Input undervoltage protecting circuit of switching power supply controller

Abstract

The invention provides an input undervoltage protecting circuit of a switching power supply controller. The input undervoltage protecting circuit of the switching power supply controller comprises a current detection circuit, a reference voltage generating circuit, an undervoltage protecting signal generating circuit and a pulse outputting control circuit. The current detection circuit comprises a controller internal resistor R2 and a controller external resistor R1, and the resistance value of the R2 is far smaller than that of the R1. The reference voltage generating circuit comprises an internal resistor R3 and a reference current source Iref, and the R3 and the R2 are resistors of the same type in the controller. The undervoltage protecting signal generating circuit comprises a comparator comp. A protecting point input voltage Vin(p) meets the formula (please see the formula in the specification). When the input voltage Vin of a switching power supply drops to be lower than the protecting point input voltage Vin(p), the output end UVP of the comparator comp generates undervoltage protecting signals to control the pulse outputting control circuit to cut off pulse output of GATE pins of the controller. According to the input undervoltage protecting circuit of the switching power supply controller, the peripheral circuits of the controller are simplified, the loss is small, meanwhile, the precision of input undervoltage protecting is high, and process bias is small. The invention further provides an input undervoltage protecting circuit with feed-forward compensation, the feed-forward compensation current Icom is in proportion to input voltages, the precision is high, and the process bias is small.

Description

technical field [0001] The invention relates to an input undervoltage protection circuit of a switching power supply controller, and relates to an input undervoltage protection circuit with feedforward compensation. Background technique [0002] like figure 1 Shown is the application circuit diagram of a typical switching power converter that does not include a feedforward compensation circuit (or called an overpower compensation circuit). The GATE pin is the drive output of the controller; the CS pin detects the voltage of the current sampling resistor RCS To determine the current flowing through the power MOS tube, it is often called the current loop; the operating frequency of the controller can be set by designing the resistance Ri from the RI pin to the "ground"; UVP is the input undervoltage protection function, at the minimum input voltage A protection voltage value is designed below. When the input voltage is lower than this value, the controller GATE stops outputti...

AI Technical Summary

Problems solved by technology

However, the input under-voltage protection and feed-forward compensation functions are separated from each other, which not only makes the peripheral resistors more, but also has a large loss through the resistors.

If the resistor R2 is built inside the controller in order to simplify the peripheral circuit, however, the resistor precision in the semiconductor process is poor and the temperature coefficient is large, which will lead to poor accuracy of the input undervoltage protection

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