CN203608439U - LED constant current power supply with over-temperature protection - Google Patents

Abstract

The utility model relates to an LED constant-current power supply with over-temperature protection, comprising an LED module, an input rectification filter circuit, a switching power supply circuit, a PWM control circuit, a current feedback circuit, and an output rectification filter circuit. The input end of the PWM control circuit is connected to the mains, and the output end is connected to the LED module through the switching power supply circuit and the output rectification filter circuit in turn. The input end of the PWM control circuit is connected to the LED module through the current feedback circuit, and the output end is connected to the switching power supply circuit. A detection device, the temperature detection device detects the temperature signal of the LED module, and transmits the temperature signal to the input terminal of the PWM control circuit. The PWM control circuit timely adjusts the output current of the switching power supply circuit according to the temperature change of the LED detected by the thermistor to ensure that the temperature of the LED is within a suitable range, and can respond to the sudden abnormal temperature of the LED in time to extend the service life of the LED. .

Description

A LED constant current power supply with over-temperature protection

technical field

The utility model relates to the field of constant current power supplies, in particular to an LED constant current power supply with over-temperature protection.

Background technique

LED is a current-driven low-voltage unidirectional conductive device, which belongs to semiconductor power devices. Its volt-ampere characteristic curve is nonlinear, and the current flowing through the PN junction is not proportional to the voltage loaded on both ends of the PN junction. When changing, the current flowing through the PN junction will have a large change. At the same time, the PN junction has a negative temperature coefficient. As the temperature rises, the tube voltage drop decreases, which further increases the current flowing through the chip. If a constant voltage source is used to drive , it is very easy to cause the current in the chip to increase sharply due to the increase of temperature, resulting in spectral shift, causing light decay, and seriously causing LED burnout; most of the LED driving power supply adopts constant current driving mode at present, but constant current power supply It is strictly forbidden to open the load, the output voltage is prone to change within a certain range with the change of the load resistance, and the number of LEDs is limited in actual use. The current LED constant current drive power supply does not have a temperature protection device, and cannot adjust the input current in time according to the temperature change of the LED. The actual service life of the LED is far lower than the theoretical service life, and it cannot cope with the sudden abnormal temperature of the LED.

Contents of the invention

The technical problem to be solved by the utility model is to provide an LED constant-current power supply with over-temperature protection, which can solve the problem that the existing LED constant-current power supply cannot adjust the input current in time according to the temperature change of the LED, causing the actual service life of the LED to be far away. It is lower than the theoretical service life, and it cannot cope with the problem of sudden abnormal temperature of the LED.

The utility model is realized through the following technical solutions:

An LED constant-current power supply with over-temperature protection, comprising an LED module, an input rectification filter circuit, a switching power supply circuit, a PWM control circuit, a current feedback circuit, and an output rectification filter circuit. The input end of the input rectification filter circuit is connected to the market Electricity, the output terminal is connected to the LED module through the switching power supply circuit and the output rectification filter circuit in turn, the input terminal of the PWM control circuit is connected to the LED module through the current feedback circuit, and the output terminal is connected to the switching power supply circuit and also includes a temperature detection device. The temperature detection device detects the temperature signal of the LED module, and transmits the temperature signal to the input terminal of the PWM control circuit.

AC mains power is converted into DC by resistor R1, capacitor C1, full-bridge rectifier circuit D1, inductor L1, capacitor C2, and rectifier diode D2, which form the input rectifier and filter circuit, and then input to the switching power supply circuit.

The switching power supply circuit is composed of an enhanced N-channel insulated gate field effect transistor Q1 and a transformer T1, the source of the field effect transistor Q1 is grounded through a resistor R2, the gate is connected to the output end of the PWM control circuit, and the drain is connected to the output terminal of the PWM control circuit through The primary winding of the transformer T1 is connected to the output terminal of the input rectification filter circuit; the secondary winding of the transformer T1 is connected to the output rectification filter circuit.

