TW201347596A - Diving circuit of light emitting diode - Google Patents

Abstract

A diving circuit of light emitting diode (LED) is provided. The diving circuit comprises a rectifier unit and a bleeder circuit. The rectifier provides an input voltage. The bleeder circuit provides a holding current. The holding current relates to the input voltage increasing to reduce.

Description

Light-emitting diode driving circuit

The invention relates to a lighting technology of a light-emitting diode, in particular to a driving device for a light-emitting diode.

With the rapid development of lighting technology, light emitting diodes (LEDs) have become a new generation of light sources, gradually replacing resistive lighting sources such as halogen lamps and tungsten lamps. A new generation of light source-LEDs are characterized by small size, power saving and durability. In addition, the LED has a low operating voltage, can actively emit light and has a certain brightness, so LED has been widely used in various fields requiring illumination.

However, the most commonly used dimmer in early resistive lighting (eg, halogen, tungsten, etc.) technology is the Tri-electrode AC switch (TRIAC). The TRIAC provides voltage according to its conduction conditions to fine tune the illuminating effect of the illuminating elements of the resistive lighting device. Therefore, it is currently the most widely used method to replace the tungsten lamp with the LED lamp without changing the original lighting device base and the dimmer switch.

However, due to the unique characteristics of the TRIAC dimmer, the operation is more difficult. In short, when directly controlling the brightness of the LED light source through the TRIAC dimmer, it is necessary to keep a certain holding current flowing. If the holding current cannot be maintained, the TRIAC will not be kept on. The state, which in turn causes the LED to flicker. Therefore, when using TRIAC dimming, a blood flow circuit is required to solve this problem.

The current blood circuit circuit of the conventional TRIAC dimmer 900 is shown in FIG. The holding current I_hold through the bridge rectifier circuit 9 shown in Fig. 1 is an important factor that causes the TRIAC to remain in the conducting state, which can be obtained by the following formula:

It can be seen from the above formula that the holding current I_hold can be adjusted through the input voltage Vin. That is, when the holding current I_hold value is insufficient to cause the TRIAC to remain in the on state, the input voltage Vin may be increased to increase the holding current I_hold. However, in this method, when the input voltage Vin rises, the holding current I_hold rises accordingly, as shown in FIG. 2, resulting in a large power loss.

Therefore, how to develop a state in which the TRIAC can be kept in a state of being turned on to avoid flickering of the LED light source without causing a large power loss has become an urgent problem in the technical field of the present invention.

In view of this, one aspect of the present invention is to provide a driving circuit for an LED to avoid flickering of the LED light source and to reduce power loss.

According to a specific embodiment, a driving circuit for a light emitting diode of the present invention includes a rectifying unit and a first-class blood circuit. The rectifying unit outputs an input voltage. In addition, the above-described bleed circuit generates and maintains a holding current. In the above, the holding current of the blood flowing circuit decreases as the input voltage rises to reduce power loss.

Further, in practical applications, in the driving circuit of the light-emitting diode of the present invention, the bleeding circuit utilizes a characteristic of a metal oxide semiconductor (MOS) such that the holding current decreases as the input voltage rises to reduce power loss.

More specifically, in the driving circuit of the light-emitting diode of the present invention, the metal oxide semiconductor is an enhancement mode metal oxide semiconductor, such as a metal oxide semiconductor such as an enhancement MOSFET, or an equivalent metal oxide semiconductor.

Further, in the driving circuit of the light-emitting diode of the present invention, the rectifying unit is a bridge rectifier that converts an AC power source and outputs the input voltage. In addition, the bridge rectifier can also convert the DC power supply and output the above input voltage to drive at least one LED.

Compared with the prior art, the driving circuit of the LED of the embodiment of the present invention can utilize the improved bleed circuit to keep the TRIAC in an on state to avoid flickering of the LED light source without causing a large power loss.

The advantages and spirit of the present invention will be further understood from the following detailed description of the invention.

Please refer to Figure 3. 3 is a circuit diagram of a driving circuit of a light emitting diode according to a preferred embodiment of the present invention. As shown in FIG. 3, the present invention provides a driving circuit 100 for a light emitting diode comprising a rectifying unit 1 and a first-class blood circuit 2.

The rectifying unit 1 outputs an input voltage Vin for driving at least one light emitting diode (not shown). In this embodiment, the rectifying unit 1 is a bridge rectifier that converts an AC power source and outputs the input voltage Vin. Furthermore, it is known to those skilled in the art that the bridge rectifier can also convert a DC power supply and output the input voltage Vin.

