TWI780745B - Consistent illuminance control circuit - Google Patents

Abstract

A consistent illuminance control circuit includes a voltage converted unit, a LED unit, an illuminance compensation unit and a converted control unit. The voltage converted unit receives a input voltage and converts the input voltage into a output voltage. The LED unit receives the output voltage. A temperature sensor of the illuminance compensation unit senses a temperature of the LED unit and outputs a temperature signal. A voltage limiting element receives the temperature signal and outputs an illuminance compensating signal. The converted control unit receives the illuminance compensating signal and a voltage divided signal, and the converted control unit outputs a converted control signal to the voltage converted unit for controlling the voltage converted of voltage converted unit.

Description

LED control circuit for stable illumination

The invention relates to an LED control circuit, in particular to an LED control circuit with stable illuminance.

LED has high conversion efficiency, small size, long life, etc., and has become one of the main lighting equipment, such as display backlight modules, automobile and motorcycle lights, phototherapy, optical communication, etc., and many applications are on LED The demand for illuminance stability is getting higher and higher. Since the illuminance of the LED is quite sensitive to its input current, it is necessary for the control circuit to provide a highly stable current to stabilize its illuminance, but since the illuminance of the LED is also affected by its operating temperature, even if the control circuit provides a highly stable current Still can't keep the illuminance of LED stable.

The main purpose of the present invention is that the illuminance compensation unit provides compensation when the temperature of the LED unit changes, so that the illuminance of the LED unit can be kept stable.

An LED control circuit with stable illumination of the present invention includes a voltage conversion unit, an LED unit, an illumination compensation unit and a modulation control unit. The voltage conversion unit receives an input voltage and converts it to output an output voltage. The LED unit electrically connected to the voltage conversion unit to receive the input output voltage to generate light, the illuminance compensation unit has a temperature sensing element and a voltage limiting element, the temperature sensing element is used to sense the temperature of the LED unit and output a temperature signal, the voltage limiting element is electrically connected to the temperature Inductive element, the voltage limiting element receives the temperature signal and a voltage limiting signal, and the voltage limiting element outputs an illumination compensation signal, the modulation control unit is electrically connected to the illumination compensation unit to receive the illumination compensation signal, the modulation The control unit is electrically connected to the voltage conversion unit through a voltage divider circuit to receive a voltage divider signal, and the modulation control unit outputs a modulation control signal to the voltage conversion unit according to the illumination compensation signal and the voltage divider signal, to control the voltage conversion of the output voltage by the voltage conversion unit.

In the present invention, when the temperature of the LED unit rises, the illuminance compensation unit controls the modulation control unit to increase the frequency of the modulation control signal output by it, so that the potential of the output voltage output by the voltage conversion unit rises, The illuminance of the LED unit can be kept stable regardless of temperature.

100: LED control circuit for stable illumination

110: Voltage conversion unit

111: Input inductance

112: The first power transistor

113: Second power transistor

114: output capacitance

115: Zero voltage detector

116: Voltage level converter

117: delay unit

120: LED unit

130: Illumination compensation unit

131: Temperature sensing element

131a: Thermistor

131b: reference resistance

132: Voltage limiting element

132a: first comparator

132b: the first transmission gate

132c: the second transmission gate

132d: Inverter

132e: output terminal

140:Modulation control unit

141: Second comparator

142: Clock signal generator

143: Flip-flop

150: Voltage divider circuit

V _in : input voltage

V _out : output voltage

V _rt : temperature signal

V _lim : Voltage limit signal

V _ic : illumination compensation signal

V _fb : divided voltage signal

PFM: modulation control signal

N: output node

V _com1 : the first comparison signal

V _com2 : The second comparison signal

V _zcd : Zero voltage control signal

V _ref : Reference voltage

clk: clock signal

I _out : output current

Figure 1: According to an embodiment of the present invention, a circuit diagram of an LED control circuit for stabilizing illuminance.

Figure 2: A circuit diagram of a voltage limiting element according to an embodiment of the present invention.

Please refer to Figure 1, which is an embodiment of the present invention, a circuit diagram of an LED control circuit 100 with stable illuminance. In this embodiment, the LED control circuit 100 with stable illuminance includes a voltage conversion unit 110, an LED unit 120 , an illumination compensation unit 130 , a modulation control unit 140 and a voltage dividing circuit 150 .

The voltage conversion unit 110 is used for receiving an input voltage V _in for conversion and outputting an output voltage V _out to the LED unit 120 , so as to control the illuminance of the LED unit 120 through voltage conversion. In this embodiment, the voltage conversion unit 110 has an input inductor 111, a first power transistor 112, a second power transistor 113 and an output capacitor 114, and one end of the input inductor 111 receives the input voltage V _in , the other end of the input inductor 111 is electrically connected to one end of the first power transistor 112 and one end of the second power transistor 113, the other end of the first power transistor 112 is grounded, and the second power transistor 113 The other end of the output capacitor 114 is electrically connected to the LED unit 120, the other end of the output capacitor 114 is grounded, the first power transistor 112 and the second power transistor 113 are output by the modulation control unit 140 A modulation control signal PFM is used for voltage modulation of the input voltage _Vin .