The rectifying and filtering circuit is composed of a rectifying diode D3 and a capacitor C3, and the output end of the switching power supply circuit is connected to the LED module through the rectifying diode D3 and the capacitor C3 in sequence.

The current feedback circuit includes a resistor R4 connected in series with the LED module and an operational amplifier U1, the output terminal of the operational amplifier U1 is connected to the input terminal of the PWM control circuit, the non-inverting input terminal of the operational amplifier U1 is connected to a reference voltage, The inverting input terminal of the operational amplifier U1 is connected to the resistor R4 and the common terminal of the LED module.

The temperature detecting device is a PTC thermistor connected in parallel with the LED module.

The power terminal of the PWM control circuit is connected to the output terminal of the input rectification filter circuit through a resistor R3.

The LED module is composed of a plurality of LED lamps connected in series, and each LED lamp is connected with a zener diode D4 in reverse parallel.

Compared with the prior art, the utility model has the following advantages:

The PWM control circuit timely adjusts the output current of the switching power supply circuit according to the temperature change of the LED detected by the thermistor to ensure that the temperature of the LED is within a suitable range, and can respond to the sudden abnormal temperature of the LED in time to extend the service life of the LED. .

Description of drawings

Fig. 1 is a structural block diagram of the utility model.

Fig. 2 is the circuit diagram of the utility model.

Detailed ways

As shown in Figure 1 and Figure 2, an LED constant current power supply with over-temperature protection includes LED modules, input rectification and filter circuits, switching power supply circuits, PWM control circuits, current feedback circuits, and output rectification and filter circuits. The input end of the input rectification filter circuit is connected to the mains, the output end is connected to the LED module through the switching power supply circuit and the output rectification filter circuit in turn, the input end of the PWM control circuit is connected to the LED module through the current feedback circuit, and the output end is connected to the switching power supply The circuit also includes a temperature detection device, the power supply end of the PWM control circuit is connected to the output end of the input rectification filter circuit through a resistor R3, the temperature detection device detects the temperature signal of the LED module, and transmits the temperature signal to the PWM control circuit input.

AC 220V city power is converted into 350V DC by resistor R1, capacitor C1, full-bridge rectifier circuit D1, inductor L1, capacitor C2, and rectifier diode D2, which form the input rectifier filter circuit, and then input to the switching power supply circuit.

The switching power supply circuit is composed of an enhanced N-channel insulated gate field effect transistor Q1 and a transformer T1, the source of the field effect transistor Q1 is grounded through a resistor R2, the gate is connected to the output end of the PWM control circuit, and the drain is connected to the output terminal of the PWM control circuit through The primary winding of the transformer T1 is connected to the output terminal of the input rectification filter circuit; the secondary winding of the transformer T1 is connected to the output rectification filter circuit.

The rectifying and filtering circuit is composed of a rectifying diode D3 and a capacitor C3, and the output end of the switching power supply circuit is connected to the LED module through the rectifying diode D3 and the capacitor C3 in sequence.

The current feedback circuit includes a resistor R4 connected in series with the LED module and an operational amplifier U1, the output terminal of the operational amplifier U1 is connected to the input terminal of the PWM control circuit, the non-inverting input terminal of the operational amplifier U1 is connected to a reference voltage, The inverting input terminal of the operational amplifier U1 is connected to the common terminal of the resistor R4 and the LED module; the resistor R4 is connected in series with the LED module, and the current flowing through the LED module also flows through the resistor R4 at the same time. When the current changes, the transformed current will generate a variable voltage at both ends of the resistor R4, and this variable voltage is added to the inverting input terminal of the operational amplifier U1, and the variable voltage is connected to the reference voltage connected to the non-inverting input terminal of the operational amplifier U1. In comparison, an amplified variable voltage is obtained at the output of the operational amplifier U1, and the amplified variable voltage is input into the PWM control circuit to change the duty cycle of the PWM output rectangular voltage, thereby controlling the oscillation frequency of the switching power supply, and then changing the switching power supply. The output voltage keeps the current in the LED module constant.

