Starting circuit

Abstract

The invention provides a starting circuit. A voltage limiting circuit composed of a P-MOS tube circuit, a voltage stabilizing circuit or a voltage clamp circuit is used to control the range of outputvoltage, it is ensured that the output voltage is within the working voltage range of a post boost circuit of the starting circuit of a post power supply module with a super wide input voltage range.An adjustable driving circuit samples an input voltage, and it is ensured that the starting circuit does not influence post power supply due to voltage difference of the starting circuit itself duringlow-voltage work; and during high-voltage work, the output voltage is controlled within the voltage range, and it is ensured that the output voltage of the starting circuit in a working voltage interval satisfies the working voltage range of the post boost circuit. Loss of the circuit in the working state is extremely low.

Description

technical field [0001] The invention relates to a starting circuit of a switching power supply, in particular to a starting circuit in a switching power supply for supplying power to a control circuit or a control IC of a power stage circuit, or to supplying power to a step-up circuit after the starting circuit. Background technique [0002] Start-up circuits are widely used in the field of switching power supplies. In switching power supply products, no matter the primary power supply (AC-DC converter) or the secondary power supply (DC-DC converter), it is necessary to obtain energy from the input terminal and provide a stable power supply voltage for the subsequent control circuit or control IC. Power supply, so as to drive the switch on and off by controlling the operation of the circuit, and control the inductive device to transfer energy periodically. [0003] In general switching power supplies, in order to solve the problem that when the input voltage is lower than t...

AI Technical Summary

Problems solved by technology

However, due to the large voltage difference between the voltage clamping circuit Vin and Vo, the starting voltage of the second stage boost circuit is limited.

Traditional voltage clamping circuit schemes such as figure 2 As shown (the load is the post-stage boost circuit), the working principle of the circuit is: the moment the product is powered on, the transistor Q1 is turned on, and the emitter current of the transistor Q1 rapidly charges the capacitor C2. When the voltage of the capacitor C2 (that is, the output of the starting circuit is positive) When the voltage provided by the terminal to the power supply terminal Vcc of the control IC) climbs to the regulated value of the Zener diode D1 minus the conduction voltage drop between the base and emitter of the transistor Q1, the Vcc voltage will stabilize and no longer increase. When the Vcc voltage reaches When the voltage of the booster circuit is working, the booster circuit starts to work to establish the power supply voltage of the subsequent control circuit or control IC, but when the circuit is working at low voltage, the transistor Q1 is in the amplification area, and the voltage drop on Q1 and resistor R2 is large, which limits The voltage value of Vcc under low voltage limits the starting voltage of the boost circuit, which makes it difficult to start the switching power supply system when Vin is low.

With other types of voltage stabilizing circuits or voltage clamping circuits, the problem of excessive voltage drop under low voltage will also occur.

[0004] To sum up, the limitation of the switching power supply starting circuit with wide voltage range in the industry at present is: for products using a two-stage power supply circuit scheme or a single-stage power supply circuit scheme, the first-stage voltage clamping circuit will have excessive input and output voltage differences under low voltage. Large, the problem that the boost circuit or the post-stage control circuit cannot be started, and the starting voltage range from extremely low voltage to high voltage cannot be met

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