A main and standby power supply switching circuit

Abstract

The present invention discloses a main-standby power switching circuit, which includes a switching transistor, a controllable precision voltage regulator, an output feedback module and an AC feedback module. The main-standby power switching circuit is used to be arranged between an AC-DC power supply module, a battery power supply module and a power supply output terminal, and controls the power supply mode of the power supply output terminal according to an AC voltage signal and the output voltage of the battery power supply module. The function of the main-standby power switching circuit is: when the AC voltage signal is greater than a threshold value, the AC-DC power supply module is preferentially used to supply power to the power supply output terminal, and when the AC voltage signal is less than the threshold value and the output voltage of the battery power supply module is normal, the battery power supply module is used to supply power to the power supply output terminal. The power supply mode can only be switched from the AC-DC power supply module to the battery power supply module, and the battery power supply module cannot be powered independently. Therefore, during the transportation of the product, the battery power supply module will not supply power, thereby avoiding the loss caused by battery discharge during the transportation of the product.

Description

Technical Field

[0001] The invention belongs to the field of electronic technology, and in particular relates to a main-standby power supply switching circuit. Background Art

[0002] The fire emergency lighting system mainly includes accident emergency lighting, emergency exit signs and indicator lights. It is an emergency lighting device set up to guide trapped people to evacuate or launch fire fighting and rescue operations after the normal lighting power supply is cut off in the event of a fire. In order to ensure high reliability in the event of an accident, the emergency light needs to have an AC power supply as the main power supply and a battery power supply as the backup power supply. In the event of an accident, the AC power supply is usually cut off or fails, so the power supply needs to be switched to battery power.

[0003] The existing main and standby power switching methods usually require the use of MCU to sample input and output signals to determine the working status of the main and standby power, and then send signals to control the switching circuit. Using MCU to control the circuit will be affected by the working environment and may send out error signals (MCU has a certain probability of soft errors during long-term operation). In addition, when using MCU, there is a delay in MCU sampling, which will cause a delay in the main and standby power switching. The circuit is complex, the reliability is relatively low, there are many components, and the cost is relatively high. Summary of the invention

[0004] The purpose of the present invention is to provide a main-standby power supply switching circuit, which controls the switching of power supply modes by detecting AC voltage signals and output voltage signals of battery power supply modules through a circuit composed of analog devices, thereby solving the problems of high delay and low reliability caused by MCU sampling control.

[0005] The technical solution of the present invention is a main-standby power switching circuit, which is used to be arranged between an AC-DC power supply module, a battery power supply module and a power supply output terminal, and the main-standby power switching circuit includes:

[0006] A switching transistor, whose source is connected to the output end of the battery power supply module, whose drain is connected to the anode of a diode, and whose cathode is connected to the power supply output end; the power supply output end is connected to the output end of the AC-DC power supply module;

[0007] A controllable precision voltage-stabilizing source, whose cathode is connected to the gate of the switching transistor via a first resistor and whose anode is grounded;

[0008] An output feedback module, whose input end is connected to the power supply output end, and whose output end is connected to the reference end of the controllable precision voltage-stabilizing source; when the voltage of the power supply output end is within a normal range, the open-circuit voltage of the output end of the output feedback module is greater than the on-voltage of the controllable precision voltage-stabilizing source;

[0009] An AC feedback module, whose input end is connected to the output end of the AC voltage signal detection module, and whose output end is connected to the reference end of the controllable precision voltage-stabilizing source; when the AC voltage signal is greater than the threshold value, the AC feedback module pulls down the reference end voltage of the controllable precision voltage-stabilizing source to make it non-conductive;

[0010] The output feedback module or the AC feedback module is provided with an energy storage capacitor, and the energy storage capacitor is used to drive the controllable precision voltage regulator to turn on and turn on the switching transistor when the AC voltage signal drops below a threshold and the power supply mode of the power supply output end is switched from the AC-DC power supply module to the battery power supply module.

[0011] A further improvement of the present invention is that the output feedback module includes a first node, the first node is connected to the reference end of the controllable precision voltage-stabilizing source through a second resistor, a voltage-stabilizing diode, a third resistor, a fourth resistor and a filter capacitor are connected in parallel between the first node and the ground end; and an adjustable resistor is connected between the power supply output end and the first node.

