CN202663614U - Low-power light emitting diode (LED) constant-current power supply - Google Patents

Abstract

The utility model discloses a low-power light emitting diode (LED) constant-current power supply, which comprises a primary side circuit, a secondary side circuit and a control circuit, wherein the primary side circuit is coupled with the secondary side circuit through a transformer; the primary side circuit comprises an input rectification filter circuit and a switch energy conversion circuit; the switch energy conversion circuit comprises a metal oxide semiconductor (MOS) tube and a primary winding of the transformer; the control circuit comprises a pulse width modulation (PWM) control chip, a current sampling resistor and a chip power supply circuit; the gate of the MOS tube is connected with the gate driving pin of the PWM control chip through a driving resistor; the drain of the MOS tube is connected with the first end of the primary winding of the transformer; the second end of the primary winding of the transformer is connected with a positive electrode of the output end of the input rectification filter circuit; the source of the MOS tube is grounded through the current sampling resistor; and the current detection pin of the PWM control chip is connected with the source of the MOS tube. The low-power LED constant-current power supply can stabilize output current without depending on feedback of a secondary side and is simple in circuit and relatively low in cost; and the reliability of the circuit is improved.

Description

A low power LED constant current power supply

[technical field]

The utility model relates to a switching power supply, in particular to a low-power LED constant-current power supply.

[Background technique]

LED constant current power supply is a kind of LED power supply. It uses a switching power converter to make an isolated constant current power supply. Its output current is constant and adjustable. Low-power LED constant-current power supply with a power of less than 30W is mainly used as a driving power supply for LED fluorescent lamps, bulb lamps and other low-power LED lights or as a charger.

The traditional isolated drive power supply uses secondary side feedback technology to keep the output current constant, which has a better constant current effect. Secondary side feedback constant current technology needs to add secondary side feedback circuit, need to add comparison circuit, voltage regulator circuit, optocoupler isolation, precision resistance sampling, etc. Therefore, the secondary side feedback increases the cost, and the added components reduce the reliability of the circuit to a certain extent.

[Content of the invention]

The technical problem to be solved by the utility model is to provide a low-power LED constant-current power supply with simple circuit, low cost and good reliability.

In order to solve the above technical problems, the technical solution adopted by the utility model is that a low-power LED constant current power supply includes a primary circuit, a secondary circuit and a control circuit, and the primary circuit and the secondary circuit are coupled through a transformer; The primary side circuit includes an input rectification filter circuit and a switch energy conversion circuit, the switch energy conversion circuit includes a MOS tube and the primary winding of the transformer, and the control circuit includes a PWM control chip, a current sampling resistor And the chip power supply circuit, the gate of the MOS tube is connected to the gate drive pin of the PWM control chip through the drive resistor, the drain of the MOS tube is connected to the first end of the primary winding of the transformer, and the second end of the primary winding of the transformer is connected to the input rectification filter The positive pole of the output terminal of the circuit; the source of the MOS tube is grounded through the current sampling resistor, and the current detection pin of the PWM control chip is connected to the source of the MOS tube.

In the low-power LED constant current power supply described above, the control circuit includes a grounding resistor and a grounding diode, one end of the grounding resistor is grounded, the other end is connected to the anode of the grounding diode, and the cathode of the grounding diode is connected to the PWM control chip. the gate drive pin.

In the low-power LED constant-current power supply described above, the chip power supply circuit includes a start-up power supply circuit and a working power supply circuit, the start-up power supply circuit includes a start-up resistor, and the power supply pin of the PWM control chip is output by connecting the rectifier filter circuit through the start-up resistor The positive pole of the terminal; the transformer includes an auxiliary winding, and the working power supply circuit includes a rectifier diode and a filter circuit; one end of the auxiliary winding is connected to the anode of the rectifier diode, and the other end is grounded; the cathode of the rectifier diode is connected to the input end of the filter circuit, and the output of the filter circuit The anode of the terminal is connected to the power supply pin of the PWM control chip, and the cathode of the output terminal of the filter circuit is grounded.

In the low-power LED constant current power supply described above, the control circuit includes a compensation circuit, and the compensation circuit includes a compensation resistor, a first compensation capacitor and a second compensation capacitor; after the compensation resistor is connected in series with the first compensation capacitor, One end is connected to the compensation pin of the PWM control chip, and the other end is grounded; one end of the second compensation capacitor is connected to the compensation pin of the PWM control chip, and the other end is grounded.

