TWI686102B - Driving circuit of light-emitting diode - Google Patents

Abstract

A driving circuit of a light-emitting diode includes a chip, a bridge rectifier, a first diode, a second diode, and a first capacitor. The light-emitting diode includes an anode and a cathode, and the cathode of the light-emitting diode is grounded. The chip has a first input pin, a second input pin and an output pin. The output pin is coupled to the anode of the light emitting diode through a resistor. The bridge rectifier is connected to the AC voltage source and has a grounding terminal and a current output terminal. The current output terminal is connected to the first input pin of the chip. The cathode of the first diode is connected to the second input pin of the chip. The cathode of the second diode is connected to the anode of the first diode, and the anode of the second transistor is grounded. The cathode terminal of the first capacitor is connected to the anode of the first diode. The anode terminal of the first capacitor is connected to the current output terminal of the bridge rectifier.

Description

Driving circuit of light-emitting diode

The present invention relates to a light-emitting diode driving circuit, and particularly to a light-emitting diode driving circuit that can reduce the occurrence of flicker.

Generally speaking, in order to reduce the consumption of energy, the process of transmission of commercial power from the power plant to the messenger side will be transmitted by AC. Taiwan’s commercial power is 60Hz AC. When the backlight of the LED screen uses commercial power as the power source, the human eye Will receive a flickering visual sense due to the backlight flickering, causing flickering.

In order to reduce the occurrence of the flash screen phenomenon that is easily noticeable by human eyes, it is necessary to invent a light-emitting diode drive circuit that can reduce the flash screen.

In one embodiment of the driving circuit of the light emitting diode of the present invention, the driving circuit includes a chip, a bridge rectifier, a first diode, a second diode, and a first capacitor. The light-emitting diode includes an anode and a cathode, and the cathode of the light-emitting diode is grounded. The chip has a first input pin, a second input pin and an output pin. The output pin is coupled to the anode of the light emitting diode through a resistor. The bridge rectifier is connected to the AC voltage source and has a grounding terminal and a current output terminal. The current output terminal is connected to the first input pin of the chip. The cathode of the first diode is connected to the second input pin of the chip. The cathode of the second diode is connected to the anode of the first diode, and the anode of the second diode is grounded. The cathode terminal of the first capacitor is connected to the anode of the first diode, and the anode terminal of the first capacitor is connected to the current output terminal of the bridge rectifier.

In one embodiment, when the driving circuit operates in the first mode, the driving current of the driving circuit flows from the current output end of the bridge rectifier to the first input pin of the chip, and then flows from the output pin of the chip to the light emitting Diode.

In one embodiment, when the input voltage generated by the AC voltage source is higher than the forward bias of the light emitting diode but lower than the sum of the forward bias of the light emitting diode and the crossover voltage of the first capacitor, the driving The circuit operates in the first mode.

In one embodiment, when the driving circuit operates in the second mode, the driving current of the driving circuit flows from the current output end of the bridge rectifier to the second input pin of the chip, and then flows from the output pin of the chip to the light emitting Diode.

In one embodiment, when the input voltage generated by the AC voltage source is higher than the sum of the forward bias of the light emitting diode and the crossover voltage of the first capacitor, the driving circuit operates in the second mode.

In one embodiment, when the driving circuit operates in the third mode, the driving current of the driving circuit flows from the first capacitor to the first input pin of the chip, and then from the output pin of the chip to the light emitting diode.

In one embodiment, when the voltage across the first capacitor is higher than the input voltage generated by the AC voltage source and higher than the forward bias of the light emitting diode, the driving circuit operates in the third mode.

In one embodiment, the chip includes a first operational amplifier, a first transistor, a second operational amplifier, and a second transistor. The non-inverting input terminal of the first operational amplifier is connected to the reference voltage. The drain of the first transistor is connected to the first input pin of the chip, the gate of the first transistor is connected to the output of the first operational amplifier, and the source of the first transistor is connected to the output pin of the chip The negative input terminal of the first operational amplifier. The non-inverting input terminal of the second operational amplifier is also connected to the reference voltage. The drain of the second transistor is connected to the second input pin of the chip, and the gate of the second transistor is connected to the second The output terminal of the operational amplifier, and the source electrode of the second transistor is connected to the output pin of the chip and the negative phase input terminal of the second operational amplifier.

In one embodiment, the chip further has a third input pin, and the driving circuit further includes a second capacitor, which is coupled between the anode of the light emitting diode and the third input pin of the chip.

