Circuit for improving on-load efficiency of power supply

Abstract

The utility model provides a circuit for improving power supply on-load efficiency, which cuts off a dummy load in a loop by detecting the magnitude of current in an output rectification loop, so that the dummy load does not consume energy of the output loop any more, and the power supply on-load efficiency is improved. The flyback switching power supply comprises an output loop arranged on the flyback switching power supply, a dummy load resistor R7 is arranged in the output loop, the flyback switching power supply further comprises an automatic detection circuit, the automatic detection circuit detects whether the current of the output loop is larger than a set value or not, and if the current is larger than the set value, connection of the dummy load R7 is cut off; and if the current is smaller than the set value, the dummy load resistor R7 does not work, and the dummy load resistor R7 works normally.

Description

Technical Field

[0001] The utility model relates to the technical field of flyback switching power supply circuits, in particular to a circuit for improving power supply load efficiency. Background Art

[0002] At present, multi-channel output flyback switching power supplies have one or more load resistors, also called minimum resistors, at each output voltage end. This resistor mainly plays the role of stabilizing the output voltage. If this resistor is not connected, the no-load output voltage will fluctuate, resulting in unstable output. The main reason is that the output of the flyback converter is a current source characteristic and cannot work in an open circuit. Otherwise, too much energy will accumulate, causing the internal temperature of the power supply to rise, which will not only affect the service life of the internal components of the voltage end, but also cause the output voltage to soar.

[0003] In the actual circuit, due to the existence of the feedback circuit and the line impedance, it is impossible to have a real open circuit operation. In addition to the load function, the dummy load also has the function of discharging the residual electricity when the power is off. At the same time, the dummy load is very important in the application of switching power supply failure. The dummy load can be used to determine whether it is a power supply problem or a load problem. Specifically, after connecting the dummy load to the voltage output end, the voltage at both ends is measured to determine whether the switching power supply is working normally. This dummy load can be a resistive load, an inductive load or a capacitive load. Different circuit outputs should be connected to the corresponding characteristic load according to the actual situation. In practical applications, resistive loads are often used. Resistive loads are generally placed in the secondary winding in the form of resistors. However, when the flyback switching power supply is working normally, each output provides the corresponding working voltage to the electrical equipment. At this time, the dummy loads connected to it are also consuming the power of the power supply. The power consumed by the dummy load is converted into heat energy, which increases the internal temperature of the power supply, affects the service life of the internal components of the power supply, and easily causes the components to fail prematurely due to excessive temperature. Utility Model Content

[0004] In view of the problem that the resistive load used in the existing flyback switching power supply consumes the power of the power supply, generates heat, causes the internal temperature of the power supply to rise, and affects the service life of the internal components of the power supply, the utility model provides a circuit for improving the load efficiency of the power supply, which cuts off the dummy load in the circuit by detecting the current size in the output rectifier circuit, so that the dummy load no longer consumes energy of the output circuit, thereby improving the load efficiency of the power supply.

[0005] The technical solution is as follows: a circuit for improving the load efficiency of a power supply, comprising an output circuit arranged in a flyback switching power supply, wherein a dummy load resistor R7 is arranged inside the output circuit, and characterized in that: it also includes an automatic detection circuit, wherein the automatic detection circuit detects whether the current of the output circuit is greater than a set value, and if the current is greater than the set value, the connection of the dummy load R7 is cut off; if the current is less than the set value, it does not work, and at this time the dummy load resistor R7 works normally in the output circuit.

[0006] It is further characterized in that: the output circuit includes a primary side pin 1 of the transformer T1 connected to the output voltage terminal V+, a primary side pin 2 of the transformer T1 connected to the drain of the MOS tube Q3, a gate of the MOS tube Q3 connected to the drive pulse terminal DRV of the output circuit, a source of the MOS tube Q3 connected to the ground through a resistor R1, a secondary side pin 3 of the transformer T1 connected to one end of the inductor L1 and the positive electrode of the electrolytic capacitor CD2, the other end of the inductor L1 connected to the positive electrode of the electrolytic capacitor CD3 and the automatic detection circuit, a secondary side pin 4 of the transformer T1 connected to one end of the capacitor C1 and the negative electrode of the diode D1, the negative electrode of the diode D1, the other end of the resistor R2, the negative electrode of the electrolytic capacitor CD2 and the negative electrode of the electrolytic capacitor CD3 are connected and then connected to the automatic detection circuit;

