CN201571238U - LED constant current switch power circuit - Google Patents

Abstract

The utility model discloses a LED constant current switching power supply circuit, which is characterized in that: a controllable power supply and a feedback circuit are provided, the output end of the controllable power supply is connected with an LED, and the feedback circuit is provided with a thermistor R5. The thermistor R5 is close to the LED, and the feedback end of the feedback circuit is connected to the controllable power supply. Its remarkable beneficial effects are: simple structure, low cost, and protection of LED lamps from being burned due to excessive temperature.

Description

LED constant current switching power supply circuit

technical field

The utility model belongs to the technical field of LED power supply and protection, in particular relates to a constant current switching power supply circuit for LEDs.

Background technique

LED lights have the advantages of energy saving, environmental protection, long service life, and rich colors. LED lighting technology has been widely used in indoor and outdoor lighting, and many fields of colored light scene lights. The working environment of LED lights is high current and low voltage. At the same time, LED lamps will generate a lot of heat energy during operation, and LED lamps are easy to affect the service life of LED lamps or even burn out LED lamps due to the high temperature of the environment or itself.

The disadvantage of the prior art is that the working temperature of the LED lamp cannot be effectively controlled, and the LED lamp is easily burned due to excessive temperature.

Utility model content

The purpose of the utility model is to provide an LED constant current switching power supply circuit, which can prolong the service life of the LED lamp and protect the LED lamp from being burned due to excessive temperature.

In order to solve the above technical problems, the technical scheme of the utility model is as follows: a LED constant current switching power supply circuit, the key of which is: a controllable power supply and a feedback circuit are provided, the output end of the controllable power supply is connected to an LED, and the feedback circuit The circuit is provided with a thermistor, the thermistor is close to the LED, and the feedback end of the feedback circuit is connected to the controllable power supply.

The controllable power supply is provided with a DC power supply and a transformer, the positive power supply terminal of the DC power supply is connected to the first end of the input primary coil of the transformer, the second terminal of the input primary coil is connected to the anode of the second diode, The first capacitor of the cathode series of the second diode is connected to the positive power supply end of the DC power supply, the two ends of the first capacitor are connected in parallel with the first resistor, and the second end of the input primary coil is also connected to The collector of the triode, the emitter of the triode is grounded, the base of the triode is connected to one end of the input secondary coil of the transformer after the third capacitor, the other end of the input secondary coil is grounded, and the base of the triode is connected to the third capacitor. The pull-up resistor is connected to the positive power supply terminal of the DC power supply, and the base of the triode is also connected to the feedback circuit;

The feedback circuit is provided with a first diode, the anode of the first diode is connected to one end of the output winding of the transformer, the other end of the output winding of the transformer is grounded, and the cathode of the first diode is connected to the LED Anode, the cathode of the LED is connected to the ground after the third resistor, the cathode of the LED is also connected to the inverting input terminal of the comparator, the cathode of the first diode is connected to the front end of the fourth resistor, and the rear end of the fourth resistor A Zener diode is connected in series to ground, and the rear end of the fourth resistor is connected in series with an eighth resistor to the positive input terminal of the comparator, and the output terminal of the comparator is connected to the base of the triode.

There is a fourth capacitor in series between the positive input terminal of the comparator and the ground.

The base of the triode is connected with the cathode of the third diode, and the anode of the third diode is grounded.

The cathode of the first diode is connected to the ground after electrolyzing the capacitor.

The feedback circuit is also provided with a second triode and a sixth resistor, the anode of the LED is connected to the base of the second triode after the thermistor, and the base of the second triode is connected to the sixth resistor Then grounded, the collector of the second triode is connected to the base of the triode, and the emitter of the second triode is grounded.

The thermistor is glued together with the LED.

The triode collector output switching signal drives the primary coil of the transformer, and is coupled to the secondary coil of the transformer, and then passes through the second resistor and the third capacitor to form positive feedback to generate self-excited oscillation. The second resistor is connected in series between the secondary coil and the third between capacitors. The triode is in the switch working state, the turn-on and turn-off time is determined by the third capacitor and the second resistor, and the base of the triode is respectively connected with the collector of the second triode and the output terminal of the comparator. When the second triode or When the comparator has a certain pull-down current, the duty cycle of the triode conduction will decrease.

The thermistor is a negative temperature coefficient thermistor. When the operating temperature of the LED rises, due to the thermal coupling with the thermistor, the following negative feedback process will occur: LED temperature ↑, thermistor temperature ↑, thermistor The resistance value ↓, the collector current of the second triode ↑, the conduction duty ratio of the triode decreases ↓, the LED power ↓, and the LED temperature ↓, thereby limiting the excessive temperature of the LED.

When the LED current is too large, the voltage drop on the third resistor increases, and the following negative feedback process will occur: the voltage at the negative input terminal of the comparator exceeds the positive input terminal, the output terminal of the comparator produces a pull-down current, and the duty cycle of the triode conduction Decrease ↓, LED current ↓, thus achieving constant current.