[0012] A further improvement of the present invention is that the AC feedback module includes a second node and a third node; a sixth resistor and a second diode are connected between the second node and the reference end of the controllable precision voltage regulator; the anode of the second diode is connected to the reference end; the emitter of the second transistor is grounded, the base thereof is connected to the output end of the AC voltage signal detection module through an eighth resistor, and the collector thereof is connected to the second node; a seventh resistor is connected between the second node and the third node; the third node is connected to the output end of the AC-DC power supply module through a first diode, and the cathode of the first diode is connected to the third node.

[0013] A further improvement of the present invention lies in that the energy storage capacitor is connected between the third node and a ground terminal.

[0014] A further improvement of the present invention is that the AC voltage signal detection module includes a rectifier and filter module and an optocoupler; the input end of the rectifier and filter module is connected to the AC voltage signal input end of the AC-DC power supply module; the input end of the optocoupler is connected to the output end of the rectifier and filter module; the positive pole of the output end of the optocoupler is connected to the VCC end, and the negative pole of the output end of the optocoupler is the output end of the AC voltage signal detection module; the input-output characteristic of the rectifier and filter module satisfies that when the AC voltage signal at the AC voltage signal input end is higher than a threshold value, the optocoupler is in a conducting state.

[0015] The beneficial effects of the present invention are:

[0016] (1) The circuit voltage feedback and switching actions are implemented by analog devices, which have better reliability under long-term operating conditions and avoid soft errors caused by environmental factors in digital systems. In addition, compared with low-frequency digital systems (MCUs), systems composed of analog devices have faster response, fewer components, and lower costs.

[0017] (2) The power supply mode can only be switched from the AC-DC power supply module to the battery power supply module. The battery power supply module cannot supply power independently. Therefore, during the transportation of the product, the battery power supply module will not supply power. This can avoid the loss caused by battery discharge during the transportation of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is the circuit diagram of the main and standby power supply switching circuit;

[0019] Figure 2 It is the circuit diagram of the AC voltage signal detection module. DETAILED DESCRIPTION

[0020] like Figure 1 As shown, an embodiment of the present invention provides a main-standby power switching circuit, which is used to be arranged between an AC-DC power supply module, a battery power supply module and a power supply output terminal, and controls the power supply mode of the power supply output terminal according to an AC voltage signal and an output voltage of the battery power supply module. The function of the main-standby power switching circuit is: when the AC voltage signal is greater than a threshold value, the AC-DC power supply module is preferentially used to supply power to the power supply output terminal, and when the AC voltage signal is less than the threshold value and the output voltage of the battery power supply module is normal, the battery power supply module is used to supply power to the power supply output terminal.

[0021] In order to achieve the above functions, the main and standby power switching circuit includes: a switching transistor Q1, a controllable precision voltage regulator TL431, an output feedback module 10 and an AC feedback module 20. Specifically:

[0022] The switch transistor Q1 is a PMOS transistor, whose source is connected to the output end of the battery power supply module, whose drain is connected to the anode of a diode D3, and whose cathode is connected to the power supply output end; the power supply output end is connected to the output end of the AC-DC power supply module. When the switch transistor Q1 is turned on, the battery power supply module supplies power to the power supply output end.

[0023] In some embodiments, the model of the controllable precision voltage regulator TL431 is TL431. The internal reference voltage of TL431 is 2.5V. When the voltage of the reference terminal (R pole) is greater than 2.5V, the cathode K and the anode A of TL431 are connected. The cathode of the controllable precision voltage regulator is connected to the gate of the switching transistor Q1 through the first resistor R1, and its anode is grounded.

[0024] The input end of the output feedback module 10 is connected to the power supply output end, and the output end thereof is connected to the reference end R of the controllable precision voltage regulator TL431. When the voltage of the power supply output end is in the normal range, the open circuit voltage of the output end of the output feedback module is greater than the on-voltage of the controllable precision voltage regulator.

[0025] The output feedback module 10 has multiple implementations. In a specific embodiment, the output feedback module 10 includes a first node a. The first node a is connected to the reference terminal R of the controllable precision voltage regulator TL431 through the second resistor R2. A voltage regulator diode ZD1, a third resistor R3, a fourth resistor R4 and a filter capacitor C1 are connected in parallel between the first node a and the ground terminal GND. An adjustable resistor R5 is connected between the power supply output terminal and the first node a.

