TW200805218A - Drive circuit of light-emitting diode - Google Patents

Abstract

The present invention relates to a drive circuit of light-emitting diode (LED). The drive circuit includes a resistor connected with the LED. One end of the resistor is connected with the positive end of the LED. The drive circuit also includes a field-effect transistor (FET) and a pulse width modulation (PWM) circuit. The source electrode of the FET is connected with the other end of the resistor. The gate electrode of the FET is connected with the output end of the PWM circuit. The PWM circuit modulates the voltage of the resistor with a PWM form to control the gate electrode of the FET. The drive circuit can adjust the current through the LED.

Description

200805218 IX. Description of the Invention: [Technical Field] The present invention relates to a light-emitting diode (LED) driving circuit, and more particularly to a driving circuit capable of adjusting current through an LED. [Prior Art]

In general, the driving circuit of the LED directly drives the LED by means of a voltage source series current limiting resistor. Since the LED is driven in a forward bias mode, the voltage across it changes with current. When the voltage source is linearly sized, the change in drive current affects the voltage across the LED, causing the drive current to vary nonlinearly with voltage. When the voltage changes too much, the direction

The voltage is too large, so that the current through the LED is too large, eventually leading to LED damage. SUMMARY OF THE INVENTION In view of the above, it is necessary to provide an LED driving circuit capable of providing a constant average current. A light-emitting diode driving circuit includes a resistor for stringing with a light-emitting diode, one end of the resistor is connected to a forward end of the light-emitting diode, and the driving circuit further includes a field money tube and a pulse width modulation circuit The other end of the field effect resistance is connected. The gate of the field effect transistor is connected to the pulse pressure input-r~ wheel output terminal. The pulse width modulation circuit modulates the Ding pulse at both ends of the resistor to control the FET. Gate. Wide adjustment: The gate of the FET is controlled in a manner that allows the voltage across the resistor to be modulated at both ends of the prior art. When the voltage of the electric (4) changes, the comparison circuit outputs the pulse of the different duty cycle, the 200805218 signal, thereby adjusting the current through the LED. [Embodiment]

And FET 6. The illumination 1G provided by the embodiment of the resistor R includes an electric connection connected in series and an amplifying circuit i connected in series, a differential ', a mineral tooth wave generating circuit 4, and a comparison circuit 5 connected to the forward end of the LED of the LED The other end is connected to the source of the FET 6. The amplifying circuit 1 is an integrated operational amplifier, and two input terminals of the amplifying circuit 1 are respectively connected to both ends of the resistor R to amplify the voltage of the resistor terminal. The output terminal of the amplifying circuit 1 is connected to one input terminal of the differential amplifying circuit 2, a first reference signal Vref1 is connected to the other input of the differential amplifying circuit 2, and the differential amplifying circuit 2 differentially amplifies the voltage output from the amplifying circuit 1 with yrefi The integration circuit 3 is input afterwards. The differentially amplified voltage is integrated into the integrating circuit 3, and then input to the sawtooth wave generating circuit 4, and the integrated signal output from the integrating circuit 3 is used as a control signal of the sawtooth wave generating circuit 4. The sawtooth wave generating circuit 4 is a voltage control type circuit. The sawtooth wave output from the sawtooth wave generating circuit 4 is input to the comparison circuit 5 together with a second reference signal Vref2. Vref2 is a voltage signal with a constant voltage. When the sawtooth wave generating circuit 4 outputs a different sawtooth wave, the comparison signal 6 200805218 channel 5 outputs a pulse signal with a different duty ratio. The pulse signal output from the comparison circuit 5 is input to the gate of the FET 6, to control the operation of the FET 6, and the FET 6 controls the amount of current passing through the illuminating diode LED. The field effect transistor 6 is a PNP type field effect transistor. When the voltage across the resistor R increases, the current through the LED increases, and the ore wave generating circuit 4 outputs a mineral tooth wave having an increased period, thereby causing the comparison circuit 5 to generate The pulse signal with increased duty cycle controls the PNP type field effect transistor 7, _, thereby reducing the current through the LED to achieve the purpose of adjusting the current. Referring to FIG. 2, it is a driving circuit 20 for a light emitting diode according to a second embodiment of the present invention. The drive circuit 2 includes a resistor R connected in series, a light emitting diode LED, and an amplifying circuit 丨, a differential amplifying circuit 2, a sawtooth wave generating circuit 7, a comparing circuit 5, and a field effect transistor 8. - One end of the resistor R is connected to the forward end of the LED of the light-emitting diode, and the other end is connected to the source of the field effect transistor 8. The amplifying circuit 1 is an integrated operational amplifier, and two input terminals of the amplifying circuit 1 are respectively connected to both ends of the resistor R to amplify the voltage across the resistor R. The output end of the amplifying circuit 1 is connected to one input end of the differential amplifying circuit 2, a reference signal Vref1 is connected to the other input end of the differential amplifying circuit 2, and the differential amplifying circuit 2 differentially amplifies the voltage outputted by the amplifying circuit 1 and Vref]L. The comparison circuit 5 is input. The comparison circuit 5 pulse-width modulates the voltage output from the differential amplifier circuit 2 and the sawtooth wave signal output from the sawtooth wave generating circuit 7, and the comparison circuit 5 outputs a 7200805218 pulse width modulation signal to the gate of the FET 8 to control the field. In the operation of the effect tube 8, the field effect transistor 8 can control the magnitude of the current through the LED. The field effect transistor 8 is an NPN type field effect transistor. When the voltage across the resistor R increases, the current through the LED increases, and the differential amplifier circuit 4 outputs a voltage signal having an increased amplitude, thereby causing the comparator circuit 5 to generate a pulse signal with a reduced duty ratio to control the NPN type field effect transistor. 8, so that the current through the LED is reduced to achieve the purpose of adjusting the current.

