TWI440389B - Power converting controller and led diving circuit - Google Patents

Description

Power conversion controller and LED driving circuit

The invention relates to a power conversion controller and a light emitting diode driving circuit, in particular to a power conversion controller with an open circuit protection function and a light emitting diode driving circuit.

Compared with the traditional illumination source, the LED has the advantages of high luminous efficiency, low power consumption, long service life, and the production cost is also decreasing, and has been widely used. The LED driver circuit is typically an isolated or non-isolated constant current source for driving a string of LEDs and controlling current flow through the LEDs by current sensing.

Please refer to the first figure, which is a circuit diagram of a conventional LED driving circuit. The LED driving circuit includes a controller 10, a conversion circuit 35, a power feedback circuit 40, and a light emitting diode string 30. In this example, the conversion circuit 35 is a step-down conversion circuit including an inductor L, a capacitor C, a rectifying diode D, and a switch SW. The input end of the conversion circuit 35 is coupled to an input power source VIN, and coupled to the LED array 30 at the output end to drive the LED string 30 to emit light. A current detecting resistor R is coupled to the LED string 30 through the switch SW, and generates a current detecting signal IFB according to the current flowing through the LED string 30. The current detecting terminal CS of the controller 10 receives the current detecting signal IFB, so as to generate a control signal Gate control switch circuit SW at the output terminal DRV to switch, to control the conversion circuit 35 to perform power conversion, so that the light is turned on. The polar body string 30 is stably illuminated. The switching circuit 35 charges a starting capacitor Cin through the power feedback circuit 40 as the switch SW is switched. The starting capacitor Cin is coupled to the driving voltage terminal of the controller 10 to provide power to the controller 10.

The conventional LED driving circuit, like the circuit shown in the first figure, does not specifically detect whether the LED string is open, but the undervoltage protection of the controller 10 (UVLO, Under-Voltage). Lock Out) to achieve the function of open circuit protection, as follows:

If any of the light-emitting diodes in the light-emitting diode string 30 is damaged, an open circuit will be caused. When the light-emitting diode string 30 is opened, the switch SW cannot flow through the inductor L through the light-emitting diode string 30 even if the current is turned on, and can no longer be stored in the inductor L. Therefore, the energy storage (voltage) of the starting capacitor Cin is gradually decreased. When the voltage drops to the undervoltage protection voltage value of the controller 10, the controller 10 is triggered to perform undervoltage protection, causing the controller 10 to enter a latched state.

However, in practical applications, sometimes the input power supply VIN may be unstable for a while, especially when the input power supply VIN is rectified by the commercial power. When the input power source VIN is unstable and the voltage is lower than the lowest turn-on voltage of the LED string 30 and the current cannot be turned on, the equivalent light-emitting diode string 30 is opened and the under-voltage protection of the controller 10 is locked. live. When the input power supply VIN returns to stability, the controller 10 is still locked, causing the LED string 30 to be abnormally extinguished.

The traditional open circuit protection solution cannot effectively distinguish the open LED or the input power supply from being unstable, so that the protection cannot be accurately implemented. Any unstable power supply may cause the LED driving circuit to malfunction and the LED to be extinguished. The invention introduces a special open circuit protection unit in the LED driver controller to separately detect and judge whether the circuit needs to be open circuit protected to be separated from the undervoltage protection zone. On this basis, input power detection can also be introduced, so that the controller can recognize and respond to the instability of the input power more accurately and quickly. Moreover, the controller of the present invention can be easily converted to any circuit other than the LED driving to perform power conversion and drive different loads.

To achieve the above object, the present invention provides a power conversion controller for controlling a conversion circuit to convert power of an input power source to drive a load. The power conversion controller includes a feedback control unit, an open circuit determination unit, and a protection unit. The feedback control unit returns a signal according to one of the states representing the load to control the conversion circuit. The open circuit judging unit generates an open circuit protection signal when it is judged that the load is in an open state and continues for more than a predetermined length of time. The protection unit is coupled to the feedback control unit and the open circuit determination unit. When receiving the open circuit protection signal, a protection signal is generated to cause the feedback control unit to enter a locked state and stop controlling the conversion circuit.