In the low-power LED constant current power supply described above, the control circuit includes an overvoltage protection circuit, and the overvoltage protection circuit includes a first sampling resistor and a second sampling resistor, and the first sampling resistor and the second sampling resistor string After connecting, one end is connected to the anode of the rectifier diode, and the other end is grounded; the overvoltage protection pin of the PWM control chip is connected to the connection point between the first sampling resistor and the second sampling resistor.

The low-power LED constant current power supply described above includes an RCD snubber circuit, and the RCD snubber circuit includes a snubber diode, a snubber capacitor, a first snubber resistor and a second snubber resistor; the anode of the snubber diode is connected to the primary winding of the transformer through the first snubber resistor The first end of the snubber diode, the cathode of the snubber diode is connected to the second end of the primary winding of the transformer through the snubber capacitor; the second snubber resistor and the snubber capacitor are connected in parallel.

In the low-power LED constant-current power supply described above, the PWM control chip is the SY5800 control chip.

The low-power LED constant-current power supply of the utility model does not need to use secondary side feedback to maintain a constant output current, and does not need to add a comparison circuit, a voltage stabilizing circuit, optocoupler isolation, and precision resistance sampling on the secondary side. Not only the circuit is simple, the cost is low, and The reliability of the circuit is improved.

[Description of drawings]

Below in conjunction with accompanying drawing and specific embodiment, the utility model is described in further detail.

Fig. 1 is a circuit diagram of an embodiment of a low-power LED constant current power supply of the present invention.

Fig. 2 is a pin diagram of the PWM control chip SY5800 of the embodiment of the low-power LED constant-current power supply of the present invention.

[Detailed ways]

In the embodiment of the low-power LED constant-current power supply of the present invention shown in Fig. 1, the low-power LED constant-current power supply includes a primary side circuit, a secondary side circuit, an RCD buffer circuit and a control circuit, and the primary side circuit and the secondary side circuit pass through Transformer T1 is coupled. The primary side circuit includes input rectification filter circuit and switching energy conversion circuit,

The switching energy conversion circuit includes a MOS transistor Q1 and a primary winding of a transformer T1.

The control circuit includes PWM control chip SY5800, chip power supply circuit, compensation circuit and overvoltage protection circuit.

The gate of the MOS transistor Q1 is connected to the gate drive pin DRV of the PWM control chip SY5800 through the drive resistor R17, the drain of the MOS transistor Q1 is connected to the first end of the primary winding of the transformer T1, and the second end of the primary winding of the transformer T1 is connected to the input The positive pole of the output terminal of the rectification filter circuit. The current detection pin ISEN of the PWM control chip SY5800 is connected to the source of the MOS transistor Q1, and the source of the MOS transistor Q1 is grounded through the current sampling resistor, which is composed of resistors R18, R19, R23 and R24 connected in parallel.

In order to prevent misoperation after the gate of MOS transistor Q1 is suspended, one end of the grounding resistor R3 is grounded, the other end is connected to the anode of the grounding diode D4, and the cathode of the grounding diode D4 is connected to the gate drive pin DRV of the PWM control chip SY5800. When the SY5800 stops working, let the charge of the capacitance between the gate and the source discharge through this resistor R3.

The chip power supply circuit includes a startup power supply circuit and a working power supply circuit.

The starting power supply circuit includes a starting resistor, and the power supply pin VIN of the PWM control chip SY5800 is connected to the positive pole of the output terminal of the rectification filter circuit through the starting resistor; the starting resistor is composed of resistors R9, R10 and R11 connected in series.

The working power supply circuit is composed of auxiliary winding of transformer T1, rectifier diode D3 and filter circuit. One end of the auxiliary winding is connected to the anode of the rectifier diode D3, and the other end is grounded. The cathode of the rectifier diode D3 is connected to the input end of the filter circuit, the anode of the output end of the filter circuit is connected to the power supply pin VIN of the PWM control chip SY5800, and the cathode of the output end of the filter circuit is grounded. The filter circuit is composed of resistor R16, capacitors C3, C8 and C6.

The compensation circuit includes a compensation resistor R8, a compensation capacitor C2 and a compensation capacitor C4. After the compensation resistor R8 and the compensation capacitor C2 are connected in series, one end is connected to the compensation pin COMP of the PWM control chip SY5800, and the other end is grounded. One end of the compensation capacitor C4 is connected to the compensation pin COMP of the PWM control chip SY5800, and the other end is grounded. The compensation circuit is beneficial to improve the flickering defect of the LED lamp.

