CN209120507U - A LED linear constant current driver - Google Patents

Abstract

The utility model discloses an LED linear constant current driver, comprising a rectifier circuit, a working circuit, a constant current control circuit, a voltage detection circuit, a soft start circuit and an external control circuit. The soft start circuit comprises a charge and discharge circuit, and a resistor R7, a resistor R8, a transistor T5 and a capacitor C1 are used to form the charge and discharge circuit. When the power is cut off, the transistor T5 is saturated and turned on, and the electric energy on the capacitor C1 can be quickly released in a very short time. Powering on immediately after the power is cut off will not affect the soft start function of the product, and the problem of slow resistor discharge speed is effectively solved. An extremely simple circuit design is adopted to solve relatively complex technical problems. The utility model also has a temperature compensation control function, a soft start function and an external dimming function, and can conveniently realize the intelligent control and wireless Internet of Things of LED lamps, thereby improving the comprehensive performance of the driver and greatly reducing the cost.

Description

A LED linear constant current driver

technical field

The utility model relates to an LED drive circuit, in particular to an LED constant current soft start drive circuit.

Background technique

The linear constant current driver in the prior art adopts a charge-discharge circuit formed by a resistor and a capacitor C in parallel to realize a soft-start circuit, and uses a resistor to discharge the capacitor, and it takes a certain period of time for the electric energy stored in the capacitor to be completely released. In a short time of power-on, since the electric energy of the capacitor has not been completely released, the soft start fails.

SUMMARY OF THE INVENTION

In order to overcome the deficiencies of the prior art, the utility model provides an LED linear constant current driver with a simple circuit, no EMI, high constant current precision, a large voltage fluctuation range, a temperature compensation control function and a soft start function.

The technical scheme adopted by the utility model to solve its technical problems is:

An LED linear constant current driver includes a working loop and a soft start circuit. The working loop includes a field effect transistor T1. The contact between the drain D of the effect transistor T1 and the LED load is named node 6; the source S of the FET T1 is connected to the common ground through the resistor R2, and the gate G is connected to the node 6 through the resistor R1, and the resistor R1 The contact with the gate G of the field effect transistor T1 is named node 7, and the contact between the resistor R2 and the source S of the field effect transistor T1 is named node 10; the soft start circuit includes a charge and discharge loop, the The charging and discharging circuit is connected to the contact 7 through a one-way isolation circuit; the charging and discharging circuit includes a resistor R7, a resistor R8, a PNP transistor T5 and a capacitor C1; the resistor R7 and the resistor R8 are connected in series and then connected to the DC power supply. The positive pole, the other end is connected to the common ground, the emitter E of the transistor T5 is connected to one end of the capacitor C1 and then connected to the one-way isolation circuit, and the base B of the transistor T5 is connected to the resistor R7 and the resistor R8 The collector C is connected to the common ground, the other end of the capacitor C1 is connected to the common ground, and the contact between the emitter E of the transistor T5 and the capacitor C1 is named node 8 .

The unidirectional isolation circuit includes a diode D5 , the cathode of the diode D5 is connected to the node 8 , and the anode is connected to the node 7 .

Further, the driving circuit of the present invention further includes an external control circuit, and the external control circuit is connected to the node 7 .

The external control circuit includes a PNP transistor T4, the emitter E of the transistor T4 is connected to the node 7, the collector C is connected to the common ground, the base B is divided into two paths, one is connected to the node 7 through the resistor R5, and the other is connected to the node 7 through the resistor R5. One way is connected to the external signal control terminal through diode D6.

A dimming circuit is connected between the base B of the triode T4 and the common ground, and the dimming circuit is a potentiometer W or a photoresistor.

Further, the drive circuit of the present invention also includes a constant current control circuit, the constant current control circuit includes an NPN transistor T2, the base B of the transistor T2 is connected to the node 10, and the collector C is connected to the node 7, The emitter E is connected to the common ground.

Further, the drive circuit of the present invention also includes a voltage detection circuit, which includes a resistor R3, a resistor R4 and an NPN transistor T3. After the resistor R3 and the resistor R4 are connected in series, one end is connected to the node 6, and the other end is connected to the node 6. Connect to the common ground, wherein the junction of resistor R3 and resistor R4 is named node 11; the base B of the transistor T3 is connected to the node 11, the collector C is connected to the node 7 through the resistor R6, and the emitter E is connected to the common ground .

