TWI489908B - Light emitting diode drive circuit - Google Patents

Description

Light-emitting diode driving circuit

The invention relates to a driving circuit, in particular to a light emitting diode driving circuit.

In recent years, Light-Emitting-Diode (LED) has many characteristics suitable for illumination and is easy to dim, making the LEDs gradually gain market attention and are widely used in various lightings. In the appliance.

A light-emitting diode is a component that uses a low-voltage DC drive. Generally, it is commonly used in general lighting applications. Buck converters and buck-boost converters (Buck-Boost) Converter), or Flyback Converter as its drive circuit.

Referring to Figures 1 and 2, in a general buck converter (Fig. 1) and a step-down converter (Fig. 2), the switching element 11 is usually placed at the high side, and is driven at the high end. The switching element 11 usually adopts a high-side switch technique (High Side Driver Technique) as shown in FIG. 1, and a high-side switch driving circuit 12 is provided and controlled by a control circuit 13; or floating as shown in FIG. Grounding In the Ground mode, the reference floating ground terminal 131 of the control circuit 13 is electrically connected between the diode D and the winding L to obtain a floating ground voltage.

However, whether using high-side switch drive technology or floating grounding method, the reference ground potential (floating ground voltage) of the high-side switch drive circuit 12 or the control circuit 13 and the reference ground potential (ground terminal) of the system are different potentials, As a result, there is no unified reference ground potential for reference during the transmission, which may cause the signal to be not transmitted or detected normally.

Referring to FIG. 3 and FIG. 4, in order to solve this problem, an isolation transformer 14 is usually used as shown in FIG. 3, or an optical coupler 15 is used to transmit signals as shown in FIG. 4 to overcome the inconsistency of the reference ground potential. The impact on signal transmission.

However, the isolation transformer 14 and the optical coupler 15 both increase the circuit volume, increase the circuit cost and design complexity, and even affect the reliability of the system.

Accordingly, it is an object of the present invention to provide a light emitting diode driving circuit that can solve the above problems.

Therefore, the LED driving circuit of the present invention is suitable for driving a plurality of LEDs, and the LED driving circuit comprises: a conversion circuit, a control circuit, and a dimming signal displacement circuit.

The conversion circuit includes: a switching element, an output capacitor, an inductor, and a flywheel diode.

The switching element has a first end that receives a power signal, A second end, and a control end receiving a control signal, are controlled to switch between on and off.

The output capacitor has a first end that provides an output current to drive the light emitting diodes and a grounded second end.

The inductor and the flywheel diode are connected in series between the first end of the output capacitor and the ground, and the connection point is electrically connected to the second end of the switching element and provides a floating ground voltage.

The control circuit comprises: a switching element control end, a reference floating ground end, a dimming signal input end, a dimming signal recovery module, and a dimming control module.

The switching element control terminal is electrically connected to the control end of the switching element and provides the control signal.

The reference floating ground is electrically connected to a connection point of the inductor and the flywheel diode to receive the floating ground voltage.

The dimming signal input terminal is configured to receive a pair of dimming input signals that should have a floating ground voltage.

The dimming signal recovery module is electrically connected to the dimming signal input end and the reference floating ground end, and receives the dimming input signal and outputs a signal after the dimming input signal is recovered.

The dimming control module is electrically connected to the dimming signal recovery module and the switching element control end, receives the dimming input signal after the signal is recovered, and adjusts and outputs the control signal according to the dimmed input signal after the reply.

The dimming signal displacement circuit comprises: a dimming diode and a dimming capacitor.

The dimming diode has an anode end receiving a dimming signal and a cathode end outputting the dimming input signal.

The dimming capacitor has a first end electrically connected to the cathode end of the dimming diode, and a second end electrically connected to the floating ground voltage.

The effect of the invention is that by using the dimming capacitor and the dimming diode to replace the isolation transformer or the optical coupler in the prior art, the circuit volume and components can be saved, the circuit cost can be saved, and the signal transmission can be realized. In the absence of a uniform reference potential for reference, the signal can still be detected or transmitted normally.