In one embodiment, the third input pin of the chip is connected to the first operational amplifier and the second operational amplifier to provide the operating voltage to the first operational amplifier and the second operational amplifier.

When the driving circuit of the present invention switches between the first mode, the second mode and the third mode, since the current continues to drive the light-emitting diode, the light-emitting diode can always maintain the light-emitting state, so it does not occur Splash screen phenomenon.

1‧‧‧Drive circuit

2‧‧‧ LED

A1, A2‧‧‧Operational amplifier

AC‧‧‧AC voltage source

C1‧‧‧ First capacitor

C2‧‧‧Second capacitor

D1, D2‧‧‧ diode

DS1, DS2, LV, RS‧‧‧pin

I‧‧‧Drive current

IC‧‧‧chip

M1, M2‧‧‧Transistor

RE‧‧‧Bridge Rectifier

R‧‧‧Resistance

Vref1, Vref2 ‧‧‧ reference voltage

[FIG. 1] is a circuit diagram of an embodiment of a driving circuit of a light-emitting diode of the present invention; [FIG. 2] is a circuit diagram of an embodiment of a chip IC of FIG. 1. [FIG. 3] is a light-emitting diode of the present invention. Schematic diagram of the driving circuit operating in the first mode; [FIG. 4] is a schematic diagram of the driving circuit of the light emitting diode of the present invention when operating in the second mode; [FIG. 5] is a driving circuit of the light emitting diode of the present invention. Schematic diagram when operating in the third mode.

The driving circuit of the light-emitting diode of the present invention can continuously provide the drive current to the light-emitting diode, so that the light-emitting diode is always in the state of conducting light, so that there will be no screen flashing.

In order to fully understand the purpose, features and effects of the present invention, the following specific examples and the accompanying drawings are used to make a detailed description of the present invention, as follows:

Please refer to FIG. 1, which is a circuit diagram of an embodiment of a driving circuit of a light emitting diode of the present invention. The driving circuit 1 is used to provide the driving current I of the light-emitting diode 2 so that the light-emitting diode 2 can conduct light. As can be seen from FIG. 1, the driving circuit 1 includes a chip IC, a bridge rectifier RE, a first diode D1, a second diode D2, a coupling second capacitor C2 and a first capacitor C1. In a preferred embodiment, the first capacitor C1 may be an electrolytic capacitor. The chip IC has a first pin DS1, a second pin DS2, a third pin LV, and a fourth pin RS. The anode of the light-emitting diode 2 is coupled to the fourth pin RS of the chip IC through the resistor R, and the cathode of the light-emitting diode 2 is connected to the ground.

The bridge rectifier bridge RE has a current output terminal, a ground terminal and two voltage input terminals. The AC voltage source AC is bridged between the two voltage input terminals of the bridge rectifier bridge RE, so that the AC voltage source AC generates the same polarity output at the current output terminal of the bridge rectifier RE after full-wave rectification of the bridge rectifier RE. The current output terminal of the bridge rectifier RE is connected to the first pin DS1 of the chip IC, so that the driving current I output through the bridge rectifier RE can flow into the chip IC through the first pin DS1, and the ground terminal of the bridge rectifier bridge RE Connected to the ground.

The cathode of the first diode D1 is connected to the second pin DS2 of the chip IC, and the anode of the first diode D1 is connected to one end of the first capacitor C1. The other end of the first capacitor C1 is connected to the first pin DS1 of the chip 1. The cathode of the second diode D2 is connected to the anode of the first diode D1, and the anode of the second transistor D2 is connected to the ground. The third pin LV of the chip IC is connected to one end of the second capacitor C2, and the other end of the second capacitor C2 is connected to the anode of the light emitting diode 2.

Please refer to FIG. 2, which is a circuit diagram of an embodiment of the chip IC in FIG. 1. As can be seen from FIG. 2, the chip IC includes a first operational amplifier A1, a first transistor M1, a second operational amplifier A2, and a second transistor M2. In this embodiment, the non-inverting input terminal of the first operational amplifier A1 is connected to the reference voltage Vref1, and the non-inverting input terminal of the second operational amplifier A2 is connected to the reference voltage Vref2. First transistor The body M1 is used to direct the driving current I from the first pin DS1 of the chip IC to the fourth pin RS of the chip IC, so the drain of the first transistor M1 is connected to the first pin DS1 of the chip IC, The source of the first transistor M1 is connected to the fourth pin RS of the chip IC, and the gate of the first transistor M1 is connected to the output of the first operational amplifier A1. When the voltage at the output of the first operational amplifier A1 is high When the threshold voltage of the first transistor M1 is reached, the first transistor M1 is turned on to conduct the driving current I from the first pin DS1 of the chip IC to the fourth pin RS of the chip IC. In addition, the source of the first transistor M1 is also negatively connected to the negative input terminal of the first operational amplifier A1.