A temperature compensation circuit is connected between the node 7 and the common ground.

The beneficial effects of the utility model are: the utility model adopts the resistor R7, the resistor R8, the transistor T5 and the capacitor C1 to form a charging and discharging circuit. When the power supply is cut off, the transistor T5 is saturated and conductive, and the capacitor C1 can be quickly released in a very short time. The power on the power supply will not affect the soft-start function of the product if it is powered on immediately after the power failure, which effectively solves the problem of the slow discharge speed of the resistor. It has the advantages of high EMI and constant current accuracy, and can withstand a large voltage fluctuation range. It also has temperature compensation control function, soft start function and external dimming function, which can facilitate the realization of intelligent control of LED lamps and wireless IoT, which improves the driver. The comprehensive performance and the cost are greatly reduced, and it can be made into a dedicated integrated LED driver chip, which not only simplifies the layout design, but also greatly reduces the cost of the integrated circuit, but the function and performance have reached a very complex circuit design. grade.

Description of drawings

The present utility model will be further described below in conjunction with the accompanying drawings and embodiments.

Figure 1 is a circuit diagram of the present utility model.

Detailed ways

Referring to FIG. 1, an LED linear constant current driver includes a DC power supply, a working loop, an external control circuit, a constant current control circuit, a voltage detection circuit and a soft start circuit.

The working loop includes a field effect transistor T1, the drain D of the field effect transistor T1 is connected in series with the LED load (the LED load between node 5 and node 6) and then connected to a DC power supply (the DC power supply is composed of rectifier diodes D1-D4). The anode (node 4) of the rectifier bridge), for the convenience of description, the junction between the drain D of the FET T1 and the LED load is named node 6; the source S of the FET T1 is connected to the common through the resistor R2 Ground (node 9), the gate G is connected to the node 6 through the resistor R1, the junction between the resistor R1 and the gate G of the field effect transistor T1 is named node 7, and the resistor R2 is connected to the field effect transistor T1. The junction of the source S is named node 10 .

The soft-start circuit includes a charging and discharging circuit, and the charging and discharging circuit is connected to the contact 7 through a one-way isolation circuit.

The charging and discharging loop includes a resistor R7, a resistor R8, a PNP type triode T5 and a capacitor C1; the resistor R7 and the resistor R8 are connected in series and one end is connected to the positive electrode of the DC power supply, and the other end is connected to the common ground. The pole E is connected to one end of the capacitor C1 and then connected to the one-way isolation circuit, the base B is connected to the contact of the resistor R7 and the resistor R8, the collector C is connected to the common ground, and the other end of the capacitor C1 is connected to the common ground Ground, the junction between the emitter E of the transistor T5 and the capacitor C1 is named node 8 .

The unidirectional isolation circuit includes a diode D5 , the cathode of the diode D5 is connected to the node 8 , and the anode is connected to the node 7 .

The external control circuit is connected to the node 7. Specifically, the external control circuit includes a PNP transistor T4, the emitter E of the transistor T4 is connected to the node 7, the collector C is connected to the common ground, and the base is connected to the common ground. B is divided into two paths, one is connected to the node 7 through the resistor R5, and the other is connected to the external signal control terminal (node 12) through the diode D6.

The constant current control circuit includes an NPN transistor T2, the base B of the transistor T2 is connected to the node 10, the collector C is connected to the node 7, and the emitter E is connected to the common ground.

The voltage detection circuit includes a resistor R3, a resistor R4 and an NPN transistor T3. After the resistor R3 and the resistor R4 are connected in series, one end is connected to the node 6, and the other end is connected to the common ground, wherein the contact of the resistor R3 and the resistor R4 is named is node 11; the base B of the transistor T3 is connected to the node 11, the collector C is connected to the node 7 through the resistor R6, and the emitter E is connected to the common ground.

A temperature compensation circuit is connected between the node 7 and the common ground.