2‧‧‧Power circuit

Vac‧‧‧AC power supply

201‧‧‧The first end of the AC power supply

202‧‧‧The second end of the AC power supply

21‧‧‧Bridge rectifier module

D1‧‧‧First Diode

D2‧‧‧ second diode

D3‧‧‧ third diode

D4‧‧‧ fourth diode

22‧‧‧Electromagnetic interference filter module

Lf‧‧‧electromagnetic interference filter inductor

Cf‧‧‧Electromagnetic interference filter capacitor

C1‧‧‧Filter Capacitor

3‧‧‧Transition circuit

Q1‧‧‧Switching elements

L‧‧‧Inductance

Do‧‧‧Flywheel diode

Co‧‧‧ output capacitor

Rfb‧‧‧ feedback resistor

4‧‧‧Control circuit

FB‧‧‧reporting end

VSS‧‧‧reference floating ground

VDD‧‧‧ power supply terminal

DIM‧‧‧ dimming signal input

GATE‧‧‧ switching element control terminal

COMP‧‧‧ phase compensation end

41‧‧‧ Dimming signal recovery module

411‧‧‧ comparator

Dsh‧‧‧Sampling diode

Csh‧‧‧Sampling Capacitor

Vf‧‧‧Predetermined voltage source

42‧‧‧ dimming control module

5‧‧‧ dimming signal displacement circuit

Cdim‧‧‧ dimming capacitor

Ddim‧‧‧ dimming diode

Vref‧‧‧ equivalent power supply

9‧‧‧Lighting diode

91~93‧‧‧ Curve

Other features and effects of the present invention will be apparent from the following description of the drawings, wherein: FIG. 1 is a circuit diagram illustrating a conventional light-emitting diode using a buck converter and high-side switch drive technology. FIG. 2 is a circuit diagram illustrating a conventional LED driving circuit using a step-down converter and a floating grounding method; FIG. 3 is a circuit diagram illustrating a conventional transmission transformer using an isolation transformer FIG. 4 is a circuit diagram illustrating a conventional LED driving circuit using an optical coupler to transmit signals; FIG. 5 is a first preferred embodiment of the LED driving circuit of the present invention. FIG. 6 is a schematic circuit diagram of a dimming signal recovery module of the first preferred embodiment; FIG. FIG. 7 is an operational equivalent circuit diagram of the first preferred embodiment when a switching element is turned on; FIG. 8 is an operational equivalent circuit diagram of the first preferred embodiment when the switching element is turned off; FIG. A more detailed circuit diagram of the first preferred embodiment; FIG. 10 is an analog waveform diagram of the first preferred embodiment; FIG. 11 is another analog waveform diagram of the first preferred embodiment; Another mode of the dimming signal recovery module of the first preferred embodiment; FIG. 13 is a third analog waveform diagram of the first preferred embodiment; FIG. 14 is a fourth embodiment of the first preferred embodiment. Analog waveform diagram; and Fig. 15 is a circuit diagram showing a second preferred embodiment of a light-emitting diode driving circuit of the present invention.

Before the present invention is described in detail, it should be noted that in the following description, similar elements are denoted by the same reference numerals.

Referring to FIG. 5 and FIG. 6 , the first preferred embodiment of the LED driving circuit of the present invention is suitable for driving a plurality of LEDs 9 . The LED driving circuit comprises: a power circuit 2 and a conversion circuit 3 . A control circuit 4 and a dimming signal shift circuit 5.

The power circuit 2 receives an AC power supply Vac to output a power signal. The AC power supply Vac has a first end 201 and a second end 202. The power circuit 2 includes a bridge rectifier module 21.

The bridge rectifier module 21 has: a first diode D1 A second diode D2, a third diode D3, and a fourth diode D4.

The first diode D1 has an anode end electrically connected to the first end 201 of the AC power source Vac, and a cathode end electrically connected to the conversion circuit 3 and outputting the power signal.

The second diode D2 has an anode end electrically connected to a ground end, and a cathode end electrically connected to the first end of the alternating current power source Vac.

The third diode D3 has an anode end electrically connected to the second end 202 of the AC power source Vac, and a cathode end electrically connected to the conversion circuit 3 and outputting the power signal.

The fourth diode D4 has an anode end electrically connected to the ground end, and a cathode end electrically connected to the second end of the alternating current power source Vac.

The conversion circuit 3 is electrically connected to the power supply circuit 2 and includes: a switching element Q1, an output capacitor Co, an inductor L, and a flywheel diode Do.

