CROSS REFERENCE TO RELATED APPLICATION

The present application is based on, and claims the priority from, Chinese application number CN202010701553.5, filed on Jul. 20, 2020, the disclosure of which is hereby incorporated by reference herein in its entirety.

TECHNICAL FIELD

The disclosure relates to a starting circuit of a switching power supply, belonging to the technical field of power supply.

BACKGROUND

In a conventional switching power supply, after the switching power supply is started, there is a certain power loss in the no-load mode. In the current market, there lacks a power supply that having only a few milliwatts no-load power consumption and reaching several Watts output power. Precision theoretical calculations and a large number of actual detections prove that the no-load power consumption of a switching power cannot be reduced to several milliwatts mainly with three reasons: first, the use of a power management chip with a larger self power consumption; second, that the semiconductor element works in a state provided with static current; and third, the power consumption of the starting resistor being too large.

In addition, in the conventional switching power supply, if without other auxiliary power circuits, there is no way to directly turn off the VCC power supply of the master control chip after the product is used.

In view of the above, it is necessary to improve the existing starting circuit of a switching power supply to solve the problems mentioned above.

BRIEF DESCRIPTION OF THE DISCLOSURE

The disclosure aims to provide a starting circuit of a switching power supply that can really achieve zero or near zero power consumption in a standby mode.

The disclosure provides a starting circuit of a switching power supply which includes: an input rectifying and filtering circuit which have an input end being connected with an AC power supply; a starting circuit which have an input end being connected with an output end of the input rectifying and filtering circuit; a transformer, including: a primary coil, a secondary coil and a feedback coil, wherein the primary coil is arranged on one side of the transformer and connected with the output end of the input rectifying and filtering circuit, and the secondary coil is arranged on the other side of the transformer; an output rectifying and filtering circuit which have an input end being connected to the secondary coil of the transformer; a feedback circuit which have an input end being connected with the feedback coil and the input end further being connected with an output end of the output rectifying and filtering circuit; a first photoelectric coupler which is connected with an output end of the starting circuit and an external battery respectively; and a power management chip which is respectively connected with an output end of the first photoelectric coupler, an output end of the feedback circuit, and the primary coil of the transformer; after the first photoelectric coupler is powered on, the starting circuit is turned on, and the power management chip and the transformer are started and work; after the first photoelectric coupler is powered off, the power management chip stops working and enters a standby state, and at the moment, the standby power consumption of the power management chip is equal to zero.

As a further improvement of the disclosure, the first photoelectric coupler includes: a first light emitting source which is connected with the positive electrode of external battery; and a first light receiver, one end of which is connected with the output end of the starting circuit, and the other end of which is connected with the power management chip; wherein after the first light emitting source is powered on, the first light receiver output a voltage to make the starting circuit and the power management chip turn-on.

As a further improvement of the disclosure, the starting circuit includes at least one starting resistor which is connected between the output end of the input rectifying and filtering circuit and the first light receiver.

As a further improvement of the disclosure, the output rectifying and filtering circuit includes: a diode which is connected with the secondary coil of the transformer; and an output filter capacitor, wherein the diode is connected in series with the secondary coil, and the output filter capacitor is connected in parallel with the secondary coil.

As a further improvement of the disclosure, the feedback circuit includes: a direct current negative feedback resistor, one end of which is connected with the feedback coil, and the other end of which is connected with the power management chip, wherein the direct current negative feedback resistor is connected with the CS pin of the power management chip; and a reverse cut-off rectifier tube, one end of which is connected with the feedback coil, and the other end of which is connected with the first photoelectric coupler.

As a further improvement of the disclosure, the starting circuit of the switching power supply further includes: a switching element which is connected between the power management chip and the transformer, and the switching element is used for controlling the transformer to start or turn off according to a control signal which is outputted by the power management chip.

As a further improvement of the disclosure, the switching element is a field effect transistor; the field effect transistor comprises a gate electrode which is connected with a Gate pin of the power management chip, a drain electrode which is connected with a primary coil of the transformer, and a source electrode which is grounded; wherein a parasitic diode is connected between the source electrode and the drain electrode, and the parasitic diode unidirectionally turns on along the direction from the source electrode to the drain electrode.

As a further improvement of the disclosure, the starting circuit of the switching power supply further includes: a battery detection circuit which includes: a voltage stabilizing tube which is connected with the output rectifying and filtering circuit, a fourth resistor which is connected in series with the voltage stabilizing tube, and a second photoelectric coupler which is connected in series with the fourth resistor, wherein the second photoelectric coupler includes a second light emitting source and a second light receiver, wherein the second light emitting source is connected with the fourth resistor, and the second light receiver is connected with the power management chip.

As a further improvement of the disclosure, one end of the second light receiver is connected with the FB pin of the power management chip, and the other end is grounded.

As a further improvement of the disclosure, the power management chip is further provided with an RT pin, and the RT pin is grounded through a timing resistor.

The disclosure has the beneficial effects below: the first photoelectric coupler is used for driving the power management chip to start or stop. After the first photoelectric coupler is powered on, the starting circuit turns on, then the power management chip and the transformer are started to work. After the first photoelectric coupler is powered off, the power management chip stops working and enters a standby state. At this moment, the standby power consumption of the power management chip is equal to zero. Compared with the prior art, the starting circuit of the switching power supply as disclosed can really achieve zero power consumption in a standby mode.

