High-voltage slow-start switching circuit using MOS (Metal Oxide Semiconductor)

Abstract

The utility model relates to the technical field of new energy automobiles, and discloses a high-voltage slow-start switch circuit using an MOS, which comprises a main circuit, a high-voltage direct-current power supply, a control circuit and an auxiliary power supply, the output end of the high-voltage direct-current power supply is connected with the input end of the control circuit, and the auxiliary power supply is connected to the control circuit in parallel; the N-MOS tube Q1, the second capacitor C2, the fourth resistor R5, the second resistor R3, the first resistor R2 and the first capacitor C1 are connected in series, and the second resistor R3, the first diode D2 and the first resistor R2 are connected in series. According to the utility model, the independent auxiliary power supply is creatively used to control the on-off of the N-MOS tube Q1, the linear region characteristic of the N-MOS tube Q1 is fully utilized, and by controlling the G-S voltage rising curve of the N-MOS tube Q1, the starting time is delayed, the starting current is limited, and the same effect as that of a relay pre-charging circuit is achieved.

Description

Technical Field

[0001] The utility model relates to the technical field of new energy vehicles, in particular to a high-voltage slow-start switch circuit utilizing MOS. Background Art

[0002] At present, in the field of new energy / electric vehicles, high-voltage power batteries power on-board DC / DC, DC / AC and other equipment. In order to extend the battery life and prevent the battery from consuming extra power, DC / DC, DC / AC and other equipment need to be completely disconnected from the high-voltage input and the power battery when not working. In order to achieve the disconnection, a relay is usually connected in series in the high-voltage circuit, and the relay is controlled to achieve the disconnection from the high-voltage battery. According to the circuit requirements, there will be a large-capacity capacitor at the back end of the relay. If the relay is turned on directly, the initial voltage on the capacitor is 0. At the moment of turning on, the power battery charges the capacitor. Since the resistance of the series circuit is very small, the power battery voltage can reach up to 750VDC (the current maximum charging voltage of the national standard charging pile). According to I=V / R, the instantaneous current I will be very large, up to several hundred amperes. The power consumption at the moment of the relay turning on is very large, and the contacts are very easy to burn. Therefore, if a high-voltage relay is used for switching, there must be a matching pre-charging circuit to reduce the power consumption at the moment of turning on. For example Figure 1 As shown, Figure 1 In the figure, K1 is the main switch relay, and K2 is the pre-charge relay, which is connected in series with R to form a pre-charge circuit. When power is turned on, K1 is disconnected first, and the pre-charge relay K2 is closed first through control. Since the circuit of K2 is connected in series with the current limiting resistor R, after K2 is turned on, the input high voltage charges the rear-end capacitor through R. The maximum charging current I=V in / R, and the appropriate current limiting resistor can be selected according to the charging time and the charging current limit. Generally speaking, the larger the resistance, the longer the pre-charge time and the smaller the charging current. The smaller the resistance and the shorter the pre-charge time, the greater the charging current. When the rear-end capacitor C is fully charged, the voltages before and after the main relay K1 are basically equal. At this time, the main relay K1 is turned on again, and the pre-charge relay K2 is turned off. In this way, the switch of the high-voltage circuit can be realized without causing damage to the device when it is turned on.

[0003] The disadvantages of the above prior art are that the relay is large in size and two relays are required, which is difficult to design in products with limited space. In addition, the relay is a mechanical structure and has low vibration and impact resistance. The two relays require timing control, which is also quite troublesome.

[0004] Therefore, we propose a high-voltage slow-start switch circuit using MOS. Utility Model Content

[0005] The purpose of the utility model is to provide a high-voltage slow-start switch circuit using MOS. In order to solve the problems of using relays as pre-charging circuits, such as large size, difficult control, easy burning of contacts, and weak vibration resistance of mechanical structure, a circuit using N-MOS tube Q1 to replace relays is adopted, which is suitable for adding to the positive end of high-voltage input to replace two relays. The biggest advantage of this circuit is its small size and high reliability. Using semiconductor devices to replace relays has strong vibration resistance, and is particularly suitable for applications in vibration environments such as vehicles.