[0007] The automatic detection circuit includes a current transformer LL1, wherein pin 1 of the current transformer LL1 is connected to the cathode of the diode D1, the other end of the resistor R2, the cathode of the electrolytic capacitor CD2 and the cathode of the electrolytic capacitor CD3, pin 2 of the current transformer LL1 is connected to one end of the resistor R3 and the anode of the diode D2, the cathode of the diode D2 is connected to one end of the resistor R5, one end of the resistor R4 and one end of the capacitor C2, the other end of the resistor R5 is connected to the base of the transistor Q1, and the transistor Q1 The collector of the transistor is connected to one end of the resistor R6 and the base of the transistor Q2. The collector of the transistor Q2 is connected to one end of the dummy load resistor R7. The other end of the resistor R6 and the other end of the resistor R7 are connected to the other end of the inductor L1, the positive electrode of the electrolytic capacitor CD2 and the output voltage terminal 24V+. Pin 3 of the current transformer LL1 is connected to the other end of the resistor R3, the other end of the resistor R4, the other end of the capacitor C2, the emitter of the transistor Q1, the emitter of the transistor Q2 and the output voltage terminal 24VG.

[0008] After adopting the above structure, an automatic detection circuit connected to the dummy load resistor R7 is provided inside the output circuit of the flyback switching power supply, which can detect the current of the output circuit. When the current is greater than the set current value, the automatic detection circuit will automatically cut off the connection of the dummy load, so that the dummy load no longer consumes energy of the output circuit, thereby reducing the load loss of the power supply and improving the load working efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 This is a circuit schematic diagram of the utility model. DETAILED DESCRIPTION

[0010] like Figure 1 As shown, a circuit for improving the load efficiency of a power supply includes an output circuit A arranged in a flyback switching power supply, a dummy load resistor R7 is arranged inside the output circuit A, and the output circuit outputs a 24V voltage. Specifically, the output loop A includes a primary side pin 1 of the transformer T1 connected to the output voltage terminal V+, a primary side pin 2 of the transformer T1 connected to the drain of the MOS tube Q3, a gate of the MOS tube Q3 connected to the drive pulse terminal DRV of the output loop, a source of the MOS tube Q3 connected to ground through a resistor R1, a secondary side pin 3 of the transformer T1 connected to one end of the inductor L1 and the positive electrode of the electrolytic capacitor CD2, the other end of the inductor L1 connected to the positive electrode of the electrolytic capacitor CD3 and the automatic detection circuit, a secondary side pin 4 of the transformer T1 connected to one end of the capacitor C1 and the negative electrode of the diode D1, the negative electrode of the diode D1, the other end of the resistor R2, the negative electrode of the electrolytic capacitor CD2 and the negative electrode of the electrolytic capacitor CD3 are connected and then connected to the automatic detection circuit B, the automatic detection circuit B detects whether the current of the output loop A is greater than a set value, if the current is greater than the set value, the connection of the dummy load R7 is cut off; if the current is less than the set value, it does not work, and at this time the dummy load resistor R7 works normally in the output loop A.

[0011] Specifically, the automatic detection circuit B includes a current transformer LL1, wherein the pin 1 of the current transformer LL1 is connected to the cathode of the diode D1, the other end of the resistor R2, the cathode of the electrolytic capacitor CD2 and the cathode of the electrolytic capacitor CD3, the pin 2 of the current transformer LL1 is connected to one end of the resistor R3 and the anode of the diode D2, the cathode of the diode D2 is connected to one end of the resistor R5, one end of the resistor R4 and one end of the capacitor C2, the other end of the resistor R5 is connected to the base of the transistor Q1, and the transistor Q1 The collector of the transistor is connected to one end of the resistor R6 and the base of the transistor Q2. The collector of the transistor Q2 is connected to one end of the dummy load resistor R7. The other end of the resistor R6 and the other end of the resistor R7 are connected to the other end of the inductor L1, the positive electrode of the electrolytic capacitor CD2 and the output voltage terminal 24V+. Pin 3 of the current transformer LL1 is connected to the other end of the resistor R3, the other end of the resistor R4, the other end of the capacitor C2, the emitter of the transistor Q1, the emitter of the transistor Q2 and the output voltage terminal 24VG.

[0012] The working principle of the utility model is as follows:

