Switching power supply circuit

Abstract

The invention discloses a switching power supply circuit, which comprises a starting circuit, a pulse width modulation (PWM) controller, a starting turn-off circuit, a main power tube and a main transformer, wherein the starting turn-off circuit comprises a first resistor, a turn-off triode, a charging capacitor, a first voltage sharing resistor and a second voltage sharing resistor; a connection point between the current sampling end of the PWM controller and a source of the main power tube is connected to the voltage reference end of the starting circuit through the first resistor; one circuit of the output end of the PWM controller is connected to the voltage reference end of the starting circuit through the charging capacitor and the other circuit of the output end of the PWM controller is connected to the voltage reference end of the starting circuit through the first voltage sharing resistor and the second voltage sharing resistor sequentially; a connection point between the first voltage sharing resistor and the second voltage sharing resistor is connected to a base of the turn-off triode; a collector of the turn-off triode is connected to the control end of the starting circuit; and an emitter of the turn-off triode is connected to the voltage reference end of the starting circuit.

Description

Technical field [0001] The present invention relates to a switching power supply circuit, in particular to a switching power supply circuit capable of generating small short-circuit power consumption when the output is short-circuited. Background technique [0002] In power electronic systems such as photovoltaic inverters and high-voltage inverters, an auxiliary power supply is required to output low-voltage direct current to supply power to its control part. The power input terminal voltage range of this system is very wide, as low as one or two hundred volts, up to Thousands of volts. For a switching power supply with such a wide input terminal voltage range, its starting circuit is more difficult to design, because it is necessary to take into account the starting time at low voltage input, the starting line loss during normal operation, and the short-circuit power consumption when the output is short-circuited. [0003] Such as figure 1 As shown, in the prior art, a switching...

AI Technical Summary

Problems solved by technology

[0009] but, figure 1 The switching power supply circuit shown has the following disadvantages: when the circuit output is short-circuited, in each switching cycle, when the PWM controller detects that the voltage of its current sampling terminal CS reaches its threshold voltage (UC3843 is 1V), its output terminal OUTPUT immediately Turn off the output of the pulse width modulation voltage signal to prevent the saturation of the main transformer T1 and the overcurrent of the main power tube Qa

Since the auxiliary winding Nt has no output when the output is short-circuited, there is no voltage on the filter capacitor C2, the transistor Q1 will not be turned on, the starting circuit A1 will always work, and the loss on the power dissipation resistor R1 will be very high

Especially in the case of high voltage and wide voltage input, for the auxiliary power supply with an input range of 100V-1000V DC, in order to prevent the start-up extension time at 100V input from being too long, the resistance value of the power consumption resistor R1 should not exceed 100KΩ. In this way, in the case of 1000V input, the loss on the power dissipation resistor R1 will reach In this way, the power consumption resistor R1 must choose a cement resistor with a large volume, and its power consumption is too large (under normal circumstances, the short-circuit power consumption of the auxiliary power supply needs to be controlled at about 1-2W), which does not meet the short-circuit power consumption index when the output is short-circuited. , affecting the reliability of the entire power electronic system

Images