[0006] The embodiment of the present application provides a high-voltage slow-start switch circuit using MOS, including a main circuit and a high-voltage DC power supply, and also including a control circuit and an auxiliary power supply, wherein the output end of the high-voltage DC power supply is connected to the input end of the control circuit, and the auxiliary power supply is connected in parallel to the control circuit;

[0007] The control circuit includes an N-MOS tube Q1, a first capacitor C1, a second capacitor C2, a third capacitor C3, a first diode D2, a second diode D3, a first resistor R2, a second resistor R3, a third resistor R4 and a fourth resistor R5. The N-MOS Q1 is connected to the positive end of the input high-voltage DC power supply, the N-MOS tube Q1, the second capacitor C2, the fourth resistor R5, the second resistor R3, the first resistor R2 and the first capacitor C1 are connected in series, the third resistor R4 is connected in parallel with the second diode D3, and the second resistor R3, the first diode D2 and the first resistor R2 are connected in series.

[0008] Preferably, the auxiliary power supply is a 13V power supply, and the auxiliary power supply supplies power to the control circuit.

[0009] Preferably, the second diode D3 is a voltage stabilizing diode, which is used to limit the gate-source voltage of the N-MOS transistor Q1.

[0010] Preferably, the fourth resistor R5 is a damping resistor.

[0011] Preferably, the first resistor R2, the first capacitor C1 and the first diode D2 are used to ensure that the N-MOS transistor Q1 is in an off state when it is just powered on.

[0012] Preferably, after power-on, the gate voltage of the N-MOS tube Q1 rises slowly. When the gate-source voltage Vgs is high enough to turn on the first diode D2, all the charges charge C1 with the time constant of the first resistor R2*the first capacitor C1, and the gate-source voltage Vgs rises at the same speed until the MOS tube Q1 is turned on to generate a surge current.

[0013] Compared with the prior art, the technical solution of this application has the following beneficial effects:

[0014] The utility model creatively uses an independent auxiliary power supply to control the switch of the N-MOS tube Q1, and fully utilizes the linear region characteristics of the N-MOS tube Q1, and controls the GS voltage rising curve of the N-MOS tube Q1 to delay the starting time and limit the starting current, thereby achieving the same effect as the relay precharging circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Other features, objects and advantages of the present invention will become more apparent by reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0016] Figure 1 It is a circuit schematic diagram of a high-voltage slow-start switch circuit in the prior art;

[0017] Figure 2 The utility model is a circuit schematic diagram of a high-voltage slow-start switch circuit using MOS. DETAILED DESCRIPTION

[0018] See also Figure 2 The utility model provides a technical solution: a high-voltage slow-start switch circuit using MOS, including a main circuit and a high-voltage DC power supply, and also including a control circuit and an auxiliary power supply, wherein the output end of the high-voltage DC power supply is connected to the input end of the control circuit, and the auxiliary power supply is connected in parallel to the control circuit;

[0019] The control circuit includes an N-MOS tube Q1, a first capacitor C1, a second capacitor C2, a third capacitor C3, a first diode D2, a second diode D3, a first resistor R2, a second resistor R3, a third resistor R4 and a fourth resistor R5. The N-MOS Q1 is connected to the positive end of the input high-voltage DC power supply, the N-MOS tube Q1, the second capacitor C2, the fourth resistor R5, the second resistor R3, the first resistor R2 and the first capacitor C1 are connected in series, the third resistor R4 is connected in parallel with the second diode D3, and the second resistor R3, the first diode D2 and the first resistor R2 are connected in series.

[0020] In a specific implementation of the present utility model, the auxiliary power supply is a 13V power supply, and the auxiliary power supply is used to power the control circuit.