1. Constant current control part

It is realized by the working loop and the constant current control circuit. The mains (220VAC) is connected to the AC input terminals 1 and 2 of the rectifier bridge respectively. After rectification, a peak value is output at the DC voltage output terminals 3 and 4 of the rectifier bridge as the input AC voltage. 1.414 times the DC pulsating voltage, if the input voltage is AC220 V, the peak voltage of the output terminals 3 and 4 is DC311.08V, and the working current loop of the LED load is formed by the FET T1 and the resistor R2. The working current of the LED load is controlled by the FET T1, and the working state of the FET T1 is controlled by the constant current control circuit composed of the transistor T2, the resistor R1 and the resistor R2, and the resistor R1 is the FET T1. The gate G provides a working voltage. The level of this voltage directly affects the output current of the FET T1. Therefore, effectively controlling this level also directly controls the current of the LED load. The resistor R2 is used to detect the LED load current. When the current passes through the resistor R2, a voltage will be generated at both ends of the resistor R2. The magnitude of this voltage is related to the resistance value of the resistor R2 and the current I through the resistor R2. Its calculation formula is: V=I·R, this voltage is sampled and amplified by the triode T2, and the working state of the gate G of the field effect transistor T1 is controlled through the collector C of the triode T2. It is assumed that the working current of the LED load is set to 100mA, and The magnifying area window of the transistor T2 is between 0.5-0.6V, and the sampling voltage is set at 0.5V. Then, according to the principle of V=I·R, the resistance value of the resistor R2 is calculated to be 5 ohms. Therefore, when the LED load is When the current is greater than the set value, the sampling voltage will increase proportionally. Due to the amplification effect of the triode T2, the potential of the collector C is pulled down, which directly controls the working voltage of the gate G of the field effect transistor T1, so that the field The output current of the effect transistor T1 decreases; when the current of the LED load is less than the set value, the sampling voltage will decrease proportionally. The output current of the effect transistor T1 increases, so the current of the LED load is locked at the set value.

2. Voltage detection control part

It is realized by the voltage detection circuit. During operation, there is a certain voltage difference between the DC output voltage of the rectifier circuit and the voltage of the LED load. This voltage difference is borne by the field effect transistor T1 and the resistor R2, and the voltage difference signal is also directly reflected in the Between the resistor R3 and the resistor R4, after being divided by the resistor R3 and the resistor R4, it is fed to the base B of the transistor T3 through the node 11. After being amplified by the transistor T3, it is fed to the gate G of the field effect transistor T1 through the resistor R6 (node 7).

Under normal circumstances, when the power supply voltage (AC input voltage) changes, the voltage difference also changes at the same time. Under the normal state of the power supply voltage, the transistor T3 remains at the lower limit of the initial working area, and the potential of the collector C remains Within an appropriate range, the FET T1 supplies the LED load with a normal current.

When the supply voltage is lower than the normal value, the potential of the node 11 drops, the transistor T3 is turned off, and the potential of the collector C rises, which compensates the voltage of the gate G of the field effect transistor T1 to a certain extent. In this way, the power supply voltage fluctuates downward at a certain level. The FET T1 can still maintain a stable current output within the range.

If the power supply voltage fluctuates upwards and exceeds the normal value, the potential of node 11 also rises. Due to the amplification effect of transistor T3, the potential of collector C of transistor T3 decreases accordingly, and the potential of node 7 is pulled down through resistor R6. , which reduces the output current of the field effect transistor T1, effectively suppresses the rise of reactive power caused by the rising input voltage, and greatly reduces the temperature of the field effect transistor T1 due to reactive power consumption.

In addition, since resistor R3 and resistor R4 form a voltage divider detection circuit, resistor R3 can also be skipped at node 6 and directly connected to node 5 (equivalent to the 4th terminal of the rectifier bridge), and its working principle is the same.