[0026] During the power supply process of the battery power supply module, its output voltage will continue to decrease, and over-discharge of the battery will adversely affect its life. Therefore, the input-output characteristics of the output feedback module 10 are adjusted by the adjustable resistor R5, so that when the battery is over-discharged, the output voltage of the output feedback module 10 is lower than the turn-on voltage of the controllable precision voltage regulator TL431, so that the switching transistor Q1 is turned off and the battery power supply module stops supplying power.

[0027] In another specific embodiment, the output feedback module 10 can be implemented by using an operational amplifier in combination with a voltage divider circuit. The operational amplifier in combination with a specific feedback loop can achieve an amplification function of any proportion, which is equivalent to using a resistor network for voltage division.

[0028] The input end of the AC feedback module 20 is connected to the output end of the AC voltage signal detection module, and the output end of the AC feedback module 20 is connected to the reference end R of the controllable precision voltage regulator TL431; when the AC voltage signal supplying power to the AC-DC power supply module is greater than the threshold, the AC feedback module 20 pulls down the reference end voltage of the controllable precision voltage regulator TL431 to make it non-conductive. At this time, the AC-DC power supply module supplies power to the power supply output end, and the switching transistor Q1 is in the off state.

[0029] An energy storage capacitor is provided in the output feedback module 10 or the AC feedback module 20. The energy storage capacitor is used to drive the controllable precision voltage regulator TL431 to turn on and turn on the switching transistor when the AC voltage signal drops below the threshold and the power supply mode of the power supply output end is switched from the AC-DC power supply module to the battery power supply module, thereby achieving the purpose of switching the power supply mode.

[0030] In order to realize the function of the AC feedback module 20, the AC feedback module includes a second node b and a third node c. A sixth resistor R6 and a second diode D2 are connected between the second node b and the reference terminal R of the controllable precision voltage regulator TL431, and the anode of the second diode D2 is connected to the reference terminal R. The emitter of the second transistor Q2 is grounded, and its base is connected to the output terminal of the AC voltage signal detection module through the eighth resistor R8, and its collector is connected to the second node b. A seventh resistor R7 is connected between the second node b and the third node c. The third node c is connected to the output terminal of the AC-DC power supply module through the first diode D1, and the cathode of the first diode D1 is connected to the third node c.

[0031] In a specific embodiment, the energy storage capacitor EC1 is connected between the third node c and the ground terminal GND. In other embodiments, the energy storage capacitor EC1 may also be connected between the power supply output terminal and the ground terminal GND.

[0032] The following is a Figure 1 The working process of the specific embodiment shown is introduced:

[0033] The main and standby power switching circuit uses the AC-DC power supply module to supply power to the power supply output end by default. When the AC voltage signal (mains power) that supplies power to the AC-DC power supply module is normal, the AC-DC power supply module outputs a DC voltage to supply power to the power supply output end, and at the same time charges the energy storage capacitor EC1. The AC voltage signal detection module outputs a high level, so that the emitter and collector of the second transistor Q2 are turned on. Since the cathode of the second diode D2 is grounded by the second transistor Q2, the output voltage of the AC feedback module 20 (reference end R) is clamped to about 0.7V. At this time, the cathode K and anode A of the controllable precision voltage regulator TL431 are not conducting, the switching transistor Q1 is in the off state, and the battery power supply module does not supply power to the outside. At this time, the voltage regulator diode ZD1 in the output feedback module 10 plays a clamping role to protect the reference end R of the controllable precision voltage regulator TL431.

[0034] When the AC voltage signal is lower than the threshold value (mains undervoltage or disconnected), the AC-DC power supply module stops working, and the AC voltage signal detection module outputs a high impedance state, so that the second transistor Q2 is not turned on, and the second diode D2 loses its clamping function. When the AC voltage signal just starts to lose power, since the energy storage capacitor EC1 stores energy and the voltage has not disappeared, the resistance values ​​of the resistors in the AC feedback module 20 and the output feedback module 10 are satisfied that the voltage of the reference end R of the controllable precision voltage regulator TL431 is greater than 2.5V under the power supply of the energy storage capacitor EC1, so that the cathode K and the anode A of the controllable precision voltage regulator TL431 are turned on, and a resistor R9 is connected between the source and the gate of the switching transistor Q1, and the resistor R9 and the first resistor R1 divide the voltage and turn on the switching transistor Q1, so that the power supply mode of the power supply output end is switched from the AC-DC power supply module to the battery power supply module.