When working stably, the voltage at the positive input terminal of the comparator is equal to the reference voltage Vref. According to the principle of constant current, the voltage drop of the third resistor tends to the voltage at the positive input terminal of the comparator to ground. The lower the voltage at the positive input terminal Vref, the third resistor The smaller the voltage drop, the smaller the LED power. In the figure, the eighth resistor and the fourth capacitor are connected to form an integral circuit. When the whole system is connected to the power supply, the voltage at the forward input terminal of the comparator rises with time in an RC charging curve, and it takes a period of time to reach the rated value, which limits the power on of the LED. When the power, to achieve soft start.

Beneficial effects: the utility model provides a LED constant current switching power supply circuit with simple structure and low cost, which can protect the LED lamp from being burned due to excessive temperature. At the same time, a constant current switching power supply is provided for the LED, which limits the power at power-on, realizes soft start, and protects the LED from being damaged due to excessive starting voltage.

Description of drawings

Fig. 1 is the connection block diagram of the utility model;

Fig. 2 is the circuit diagram of embodiment 1;

Fig. 3 is the circuit diagram of embodiment 2.

Detailed ways

Below in conjunction with accompanying drawing and embodiment the utility model is further described:

Embodiment 1: As shown in Figure 1, the utility model provides a LED constant current switching power supply circuit, the key of which is: a controllable power supply and a feedback circuit are provided, the output end of the controllable power supply is connected to an LED, and the feedback circuit The circuit is provided with a thermistor R5, the thermistor R5 is close to the LED, and the feedback end of the feedback circuit is connected to the controllable power supply.

The controllable power supply is provided with a DC power supply and a transformer T1, the positive power supply terminal of the DC power supply is connected to the first end of the input primary coil of the transformer T1, and the second terminal of the input primary coil is connected to the second diode D2 the anode of the second diode D2, the first capacitor C1 of the cathode string of the second diode D2 is connected to the positive power supply terminal of the DC power supply, the two ends of the first capacitor C1 are connected in parallel with the first resistor R1, and the input primary coil The second end of the triode Q1 is also connected to the collector of the triode Q1, the emitter of the triode Q1 is grounded, the base of the triode Q1 is connected to the third capacitor C3 connected to one end of the input secondary coil of the transformer T1, and the input secondary coil The other end of the triode Q1 is grounded, the base of the triode Q1 is connected to the positive power supply terminal of the DC power supply after the pull-up resistor R9, and the base of the triode Q1 is also connected to the feedback circuit;

The feedback circuit is provided with a first diode D1, the anode of the first diode D1 is connected to one end of the output winding of the transformer T1, the other end of the output winding of the transformer T1 is grounded, and the first diode D1 The cathode of the LED is connected to the anode of the LED, the cathode of the LED is connected to the ground after the third resistor R3, the cathode of the LED is also connected to the inverting input terminal of the comparator U, and the cathode of the first diode D1 is connected to the fourth resistor R4 At the front end, the back end of the fourth resistor R4 is connected to the positive input end of the comparator U, and the back end of the fourth resistor R4 is connected to the positive input end of the comparator U. The output terminal is connected to the base of the transistor Q1.

A fourth capacitor C4 is connected in series between the positive input terminal of the comparator U and the ground.

The base of the triode Q1 is connected to the cathode of the third diode D3, and the anode of the third diode D3 is grounded.

The cathode string of the first diode D1 is grounded after the electrolytic capacitor C2.

The feedback circuit is also provided with a second triode Q2 and a sixth resistor R6, the anode string thermistor R5 of the LED is connected to the base of the second triode Q2, and the base of the second triode Q2 The sixth resistor R6 of the pole series is connected to the ground, the collector of the second transistor Q2 is connected to the base of the transistor Q1, and the emitter of the second transistor Q2 is connected to the ground.

The thermistor R5 is glued together with the LED.

Its working process is as follows: Transistor Q1 collector outputs switching signal to drive the primary coil of transformer T1, and is coupled to the secondary coil of transformer T1 to lead out, and then through the second resistor R2, the third capacitor C3 forms positive feedback to generate self-excited oscillation, the second The resistor R2 is connected in series between the secondary coil and the third capacitor C3. The transistor Q1 is in the switch working state, the turn-on and turn-off time is determined by the third capacitor C3 and the second resistor R2, and the base of the transistor Q1 is respectively connected with the collector of the second transistor Q2 and the output terminal of the comparator U, when When the second transistor Q2 or the comparator U has a certain pull-down current, the conduction duty cycle of the transistor Q1 will decrease.

Thermistor R5 is a negative temperature coefficient thermistor. When the operating temperature of the LED rises, due to the thermal coupling with the thermistor R5, the following negative feedback process will occur: LED temperature ↑, thermistor R5 temperature ↑, The resistance value of the thermistor R5 is ↓, the collector current of the second transistor Q2 is ↑, the conduction duty cycle of the transistor Q1 is reduced ↓, the LED power is ↓, and the LED temperature is ↓, thus limiting the excessive temperature of the LED.

When the LED current is too large, the voltage drop on the third resistor R3 increases, and the following negative feedback process will occur: the voltage at the negative input terminal of the comparator U exceeds the positive input terminal, the output terminal of the comparator U produces a pull-down current, and the transistor Q1 conducts By reducing the duty cycle ↓, the LED current ↓, thus achieving a constant current.