In the present embodiment, a buck converter circuit is used as an explanation, but is not limited thereto.

The switching element Q1 has a first end connected to the cathode end of the third diode D3 and receiving the power signal, a second end, and a control end receiving a control signal, which are controlled to be turned on and off. Switch between.

The output capacitor Co has a first end that provides an output voltage and an output current to drive the light emitting diodes 9, and a grounded second end.

The flywheel diode Do has a grounded anode end and an electric A second end of the switching element Q1 is connected and a cathode terminal of a floating ground voltage is provided.

The inductor L has a first end electrically connected to the cathode end of the flywheel diode Do, and a second end electrically connected to the first end of the output capacitor Co.

The control circuit 4 includes a switching element control terminal GATE, a reference floating ground terminal VSS, a dimming signal input terminal DIM, a dimming signal recovery module 41, and a dimming control module 42.

The switching element control terminal GATE is electrically connected to the control terminal of the switching element Q1 and provides the control signal.

The reference floating ground VSS is electrically connected to the connection point of the inductor L and the flywheel diode Do to receive the floating ground voltage.

The dimming signal input terminal DIM is configured to receive a pair of dimming input signals that should be floating ground voltage.

The dimming signal recovery module 41 is electrically connected to the dimming signal input terminal DIM and the reference floating ground terminal VSS, receives the dimming input signal, and outputs a signal to the dimming input signal.

The dimming signal recovery module 41 has a comparator 411. The comparator 411 receives the dimming input signal and compares it with a predetermined voltage to output the dimming input signal after the signal is recovered. In this embodiment, The predetermined voltage is supplied using a predetermined voltage source Vf, but is not limited thereto.

The dimming input signal after the signal outputted by the dimming signal recovery module 41 is restored has a pulse width and a frequency substantially the same as the dimming signal.

The dimming control module 42 is electrically connected to the dimming signal recovery module 41 and the switching element control terminal GATE, receives the dimming input signal after the signal is recovered, and adjusts and outputs the control according to the dimmed input signal after the reply. Signal.

The dimming signal displacement circuit 5 includes: a dimming diode Ddim and a dimming capacitor Cdim.

The dimming diode Ddim has an anode terminal that receives a pair of dimming signals that should have a ground voltage, and an anode terminal that outputs the dimming input signal corresponding to the floating ground voltage.

The dimming capacitor Cdim has a first end electrically connected to the cathode end of the dimming diode Ddim, and a second end receiving the floating ground voltage.

7 and FIG. 8, which are equivalent circuit diagrams when the switching element Q1 is turned on and off, respectively, in order to make the figure clear, in FIG. 7 and FIG. 8, the AC power supply Vac and the power supply circuit 2 are fully wave rectified. The equivalent power supply Vref is used as a representative.

As shown in FIG. 7, when the switching element Q1 is turned on, the flywheel diode Do is turned off, and at this time, the second end of the switching element Q1 is relatively high, so the dimming signal shifting circuit 5 is dimmed due to the dipole The body Ddim is reverse biased and turned off, and the full-wave rectified equivalent power source Vref stores energy for the inductor L.

As shown in FIG. 8, when the switching element Q1 is turned off, the inductor L is turned on by the flywheel diode Do to turn on the flywheel diode Do. At this time, the second end of the switching element Q1 is equivalently grounded. Relatively low potential Therefore, the dimming diode Ddim in the dimming signal shifting circuit 5 is forward biased and turned on, so that the dimming signal corresponding to the grounding voltage is transmitted to the dimming capacitor Cdim, so that the dimming capacitor Cdim The voltage across the voltage is approximately equal to the voltage peak of the dimming signal.

Since the buck conversion of the conversion circuit 3 is well known in the art, it will not be described here.

Referring to FIG. 5 and FIG. 6 , the dimming signal displacement circuit 5 can receive the dimming signal corresponding to the ground voltage, and the dimming diode Ddim and the dimming capacitor Cdim receiving the floating ground voltage can be used. The dimming signal is adjusted to a dimming input signal corresponding to the floating ground voltage, and the comparator 411 of the dimming signal recovery module 41 is compared with the predetermined voltage to obtain the dimming input after the signal is recovered. Signal.