The invention also provides a light emitting diode driving circuit, the light emitting diode driving circuit comprises a light emitting diode module, a converting circuit and a power conversion controller. The conversion circuit is configured to convert the power of an input power source to drive the light emitting diode module to emit light. The power conversion controller returns a signal according to one of the states representing a load to control the conversion circuit for power conversion. The power conversion controller returns a signal according to one of the states representing a load to control the conversion circuit for power conversion. The power conversion controller performs an open circuit protection function to stop the conversion circuit for power conversion when determining that the load is in an open state for more than a predetermined length of time. The power conversion controller further detects an input voltage of the input power source, and suspends the open circuit protection function when the input voltage is lower than a predetermined undervoltage value.

The above summary and the following detailed description are exemplary in order to further illustrate the scope of the claims. Other objects and advantages of the present invention will be described in the following description and drawings.

Please refer to the second figure, which is a circuit diagram of a power conversion circuit according to the present invention. The power conversion circuit includes a power conversion controller 100, a conversion circuit 135, and a load 130. The conversion circuit 135 is a switching conversion circuit including at least one switch for converting the power of an input power source VIN into a voltage source or a current source to drive the load 130 according to (at least) a control signal Gate of the power conversion controller 100.

The power conversion controller 100 includes a feedback control unit 110, an open circuit determination unit 120, and a protection unit 115. The feedback control unit 110 controls the conversion circuit 135 according to the feedback signal FB generating the feedback signal FB representing one of the electrical states of the load 130. The electrical state of the load 130 may be the voltage applied by the load 130 and the current flowing through it. When the reactive load 130 is driven, the feedback signal FB represents a detection signal of the electrical state. The open circuit determining unit 120 generates an open circuit protection signal OP when it is determined that the load 130 is in an open state and continues for more than a predetermined length of time. The judgment of the open circuit state may be based on the detection signal of the load (for example, the feedback signal FB mentioned above) to determine whether the voltage of the load is higher than a reasonable driving voltage range, and whether the current of the load is lower than a reasonable driving current range; The internal signal of the control unit 110 is given, for example, whether the duty cycle of the pulse width modulation signal is too high or too low, whether the frequency of the pulse width modulation signal is too high or too low, and whether the above situation continues for more than a predetermined length of time. The predetermined length of time is used to eliminate the open circuit judgment misjudgment that may be caused by the instability of the input power source VIN or other temporary circuit abnormalities. When the above condition is satisfied, the open circuit determination unit 120 outputs the open circuit protection signal OP to the protection unit 115. The protection unit 115 is coupled to the feedback control unit 110 and the open circuit determination unit 120. When receiving the open circuit protection signal OP, a protection signal LA is generated to cause the feedback control unit 110 to enter a locked state to stop outputting the control signal Gate, that is, to stop the control conversion. The circuit causes the conversion circuit to stop transmitting power to the output. The feedback control unit 110 in the locked state needs to wait for the power conversion controller 100 to be reset before releasing the locked state and returning to normal operation.

Next, please refer to the third figure, which is a circuit diagram of a light emitting diode driving circuit according to a first preferred embodiment of the present invention. The LED driving circuit includes a power conversion controller 200, a conversion circuit 235, and a light emitting diode module 230. The conversion circuit 235 includes a switch SW, a transformer T, a rectifying diode D2, and an output capacitor Cout. In this embodiment, the conversion circuit 235 is a flyback conversion circuit. The primary side of the transformer T is coupled to an input power supply VIN, the other end is coupled to the switch SW, and the secondary side is rectified by the rectifying diode D2 to store power in the output capacitor Cout, wherein the input power supply VIN is transmitted through a bridge rectifier circuit. 250 pairs of AC power VAC rectification. In this embodiment, the LED module is composed of a plurality of LED strings. Ensuring that each of the light-emitting diodes flows through approximately equal currents, and additionally adding a current sharing circuit 240, and coupling each of the light-emitting diode strings in the light-emitting diode module 230 to cause the light-emitting diodes to flow through approximately equal currents. . The current of the current sharing circuit 240 can be set via the current setting resistor Ri. The set resistor Ri is coupled to a set voltage Vcc, so that the set resistor Ri flows through a set current, and the set current is mirrored by the current sharing circuit 240 to each of the LED strings. The current sharing circuit 240 includes a minimum voltage detection function, and outputs the lowest voltage in the negative terminal of the LED string (ie, the end point of the coupling current sharing circuit 240) as the feedback signal FB, so that the LED is driven. The circuit has the highest drive efficiency.

