected in parallel; according to the utility model, a more efficient peak voltage absorption effect can be achieved, the power loss of the circuit can be effectively reduced, and the reliability of the circuit can be improved at the same time.

Description

Technical Field

[0001] The utility model relates to the technical field of absorption circuits, in particular to a protection circuit. Background Art

[0002] With the development of power electronics technology, power inverter circuits are gradually developing towards integration and light weight. In order to overcome the current drawbacks, a control strategy of increasing the switching frequency is usually adopted. When the inverter circuit is in a high-frequency state, the parameters such as parasitic inductance and distributed capacitance in the inverter circuit cannot be ignored. At the moment of power device switching, the spike voltage generated by the parasitic parameters will bring a high breakdown risk to the electronic components in the inverter circuit, so they need to be suppressed by an absorption circuit.

[0003] In the switching power supply circuit, in order to prevent the switch tube from being damaged by the voltage spike generated by the oscillation of the transformer leakage inductance and the switch tube junction capacitance during the switching process, an RCD absorption circuit is generally added to absorb the large voltage spike to protect the switch tube. Figure 1 As shown, it mainly includes a peak voltage input terminal IN1, a power connection terminal IN2, a resistor R111, a resistor R222, a capacitor C111 and a diode D111, wherein the peak voltage input terminal IN1 is used to connect the switch tube in the switch power circuit, and the power connection terminal IN2 is used to connect the voltage input terminal in the switch power circuit. When the switch tube is turned off, the voltage of the primary coil of the transformer in the switch power circuit is reversed, and at the same time, the diode D111 is turned on, and the leakage inductance releases energy to directly charge the capacitor C111, and the voltage across the capacitor C111 rises rapidly. When the diode D111 is turned off, the capacitor C111 is discharged through the resistor R222, so as to suppress the voltage spike of the switch tube.

[0004] However, the existing absorption circuit has poor absorption effect on the peak voltage, and in the application of the flyback converter, since the absorption circuit operates at a high frequency, the corresponding absorption diode also uses a high-frequency tube. However, the RCD circuit composed of a high-frequency diode can only absorb the peak voltage, and has little improvement on the EMI problem that occurs during the circuit operation, resulting in reduced reliability of the absorption circuit. Utility Model Content

[0005] The utility model aims to provide a protection circuit, aiming to provide a protection circuit that can absorb peak voltage more efficiently, effectively reduce the power loss of the circuit, and improve the reliability of the circuit.

[0006] The utility model is achieved in this way:

[0007] A protection circuit comprises a power switch tube Q1, a first absorption unit and a second absorption unit are connected between a drain and a source of the power switch tube Q1, the source of the power switch tube Q1 is connected to ground, and the first absorption unit and the second absorption unit are connected in parallel;

[0008] The second absorption unit includes a first diode D1 and a second diode D2 whose anodes are connected to the drain of the power switch tube Q1, the first diode D1 and the second diode D2 are connected in parallel, and the cathodes of the first diode D1 and the second diode D2 are connected to a first resistor R1 and an RC series branch, the first resistor R1 is connected in parallel to the RC series branch, one end of the first resistor R1 connected in parallel to the RC series branch is connected to the cathodes of the first diode D1 and the second diode D2, and the other end of the first resistor R1 connected in parallel to the RC series branch is connected to the source of the power switch tube Q1.

[0009] Furthermore, the first absorption unit is a varistor VR1.

[0010] Furthermore, the first absorption unit is a transient voltage suppressor diode TVS1.

[0011] Further, the cathodes of the first diode D1 and the second diode D2 are connected to a third diode D3, the anode of the third diode D3 is connected to the cathodes of the first diode D1 and the second diode D2, the cathode of the third diode D3 is connected to the power supply VCC, and the cathode of the third diode D3 is connected to a fourth resistor R4, one end of the fourth resistor R4 is connected to the power supply VCC, and the other end of the fourth resistor R4 is connected to the ground.

[0012] Furthermore, the RC series branch includes a first capacitor C1 and a second resistor R2, one end of the first capacitor C1 is one end of the RC series branch, the other end of the first capacitor C1 is connected in series with one end of the second resistor R2, and the other end of the second resistor R2 is the other end of the RC series branch.

[0013] Furthermore, the RC series branch further includes a third resistor R3, and the third resistor R3 is connected in parallel with the second resistor R2.