Similarly, the second transistor M2 is used to direct the driving current I from the second pin DS2 of the chip IC to the fourth pin RS of the chip IC, so the drain of the second transistor M2 is connected to the chip IC The second pin DS2, the source of the second transistor M2 is connected to the fourth pin RS of the chip IC, the gate of the second transistor M2 is connected to the output terminal of the second operational amplifier A2, when the second operational amplifier When the voltage at the output terminal of A2 is higher than the threshold voltage of the second transistor M2, the second transistor M2 will conduct the driving current I from the second pin DS2 of the chip IC to the fourth pin RS of the chip IC. In addition, the source of the second transistor M2 is also negatively connected to the negative input terminal of the second operational amplifier A2.

The first operational amplifier A1 and the second operational amplifier A2 are additionally connected to the third pin LV of the chip IC, and the operating voltage is provided to the first operational amplifier A1 and the second operational amplifier A2 by the voltage across the second capacitor C2.

Please refer to FIG. 3, which is a schematic diagram of the driving circuit of the light emitting diode of the present invention when operating in the first mode. As can be seen from FIG. 3, when the AC voltage source AC undergoes full-wave rectification by the bridge rectifier bridge RE, the input voltage (that is, the voltage at the current output end of the bridge rectifier RE) gradually increases and begins to be greater than that of the light-emitting diode 2. When the forward bias voltage and the crossover voltage of the first capacitor C1 are used, the driving circuit 1 operates in the first mode. At this time, since the input voltage is greater than the forward bias voltage of the light-emitting diode 2, the light-emitting diode 2 is caused. When the light is turned on, the driving current I will flow into the first pin DS1 of the chip IC. When the driving circuit 1 operates in the first mode, the path of the driving current I is shown by the arrow in FIG. 3.

Please refer to FIG. 4, which is a schematic diagram of the driving circuit of the light emitting diode of the present invention when operating in the second mode. When the input voltage continues to increase, when it is greater than the sum of the voltage across the light-emitting diode 2 and the first capacitor C1, the driving circuit 1 will change from operating in the first mode to operating in the second mode, due to the input The voltage continues to increase, but the voltage across the first capacitor C1 begins to remain unchanged due to the conduction of the first diode C1, and the input voltage will be greater than the forward bias of the light-emitting diode 2 and the voltage across the first capacitor C1 The sum of the cross pressure. When the driving circuit 1 is switched to operate in the second mode, the first diode C1 is turned on, so that the driving current I flows into the second pin DS2 of the chip IC. At this time, the input voltage should be higher than the sum of the forward bias of the light-emitting diode 2 and the crossover voltage of the first capacitor C1, and because the input voltage is still higher than the light-emitting diode after the voltage drop of the first capacitor C1 The forward bias of 2 can make the light-emitting diode 2 turn on and emit light. When the driving circuit 1 operates in the second mode, the path of the driving current I is shown by the arrow in FIG. 4.

Please refer to FIG. 5, which is a schematic diagram of the driving circuit of the light emitting diode of the present invention when operating in the third mode. As can be seen from FIG. 5, when the input voltage starts to decrease, the driving circuit 1 will switch from operating in the second mode to operating in the third mode. When the input voltage gradually decreases and begins to be smaller than the crossover voltage of the first capacitor C1, the driving circuit 1 will switch to operate in the third mode, at this time the first capacitor C1 will start to discharge, and the driving current I flows from the first capacitor C1 to The first pin DS1 of the chip IC, as long as the voltage across the first capacitor C1 is still higher than the forward bias of the light-emitting diode 2, the light-emitting diode 2 can turn on and emit light until the input voltage gradually It starts to increase until the input voltage is higher than the forward bias of the light-emitting diode 2, at which time the driving circuit 1 will switch to operate in the first mode. When the driving circuit 1 operates in the third mode, the path of the driving current I is shown by the arrow in FIG. 5.