[0013] The output circuit of the flyback switching power supply has a dummy load resistor R7 inside the output circuit. The current sensed by the current transformer LL1 flows through the resistor R3, the diode D2, the resistor R4, and the resistor R5. When the base voltage of the transistor Q1 is greater than 0.7V, its base and emitter are forward biased, and the transistor Q1 is turned on. At this time, the base voltage of the transistor Q2 is pulled down, the transistor Q2 is turned off, and the dummy load resistor R7 is disconnected. At this time, the 24V output circuit load current has disconnected the dummy load, and the efficiency of the power supply is improved when it is loaded. At the same time, according to the schematic diagram Figure 1 It can be seen that when the dummy load resistor R7 is completely disconnected, the base current of the transistor Q2 must be 0A. When the transistor Q1 is fully turned on, the current I=U / R=24V / 20K=1.2mA flowing through the resistor R6. Therefore, when the CE pole of the transistor Q1 is fully turned on, the collector current Ic1 must be greater than 1.2 mA. At this time, the base current flowing through the transistor Q2 will be 0mA, the transistor Q2 is cut off, and the dummy load resistor R7 is disconnected. Assuming that the amplification factor of transistor Q1 is β=200, the current flowing through the base of transistor Q1 at this time = Ic1 / β=1.2mA / 200=6uA, the voltage across the resistor R5 is about 28mV according to U=IR=6*4.7K, the diode D2 conduction voltage drop is 0.7V (according to the technical specification) and the base and emitter of transistor Q1 are 0.7V (according to the technical specification). Therefore, when transistor Q1 is turned on, the voltage across resistor R3 is equal to the voltage across diode D2 + the voltage across resistor R5 + the voltage across the base and emitter of transistor Q1, which is about 1.4V (the voltage across resistor R5 can be ignored). It can be inferred that the current flowing through resistor R3 is about 3mA. According to the current transformer 1:100, the output loop current can be calculated to be 300mA. That is, when the output load loop current is greater than 300mA, the dummy load in the output loop is automatically disconnected. In this circuit, the on-load current of the dummy load can be disconnected according to the setting needs, and the threshold value of the dummy load disconnection can be set by changing the resistance value of the resistor R3. When the resistance value of the resistor R3 becomes larger, the on-load disconnection dummy load current of the output circuit will become smaller. Similarly, when the resistance value of the resistor R3 becomes smaller, the on-load disconnection dummy load current of the output circuit will become larger.

[0014] The above are only preferred specific implementations of the utility model, but the protection scope of the utility model is not limited thereto. Any changes or substitutions that can be easily thought of by anyone familiar with the technology within the technical scope disclosed by the utility model should be included in the protection scope of the utility model. Therefore, the protection scope of the utility model should be based on the protection scope of the claims.

Claims

1. A circuit for improving power supply load efficiency, comprising an output circuit arranged in a flyback switching power supply, wherein a dummy load resistor R7 is arranged inside the output circuit, and characterized in that: It also includes an automatic detection circuit, which detects whether the current of the output circuit is greater than a set value. If the current is greater than the set value, the connection of the dummy load resistor R7 is cut off; if the current is less than the set value, it does not work, and the dummy load resistor R7 works normally in the output circuit.

2. A circuit for improving power supply load efficiency according to claim 1, characterized in that: The output circuit includes a primary side pin 1 of the transformer T1 connected to the output voltage terminal V+, a primary side pin 2 of the transformer T1 connected to the drain of the MOS tube Q3, a gate of the MOS tube Q3 connected to the drive pulse terminal DRV of the output circuit, a source of the MOS tube Q3 grounded through a resistor R1, a secondary side pin 3 of the transformer T1 connected to one end of the inductor L1 and the positive electrode of the electrolytic capacitor CD2, the other end of the inductor L1 connected to the positive electrode of the electrolytic capacitor CD3 and the automatic detection circuit, a secondary side pin 4 of the transformer T1 connected to one end of the capacitor C1 and the negative electrode of the diode D1, the negative electrode of the diode D1, the other end of the resistor R2, the negative electrode of the electrolytic capacitor CD2 and the negative electrode of the electrolytic capacitor CD3 are connected and then connected to the automatic detection circuit.

3. A circuit for improving power supply load efficiency according to claim 2, characterized in that: The automatic detection circuit includes a current transformer LL1, wherein pin 1 of the current transformer LL1 is connected to the cathode of the diode D1, the other end of the resistor R2, the cathode of the electrolytic capacitor CD2 and the cathode of the electrolytic capacitor CD3, pin 2 of the current transformer LL1 is connected to one end of the resistor R3 and the anode of the diode D2, the cathode of the diode D2 is connected to one end of the resistor R5, one end of the resistor R4 and one end of the capacitor C2, the other end of the resistor R5 is connected to the base of the transistor Q1, and the collector of the transistor Q1 is connected to the cathode of the transistor Q1. The electrode is connected to one end of the resistor R6 and the base of the transistor Q2. The collector of the transistor Q2 is connected to one end of the dummy load resistor R7. The other end of the resistor R6 and the other end of the dummy load resistor R7 are connected to the other end of the inductor L1, the positive electrode of the electrolytic capacitor CD2 and the output voltage terminal 24V+. Pin 3 of the current transformer LL1 is connected to the other end of the resistor R3, the other end of the resistor R4, the other end of the capacitor C2, the emitter of the transistor Q1, the emitter of the transistor Q2 and the output voltage terminal 24VG.

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