[0014] Compared with the prior art, the beneficial effects of the utility model are:

[0015] In practical applications, when the power switch tube Q1 is disconnected, the spike voltage generated by the parasitic inductance and capacitance is charged to the RC series branch through the first diode D1 and the second diode D2, so that the spike voltage is stored in the RC series branch in the form of electrical energy, thereby suppressing the voltage at the DS terminal of the power switch tube Q1; when the RC series branch is charged, the first diode D1 and the second diode D2 can prevent the RC series branch from discharging through the power switch tube Q1, thereby preventing the drain current of the power switch tube Q1 from increasing; the electrical energy stored in the RC series branch can only be discharged to the first resistor R1; if the turn-off current is too large when the power switch tube Q1 is disconnected, the generated spike voltage exceeds the absorption capacity of the RC series branch, and the first absorption unit can quickly absorb the excess current, so that the spike voltage at the DS terminal of the power switch tube Q1 is less than its maximum withstand voltage value, thereby protecting the power switch tube Q1 from being broken down by overvoltage;

[0016] At the same time, the first diode D1 is a high-frequency diode, the second diode D2 is a low-frequency diode, and the second absorption unit adopts the method of using the high-frequency diode and the low-frequency diode in parallel. Due to the inherent characteristics of the high-frequency diode, the first diode D1 has a faster conduction speed and will be turned on instantly and quickly when absorbing the peak voltage, which makes up for the problem that the second diode D2 is easy to burn out due to slow conduction. The high-frequency diode and the low-frequency diode are used in parallel to ensure that the second diode D2 will not burn out. At the same time, the slow reverse recovery speed of the low-frequency diode is utilized to reversely extract part of the energy of the RC series branch, so that the oscillation frequency and amplitude of the peak voltage are reduced, thereby achieving the purpose of improving EMI. The utility model can play a more efficient peak voltage absorption role, and can effectively reduce the power loss of the circuit, while improving the reliability of the circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solution of the implementation mode of the utility model, the drawings required for use in the implementation mode will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the utility model and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 This is the schematic diagram of the existing RCD absorption circuit;

[0019] Figure 2 It is a schematic diagram of an embodiment of the utility model;

[0020] Figure 3 It is a schematic diagram of another embodiment of the utility model;

[0021] Figure 4 It is a principle diagram of another embodiment of the utility model. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical scheme and advantages of the embodiments of the utility model clearer, the technical scheme in the embodiments of the utility model will be clearly and completely described below in conjunction with the drawings in the embodiments of the utility model. Obviously, the described embodiments are part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments in the utility model, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the scope of protection of the utility model. Therefore, the following detailed description of the embodiments of the utility model provided in the drawings is not intended to limit the scope of the utility model for which protection is sought, but merely represents the selected embodiments of the utility model. Based on the embodiments in the utility model, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the scope of protection of the utility model.

[0023] See also Figures 2 to 4 , a protection circuit, comprising a power switch tube Q1, a first absorption unit and a second absorption unit are connected between the drain and the source of the power switch tube Q1, the source of the power switch tube Q1 is connected to the ground, and the first absorption unit and the second absorption unit are connected in parallel;

[0024] The second absorption unit includes a first diode D1 and a second diode D2 whose anodes are connected to the drain of the power switch tube Q1, the first diode D1 and the second diode D2 are connected in parallel, and the cathodes of the first diode D1 and the second diode D2 are connected to a first resistor R1 and an RC series branch, the first resistor R1 is connected in parallel to the RC series branch, one end of the first resistor R1 connected in parallel to the RC series branch is connected to the cathodes of the first diode D1 and the second diode D2, and the other end of the first resistor R1 connected in parallel to the RC series branch is connected to the source of the power switch tube Q1.

[0025] In practical applications, when the power switch tube Q1 is disconnected, the spike voltage generated by the parasitic inductance and capacitance is charged to the RC series branch through the first diode D1 and the second diode D2, so that the spike voltage is stored in the RC series branch in the form of electrical energy, thereby suppressing the voltage at the DS terminal of the power switch tube Q1; when the RC series branch is charged, the first diode D1 and the second diode D2 can prevent the RC series branch from discharging through the power switch tube Q1, thereby preventing the drain current of the power switch tube Q1 from increasing; the electrical energy stored in the RC series branch can only be discharged to the first resistor R1; if the turn-off current is too large when the power switch tube Q1 is disconnected, the generated spike voltage exceeds the absorption capacity of the RC series branch, and the first absorption unit can quickly absorb the excess current, so that the spike voltage at the DS terminal of the power switch tube Q1 is less than its maximum withstand voltage value, thereby protecting the power switch tube Q1 from being broken down by overvoltage;

[0026] At the same time, the first diode D1 is a high-frequency diode, the second diode D2 is a low-frequency diode, and the second absorption unit adopts the method of using the high-frequency diode and the low-frequency diode in parallel. Due to the inherent characteristics of the high-frequency diode, the first diode D1 has a faster conduction speed and will be turned on instantly and quickly when absorbing the peak voltage, which makes up for the problem that the second diode D2 is easy to burn out due to slow conduction. The high-frequency diode and the low-frequency diode are used in parallel to ensure that the second diode D2 will not burn out. At the same time, the slow reverse recovery speed of the low-frequency diode is utilized to reversely extract part of the energy of the RC series branch, so that the oscillation frequency and amplitude of the peak voltage are reduced, thereby achieving the purpose of improving EMI. The utility model can play a more efficient peak voltage absorption role, and can effectively reduce the power loss of the circuit, while improving the reliability of the circuit.