The power conversion controller 200 includes a feedback control unit 210, an open circuit determination unit 220, and a protection unit 215. The feedback control unit 210 generates a control signal Gate according to the feedback signal FB to control the conversion circuit 235. A voltage divider 245 is coupled to the output of the conversion circuit 235 to generate an open circuit detection signal OPFB based on an output voltage Vout of the conversion circuit 235. The open circuit determination unit 220 receives the open circuit detection signal OPFB and determines whether the open circuit detection signal OPFB is too high, and if so, starts timing. When the open circuit detection signal OPFB is too high and continues for more than a predetermined length of time, the open circuit determining unit 220 outputs an open circuit protection signal OP. After receiving the open circuit protection signal OP, the protection unit 215 generates a protection signal LA to cause the feedback control unit 210 to enter a locked state and stop outputting the control signal Gate. Of course, the protection unit 215 can receive the protection signal of the other protection detection unit in addition to the open circuit protection signal OP of the open circuit determination unit 220, for example, the output voltage over voltage (Under Voltage) protection signal, and the output current over current (Over Current Protection signal, output current undercurrent (Under Current) protection signal, Under voltage lock out protection signal, etc., and corresponding protection signals are given temporary protection (ie, the abnormal state is restored immediately after removal) ) or lock protection (ie, the power conversion controller must be restarted to resume operation). Next, the operations of the feedback control unit 210 and the open circuit determination unit 220 will be described in detail.

The feedback control unit 210 includes an error amplifier 212 and a pulse width modulator 214. The non-inverting input terminal of the error amplifier 212 receives a reference voltage signal Vr, and the inverting input terminal receives the feedback signal FB to output an error amplification signal COMP according to the output. The pulse width modulator 214 receives the error amplification signal COMP and a triangular wave signal to generate a pulse width modulation signal PWM accordingly. The driving circuit 216 generates a control signal Gate according to the pulse width modulation signal PWM to control the switching SW in the conversion circuit 235 to perform switching. Since the feedback signal FB is generated according to the lowest voltage of the negative terminal in the LED array of the LED module 230, the minimum voltage of the negative terminal can be maintained at a predetermined negative terminal voltage, thereby improving the illumination. The efficiency of the polar body drive circuit.

The open circuit determining unit 220 includes an open comparator 222, a timing comparator 224, a current source 226, a timing switch S1, and a timing capacitor Ct. When any of the light-emitting diodes in the LED module 230 is broken due to damage, the negative terminal voltage of the corresponding LED string is lower than the predetermined negative terminal minimum voltage. At this time, the power conversion controller 200 will increase the output voltage Vout in an attempt to raise the negative terminal voltage of the above-described light emitting diode string to a predetermined negative terminal minimum voltage value. This will cause the output voltage Vout to be higher than a reasonable range, so that the level of the open circuit detection signal OPFB will be higher than a first reference level Vr1. At this time, the open comparator 222 will output the enable signal EN to enable the timer 224 to be clocked and simultaneously turn off the timer switch S1. Current source 226 will begin to charge timing capacitor Ct. When the duration of the abnormal condition is equal to the predetermined length of time, the voltage of the timing capacitor Ct will be equal to a second reference level Vr2, so that the timing comparator 224 outputs the open protection signal OP. If the duration of the abnormal condition is shorter than the predetermined length of time, the open circuit comparator 222 in the process stops outputting the enable signal EN, and the timing switch S1 is turned on to zero the charging of the timing capacitor Ct. If the predetermined length of time is longer than the length of time for some temporary circuit abnormalities, the temporary circuit abnormalities can be eliminated. For example, the power supply of the input power source Vin is unstable, and the LED module 230 is abnormally extinguished due to misjudgment. The predetermined length of time is based on the capacitance of the timing capacitor.