The LED unit 120 is electrically connected to the voltage conversion unit 110 to receive the output voltage V _out to generate an output current I _out and emit light and heat, wherein the LED unit 120 in FIG. 1 is composed of a plurality of LED strings In other embodiments, there may only be a single light-emitting diode or more light-emitting diodes, which is not limited by this case.

The illuminance compensation unit 130 has a temperature sensing element 131 and a voltage limiting element 132, the temperature sensing element 131 is used to sense the temperature of the LED unit 120 and output a temperature signal V _rt , the voltage limiting element 132 is electrically connected The temperature sensing element 131 and the voltage limiting element 132 receive the temperature signal V _rt and a voltage limiting signal V _lim , and the voltage limiting element 132 outputs an illumination compensation signal V _ic . In this embodiment, the temperature sensing element 131 has a thermistor 131a and a reference resistor 131b, one end of the thermistor 131a receives a reference voltage V _ref , and the other end of the thermistor 131a is electrically connected to an output Node N, one end of the reference resistor 131b is electrically connected to the output node N, the other end of the reference resistor 131b is grounded, and the output node N outputs the temperature signal V _rt .

A resistance value of the thermistor 131a changes with the temperature of the LED unit 120. Preferably, the thermistor 131a has a negative temperature coefficient, so that the higher the ambient temperature, the higher the resistance value of the thermistor 131a. Therefore, when the ambient temperature is higher, the potential of the temperature signal V _rt output by the output node N rises, and vice versa when the ambient temperature decreases, because the resistance value of the thermistor 131a with a negative temperature coefficient and the environment The temperature relationship curve is close to a logarithmic curve, which is suitable for temperature sensing.

Please refer to Figures 1 and 2, the voltage limiting element 132 has a first comparator 132a, a first transfer gate 132b, a second transfer gate 132c and an inverter 132d, the first comparator 132a receives the temperature The signal V _rt and the voltage limit signal V _lim are used to compare the potentials of the temperature signal V _rt and the voltage limit signal V _lim to output a first comparison signal V _com1 , and the first comparison signal V _com1 is used to determine the voltage The potential of the illumination compensation signal V _ic output by the limiting element 132 is the same as the potential of the temperature signal V _rt or the potential of the voltage limiting signal V _lim .

Please refer to FIG. 2 , the inverter 132d is electrically connected to the first comparator 132a to receive the first comparison signal V _com1 , and the inverter 132d outputs an inverted first comparison signal. The first transmission gate 132b is electrically connected to the temperature sensing element 131, the first comparator 132a and the inverter 132d, the first transmission gate 132b receives the temperature signal V _rt and receives the first comparison signal V _com1 and The reversed first comparison signal is controlled to determine whether to transmit the temperature signal V _rt to an output terminal 132e as the illumination compensation signal V _ic . The second transmission gate 132c is electrically connected to the first comparator 132a and the inverter. Commutator 132d, the second transmission gate 132c receives the voltage limit signal V _lim and is controlled by the first comparison signal V _com1 and the reverse first comparison signal to determine whether to transmit the voltage limit signal V _lim to the output The terminal 132e serves as the illumination compensation signal V _ic .

In this embodiment, the N-type transistor of the first transmission gate 132b is controlled to be turned on or off by the first comparison signal _Vcom1 , and the P-type transistor of the first transmission gate 132b is controlled by the reversed first A comparison signal controls its turn-on or cut-off, and the first ratio voltage detector 115 of the N-type transistor of the second transmission gate 132c is reversed, and the second power can be used when the input inductor 111 is discharged to zero current. Transistor 113 is turned off to prevent reverse current from being transmitted to the input terminal. The voltage level converter 116 is electrically connected to the zero voltage detector 115 and the second power transistor 113, and the zero voltage control signal V _zcd output by the zero voltage detector 115 passes through the voltage level converter 116 The voltage level is converted and sent to the second power transistor 113 . The voltage level converter 116 is used for stepping up or stepping down the zero voltage control signal V _zcd to the working voltage of the second power transistor 113 . The delay unit 117 is electrically connected to the modulation control unit 140 and the first power transistor 112, the delay unit 117 receives the modulation control signal PFM of the modulation control unit 140 and delays it, and the delay unit 117 Send the delayed modulation control signal PFM to the first power transistor 112 . The delay of the delay unit 117 is used to stagger the turn-off time of the second power transistor 113 and the turn-on time of the first power transistor 112, so as to avoid the formation of the first power transistor 112 and the second power transistor 113. The ground loop will generate a large current and cause damage to the circuit.

In the present invention, the illuminance compensation unit 130 controls the modulation control unit 140 to increase the frequency of the modulation control signal PFM output by the illuminance compensation unit 130 when the temperature of the LED unit 120 rises, so that the output output of the voltage conversion unit 110 The potential of the voltage V _out rises, so that the illuminance of the LED unit 120 can be kept stable without being affected by temperature.