3. Soft start control part

Realized by the soft-start circuit, adjust the resistance value of resistor R7 and resistor R8 to change the voltage divider ratio of the two, so that when the circuit is working normally, the base potential of the transistor T5 is high level, the transistor T5 is in the off state, and the power is turned on. When the working voltage of the field effect transistor T1 is provided by the resistor R1, the capacitor C1 is first charged by the diode D5. At the moment when the power is just turned on, the internal resistance of the two ends of the capacitor C1 is very small, and the instantaneous voltage across the two ends is approximately 0V , the voltage of the gate G of the field effect transistor T1 is pulled down and is in an off state. As the charging time increases, the voltage across the capacitor C1 rises slowly. After reaching the threshold, the FET T1 enters the working state, the output current of its drain D also rises slowly, and the current of the LED load also starts from 0. Slowly rising until the set current value, the soft-start process is completed. When the power is off, the transistor T5 is grounded through the resistor R7 due to the disappearance of the voltage at the node 4, and the transistor T5 is quickly saturated and turned on, which can be quickly turned on in a very short time. The electric energy on the capacitor C1 is released to restore the initial state when the power is turned on again in a short time, and the soft-start function of the product will not be affected when the power is turned on immediately after a power failure, which effectively solves the problem of slow discharge speed of the resistor. The function of the diode D5 is to isolate the voltage across the capacitor C1 in one direction, so as to prevent the voltage of the capacitor C1 (node 8) from flowing backward to the node 7 after the soft start is completed, resulting in a hysteresis of the response of the FET T1.

4. Temperature compensation part

It is realized by temperature compensation circuit. Transistors all have temperature-sensitive characteristics, especially small-signal transistors. In this embodiment, the transistors T2 and T3 are responsible for the current regulation of the field effect transistor T1 on the one hand, and are also a temperature sensor with good performance on the other hand. , when the operating temperature exceeds 80 degrees Celsius, the internal resistance of the transistor T2 and the transistor T3 will decrease as the temperature rises, thereby pulling down the potential of node 7, which directly reduces the output current of the field effect transistor T1, reaching For the function of temperature compensation, a temperature-sensitive element or circuit, such as a thermistor, can also be connected between node 7 and the common ground.

5. External control circuit part

In today's highly developed technology, lighting fixtures are also developing rapidly in the direction of intelligence and wireless IoT. Therefore, it is particularly necessary to provide LED drivers with intelligent interfaces.

Usually, when the external signal control terminal (node 12) is vacant, the transistor T4 is in an off state, and the operation of the entire power supply system is almost independent of it. In this embodiment, the external signal control terminal can accept a voltage amplitude of 0-5.5V, For a PWM signal with a duty cycle of 0-100%, when the PWM signal is connected, the transistor T4 works in the switching state. When the PWM signal is at a low level, the transistor T4 is turned on, pulling down the level of node 7 of the internal circuit. , forcing the FET T1 to turn off, when the PWM signal is at a high level, the transistor T4 is turned off, and the FET T1 resumes work, so that the working state of the FET T1 is consistent with the input PWM signal.

In addition, the external signal control terminal (node 12) is also compatible with 0-5.5V external voltage source input control. In some places, it is necessary to use an external voltage to control the brightness of the LED load. This interface is still suitable. In this case , the transistor T4 is in the working area of linear amplification, when its base B potential is 5V, the transistor T4 is completely cut off, plus the forward voltage drop of the diode D6 is about 0.5V, its input effective control level is up to 5.5V, when the input When the level is 0V, the transistor T4 is fully saturated and turned on. When the input voltage changes between 0-5.5V, the conduction depth of the transistor T4 changes with the change of the voltage, which also controls the output of the field effect transistor T1. The current changes accordingly.

The external signal control terminal (node 12) can also be compatible with a variety of sensor access. There are many types and specifications of commonly used sensors, such as infrared, ultrasonic, radar, photoelectric, voice control, etc. Among them, the sensor module is divided into active There are two types of output and passive output. The sensor module with active output provides a DC voltage at its output and switches between high and low levels when the sensor operates. Its voltage output has various specifications, and the common ones are 6V, 12V, and 24V. Wait. Sensors of passive output type generally provide a set of relay switch contacts, which are opened or closed when the sensor acts. The above types of sensors are suitable to be connected to this circuit. The function of the diode D6 is to isolate the voltage of various types of sensors to avoid the influence of different voltages on the circuit.

At present, commonly used transistors include NPN-type transistors, PNP-type transistors, N-type field effect transistors, and P-type field effect transistors. Professional technicians can select corresponding components according to their needs, and change the corresponding wiring method according to the type of components. , in some cases, different types of devices can be used, and their circuit working principles and functions are the same.