The temperature detection device is a PTC thermistor connected in parallel to the LED module, and the PTC thermistor is installed close to the LED module to detect changes in the temperature of the LED module. When the temperature of the LED module rises, the resistance of the PTC thermistor When the voltage increases, the voltage at both ends will increase immediately, and the increased voltage is input to the inverting input terminal of the operational amplifier U1, compared with the reference voltage, and the amplified change signal is fed back to the PWM control circuit to reduce the current input to the LED module; by setting Set the upper and lower limits of the temperature. When the real-time temperature of the LED module exceeds the upper and lower limits, reduce or increase the current input to the LED module. If the temperature rises beyond the set alarm value, the PWM control circuit will be cut off through the switching power supply circuit. current, so as to achieve the purpose of temperature control.

The LED module is composed of a plurality of LED lamps connected in series, and each LED lamp is connected in reverse parallel with a zener diode D4. The breakdown voltage of the zener diode D4 is higher than the working voltage of the LED lamp. When the LED lamp is disconnected or two When the terminal voltage rises, the Zener diode breaks down to protect the LED light.

Claims (8)

1. A LED constant-current power supply with over-temperature protection, comprising an LED module, an input rectification filter circuit, a switching power supply circuit, a PWM control circuit, a current feedback circuit, an output rectification filter circuit, and the input terminal of the input rectification filter circuit Connecting to the mains, the output terminal is connected to the LED module through the switching power supply circuit and the output rectification and filtering circuit in turn, the input terminal of the PWM control circuit is connected to the LED module through the current feedback circuit, and the output terminal is connected to the switching power supply circuit, which is characterized in that: It includes a temperature detection device, which detects the temperature signal of the LED module and transmits the temperature signal to the input terminal of the PWM control circuit. 2. A LED constant-current power supply with over-temperature protection as claimed in claim 1, characterized in that: AC mains power sequentially passes through resistor R1, capacitor C1, full-bridge rectifier circuit D1, inductor L1, capacitor C2, and rectifier diode D2 are converted into direct current and then input to the switching power supply circuit. 3. A LED constant-current power supply with over-temperature protection as claimed in claim 1, wherein the switching power supply circuit is composed of an enhanced N-channel insulated gate field effect transistor Q1 and a transformer T1, and the field The source of the effect transistor Q1 is grounded through the resistor R2, the gate is connected to the output terminal of the PWM control circuit, and the drain is connected to the output terminal of the input rectifier filter circuit through the primary winding of the transformer T1; the secondary winding of the transformer T1 is connected to the output rectifier filter circuit circuit. 4. A LED constant-current power supply with over-temperature protection as claimed in claim 1 or 3, characterized in that: the rectification filter circuit is composed of a rectifier diode D3 and a capacitor C3, and the output terminals of the switching power supply circuit are rectified sequentially The diode D3 and the capacitor C3 are connected to the LED module. 5. A LED constant-current power supply with over-temperature protection as claimed in claim 1, wherein the current feedback circuit includes a resistor R4 connected in series with the LED module and an operational amplifier U1, the operational amplifier U1 The output terminal is connected to the input terminal of the PWM control circuit, the non-inverting input terminal of the operational amplifier U1 is connected to a reference voltage, and the inverting input terminal of the operational amplifier U1 is connected to the common terminal of the resistor R4 and the LED module. 6. A LED constant-current power supply with over-temperature protection as claimed in claim 1, wherein the temperature detection device is a PTC thermistor connected in parallel to the LED module. 7. The LED constant-current power supply with over-temperature protection as claimed in claim 1, wherein the power supply end of the PWM control circuit is connected to the output end of the input rectification filter circuit through a resistor R3. 8. The LED constant current power supply with over-temperature protection as claimed in claim 1, characterized in that: the LED module is composed of a plurality of LED lamps connected in series, and each LED lamp is connected in reverse parallel with a zener Diode D4.

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