The bleed circuit 2 generates and maintains a holding current I_hold. As can be seen from FIG. 3, the bleed circuit 2 is composed of MOSFETs Q1, Q2, resistors R1, R2, R3, R4, capacitor C1 and control circuit 21 to generate and maintain the holding current I_hold. The holding current I_hold is the sum of the holding current I_hold1 holding current I_hold2.

In this embodiment, the holding current I_hold1 can be obtained by the following formula:

It can be seen from the above formula that when the voltage VDD and the voltage VthQ1 remain fixed, the current I_hold1 is a fixed current.

Further, in the present embodiment, the holding current I_hold2 can be obtained by the following formula:

It can be seen from the above formula that when the input voltage Vin rises, the voltage VGQ2 will rise, and the holding current I_hold2 will decrease. Therefore, in summary, when the input voltage Vin rises, the holding current I_hold will decrease as shown in FIG.

In particular, the bleeding circuit 2 utilizes characteristics of a metal oxide semiconductor (MOS), such as an enhancement mode metal oxide semiconductor, but the invention is not limited thereto, so that the holding current will As the input voltage Vin rises, it drops to reduce power loss.

Compared with the prior art, the driving circuit of the LED of the embodiment of the present invention can utilize the improved bleed circuit to keep the TRIAC in an on state to avoid flickering of the LED light source without causing a large power loss. In addition, the skilled person knows that the improved bleed circuit can also be used as a feedback signal for controlling the rear LED driving circuit to increase the linearity of the TRIAC dimming. For example, Buck, Boost, Buck-Boost, Forward, Flyback, Half-Bridge, Push Structures such as Push-Pull, Full-Bridge, and Linear Regulator can be applied with improved bleed circuits to increase the linearity of TPIAC dimming.

The features and spirit of the present invention will be more apparent from the detailed description of the preferred embodiments. On the contrary, the intention is to cover various modifications and equivalents within the scope of the invention as claimed. Therefore, the scope of the patented scope of the invention should be construed in the broadest

100. . . Light-emitting diode driving circuit

1. . . Rectifier unit

2. . . Bleeding circuit

I_hold. . . Hold current

I_hold1. . . Hold current

I_hold2. . . Hold current

Q1. . . MOSFET

Q2. . . MOSFET

R1. . . resistance

R2. . . resistance

R3. . . resistance

R4. . . resistance

C1. . . capacitance

twenty one. . . Control circuit

Vin. . . Input voltage

VDD. . . Voltage

VGQ2. . . Voltage

VthQ1. . . Voltage

VDSQ2. . . Voltage

Figure 1 shows a conventional circuit diagram.

Figure 2 shows a conventional current versus voltage relationship.

Figure 3 is a circuit diagram of a preferred embodiment of the present invention.

Figure 4 is a graph showing current versus voltage for a preferred embodiment of the present invention.

100. . . Light-emitting diode driving circuit

1. . . Rectifier unit

2. . . Bleeding circuit

I_hold, I_hold1, I_hold2. . . Hold current

Q1, Q2. . . MOSFET

R1, R2, R3, R4. . . resistance

C1. . . capacitance

twenty one. . . Control circuit

Vin, VDD, VGQ2, VthQ1, VDSQ2. . . Input voltage

Claims (7)

A driving circuit for a light emitting diode, comprising: a rectifying unit that outputs an input voltage; and a first-class blood circuit that generates and maintains a holding current; wherein the holding current of the blood flowing circuit follows the input The voltage rises and falls to reduce power loss. The driving circuit of the light emitting diode according to claim 1, wherein the blood flowing circuit utilizes a characteristic of the metal oxide semiconductor such that the holding current decreases as the input voltage rises to reduce power loss. The driving circuit of the light emitting diode according to the second aspect of the invention, wherein the metal oxide semiconductor is an enhanced metal oxide semiconductor. The driving circuit of the light emitting diode according to claim 1, wherein the rectifying unit is a bridge rectifier that converts an AC power source and outputs the input voltage. The driving circuit of the light emitting diode according to claim 1, wherein the rectifying unit is a bridge rectifier that converts a DC power supply and outputs the input voltage. The driving circuit of the light emitting diode according to claim 1, wherein the input voltage is used to drive at least one light emitting diode. The driving circuit of the light emitting diode according to claim 6 is applied to a feedback signal for controlling a driving circuit of the at least one light emitting diode.