Main and standby redundant dual-input power supply rapid switching circuit

Abstract

The invention discloses a main and standby redundant dual-input power supply quick switching circuit, which comprises a main switching power supply, a standby switching power supply, a power supply output end, a comparison circuit and a switching circuit, a PWM signal end is further led out from the positive electrode of the primary side of the main switching power supply, and the comparison circuit is used for comparing the voltage of the PWM signal end with the voltage of the reference voltage end Vref and outputting a main power supply control signal and a standby power supply control signal according to the comparison result. Monitoring and judgment are carried out based on PWM signals of the secondary side of the transformer, when the input alternating-current power supply is powered down or the interior of the switching power supply is damaged, the PWM signals disappear immediately, the comparison circuit automatically changes the states of the main power supply control signals and the standby power supply control signals, the main switching power supply is switched to the standby switching power supply, and the switching power supply is switched to the standby switching power supply. The method has the advantages of quick judgment and high accuracy.

Description

Technical Field

[0001] The invention relates to a power switching circuit. Background Art

[0002] In many important and special electronic equipment application scenarios, uninterrupted power supply is a basic requirement. In order to meet this requirement, a dual-input power supply system is usually used, which has two sets of switching power supply equipment that can output the same specification of DC voltage at the same time. Under normal working conditions, the main switching power supply is responsible for power supply, and when the main switching power supply is abnormal, the system needs to automatically switch to the backup switching power supply to ensure the continuous and stable operation of the electronic equipment.

[0003] The traditional dual power switching solution mainly relies on monitoring the power supply voltage to determine the working status of the main power supply, that is, whether the voltage of the input AC power supply is normal is determined to determine whether it is necessary to switch to the backup power supply. However, there is a zero-crossing point in the voltage waveform of the AC power supply, and its instantaneous voltage value is small, so it is difficult to use it as a direct criterion for power failure. In order to solve this problem, a rectifier filter circuit is generally added to process the AC power, and then the filtered DC voltage is compared with the preset threshold to determine whether a power failure occurs. In order to ensure the reliability of the judgment, the filtering time is usually set to 3 to 5 AC cycles, corresponding to 50Hz AC, and the delay time is 60 to 100 milliseconds. This delay causes the subsequent circuit to work abnormally or even freeze during the power switching process. Moreover, if the input AC power supply is normal, but the switching power supply is damaged and cannot output, this method cannot determine that the power supply needs to be switched, and it will still cause abnormal power supply in the subsequent stage.

[0004] In addition, some occasions use a monitoring method based on DC output voltage to determine whether there is a power failure. This method can avoid the problem of missed judgment when the AC power supply is normal but the switching power supply is abnormal, but this method is difficult to meet the requirements of timeliness and accuracy at the same time. For example, for a 5V DC output, the power failure judgment criterion is generally set to 4.8V. However, in high-precision circuits, a lower threshold cannot quickly identify a voltage drop in time. If the threshold is increased to 4.9V for fast switching, the ripple of the switching power supply may cause misjudgment, resulting in unnecessary power switching. Summary of the invention

[0005] The present invention proposes a main-standby redundant dual-input power supply fast switching circuit, the purpose of which is to solve the problem of untimely and inaccurate power supply status judgment.

[0006] The technical solution of the present invention is as follows: A main-standby redundant dual-input power supply fast switching circuit comprises a main switching power supply, a standby switching power supply and a power supply output terminal, wherein the main switching power supply and the standby switching power supply both comprise a transformer, a rectifier diode V1, a switch transistor V2 and a capacitor C1, wherein the primary side of the transformer is connected to a DC power supply through the switch transistor V2, wherein the DC power supply is obtained by rectifying and filtering the input AC power supply, wherein the positive electrode of the secondary side is connected to the positive electrode of the rectifier diode V1 and the negative electrode is grounded, wherein the negative electrode of the rectifier diode V1 is connected to one end of the capacitor C1, and the other end of the capacitor C1 is grounded, wherein the capacitor C1 is the positive output terminal of the switch power supply, wherein the main-standby redundant dual-input power supply fast switching circuit further comprises a comparison circuit and a switching circuit; wherein the positive electrode of the primary side of the main switching power supply also leads to a PWM signal terminal; The comparison circuit is used to compare the voltage of the PWM signal terminal with the voltage of the reference voltage terminal Vref, and output the main power control signal and the backup power control signal according to the comparison result; The switching circuit includes a switching transistor V4 controlled by a main power supply control signal and a switching transistor V5 controlled by a backup power supply control signal. The positive output end of the main switching power supply is connected to the power supply output end through the switching transistor V4, and the positive output end of the backup switching power supply is connected to the power supply output end through the switching transistor V5.