In addition, the transformer T in this embodiment has an auxiliary coil for emitting light When the polar body driving circuit is in operation, power can be stored in an initial capacitor Cin through an input diode D1 for operation of the power conversion controller 200. Since the transformer T can no longer transmit power to the starting capacitor Cin through the input diode D1 when the LED module 230 is open or other circuit abnormality occurs, the power conversion controller 200 may first enter the undervoltage protection. Therefore, the starting capacitor Cin needs to select a capacitor having a sufficient capacitance value to maintain the power conversion controller 200 longer than the predetermined length of time of the open circuit determining unit 220 when an abnormality such as an open circuit occurs. Of course, the power conversion controller 200 can also directly couple the power supply independent of the input power source VIN to receive the power required for operation, thereby avoiding the limitation of the above circuit setting.

Please refer to the fourth figure, which is a circuit diagram of a light emitting diode driving circuit according to a second preferred embodiment of the present invention. The LED driving circuit includes a power conversion controller 300, a conversion circuit 335, and a light emitting diode module 330. The conversion circuit 335 includes a switch SW, an inductor L1, a rectifying diode D3, and an output capacitor Cout. In this embodiment, the conversion circuit 335 is a step-down conversion circuit that converts the power of an input power source VIN to drive the LED module 330. The input power source VIN is formed by rectifying an AC power source through a bridge rectifier circuit 350. A starting capacitor Cin is coupled to the input power source VIN through a starting resistor Rst to generate a driving voltage Vdd. When the system is started and the input power supply VIN is started, power is stored in the start capacitor Cin through the start resistor Rst to activate the power conversion controller 300. When the power conversion controller 300 starts and begins to control the switching of the switch SW, the conversion circuit 335 will additionally provide power through the power feedback circuit 340 to maintain the voltage value of the driving voltage Vdd to enable the power conversion controller 300 to continue normal operation.

The power conversion controller 300 includes a feedback control unit 310, an input power detection unit 312, an open circuit determination unit 320, and a protection unit 315. The feedback control unit 310 includes a clock generator 302, a comparator 304, a gate 306, and an SR flip-flop 308. The clock generator 302 generates one of the fixed period clock signals Clk. And gate 304 receives a dimming signal DIM timely pulse The Clk is configured to trigger the set terminal S of the SR flip-flop 308 according to the clock signal Clk and the dimming signal DIM to generate a control signal Gate at the output terminal Q to turn on the switch SW. A current detecting resistor Rse is coupled to the switch SW to detect the magnitude of the current flowing through the switch SW and generate a current detecting signal Ise. The non-inverting input of the comparator 304 receives the current detecting signal Ise and the inverting input receives a third reference voltage signal Vr3. When the switch SW is turned on, the level of the current detecting signal Ise rises. When the level of the current detecting signal Ise rises to the level of the third reference voltage signal Vr3, the comparator 304 outputs a high level signal to the reset terminal R of the SR flip-flop 308, so that the SR flip-flop 308 stops outputting. The control signal Gate is turned off the switch SW.