Referring to FIG. 6 and FIG. 9 , FIG. 9 is a schematic diagram of a more detailed circuit of the embodiment, wherein the control circuit 4 further includes: a power terminal VDD for receiving power, a feedback terminal FB, and a phase compensation. The power supply terminal VDD is used to supply the power required by the control circuit 4, and the feedback terminal FB is configured to receive a feedback signal corresponding to the inductor L current and the output current, and the phase compensation terminal COMP is used to compensate the The phase of the feedback signal makes the system stable. The control circuit 4 controls the switching element Q1 to be turned on and off by the received feedback signal, and causes the conversion circuit 3 to output the stable output current to drive the LED module 9.

The power circuit 2 further includes an electromagnetic interference filter module 22 and a filter capacitor C1.

The electromagnetic interference filter module 22 has an electromagnetic interference filter inductor Lf and an electromagnetic interference filter capacitor Cf.

The electromagnetic interference filter inductor Lf has a first end electrically connected to the first end 201 of the AC power source Vac, and a second end electrically connected to the anode end of the first diode D1.

The EMI filter capacitor Cf has a first end electrically connected to the second end of the EMI filter inductor Lf, and a second end electrically connected to the second end 202 of the AC power source Vac.

It is to be noted that, in this embodiment, the electromagnetic interference filter module 22 is only illustrated by an electromagnetic interference filter inductor Lf and an electromagnetic interference filter capacitor Cf, mainly as an electromagnetic interference filter (EMI Filter). The EMI filter has various implementations, and those skilled in the art may also change accordingly, and are not limited thereto.

The filter capacitor C1 has a first end electrically connected to the first end of the switching element Q1, and a second end electrically connected to the ground end.

The conversion circuit 3 further includes a feedback resistor Rfb connected in series between the inductor L and the flywheel diode Do to generate the feedback signal corresponding to the inductor L current and the output current, and input Go to the feedback terminal FB to achieve the feedback control of the inductor L current and the output current.

Referring to FIG. 6, FIG. 9, and FIG. 10, FIG. 10 is an analog waveform diagram performed by using the circuits of FIG. 6 and FIG. 9, wherein the curve 91 is the input dimming signal, and its duty ratio is (duty ratio). 90%, the frequency is 600Hz, after the dimming signal displacement circuit 5 corresponds to the floating ground voltage processing, the output dimming input signal is the curve 92, as can be seen in FIG. Due to the influence of the floating ground voltage, the lowest potential of the curve 92 and the curve 91 are not the same, and the high potential value of the curve 92 also has a floating phenomenon, and the signal obtained by the dimming signal recovery module 41 is processed. The dimming input signal after the reply is the curve 93. As can be seen from FIG. 10, the pulse width and frequency of the dimming input signal (curve 93) after the signal is recovered are the same as the dimming signal (curve 91).

Referring to FIG. 6 , FIG. 9 and FIG. 11 , FIG. 11 is an analog waveform diagram performed by using the circuits of FIG. 6 and FIG. 9 , wherein the curve 91 is the input dimming signal, and the conduction rate is 10%. The frequency is 600 Hz, the curve 92 is the dimming input signal processed by the dimming signal displacement circuit 5 corresponding to the floating ground voltage, and the curve 93 is the dimming input signal after the signal processed by the dimming signal recovery module 41 is recovered. As can be seen from FIG. 11, the pulse width and frequency of the dimming input signal (curve 93) after the signal is recovered are also the same as the dimming signal (curve 91).

Referring to FIG. 12, another aspect of the dimming signal recovery module 41 in the first embodiment is different from the first embodiment in that the comparator 411 has a positive phase input terminal and a Inverting input.

The dimming signal recovery module 41 further has a sampling diode Dsh, a sampling capacitor Csh, and a predetermined voltage source Vf.

The sampling diode Dsh has an anode terminal for receiving the dimming input signal and a cathode terminal electrically connected to the positive phase input terminal of the comparator 411.

The sampling capacitor Csh has a first end electrically connected to the cathode end of the sampling diode Dsh, and a second end receiving the floating ground voltage.

The predetermined voltage source Vf has a first end electrically connected to the inverting input terminal of the comparator 411 and providing the predetermined voltage, and a second end electrically connected to the second end of the sampling capacitor Csh.