When working stably, the voltage at the positive input terminal of the comparator U is equal to the reference voltage Vref. According to the principle of constant current, the voltage drop of the third resistor R3 tends to the voltage at the positive input terminal of the comparator U to ground, and the lower the voltage at the positive input terminal Vref, The smaller the voltage drop of the third resistor R3 is, the smaller the LED power is. In the figure, the eighth resistor R8 and the fourth capacitor C4 are connected to form an integral circuit. When the whole system is connected to the power supply, the voltage at the positive input terminal of the comparator U rises with time in an RC charging curve, and it takes a period of time to reach the rated value, which limits The power when the LED is powered on to achieve soft start.

In this utility model, not only limited to the circuit structure expressed in embodiment 1, there are many ways to construct controllable power supply and feedback circuit, all of which are within the scope of protection of this utility model, such as embodiment 2, the structure of this embodiment 2 is as follows :

The positive power supply terminal of the DC power supply BT1 is connected to the emitter of the PNP transistor Q, and the collector of the PNP transistor Q and the negative power supply terminal of the DC power supply BT1 supply power to the LED; the anode of the LED is connected to the collector of the PNP transistor Q1, The cathode is connected to the negative power supply terminal of the DC power supply BT1.

DC power supply BT1 and PNP transistor Q form a controllable power supply.

A resistor R is connected in parallel between the base and the collector of the PNP transistor Q, and a thermistor R5 is connected in parallel between the base and the emitter of the PNP transistor Q, and the thermistor R5 is close to the LED.

Resistor R and thermistor R5 form a feedback circuit.

Its workflow is as follows:

The temperature of LED lamp D1 increases → the resistance value of thermistor R5 decreases → the base voltage of PNP transistor Q1 increases → the collector current of PNP transistor Q1 decreases → the power of LED lamp D1 decreases → the temperature of LED lamp D1 decreases, thus protecting the temperature of LED lamp D1 Not too high.

Claims (7)

1. LED constant current switch power circuit, it is characterized in that: be provided with controllable electric power and feedback circuit, the output of this controllable electric power is connected with LED, described feedback circuit is provided with thermistor (R5), this thermistor (R5) is near described LED, and the feedback end of this feedback circuit connects described controllable electric power.

2. LED constant current switch power circuit according to claim 1, it is characterized in that: described controllable electric power is provided with DC power supply and transformer (T1), first end of the described transformer of positive supply termination (T1) the input primary coil of this DC power supply, the anode of second termination, second diode (D2) of this input primary coil, connect the positive power source terminal of described DC power supply behind negative electrode string first electric capacity (C1) of this second diode (D2), the two ends of this first electric capacity (C1) also are connected to first resistance (R1), second end of described input primary coil also is connected with the collector electrode of triode (Q1), the grounded emitter of this triode (Q1), connect an end of described transformer (T1) input secondary coil behind base stage string the 3rd electric capacity (C3) of this triode (Q1), the other end ground connection of this input secondary coil, connect the positive power source terminal of described DC power supply behind the base stage string pull-up resistor (R9) of described triode (Q1), the base stage of this triode (Q1) also connects described feedback circuit;

Described feedback circuit is provided with first diode (D1), the anode of this first diode (D1) connects an end of described transformer (T1) output winding, the other end ground connection of this transformer (T1) output winding, the negative electrode of described first diode (D1) connects the anode of LED, negative electrode string the 3rd resistance (R3) the back ground connection of this LED, the negative electrode of this LED also connects the reverse input end of comparator (U), the negative electrode of described first diode (D1) connects the front end of the 4th resistance (R4), rear end string voltage stabilizing didoe (D4) the back ground connection of the 4th resistance (R4), the positive input that meets described comparator (U) behind the 8th resistance (R8) is also gone here and there in the rear end of the 4th resistance (R4), the base stage of the described triode of output termination (Q1) of this comparator (U).

3. LED constant current switch power circuit according to claim 2 is characterized in that: string just has the 4th electric capacity (C4) between the positive input of described comparator (U) and the ground.

4. LED constant current switch power circuit according to claim 2 is characterized in that: the base stage of described triode (Q1) is connected with the negative electrode of the 3rd diode (D3), the plus earth of the 3rd diode (D3).

5. LED constant current switch power circuit according to claim 2 is characterized in that: electric capacity (C2) back ground connection is separated in the negative electrode crosstalk of described first diode (D1).

6. LED constant current switch power circuit according to claim 2, it is characterized in that: described feedback circuit also is provided with second triode (Q2) and the 6th resistance (R6), connect the base stage of second triode (Q2) behind the anode series thermistor (R5) of described LED, base stage string the 6th resistance (R6) the back ground connection of this second triode (Q2), the collector electrode of this second triode (Q2) connects the base stage of described triode (Q1), the grounded emitter of this second triode (Q2).

7. LED constant current switch power circuit according to claim 1 is characterized in that: described thermistor (R5) fits together with described LED.

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