[0021] In a specific implementation of the present invention, the second diode D3 is a voltage stabilizing diode, which is used to limit the gate-source voltage of the N-MOS transistor Q1.

[0022] In a specific implementation of the present utility model, the fourth resistor R5 is a damping resistor.

[0023] In a specific implementation of the present utility model, the first resistor R2, the first capacitor C1 and the first diode D2 are used to ensure that the N-MOS tube Q1 is in the off state when it is just powered on.

[0024] In the specific implementation of the utility model, after power-on, the gate voltage of the N-MOS tube Q1 rises slowly. When the gate-source voltage Vgs is high enough to turn on the first diode D2, all the charges are charged to C1 with the time constant of the first resistor R2*the first capacitor C1, and the gate-source voltage Vgs rises at the same speed until the MOS tube Q1 is turned on to generate an impact current.

[0025] The utility model is also worth explaining:

[0026] 1.N-MOS Q1 is connected to the positive terminal of the input high voltage. At the moment the auxiliary power supply (13V+ / 13V-) is powered on, the control circuit increases the voltage on the load capacitor C3 from 0 to the same as the input high voltage + at a certain rate. The speed of voltage rise is determined by the time constant C2*R3.

[0027] 2. The second capacitor C2>>(Cgs+Cgd); Cgs: equivalent gate-source capacitance of MOS tube; Cgd: gate-drain capacitance of MOS tube;

[0028] 3. The second resistor R3 is determined by the allowable inrush current;

[0029] 4.R3=(Cload*Vmax) / (C2*Irush); Vmax is the maximum input voltage. Cload is the load capacitance, which is Figure 2 The sum of the third capacitor C3 and the capacitance of the following circuits. Irush is the amplitude of the allowed rush current.

[0030] 5. MOS tube selection:

[0031] The drain breakdown voltage Vds must be selected to be a MOS tube with Vds higher than the maximum input voltage Vmax and the maximum input transient voltage. Generally, Vds ≥ Vmax * 120% is selected.

[0032] The gate-source voltage Vgs Zener diode D3 is used to protect the gate of the N-MOS tube Q1 to prevent it from overvoltage breakdown. Obviously, the gate-source voltage Vgs of the N-MOS tube Q1 must be higher than the maximum reverse breakdown voltage of the Zener diode D1. Generally, the gate-source voltage Vgs of the N-MOS tube Q1 is 20V, and a 12V Zener diode is recommended.

[0033] On-resistance Rds(on). MOS tube must be able to dissipate the heat caused by the on-resistance Rds_on. The heat dissipation calculation formula is:

[0034] Pon=Rds(on)*Idc*Idc, where Idc is the maximum input current.

[0035] When the utility model is in use:

[0036] 1. Add DC high voltage to the input, and the auxiliary power supply is powered on (the output of the auxiliary power supply is usually generated by the input high voltage through an independent circuit). The 13V of the auxiliary power supply charges the first capacitor C1 through the first resistor R2, and the other part supplies power to the G pole of the N-MOS tube Q1 through the second resistor R3. Therefore, the voltage Vgs between the G pole and the S pole of the N-MOS tube Q1 rises slowly following the voltage of C1.

[0037] 2. When the turn-on threshold Vth of the N-MOS tube Q1 is reached, the N-MOS tube Q1 starts to turn on, the voltage Vds of the D pole and the S pole of the N-MOS tube Q1 starts to decrease, and the current ID flowing through the D pole and the S pole starts to increase from 0. At this time, the Vgs voltage continues to rise. When the Vgs voltage reaches the voltage to enter the Miller platform period, the current ID reaches the maximum value, and the MOS tube enters the Miller platform. In the Miller platform period, as Vds decreases, all the charges are charged to the second capacitor C2 to maintain the Vgs voltage unchanged. In the late Miller platform period, as C2 is gradually fully charged, the MOS tube is fully turned on. At this time, Vds will no longer decrease, maintaining a very small stable value, and Vgs continues to increase until it reaches the highest drive level. This is a complete slow start process.