The driving circuit of the utility model can be equivalent to a two-terminal constant current module, and no additional working power supply is required during operation, so the pressure difference can be made very small, and the concept of low pressure difference of linear drive is realized. In addition, since the LED load and the driving circuit of the present invention are in a series relationship, the LED load can be connected in series to the positive terminal of the DC power supply or to the negative terminal of the DC power supply. When necessary, a plurality of the driving circuits of the present invention can also be used in series, so as to improve the power consumption carrying capacity of the circuits.

The utility model adopts an extremely simple circuit design, solves the relatively complex technical problems, improves the comprehensive performance of the driver and greatly reduces the cost, and can be made into a dedicated integrated LED driver chip, which not only simplifies the layout design, but also makes the integrated circuit The cost is greatly reduced, but the function and performance have reached a level that can only be completed by very complex circuit design. Based on the principle of the invention, the technical personnel in the professional field can make some adaptive modifications without departing from the purpose of the invention. The direct replacement or equivalent change of electronic components or circuits made under the premise of the present invention still falls within the scope of the present invention.

Claims (7)

1. An LED linear constant current driver, comprising a working loop and a soft-start circuit, the working loop includes a field effect transistor T1, the drain D of the field effect transistor T1 is connected in series with the LED load and then connected to the positive pole of the DC power supply, so the The junction between the drain D of the FET T1 and the LED load is named node 6; the source S of the FET T1 is connected to the common ground through the resistor R2, the gate G is connected to the node 6 through the resistor R1, and the The contact between the resistor R1 and the gate G of the field effect transistor T1 is named node 7, and the contact between the resistor R2 and the source S of the field effect transistor T1 is named node 10; the soft-start circuit includes a charge and discharge loop, The charging and discharging loop is connected to the contact 7 through a one-way isolation circuit; it is characterized in that the charging and discharging loop includes a resistor R7, a resistor R8, a PNP transistor T5 and a capacitor C1; the resistor R7 and the resistor R8 are connected in series and then connected at one end The positive pole of the DC power supply, the other end is connected to the common ground, the emitter E of the transistor T5 is connected to one end of the capacitor C1 and then connected to the one-way isolation circuit, and the base B of the transistor T5 is connected to the The junction of the resistor R7 and the resistor R8, the collector C is connected to the common ground, the other end of the capacitor C1 is connected to the common ground, and the junction between the emitter E of the transistor T5 and the capacitor C1 is named node 8 . 2 . The LED linear constant current driver according to claim 1 , wherein the unidirectional isolation circuit comprises a diode D5 , the cathode of the diode D5 is connected to the node 8 , and the anode is connected to the node 7 . 3 . 3 . The LED linear constant current driver according to claim 1 , wherein the driving circuit further comprises an external control circuit, and the external control circuit is connected to the node 7 . 4 . 4. The LED linear constant current driver according to claim 3, wherein the external control circuit comprises a PNP type triode T4, the emitter E of the triode T4 is connected to the node 7, and the collector C is connected to the common ground, The base B is divided into two paths, one is connected to the node 7 through the resistor R5, and the other is connected to the external signal control terminal through the diode D6. 5. The LED linear constant current driver according to claim 1, characterized in that the drive circuit further comprises a constant current control circuit, the constant current control circuit comprises an NPN type triode T2, and the base B of the triode T2 is connected to For the node 10, the collector C is connected to the node 7, and the emitter E is connected to the common ground. 6. The LED linear constant current driver according to claim 1, characterized in that the driving circuit further comprises a voltage detection circuit, the voltage detection circuit comprises a resistor R3, a resistor R4 and an NPN transistor T3, the resistor R3 and the resistor After R4 is connected in series, one end is connected to the node 6, and the other end is connected to the common ground, wherein the junction of the resistor R3 and the resistor R4 is named node 11; the base B of the triode T3 is connected to the node 11, and the collector C passes through the resistor R6 is connected to the node 7, and the emitter E is connected to the common ground. 7 . The LED linear constant current driver according to claim 1 , wherein a temperature compensation circuit is connected between the node 7 and the common ground. 8 .