In summary, the present invention complies with the requirements of the invention patent and submits a patent application according to law. However, the above description is only a preferred embodiment of the present invention, and the present invention is not limited to the above-mentioned materials, and equivalent modifications or changes made by those skilled in the art of the present invention in accordance with the spirit of the present invention. All should be covered by the following patent application. [Simple diagram]

1 is a schematic view showing a driving circuit of a first embodiment of the present invention. 2 is a schematic diagram of a driving circuit of a second embodiment of the present invention. [Description of main component symbols] Amplifier circuit Integral circuit Comparison circuit Drive circuit 1 Differential amplifier circuit 3 Mine tooth wave generation circuit 5 Field effect transistor 10, 20 2 4, Ί 6 - 8 8

Claims (1)

200805218 X. Patent application scope: 1. A kind of light-emitting diode driving circuit, which comprises a resistor for connecting with a light-emitting diode, one end of which is connected to the positive end of the light-emitting diode, and the improvement is in the driving The circuit further includes a field effect transistor and a pulse width modulation circuit, wherein the source of the field 1 tube is connected to the other end of the resistor, and the second pulse of the field effect transistor is connected to the output end of the circuit, and the pulse width modulation The circuit modulates the voltage of the two resistors to control the illuminating diode of the field effect transistor. The illuminating diode driving circuit according to claim 1, wherein the pulse width modulating circuit comprises an amplifying circuit connected in series And an integrating circuit, a mineral tooth wave generating circuit and a comparing circuit, wherein the input ends of the amplifying circuit are respectively connected at two ends of the resistor. The output end of the sawtooth wave generating circuit is connected to one input end of the comparing circuit, and the other input end of the comparing circuit The light-emitting diode driving circuit of the second aspect of the invention, wherein the pulse width modulation circuit further comprises a differential amplification circuit, the differential The large circuit performs a differential operation on the voltage of the amplifying circuit and then inputs the integrating circuit. 4. The light-emitting diode driving circuit according to claim 2, wherein the voltage value of the reference voltage is constant. The illuminating diode driving circuit according to the second aspect of the invention, wherein the FET is a PNP type field effect transistor. The illuminating diode driving circuit according to claim 2, wherein the amplifying circuit The illuminating diode driving circuit of the first aspect of the invention, wherein the pulsing modulating circuit comprises an amplifying circuit, a spur wave generating circuit and a comparison electric power 200805218, the input of the amplifying circuit The terminals are respectively connected at two ends of the resistor, the output end of the amplifying circuit is connected to one input end of the comparison circuit, and the other input end of the comparison circuit is connected to the output end of the sawtooth wave generating circuit. The light emitting diode driving circuit, wherein the pulse width modulation circuit further comprises a differential amplifying circuit, and the voltage of the differential amplifying circuit outputting the amplifying circuit The differential circuit is input to the comparison circuit. The light-emitting diode driving circuit according to the seventh aspect of the invention, wherein the field effect transistor is an NPN type field effect transistor. 10. As described in claim 7 The LED driving circuit, wherein the amplifying circuit is an integrated operational amplifier.