Auxiliary source circuit for switch power supply

Abstract

The invention discloses an auxiliary source circuit for a switch power supply, which comprises a first diode, a second diode, a first inductor, a first capacitor and a second capacitor, and is characterized in that one end of the first capacitor is connected with the positive end of an input voltage Vin, the other end of the first capacitor is connected with one end of the first inductor and the anode of the second diode, the other end of the first inductor is connected with the cathode of the first diode, the cathode of the second diode is connected with the positive end of the second capacitor, the negative end of the input voltage Vin is connected with the anode of the first diode and the negative end of the second capacitor, and the voltage of the second capacitor is the output voltage Vo of the auxiliary source circuit. The invention has the beneficial effects that: 1. the invention can provide the auxiliary power supply voltage in full output range for circuits with wide output range; 2. the invention has low energy consumption, simple structure and low cost; and 3. the lossless absorption of the switch tube in the main circuit is realized.

Description

technical field [0001] The invention relates to an auxiliary source circuit suitable for switching power supplies. Specifically, it should be a low-loss auxiliary power supply circuit used in switching power supplies. Background technique [0002] In the switching power supply circuit, the power supply of the control circuit is generally powered by the auxiliary winding of the transformer, refer to figure 1 , the output voltage of the auxiliary winding is Va, the output voltage of the secondary winding is Vo1, the output voltage of the main circuit is Vo, and the auxiliary winding supplies power to the control circuit through the three-terminal voltage regulator circuit. However, in a switching power supply circuit with wide-range output, if the output voltage Vo is extremely low, then Vo1 is extremely low, and the voltage Va of the auxiliary winding will also be very low, which may not be able to provide the voltage required by the control circuit; at the same time, if it ...

AI Technical Summary

Problems solved by technology

However, in a switching power supply circuit with wide-range output, if the output voltage Vo is extremely low, then Vo1 is extremely low, and the voltage Va of the auxiliary winding will also be very low, which may not be able to provide the voltage required by the control circuit; at the same time, if it meets The voltage amplitude of Va at low output voltage is reduced, and the loss of the three-terminal voltage regulator circuit in the auxiliary circuit will be very high at high output voltage

[0003] In the prior art, there is also a method of providing auxiliary power without using the auxiliary winding of the transformer, such as US Patent US6233165, refer to figure 2 , although the auxiliary source circuit in this way is not limited by the output voltage, but because the energy of the auxiliary source provided by the circuit is related to the size of the capacitor C1, if it is necessary to meet a wide output voltage range, the capacity of the capacitor C1 is relatively large , which is equivalent to a large capacitor connected in parallel with the drain and source of the main switching tube, the switching loss of the switching tube is relatively large, and the resistance R2 in the loop further increases the loss of the circuit, which is not conducive to the high efficiency of the power supply

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