CN2631184Y - LED drive circuit - Google Patents

Abstract

The utility model provides a luminescent diode driving circuit, the characteristics are that: the utility model comprises resistances (R1)-(R8), dynatrons (Q1)-(Q3), a calculation amplifier (A) and a luminescence diode (LED), in which the other end of the resistance (R1) is connected with the I/O interface of the single chip (CPU), the emitter of the dynatrons (Q3) is connected with the driving voltage (Vcc), in which the resistances (R4), (R5), (R6), (R7), (R8) use precise resistance with the same temperature coefficient. The utility model can be applied in physical optic instrument with the luminescent diode as the light source, such as used to determine the concentration and refraction ratio of the solutions of hand hold refraction instrument, and has the advantages of low cost, stable light source and automatic opening and closing.

Description

LED driver circuit

technical field

The utility model relates to a light source drive circuit, in particular to a light emitting diode drive circuit.

Background technique

Physical optical instruments using light-emitting diodes (LEDs) as light sources, such as hand-held refractometers for measuring solution concentration and refractive index, require very stable light sources, that is, require very stable driving currents for LEDs, and in some cases require The light source can be switched on and off automatically. However, in a common LED driving circuit, as shown in FIG. 1 , the LED and the resistor R are connected in series in the circuit of the power supply Vcc to make the LED emit light. Or connect a triode Q in series in the circuit as shown in Figure 2, and its base is connected with the I/O interface of the single-chip CPU to control the conduction or cut-off of the triode Q, even if the series circuit is turned on or off, thereby controlling LED automatic switch. None of these circuits can achieve the stability of the LED light source. Although there are integrated circuit devices specially designed for driving LEDs on the market, the cost is relatively high.

Contents of the invention

In order to solve the technical problem of unstable LED light source, the utility model provides a light emitting diode driving circuit with stable light source.

According to the above purpose, the utility model provides a light-emitting diode driving circuit, which is characterized in that it is composed of resistors R1-R8, transistors Q1-Q3, operational amplifier A and light-emitting diode LED; wherein resistor R2 is connected to the base of transistor Q2, and the resistor R3 is connected to the emitter of transistor Q2, and the other end of resistors R2 and R3 are connected to the collector of transistor Q1; the anode of light-emitting diode LED is connected to the collector of transistor Q2 and resistor R5, and the other end of resistor R5 is in phase with resistor R4 and operational amplifier A The input terminal (+) is connected, and the negative pole of the light-emitting diode LED is connected to the collector of the transistor Q3; the inverting input terminal (-) of the operational amplifier A is connected to the emitter of the transistor Q3 and the resistor R8 through the resistor R7, and the output terminal of the operational amplifier A is connected to the transistor Q3 via the resistor R7. Resistor R6 is connected to the base of triode Q3; wherein, the emitter of triode Q1, and the other end of resistors R4 and R8 are grounded; wherein, the other end of resistor R1 is connected to the I/O interface of the single-chip CPU, and the emitter of triode Q2 is connected to the driving voltage Vcc connect.

In the above device, the resistors R4, R5, R6, R7 and R8 are precision resistors with the same temperature coefficient.

Due to the adoption of the above technical measures, the utility model has the advantages of low cost, stable light source and automatic switch compared with the common LED driving circuit.

Description of drawings

Figure 1 is a common LED drive circuit diagram.

Figure 2 is a circuit diagram of an LED driver with switch control.

Fig. 3 is a circuit diagram of the utility model.

Detailed ways

As shown in Figure 3: the utility model is actually a V-I conversion circuit, which converts a fixed voltage V into a corresponding current I.

Q1 and Q2 are switching transistors, and Q3 is a follower that amplifies the current. R1 and R2 are current limiting resistors, R3 is the pull-up resistor of transistor Q1, R4 and R5 form a voltage divider network to provide a suitable voltage Vp for the non-inverting input terminal (+ terminal) of operational amplifier A, and R6 is a current limiting resistor. R7 implements negative feedback, R8 implements V-I conversion, and the magnitude of the current flowing on R8 is equal to the magnitude of the driving current I of the light-emitting diode LED. In order to ensure the stability of the LED driving current, R4, R5, R6, R7, and R8 must all be precision resistors with the same temperature coefficient.

The CPU is the I/O port of the single-chip microcomputer, and controls the switch of the LED. When the output of the I/O port of the CPU is low level, Q1 and Q2 are in the cut-off state, the light-emitting diode LED has no driving current, the LED does not emit light, and is in the off state. When the output of the I/O port of the CPU is high level, Q1 and Q2 are in a saturated conduction state, and the voltage appearing at the anode of the light-emitting diode LED is about Vcc. According to the principle of "virtual short" and "virtual break" of the operational amplifier under the condition of deep negative feedback:

Vp＝Vcc×R4÷(R4+R5)

Vn=Vp Because the current at the input terminal of the operational amplifier is very small, it is about zero, therefore, Vn≈Vr8. The current flowing through R8 is actually equal to the driving current I of the light-emitting diode LED. therefore,

I＝Vcc×R4÷(R4+R5)÷R8; carefully select the resistance values of R4, R5 and R8 to obtain a suitable LED drive current.

Claims (2)

1. A light-emitting diode drive circuit, characterized in that it is composed of resistors (R1)-(R8), triodes (Q1)-(Q3), operational amplifier (A) and light-emitting diodes (LED); wherein the resistor (R2) It is connected to the base of the triode (Q2), the resistor (R3) is connected to the emitter of the triode (Q2), and the other end of the resistors (R2) and (R3) are connected to the collector of the triode (Q1); among them, the anode of the light-emitting diode (LED) Connect with transistor (Q2) collector, resistor (R5), the other end of resistor (R5) is connected with resistor (R4), operational amplifier (A) in-phase input (+), light-emitting diode (LED) negative pole and transistor (Q3) Collector connection; the inverting input terminal (-) of the operational amplifier (A) is connected to the emitter of the triode (Q3) and the resistor (R8) through the resistor (R7), and the output terminal of the operational amplifier (A) is connected to the resistor (R6) Connect with the base of the triode (Q3); among them, the emitter of the triode (Q1), the other end of the resistors (R4) and (R8) are grounded; among them, the other end of the resistor (R1) is connected to the I/O interface of the microcontroller (CPU) , the emitter of the triode (Q2) is connected to the driving voltage (Vcc). 2. The LED driving circuit according to claim 1, wherein the resistors (R4), (R5), (R6), (R7), and (R8) are precision resistors with the same temperature coefficient.

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