In summary, the driving circuit of the light-emitting diode of the present invention can keep the diode turned on and emit light in the first mode, the second mode and the third mode respectively, so there will be no flash screen phenomenon. .

The present invention has been disclosed in the above with preferred embodiments, but those skilled in the art should understand that this embodiment is only used to depict the present invention and should not be interpreted as limiting the scope of the present invention. It should be noted that all changes and substitutions equivalent to this embodiment should be included within the scope of the present invention. Therefore, the scope of protection of the present invention shall be subject to those defined in the scope of patent application.

1‧‧‧Drive circuit

2‧‧‧ LED

AC‧‧‧AC voltage source

C1‧‧‧ First capacitor

C2‧‧‧Second capacitor

D1, D2‧‧‧ diode

DS1, DS2, LV, RS‧‧‧pin

I‧‧‧Drive current

IC‧‧‧chip

RE‧‧‧Bridge Rectifier

R‧‧‧Resistance

Claims (9)

A driving circuit for driving a light-emitting diode. The light-emitting diode includes an anode and a cathode. The cathode of the light-emitting diode is grounded. The drive circuit includes: a chip with a first input connection Pin, a second input pin and an output pin, the output pin is coupled to the anode of the light-emitting diode; a bridge rectifier, bridged to an AC voltage source, has a ground terminal and a current output Terminal, the current output terminal is connected to the first input pin of the chip; a first diode with a first cathode and a first anode, the first cathode is connected to the second input pin; one The second diode has a second cathode and a second anode, the second cathode is connected to the first anode of the first diode, and the second anode is grounded; and a first capacitor has a A third cathode end and a third anode end, the third cathode end is connected to the first anode of the first diode, and the third anode end is connected to the current output end of the bridge rectifier; wherein the chip includes There are: a first operational amplifier with a first positive phase input terminal, a first negative phase input terminal and a first output terminal, the first positive phase input terminal is connected to a reference voltage; a first transistor , With a first source, a first drain and a first gate, the first drain is connected to the first input pin of the chip, the first A gate is connected to the first output of the first operational amplifier, and the first source is connected to the output pin of the chip and the negative input of the first operational amplifier; a second operational amplifier, It has a second positive phase input terminal, a second negative phase input terminal and a second output terminal, the second positive phase input terminal is connected to the reference voltage; and a second transistor with a second source , A second drain and a second gate, the second drain is connected to the second input pin of the chip, the second gate is connected to the second output of the second operational amplifier, and The second source is connected to the output pin of the chip and the negative input terminal of the second operational amplifier. The driving circuit as described in item 1 of the application scope, wherein when the driving circuit operates in a first mode, a driving current of the driving circuit flows out from the current output terminal of the bridge rectifier to the first input of the chip Pin, and then from the output pin of the chip through a resistor to the light-emitting diode. The driving circuit as described in item 2 of the application scope, wherein when an input voltage generated by the AC voltage source is higher than a forward bias of the light emitting diode but lower than the forward bias and the first capacitor When the sum of the voltages is crossed, the driving circuit operates in the first mode. The driving circuit as described in item 1 of the application scope, wherein when the driving circuit operates in a second mode, one of the driving currents of the driving circuit flows out from the current output end of the bridge rectifier to the second input of the chip Pin, and then flow out from the output pin of the chip to the light emitting diode. The driving circuit as described in item 4 of the application scope, wherein when an input voltage generated by the AC voltage source is higher than a sum of a forward bias of the light-emitting diode and a crossover voltage of the first capacitor, the The drive circuit operates in this second mode. The driving circuit as described in item 1 of the application scope, wherein when the driving circuit operates in a third mode, a driving current of the driving circuit flows out from the first capacitor to the first input pin of the chip, and then Then it flows out from the output pin of the chip to the light emitting diode. The driving circuit as described in item 6 of the application scope, wherein when the voltage across the first capacitor is higher than an input voltage generated by the AC voltage source and higher than a forward bias voltage of the light emitting diode, The driving circuit operates in the third mode. The driving circuit as described in item 1 of the application scope, wherein the chip further has a third input pin, and the driving circuit further includes a second capacitor coupled to the anode of the light emitting diode And the third input pin. The driving circuit as described in item 8 of the application scope, wherein the third input pin of the chip is connected to the first operational amplifier and the second operational amplifier to provide an operating voltage to the first operational amplifier and the first operational amplifier Two operational amplifiers.

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