When the light-emitting diode module 330 is opened, no current flows through the switch SW even if the switch SW is turned on. Therefore, the comparator 304 cannot reset the SR flip-flop 308 and the SR flip-flop 308 continues to output the control signal Gate. The open circuit determining unit 320 simultaneously receives the control signal Gate and the dimming signal DIM, and counts the length of time according to the dimming signal DIM. When the control signal Gate continues to generate for a longer period of time than the dimming signal DIM by a predetermined number of pulses, an open circuit protection signal OP is generated. After receiving the open circuit protection signal OP, the protection unit 315 generates a protection signal LA to cause the feedback control unit 310 to enter a locked state and stop outputting the control signal Gate. In this embodiment, the dimming signal DIM is a pulse dimming signal, but in fact, the dimming signal DIM can also be a DC dimming signal, which can be converted into a pulse dimming signal according to the level of the DC dimming signal and input to the pulse dimming signal. The open circuit determination unit 320 is used for timing.

Compared with the embodiment shown in FIG. 3, the power conversion controller 300 in this embodiment additionally includes an input power detecting unit 312. The input power detecting unit 312 detects the voltage value of the input power VIN. When the voltage value of the input power VIN is lower than a predetermined low voltage value, a protection pause signal PA is generated to the open circuit determining unit 320, so that the open circuit determining unit 320 is suspended for opening. The signal OP is protected to avoid an open circuit misjudgment caused by the temporary instability of the input power source VIN. Even the protection pause signal PA of the input power detecting unit 312 can also be used to stop the open circuit determining unit. The operation of the 320 or/and protection unit 315, even the operation of the feedback control unit 310, reduces the overall power consumption of the power conversion controller 300. In this way, the lower capacitance value of the starting capacitor Cin can still avoid the problem that the power conversion controller 300 enters the undervoltage protection before the open circuit protection, thereby achieving the advantage of reducing the cost of the LED driving circuit.

As described above, the present invention fully complies with the three requirements of the patent: novelty, advancement, and industrial applicability. The invention has been described above in terms of the preferred embodiments, and it should be understood by those skilled in the art that the present invention is not intended to limit the scope of the invention. It should be noted that variations and permutations equivalent to those of the embodiments are intended to be included within the scope of the present invention. Therefore, the scope of the invention is defined by the scope of the following claims.

Prior art:

10‧‧‧ Controller

30‧‧‧Lighting diode strings

35‧‧‧Transition circuit

40‧‧‧Power feedback circuit

L‧‧‧Inductance

C‧‧‧ capacitor

D‧‧‧Rectifying diode

IFB‧‧‧ current detection signal

CS‧‧‧current detection terminal

DRV‧‧‧ output

Gate. . . Control signal

Cin. . . Start capacitor

VDD. . . Drive voltage terminal

this invention:

100, 200, 300. . . Power conversion controller

110, 210, 310. . . Feedback control unit

115, 215, 315. . . Protection unit

1 20, 220, 320. . . Open circuit judgment unit

130. . . load

135, 235, 335. . . Conversion circuit

212. . . Error amplifier

214. . . Pulse width modulator

222. . . Open comparator

224. . . Timing comparator

226. . . Battery

230, 330. . . Light-emitting diode module

240. . . Current sharing circuit

245. . . Voltage divider

250, 350. . . Bridge rectifier circuit

302. . . Clock generator

304. . . Comparators

306. . . Gate

308. . . SR flip-flop

312. . . Input power detection unit

340. . . Power feedback circuit

PWM. . . Pulse width modulation signal

FB. . . Feedback signal

OP. . . Open circuit protection signal OP

Gate. . . Control signal

VIN. . . Input power

LA. . . Protection signal

T. . . transformer

D2, D3. . . Rectifier diode

Cout. . . Output capacitor

PA. . . Protection pause signal

VAC. . . AC power

Ri. . . Setting resistance

Vcc. . . Setting voltage

Vout. . . The output voltage

OPFB. . . Open circuit detection signal

Vr. . . Reference voltage signal

COMP. . . Error amplification signal

S1. . . Timing switch

Ct. . . Timing capacitor

Vr1. . . First reference level

EN. . . Enable signal

Vr2. . . Second reference level

D1. . . Input diode

Cin. . . Start capacitor

Vdd. . . Driving voltage

Rst. . . Startup resistor

Clk. . . Clock signal

DIM. . . Dimming signal

Rse. . . Current detecting resistor

Ise. . . Current detection signal

Vr3. . . Third reference voltage signal

S. . . Setting end

R. . . Reset end

Q. . . Output

The first figure is a schematic circuit diagram of a conventional LED driving circuit.