[0035] After the power supply mode is switched, the output feedback module 10 continuously detects the output voltage. When the battery power is normal, the output feedback module 10 continuously maintains the voltage of the reference terminal R of the controllable precision voltage regulator TL431 greater than 2.5V, so that the battery power supply module continues to supply power until the power in the battery power supply module is exhausted, so that the voltage of the reference terminal R of the controllable precision voltage regulator TL431 is lower than 2.5V. During the power supply process of the battery power supply module, the voltage of the energy storage capacitor EC1 gradually decreases until it enters a steady state (the same as the voltage of the reference terminal R).

[0036] In this embodiment, the power supply mode can only be switched from the AC-DC power supply module to the battery power supply module. The battery power supply module cannot supply power independently. Therefore, during the transportation of the product, the battery power supply module will not supply power. This can avoid the loss caused by battery discharge during the transportation of the product.

[0037] like Figure 1 , 2 As shown, in this embodiment, the AC voltage signal detection module includes a rectifier filter module and an optocoupler. The input end of the rectifier filter module is connected to the AC voltage signal input end of the AC-DC power supply module for receiving the AC voltage signal. The input end of the optocoupler is connected to the output end of the rectifier filter module. The positive pole of the output end of the optocoupler is connected to the VCC end, and the negative pole of the output end of the optocoupler is the output end of the AC voltage signal detection module.

[0038] The rectifier and filter module is composed of a resistor R10, a resistor R11, a capacitor C11 and a diode D11, which is used for half-wave rectification, voltage division and filtering. The input-output characteristics of the rectifier and filter module satisfy that when the AC voltage signal at the AC voltage signal input end is higher than the threshold, the optocoupler is in the on state.

[0039] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A main power supply switching circuit, used to be arranged between an AC-DC power supply module, a battery power supply module and a power supply output terminal, characterized in that The main and standby power supply switching circuit comprises: A switching transistor, whose source is connected to the output end of the battery power supply module, whose drain is connected to the anode of a diode, and whose cathode is connected to the power supply output end; the power supply output end is connected to the output end of the AC-DC power supply module; A controllable precision voltage-stabilizing source, whose cathode is connected to the gate of the switching transistor via a first resistor and whose anode is grounded; An output feedback module, whose input end is connected to the power supply output end, and whose output end is connected to the reference end of the controllable precision voltage-stabilizing source; when the voltage of the power supply output end is within a normal range, the open-circuit voltage of the output end of the output feedback module is greater than the on-voltage of the controllable precision voltage-stabilizing source; An AC feedback module, whose input end is connected to the output end of the AC voltage signal detection module, and whose output end is connected to the reference end of the controllable precision voltage-stabilizing source; when the AC voltage signal is greater than the threshold value, the AC feedback module pulls down the reference end voltage of the controllable precision voltage-stabilizing source to make it non-conductive; The output feedback module or the AC feedback module is provided with an energy storage capacitor, and the energy storage capacitor is used to drive the controllable precision voltage regulator to turn on and turn on the switching transistor when the AC voltage signal drops below a threshold and the power supply mode of the power supply output end is switched from the AC-DC power supply module to the battery power supply module; The output feedback module includes a first node, the first node is connected to the reference end of the controllable precision voltage-stabilizing source through a second resistor, a voltage-stabilizing diode, a third resistor, a fourth resistor and a filter capacitor are connected in parallel between the first node and the ground end; an adjustable resistor is connected between the power supply output end and the first node; The AC feedback module includes a second node and a third node; a sixth resistor and a second diode are connected between the second node and the reference end of the controllable precision voltage regulator; the anode of the second diode is connected to the reference end; the emitter of the second transistor is grounded, the base is connected to the output end of the AC voltage signal detection module through an eighth resistor, and the collector is connected to the second node; a seventh resistor is connected between the second node and the third node; the third node is connected to the output end of the AC-DC power supply module through a first diode, and the cathode of the first diode is connected to the third node; The AC voltage signal detection module includes a rectifier and filter module and an optocoupler; the input end of the rectifier and filter module is connected to the AC voltage signal input end of the AC-DC power supply module; the input end of the optocoupler is connected to the output end of the rectifier and filter module; the positive pole of the output end of the optocoupler is connected to the VCC end, and the negative pole of the output end of the optocoupler is the output end of the AC voltage signal detection module; the input-output characteristic of the rectifier and filter module satisfies that when the AC voltage signal at the AC voltage signal input end is higher than the threshold value, the optocoupler is in the on state.

2. A main-standby power switching circuit according to claim 1, characterized in that: The energy storage capacitor is connected between the third node and the ground terminal.

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