In this aspect, by adding the sampling diode Dsh and the sampling capacitor Csh, the sample & hold function can be provided to avoid the load when the comparator 411 has poor characteristics (the input impedance is not large enough). The effect causes the dimming input signal to be distorted.

Referring to FIG. 9 , FIG. 13 and FIG. 14 , FIG. 13 and FIG. 14 show analog waveform diagrams performed by using the circuits of FIG. 9 and FIG. 12 , curve 91 is the input dimming signal, and curve 92 is dimming. Input signal, curve 93 is the dimming input signal after the signal is recovered. The conduction signal of the dimming signal of curve 91 in FIG. 13 is 90%, the frequency is 600 Hz, and the conductivity of the dimming signal of curve 91 in FIG. 14 is 10 %, the frequency is 600 Hz, as seen in FIG. 13 and FIG. 14 , after the dimming signal displacement circuit 5 and the dimming signal recovery module 41 are processed, the dimming input signal after the obtained signal is recovered (curve 93) The pulse width and frequency are the same as the dimming signal (curve 91).

Through the above description, the advantages of this embodiment can be summarized as follows:

1. By using the dimming capacitor Cdim and the dimming diode Ddim, the isolation transformer or the optical coupler in the prior art can be replaced, which can save a large amount of circuit volume and reduce circuit components, thereby greatly reducing Circuit cost, and the embodiment can be applied to the high-side switch drive technology or the floating grounding mode. When the floating ground voltage received by the reference floating ground terminal VSS of the control circuit 4 is different from the voltage of the ground terminal, the transmission process can still be performed. Normally detect or transmit signals without a uniform reference ground potential for reference.

2. It can be seen from FIG. 9 that the AC power supply Vac has been converted to a DC power supply after being rectified and filtered by the power supply circuit 2. Therefore, when the present embodiment is to be applied to a DC voltage input, the power supply circuit 2 only needs to be omitted. The DC power signal can be directly received by the first end of the switching element Q1, which can increase the flexibility of the application.

15 is a second preferred embodiment of a light emitting diode driving circuit of the present invention. The second preferred embodiment is a detailed circuit diagram similar to the first preferred embodiment. The second preferred embodiment The difference from the first preferred embodiment is that in the conversion circuit 3, the flywheel diode Do has an anode end electrically connected to the first end of the output capacitor Co, and a cathode end; the inductor L has A first end electrically connected to the second end of the switching element Q1 and a second end connected to the ground; the feedback resistor Rfb is connected in series between the cathode end of the flywheel diode Do and the first end of the winding L.

In the present embodiment, a buck-boost converter is used as an explanation, but is not limited thereto.

Since the step-down conversion of the conversion circuit 3 is well known in the art, and the operation mode of the control circuit 4 and the dimming signal shift circuit 5 is similar to the above, it is no longer mentioned herein.

Thus, the second preferred embodiment can achieve the same purpose and effect as the first preferred embodiment described above.

In summary, the present invention can not only save circuit volume and cost, reduce design complexity, but also improve system reliability and increase application flexibility, so that the object of the present invention can be achieved.

The above is only the preferred embodiment of the present invention, and the scope of the present invention is not limited thereto, that is, the simple equivalent changes and modifications made by the patent application scope and patent specification content of the present invention, All remain within the scope of the invention patent.

2‧‧‧Power circuit

Vac‧‧‧AC power supply

201‧‧‧The first end of the AC power supply

202‧‧‧The second end of the AC power supply

21‧‧‧Bridge rectifier module

D1‧‧‧First Diode

D2‧‧‧ second diode

D3‧‧‧ third diode

D4‧‧‧ fourth diode

3‧‧‧Transition circuit

Q1‧‧‧Switching elements

L‧‧‧Inductance

Do‧‧‧Flywheel diode

Co‧‧‧ output capacitor

4‧‧‧Control circuit

VSS‧‧‧reference floating ground

DIM‧‧‧ dimming signal input

GATE‧‧‧ switching element control terminal

41‧‧‧ Dimming signal recovery module

42‧‧‧ dimming control module

5‧‧‧ dimming signal displacement circuit

Cdim‧‧‧ dimming capacitor

Ddim‧‧‧ dimming diode

9‧‧‧Lighting diode

Claims (10)