[0007] As a further improvement of the active-standby redundant dual-input power supply fast switching circuit: the comparison circuit includes a diode V3, a comparator U1 and a comparator U2; The PWM signal terminal is connected to the positive electrode of the diode V3, the negative electrode of the diode V3 is connected to the inverting input terminal of the comparator U1, the output terminal of the comparator U1 is used to output the main power control signal and is connected to the switching transistor V4, and the output terminal of the comparator U1 is also connected to the inverting input terminal of the comparator U2; the output terminal of the comparator U2 is used to output the standby power control signal and is connected to the switching transistor V5; The reference voltage terminal Vref is connected to the non-inverting input terminal of the comparator U1 and the non-inverting input terminal of the comparator U2 respectively.

[0008] As a further improvement of the active-standby redundant dual-input power supply fast switching circuit: the cathode of the diode V3 is also grounded through a capacitor C2 and a resistor R connected in parallel.

[0009] As a further improvement of the active-standby redundant dual-input power supply fast switching circuit: the voltage of the reference voltage terminal Vref is half of the rated voltage of the power supply output terminal.

[0010] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention monitors and judges based on the PWM signal on the secondary side of the transformer. When the input AC power fails or the switching power supply is damaged, the PWM signal will disappear immediately, and the comparison circuit will automatically change the state of the main power control signal and the backup power control signal, so that the switching transistor V4 is turned off and the switching transistor V5 is turned on, switching from the main switching power supply to the backup switching power supply, with fast judgment and high accuracy.

[0011] 2. The circuit structure of the present invention is simple, and only a few conventional components need to be added to realize fast and accurate judgment of power failure. It is particularly suitable for electronic devices such as communication management machines and intelligent gateways that have high requirements on the size and reliability of power supply equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a circuit diagram of the present invention. DETAILED DESCRIPTION

[0013] The technical solution of the present invention is described in detail below with reference to the accompanying drawings: like Figure 1 , a main-standby redundant dual-input power supply fast switching circuit, including a main switching power supply, a standby switching power supply and a power supply output terminal.

[0014] The main switching power supply and the standby switching power supply both include a transformer, a rectifier diode V1, a switching transistor V2 and a capacitor C1. The primary side of the transformer is connected to a DC power supply through the switching transistor V2, and the DC power supply is obtained by rectifying and filtering the input AC power supply. The positive electrode of the secondary side is connected to the positive electrode of the rectifier diode V1 and the negative electrode is grounded. The rectifier diode V1 is used for rectification on the secondary side. The negative electrode of the rectifier diode V1 is connected to one end of the capacitor C1, and the other end of the capacitor C1 is grounded. The capacitor C1 is the positive output terminal of the switching power supply.

[0015] The positive pole of the primary side of the main switching power supply also leads to the PWM signal terminal. The PWM signal is affected by the output voltage clamp, and the positive amplitude of the signal is close to the output voltage. The PWM control signal is generated by the switching power supply control chip and is a step signal. It disappears quickly when abnormal. Only when the main switching power supply returns to normal can a signal close to the output voltage be generated.

[0016] Furthermore, the active / standby redundant dual-input power supply fast switching circuit also includes a comparison circuit and a switching circuit.

[0017] The comparison circuit includes a diode V3, a comparator U1 and a comparator U2, and is used to compare the voltage of the PWM signal terminal with the voltage of the reference voltage terminal Vref, and output a main power control signal and a standby power control signal according to the comparison result.

[0018] Specifically, the PWM signal terminal is connected to the positive electrode of the diode V3, and the negative electrode of the diode V3 is connected to the inverting input terminal of the comparator U1. The negative electrode of the diode V3 is also grounded through a capacitor C2 and a resistor R connected in parallel. The output terminal of the comparator U1 is used to output the main power control signal, and the output terminal of the comparator U1 is also connected to the inverting input terminal of the comparator U2. The output terminal of the comparator U2 is used to output the standby power control signal. In this embodiment, the comparator U1 and the comparator U2 are provided by an integrated circuit LM393 with two voltage comparators, and no additional NAND gate circuit components are required.

[0019] The reference voltage terminal Vref is connected to the non-inverting input terminal of the comparator U1 and the non-inverting input terminal of the comparator U2 respectively. Preferably, the voltage of the reference voltage terminal Vref is half of the rated voltage of the power supply output terminal.

[0020] The switching circuit includes a switching transistor V4 controlled by a main power supply control signal and a switching transistor V5 controlled by a backup power supply control signal. The positive output terminal of the main switching power supply is connected to the power supply output terminal through the switching transistor V4, and the positive output terminal of the backup switching power supply is connected to the power supply output terminal through the switching transistor V5. In this embodiment, the switching transistor V4 and the switching transistor V5 use a low internal resistance P-channel MOS tube LP4306, with an internal resistance of only 8 milliohms. When a current of 1 ampere passes through, there is only an 8 millivolt voltage drop, power consumption of 8 milliwatts, and extremely low loss. Using MOS tubes for switching has the advantages of no arcing and long life. The diode in the MOS tube can also temporarily provide a freewheeling function in the event of an abnormality in the control circuit.

