Constant current control device for switching power supply

Abstract

The invention discloses a constant current control device for a switching power supply. A gradient detection module is used for detecting the gradient of voltage on a current sampling resistor of a power supply circuit and converting the gradient into corresponding gradient voltage; voltage compensation module is used for adding the gradient voltage with the voltage of the Vref0 pin of the voltage compensation module to obtain the voltage of the Vref pin of the voltage compensation module; the voltage of the Vref pin of the voltage compensation module is taken as the threshold voltage of a turn-off comparator; the other end of the turn-off comparator is connected with voltage Vcs on the sampling resistor; and the threshold voltage is compared with the voltage Vcs on the sampling resistor, and a control signal is output to a reset signal of an R-S trigger to trigger a driving circuit and turn off a switch tube. Due to the adoption of the constant current control device, the size of a circuit system can be reduced, and the reliability of the system is improved. Constant output during input of different line voltages is ensured, and the constant current can be ensured to output during variation of a transformer Lp of the circuit.

Description

Technical field: [0001] The invention relates to the technical field of heat exchangers, in particular to heat exchangers used in refrigeration, train air conditioning and bus air conditioning. Background technique: [0002] See figure 1 , which is a schematic diagram of a primary side control pulse frequency modulation (PFM) mode switching power supply without line compensation in the prior art. When the primary side power switch tube 102 is turned off, the voltage on the auxiliary coil 106 changes with the secondary side voltage Vout, and the voltage divider Vfb passes through the error controller 120 to generate a set signal, and the output terminal Q of the flip-flop 121 is driven by Circuit DRV 122 turns 102 on. Vref is the threshold voltage of the shut-off comparator 118. When the voltage Vcs at both ends of the primary side current detection resistor 103 rises to Vref, a shut-off signal is generated, and the signal is sent to 121 as a reset signal, and then 102 is t...

AI Technical Summary

Problems solved by technology

This control method can only compensate the current control error introduced by Vin, but cannot solve the control error of the peak current of the primary side caused by the change of Lp.

However, in system production, Lp has mass production errors, and it cannot be guaranteed that Lp of the transformer must be equal, so the constant current accuracy of the system using this control method is not high

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