[0038] 3. Design appropriate values ​​of the second resistor R3 and the second capacitor C2. After the auxiliary power supply 13V is powered on, the second capacitor C2 is charged with the time constant R3*C2, so that the current ID of the N-MOS tube Q1 increases slowly, ensuring that the power of the N-MOS tube Q1 is within the tolerance range, so as to protect the N-MOS tube Q1 from damage or even failure. The input impact current can also be limited within the required range, playing the same role as the relay pre-charging circuit.

[0039] It should be noted that MOS tubes are commonly used as switching devices in low-voltage input circuits. N-MOS is used at the negative input end and P-MOS is used at the positive input end. This makes it easy to drive and control the MOS tube.

[0040] The utility model is a slow-start switch circuit for a high-voltage positive terminal. If a P-MOS is used, control is very easy to achieve. However, due to the following two reasons, the P-MOS cannot be used for control.

[0041] 1. The Rds(on) of P-MOS is very large, and the loss of MOS is very large, so it can only be used in situations where the input current is very small.

[0042] 2. There are no high-voltage P-MOS products. Due to technical and market application reasons, current P-MOS products are basically below 600V, and there are no products with higher voltage resistance.

[0043] Therefore, the utility model adopts high-voltage N-MOS for control. Usually, the Rds(on) of N-MOS can be made relatively small, and the on-resistance of high-voltage SIC N-MOS can be made below 100mR. In order to drive the N-MOS at the high-voltage positive end, the utility model creatively uses an independent auxiliary power supply to control the switch of N-MOS, and makes full use of the linear region characteristics of N-MOS. By controlling the GS voltage rising curve of N-MOS, the startup time is delayed, the startup current is limited, and the same effect as the relay pre-charging circuit is achieved.

[0044] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A high-voltage slow-start switch circuit using MOS, comprising a main circuit and a high-voltage DC power supply, It is characterized in that It also includes a control circuit and an auxiliary power supply, wherein the output end of the high-voltage DC power supply is connected to the input end of the control circuit, and the auxiliary power supply is connected in parallel to the control circuit; The control circuit includes an N-MOS tube Q1, a first capacitor C1, a second capacitor C2, a third capacitor C3, a first diode D2, a second diode D3, a first resistor R2, a second resistor R3, a third resistor R4 and a fourth resistor R5. The N-MOS Q1 is connected to the positive end of the input high-voltage DC power supply, the N-MOS tube Q1, the second capacitor C2, the fourth resistor R5, the second resistor R3, the first resistor R2 and the first capacitor C1 are connected in series, the third resistor R4 is connected in parallel with the second diode D3, and the second resistor R3, the first diode D2 and the first resistor R2 are connected in series.

2. A high voltage slow start switch circuit using MOS according to claim 1, It is characterized in that The auxiliary power supply is a 13V power supply, and the auxiliary power supply supplies power to the control circuit.

3. A high voltage slow start switch circuit using MOS according to claim 2, It is characterized in that The second diode D3 is a voltage stabilizing diode, and is used to limit the gate-source voltage of the N-MOS transistor Q1.

4. A high voltage slow start switch circuit using MOS according to claim 2, It is characterized in that The fourth resistor R5 is a damping resistor.

5. A high voltage slow start switch circuit using MOS according to claim 3, It is characterized in that The first resistor R2, the first capacitor C1 and the first diode D2 are used to ensure that the N-MOS transistor Q1 is in the off state when it is just powered on.

6. A high voltage slow start switch circuit using MOS according to claim 5, It is characterized in that After power-on, the gate voltage of the N-MOS tube Q1 rises slowly. When the gate-source voltage Vgs is high enough to turn on the first diode D2, all the charges are charged to C1 with the time constant of the first resistor R2*the first capacitor C1, and the gate-source voltage Vgs rises at the same speed until the MOS tube Q1 is turned on to generate a surge current.

Images