The second figure is a circuit diagram of a power conversion circuit according to the present invention.

The third figure is a circuit diagram of a light emitting diode driving circuit according to a first preferred embodiment of the present invention.

FIG. 4 is a circuit diagram of a light emitting diode driving circuit according to a second preferred embodiment of the present invention.

100. . . Power conversion controller

110. . . Feedback control unit

115. . . Protection unit

120. . . Open circuit judgment unit

130. . . load

135. . . Conversion circuit

Gate. . . Control signal

VIN. . . Input power

FB. . . Feedback signal

OP. . . Open circuit protection signal

LA. . . Protection signal

Claims (13)

A power conversion controller for controlling a conversion circuit to convert power of an input power source to drive a load, the power conversion controller comprising: a feedback control unit, which returns a signal according to one of the states representing the load, Controlling the conversion circuit; an open circuit determination unit, when determining that the load is in an open state for more than a predetermined length of time, generating an open circuit protection signal; a protection unit coupled to the feedback control unit and the open circuit determination unit, When receiving the open circuit protection signal, generating a protection signal to cause the feedback control unit to enter a locked state to stop controlling the conversion circuit; and an input power detection unit coupled to the input power source to detect Detecting an input voltage of the input power source, and outputting a protection pause signal when the input voltage is lower than a predetermined undervoltage value, so that the open circuit determination unit suspends outputting the open circuit protection signal. The power conversion controller of claim 1, wherein the predetermined length of time is determined by a capacitance of a timing capacitor. The power conversion controller of claim 1, wherein the load is a light emitting diode module. The power conversion controller according to claim 3, further receiving a dimming signal, wherein the power conversion controller controls the conversion circuit to adjust the illumination brightness of the LED module according to the adjustment. Optical signal adjustment. The power conversion controller of claim 4, wherein the open circuit determination unit sets the predetermined time length according to the dimming period. The power conversion controller according to claim 1 is further coupled to the conversion circuit to receive an operating power. The power conversion controller of claim 6, wherein the input power detection unit outputs the protection pause signal to stop the operation of the open circuit determination unit, the protection unit, or a combination thereof. A light emitting diode driving circuit comprising: a light emitting diode module; a converting circuit for converting power of an input power source to drive the light emitting diode module to emit light; and a power conversion controller according to Representing one of the states of the LED module to control the conversion circuit for power conversion, the power conversion controller determines that the LED module is in an open state for more than a predetermined length of time Performing an open circuit protection function to stop the conversion circuit for power conversion; wherein the power conversion controller further detects an input voltage of the input power source, and suspending the open circuit protection function when the input voltage is lower than a predetermined undervoltage value . The LED driving circuit of claim 8, further comprising a rectifying circuit for rectifying an AC input power into the input power. The illuminating diode driving circuit of claim 8, wherein the power conversion controller is coupled to the conversion circuit to receive an operating power. The illuminating diode driving circuit of claim 10, wherein the power conversion controller comprises an input power detecting unit, wherein the input power detecting unit is coupled to the input power to detect the input power The input voltage outputs a protection pause signal to stop the open circuit protection function when the input voltage is lower than a predetermined undervoltage value. The illuminating diode driving circuit of claim 11, wherein The power conversion controller further includes an open circuit determining unit, and when determining that the light emitting diode module is in an open state for more than a predetermined length of time, generating an open circuit protection signal, so that the power conversion controller performs the open circuit protection Features. The illuminating diode driving circuit of claim 8, wherein the power conversion controller stops the operation of a part of the circuit of the power conversion controller to reduce the input voltage when the input voltage is lower than the predetermined undervoltage value. Power consumption of the power conversion controller.