[0027] See also Figures 2 to 4 , the first absorption unit is a varistor VR1. In this embodiment, if the shutdown current is too large when the power switch tube Q1 is turned off, the peak voltage generated at the DS end of the power switch tube Q1 exceeds the absorption capacity of the RC series branch, and the resistance value of the varistor VR1 will decrease sharply at this time, and the peak voltage at both ends of the DS of the power switch tube Q1 can be quickly discharged. At this time, the peak voltage is released on the varistor VR1 in the form of heat, so that the peak voltage at the DS end of the power switch tube Q1 is less than its maximum withstand voltage value, thereby protecting the power switch tube Q1 from breakdown.

[0028] See also Figures 2 to 4, the first absorption unit is a transient voltage suppression diode TVS1. In this embodiment, if the shutdown current is too large when the power switch tube Q1 is turned off, and the peak voltage generated at the DS end of the power switch tube Q1 reaches the breakdown voltage of the transient voltage suppression diode TVS1 and exceeds the absorption capacity of the RC series branch, at this time, the transient voltage suppression diode TVS1 quickly changes from a high resistance state to a low resistance state, discharges the instantaneous overcurrent at both ends of the DS of the power switch tube Q1 to the ground, and at the same time, the peak voltage at both ends of the DS of the power switch tube Q1 is clamped at a lower level, thereby protecting the power switch tube Q1 from breakdown.

[0029] See also Figures 2 to 4 , the cathodes of the first diode D1 and the second diode D2 are connected to a third diode D3, the anode of the third diode D3 is connected to the cathodes of the first diode D1 and the second diode D2, the cathode of the third diode D3 is connected to the power supply VCC, and the cathode of the third diode D3 is connected to a fourth resistor R4, one end of the fourth resistor R4 is connected to the power supply VCC, and the other end of the fourth resistor R4 is connected to the ground. In this embodiment, when the RC series branch is charged, the electric energy stored in the RC series branch is discharged to the first resistor R1, and at the same time, it is discharged and consumed to the fourth resistor R4 on the bus through the third diode D3, effectively avoiding the first resistor R1 from being damaged by a large current.

[0030] See also Figures 2 to 4 The RC series branch includes a first capacitor C1 and a second resistor R2, one end of the first capacitor C1 is one end of the RC series branch, the other end of the first capacitor C1 is connected in series with one end of the second resistor R2, and the other end of the second resistor R2 is the other end of the RC series branch. In this embodiment, the second resistor R2 is used to reduce the current spike generated during the reverse recovery of the first diode D1 and the second diode D2, and the first capacitor C1 is used to consume the spike voltage.

[0031] See also Figures 2 to 4 The RC series branch further includes a third resistor R3, and the third resistor R3 is connected in parallel with the second resistor R2. In this embodiment, the third resistor R3 and the second resistor R2 are connected in parallel to effectively reduce the power consumption of the resistor.

[0032] The above description is only the preferred implementation of the utility model, and is not intended to limit the utility model. For those skilled in the art, the utility model can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the utility model shall be included in the protection scope of the utility model.

Claims

1. A protection circuit, comprising a power switch tube Q1, characterized in that: A first absorption unit and a second absorption unit are connected between the drain and source of the power switch tube Q1, the source of the power switch tube Q1 is connected to the ground, and the first absorption unit and the second absorption unit are connected in parallel; The second absorption unit includes a first diode D1 and a second diode D2 whose anodes are connected to the drain of the power switch tube Q1, the first diode D1 and the second diode D2 are connected in parallel, and the cathodes of the first diode D1 and the second diode D2 are connected to a first resistor R1 and an RC series branch, the first resistor R1 is connected in parallel to the RC series branch, one end of the first resistor R1 connected in parallel to the RC series branch is connected to the cathodes of the first diode D1 and the second diode D2, and the other end of the first resistor R1 connected in parallel to the RC series branch is connected to the source of the power switch tube Q1.

2. A protection circuit according to claim 1, characterized in that: The first absorption unit is a varistor VR1.

3. A protection circuit according to claim 1, characterized in that: The first absorption unit is a transient voltage suppression diode TVS1.

4. A protection circuit according to claim 1, characterized in that: The cathodes of the first diode D1 and the second diode D2 are connected to a third diode D3, the anode of the third diode D3 is connected to the cathodes of the first diode D1 and the second diode D2, the cathode of the third diode D3 is connected to a power supply VCC, and the cathode of the third diode D3 is connected to a fourth resistor R4, one end of the fourth resistor R4 is connected to the power supply VCC, and the other end of the fourth resistor R4 is connected to ground.

5. A protection circuit according to claim 1, characterized in that: The RC series branch includes a first capacitor C1 and a second resistor R2, one end of the first capacitor C1 is one end of the RC series branch, the other end of the first capacitor C1 is connected in series with one end of the second resistor R2, and the other end of the second resistor R2 is the other end of the RC series branch.

6. A protection circuit according to claim 5, characterized in that: The RC series branch further includes a third resistor R3, and the third resistor R3 is connected in parallel with the second resistor R2.

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