The overvoltage protection circuit includes a sampling resistor R6 and a sampling resistor R7. After the sampling resistor R6 and the sampling resistor R7 are connected in series, one end of the resistor R6 is connected to the anode of the rectifier diode D3, and the other end is grounded. The overvoltage protection pin ZCS of the PWM control chip SY5800 is connected to the connection point between the sampling resistor R6 and the sampling resistor R7.

The RCD snubber circuit includes snubber diode D2, snubber capacitor C7, snubber resistors R13, R14 and R15. The anode of the snubber diode D2 is connected to the first end of the primary winding of the transformer T1 through the snubber resistor R15, and the cathode of the snubber diode D2 is connected to the second end of the primary winding of the transformer T1 through the snubber capacitor C7. The buffer resistors R13 and R14 are connected in parallel with the buffer capacitor C7.

The above embodiments of the low-power LED constant-current power supply of the utility model do not require constant output current through secondary side feedback, and the secondary side no longer needs a comparison circuit, a voltage stabilizing circuit, optocoupler isolation, and precision resistance sampling; the utility model is not only simple in circuit, The cost is lower, and the reliability of the circuit is improved.

Claims (7)

1. A low-power LED constant current power supply, comprising a primary circuit, a secondary circuit and a control circuit, the primary circuit and the secondary circuit are coupled through a transformer; the primary circuit includes an input rectification filter circuit and a switch An energy conversion circuit, the switch energy conversion circuit includes a MOS tube and the primary winding of the transformer, it is characterized in that the control circuit includes a PWM control chip, a current sampling resistor and a chip power supply circuit, the gate of the MOS tube The pole is connected to the gate drive pin of the PWM control chip through the drive resistor, the drain of the MOS tube is connected to the first end of the primary winding of the transformer, and the second end of the primary winding of the transformer is connected to the positive pole of the output terminal of the input rectifier filter circuit; the source of the MOS tube The pole is grounded through the current sampling resistor, and the current detection pin of the PWM control chip is connected to the source of the MOS tube. 2. The low-power LED constant-current power supply according to claim 1, wherein the control circuit includes a ground-to-ground resistor and a ground-to-ground diode, one end of the ground-to-ground resistor is grounded, and the other end is connected to the anode of the ground-to-ground diode. The cathode of the diode to ground is connected to the gate drive pin of the PWM control chip. 3. The low-power LED constant-current power supply according to claim 1, wherein the chip power supply circuit includes a start-up power supply circuit and a working power supply circuit, the start-up power supply circuit includes a start-up resistor, and the power supply of the PWM control chip The pin is connected to the positive pole of the output terminal of the rectifier filter circuit through the starting resistor; the transformer includes an auxiliary winding, and the working power supply circuit includes a rectifier diode and a filter circuit; one end of the auxiliary winding is connected to the anode of the rectifier diode, and the other end is grounded; the cathode of the rectifier diode is connected to the filter circuit The input end of the circuit, the anode of the output end of the filter circuit are connected to the power supply pin of the PWM control chip, and the cathode of the output end of the filter circuit is grounded. 4. The low-power LED constant current power supply according to claim 1, wherein the control circuit includes a compensation circuit, and the compensation circuit includes a compensation resistor, a first compensation capacitor and a second compensation capacitor; the compensation resistor After being connected in series with the first compensation capacitor, one end is connected to the compensation pin of the PWM control chip, and the other end is grounded; one end of the second compensation capacitor is connected to the compensation pin of the PWM control chip, and the other end is grounded. 5. The low-power LED constant current power supply according to claim 3, wherein the control circuit includes an overvoltage protection circuit, and the overvoltage protection circuit includes a first sampling resistor and a second sampling resistor, the second sampling resistor After the first sampling resistor and the second sampling resistor are connected in series, one end is connected to the anode of the rectifier diode, and the other end is grounded; the overvoltage protection pin of the PWM control chip is connected to the connection point between the first sampling resistor and the second sampling resistor. 6. The low-power LED constant current power supply according to claim 1, characterized in that it comprises an RCD snubber circuit, and the RCD snubber circuit includes a snubber diode, a snubber capacitor, a first snubber resistor and a second snubber resistor; the anode of the snubber diode passes through The first snubber resistor is connected to the first end of the primary winding of the transformer, the cathode of the snubber diode is connected to the second end of the primary winding of the transformer through the snubber capacitor; the second snubber resistor is connected to the snubber capacitor in parallel. 7. The low-power LED constant current power supply according to any one of claims 1 to 6, wherein the PWM control chip is a SY5800 chip.

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