A kind of starting circuit and switching power supply

Abstract

The present invention discloses a starting circuit. The starting circuit comprises a first switch tube, a second switch tube and a voltage setting unit. The input end of the first switch tube is connected with the control end of the second switch tube, the control end of the first switch tube is connected with the output end of the switch power through a voltage setting unit, and the output end of the first switch tube is connected with the ground; and the input end of the second switch tube is connected with the common terminal points of the first resistor and the second resistor through a third resistor, the control end of the second switch tube is connected with the output voltage end of the power supply and is configured to obtain required driving voltage, and the output end of the second switch tube is connected with the ground. During the starting of the switch power supply, when the output voltage of the power supply is smaller than the voltage of a voltage reference unit, the first switch tube is turned off, the second switch tube is conducted, the current control loop is opened, the switch power supply works in an open loop mode, the size of the current is not limited at starting, and the starting speed is fast. The present invention further discloses a switch power supply through adoption of the starting circuit.

Description

technical field [0001] The invention relates to the technical field of switching power supplies, in particular to a starting circuit and a switching power supply. Background technique [0002] Switching power supplies are often provided with a constant current source circuit to ensure that the switching power supply can still work normally under wide voltage input conditions. Take the LED drive power supply as an example, in order to match the volt-ampere characteristics of the LED, the power supply generally uses a constant current drive method. In addition, from the perspective of cost, low and medium power LED drive power generally adopts single-stage PFC technology, and there is no auxiliary power supply, so using a constant current drive power supply is likely to cause some problems when starting. Specifically, because the LED drive power supply is in a constant current output mode, during the startup of the power supply, the DC / DC converter quickly charges the output ...

AI Technical Summary

Problems solved by technology

In addition, from the perspective of cost, low and medium power LED drive power generally adopts single-stage PFC technology, and there is no auxiliary power supply, so the use of constant current drive power supply is likely to cause some problems when starting

Specifically, because the LED drive power supply is in a constant current output mode, during the startup of the power supply, the DC / DC converter quickly charges the output capacitor, which requires a large output current, usually greater than the maximum current of the constant current source for normal operation, while the current loop The further increase of the start-up current is limited, so the start-up time is longer; on the other hand, the power supply of the main controller IC of the switching power supply mainly depends on the energy storage on the input capacitor during start-up. If the value of the input capacitor is too large, the energy storage time will be shorter. If the capacitor value is too small, it may lead to insufficient energy storage and cause startup failure, and the power supply cannot be started.

Images