An LED driving circuit is adapted to drive a plurality of LEDs. The LED driving circuit comprises: a conversion circuit comprising: a switching component having a first end receiving a power signal and a second And a control terminal receiving a control signal, controlled to switch between on and off, an output capacitor having a first end for providing an output current to drive the light emitting diodes, and a grounding a second end, an inductor and a flywheel diode, connected in series between the first end of the output capacitor and the ground, and the connection point is electrically connected to the second end of the switching element and provides a floating ground voltage; The circuit includes: a switching element control end electrically connected to the control end of the switching element and providing the control signal, a reference floating ground end electrically connected to the connection point of the inductor and the flywheel diode to receive the floating ground Voltage, a dimming signal input end for receiving a pair of dimming input signals that should have a floating ground voltage, a dimming signal recovery module, electrically connecting the dimming signal input end and the reference The grounding end receives the dimming input signal and outputs a signal to the dimming input signal, and a dimming control module electrically connects the dimming signal recovery module and the switching element control end to receive the signal reply After the dimming Entering a signal and adjusting the output of the control signal according to the dimming input signal after the reply; and a dimming signal displacement circuit comprising: a dimming diode having an anode end receiving a dimming signal, and an output The cathode end of the dimming input signal and a dimming capacitor have a first end electrically connected to the cathode end of the dimming diode and a second end receiving the floating ground voltage. The illuminating diode driving circuit of claim 1, wherein the dimming signal recovery module has a comparator, and the comparator receives the dimming input signal and compares it with a predetermined voltage to output a signal after replying. The dimming input signal. The illuminating diode driving circuit of claim 2, wherein the dimming input signal after the signal outputted by the dimming signal recovery module has a pulse width and a frequency substantially the same as the dimming signal . The illuminating diode driving circuit of claim 2, wherein the comparator has a positive phase input terminal and an inverting input terminal; the dimming signal recovery module further includes: a sampling diode having a receiving An anode end of the dimming input signal, and a cathode end electrically connected to the positive phase input end of the comparator, a sampling capacitor having a first end electrically connected to the cathode end of the sampling diode, and receiving the floating ground voltage a second end, and a predetermined voltage source having a first end electrically connected to the inverting input of the comparator and providing the predetermined voltage, and an electrical connection to the sampling capacitor The second end of the second end. The illuminating diode driving circuit of claim 2, further comprising a power supply circuit for receiving an AC power source for outputting the power signal, the AC power source having a first end and a second end, the power circuit comprising a bridge rectifier module, the bridge rectifier module having: a first diode having an anode end electrically connected to the first end of the AC power source, and a cathode end electrically connected to the first end of the switching element a second diode having an anode end electrically connected to the ground end, and a cathode end electrically connected to the first end of the alternating current power source, a third diode having a second electrically connected to the alternating current power source An anode end of the terminal, and a cathode end electrically connected to the first end of the switching element, and a fourth diode having an anode end electrically connected to the ground end and a cathode end electrically connected to the second end of the alternating current power source . The illuminating diode driving circuit of claim 5, wherein the power circuit further comprises: a filter capacitor having a first end electrically connected to the first end of the switching element, and a second electrically connected to the ground end Two ends. The illuminating diode driving circuit of claim 6, wherein the power circuit further comprises an electromagnetic interference filtering module electrically connected between the alternating current power source and the bridge rectifier module. The illuminating diode driving circuit of claim 7, wherein the EMI filtering module has: an EMI filter inductor having an electrical connection to the AC power source a first end of the first end, and a second end electrically connected to the anode end of the first diode, and an electromagnetic interference filter capacitor having a first end electrically connected to the second end of the electromagnetic interference filter inductor And a second end electrically connected to the second end of the AC power source. The illuminating diode driving circuit of claim 1, wherein the flywheel diode has a grounded anode end and a cathode end electrically connected to the second end of the switching element, the inductor A first end electrically connected to the cathode end of the flywheel diode and a second end electrically connected to the first end of the output capacitor. The illuminating diode driving circuit of claim 1, wherein the flywheel diode has an anode end electrically connected to the first end of the output capacitor, and an electrical connection electrically connecting the switching element The cathode end of the second end, the inductor has a first end electrically connected to the cathode end of the flywheel diode, and a grounded second end.