[0021] When the main switch power supply is normal, the voltage of the PWM signal after RC filtering is close to the rated voltage of the power supply output terminal and higher than the reference voltage. At this time, the main power control signal output by the comparator U1 is low level, which turns on the switch transistor V4, connects the positive output terminal of the main switch power supply with the power supply output terminal, and uses the main switch power supply to power the subsequent equipment. At the same time, since the output of the comparator U1 is low level, which is lower than the reference voltage of the in-phase input terminal of the comparator U2, the backup power control signal output by the comparator U2 is high level, which turns off the switch transistor V5, and disconnects the positive output terminal of the backup switch power supply from the power supply output terminal. This judgment does not rely on the AC power supply signal and is not affected by the AC filtering delay. As long as the PWM signal is lost, the normal power supply of the power supply output terminal cannot be guaranteed. Regardless of whether the reason is AC power failure or damage to components such as the transformer or transistor V2, the comparison circuit can quickly determine the power supply abnormality and switch the power supply. The PWM signal frequency of the switching power supply is usually around 100kHz, each switching cycle is 10 microseconds, and the fastest accurate judgment time is 3 to 5 PWM times, about 30 to 50 microseconds, which is more than 1,000 times faster than the conventional AC judgment of 60 milliseconds. Combined with the national voltage drop standard of 0.5 power frequency cycle (10 milliseconds), the power supply completes the switching within 50 microseconds and will not affect the subsequent circuits.

[0022] When the main switch power supply is abnormal, the PWM signal has no output and is 0V, which is lower than the reference voltage. At this time, the main power control signal output by the comparator U1 is high level, which will turn off the switch transistor V4 and disconnect the positive output terminal of the main switch power supply from the power supply output terminal. At the same time, since the output of the comparator U1 is high level, which is higher than the reference voltage of the in-phase input terminal of the comparator U2, the backup power control signal output by the comparator U2 is low level, which turns on the switch transistor V5, connects the positive output terminal of the backup switch power supply with the power supply output terminal, and supplies power to the subsequent equipment through the backup switch power supply.

[0023] When the main switch power supply returns to normal, the comparison circuit determines that the PWM signal has returned to normal and will switch back to the main switch power supply. Since the main power control signal and the backup power control signal are always in opposite states, the two power supplies will not be supplied at the same time.

Claims

1. A main-standby redundant dual-input power supply fast switching circuit, comprising a main switching power supply, a standby switching power supply and a power supply output terminal, wherein the main switching power supply and the standby switching power supply both comprise a transformer, a rectifier diode V1, a switch transistor V2 and a capacitor C1, wherein the primary side of the transformer is connected to a DC power supply through the switch transistor V2, wherein the DC power supply is obtained by rectifying and filtering the input AC power supply, wherein the positive electrode of the secondary side is connected to the positive electrode of the rectifier diode V1 and the negative electrode is grounded, wherein the negative electrode of the rectifier diode V1 is connected to one end of the capacitor C1, and the other end of the capacitor C1 is grounded, wherein the capacitor C1 is the positive output terminal of the switching power supply, and wherein: The main and standby redundant dual input power supply fast switching circuit also includes a comparison circuit and a switching circuit; the positive electrode of the primary side of the main switching power supply also leads to a PWM signal terminal; The comparison circuit is used to compare the voltage of the PWM signal terminal with the voltage of the reference voltage terminal Vref, and output the main power control signal and the backup power control signal according to the comparison result; The switching circuit includes a switching transistor V4 controlled by a main power supply control signal and a switching transistor V5 controlled by a backup power supply control signal. The positive output end of the main switching power supply is connected to the power supply output end through the switching transistor V4, and the positive output end of the backup switching power supply is connected to the power supply output end through the switching transistor V5.

2. The active / standby redundant dual-input power supply fast switching circuit according to claim 1, characterized in that: The comparison circuit includes a diode V3, a comparator U1 and a comparator U2; The PWM signal terminal is connected to the positive electrode of the diode V3, the negative electrode of the diode V3 is connected to the inverting input terminal of the comparator U1, the output terminal of the comparator U1 is used to output the main power control signal and is connected to the switching transistor V4, and the output terminal of the comparator U1 is also connected to the inverting input terminal of the comparator U2; The output end of the comparator U2 is used to output a backup power supply control signal and is connected to the switching transistor V5; The reference voltage terminal Vref is connected to the non-inverting input terminal of the comparator U1 and the non-inverting input terminal of the comparator U2 respectively.

3. The active / standby redundant dual-input power supply fast switching circuit according to claim 2, characterized in that: The cathode of the diode V3 is also grounded via a capacitor C2 and a resistor R connected in parallel.

4. The active / standby redundant dual-input power supply fast switching circuit according to any one of claims 1 to 3, characterized in that: The voltage of the reference voltage terminal Vref is half of the rated voltage of the power supply output terminal.

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