The scope of protection of the present invention should be defined by the scope of the appended patent application. Any changes and modifications made by anyone who is familiar with this technology without departing from the spirit and scope of the present invention belong to the scope of protection of the present invention. .

100: LED control circuit for stable illumination

110: Voltage conversion unit

111: Input inductance

112: The first power transistor

113: Second power transistor

114: output capacitance

115: Zero voltage detector

116: Voltage level converter

117: delay unit

120: LED unit

130: Illumination compensation unit

131: Temperature sensing element

131a: Thermistor

131b: reference resistance

132: Voltage limiting element

140:Modulation control unit

141: Second comparator

142: Clock signal generator

143: Flip-flop

150: Voltage divider circuit

V _in : input voltage

I _out : output current

V _out : output voltage

V _rt : temperature signal

V _lim : Voltage limit signal

V _ic : illumination compensation signal

V _fb : divided voltage signal

PFM: modulation control signal

N: output node

clk: clock signal

V _com2 : The second comparison signal

V _zcd : Zero voltage control signal

V _ref : Reference voltage

Claims (9)

An LED control circuit with stable illuminance, which includes: a voltage conversion unit that receives an input voltage for conversion and outputs an output voltage; an LED unit that is electrically connected to the voltage conversion unit to receive the output voltage to generate light; an illuminance The compensation unit has a temperature sensing element and a voltage limiting element, the temperature sensing element is used to sense the temperature of the LED unit and output a temperature signal, the voltage limiting element is electrically connected to the temperature sensing element, the voltage limiting element receiving the temperature signal and a voltage limiting signal, and the voltage limiting element outputs an illumination compensation signal; and a modulation control unit, electrically connected to the illumination compensation unit to receive the illumination compensation signal, and the modulation control unit via an The voltage dividing circuit is electrically connected to the voltage conversion unit to receive a voltage division signal, and the modulation control unit outputs a modulation control signal to the voltage conversion unit according to the illumination compensation signal and the voltage division signal to control the voltage conversion unit's voltage conversion to this output voltage. An LED control circuit with stable illumination as in claim item 1, wherein the temperature sensing element has a thermistor and a reference resistor, one end of the thermistor receives a reference voltage, and the other end of the thermistor is electrically connected to an output node, one end of the reference resistor is electrically connected to the output node, the other end of the reference resistor is grounded, and the output node outputs the temperature signal, wherein a resistance value of the thermistor varies with the temperature of the LED unit. The LED control circuit with stable illuminance as claimed in item 1, wherein the voltage limiting element has a first comparator, the first comparator receives the temperature signal and the voltage limiting signal, and the first comparator is used to compare the temperature signal and the The potential of the voltage limiting signal is outputted as a first comparison signal, and the first comparison signal is used to determine that the potential of the illumination compensation signal output by the voltage limiting element is the same as that of the temperature signal or the voltage limiting signal. The LED control circuit with stable illuminance according to claim 3, wherein the voltage limiting element has a first transmission gate, a second transmission gate and an inverter, and the inverter is electrically connected to the first comparator to receive the The first comparison signal, and the inverter outputs the inverted first comparison signal, the first transmission gate is electrically connected to the temperature sensing element, the first comparator and the inverter, and the first transmission gate receives The temperature signal is controlled by the first comparison signal and the reverse first comparison signal to determine whether to send the temperature signal to an output terminal as the illumination compensation signal, and the second transmission gate is electrically connected to the first comparison The device and the inverter receive the voltage limit signal and are controlled by the first comparison signal and the inverted first comparison signal to determine whether to send the voltage limit signal to the output terminal as the illumination compensation signal. An LED control circuit with stable illumination as in claim item 1, wherein the modulation control unit has a second comparator, a clock signal generator and a flip-flop, and the second comparator receives the illumination compensation signal and the divided voltage signal, and the second comparator outputs a second comparison signal, the flip-flop is electrically connected to the second comparator and the clock signal generator, and the flip-flop receives the second comparison signal and the clock signal The generator outputs a clock signal, and the flip-flop outputs the modulation control signal. As the LED control circuit with stable illumination in claim item 1, wherein the voltage conversion unit has an input inductor, a first power transistor, a second power transistor and an output capacitor, one end of the input inductor receives the input voltage, The other end of the input inductor is electrically connected to one end of the first power transistor and one end of the second power transistor, the other end of the first power transistor is grounded, and the other end of the second power transistor is electrically connected to One end of the output capacitor is connected to the LED unit, the other end of the output capacitor is grounded, and the first power transistor and the second power transistor are controlled by the modulation control signal. The LED control circuit with stable illumination according to claim 6, wherein the voltage conversion unit has a zero voltage detector, and the zero voltage detector is electrically connected to the input inductor, the voltage divider circuit and the second power transistor , the zero voltage detector detects whether a voltage of the input inductor is zero by the divided voltage signal And output a zero-voltage control signal, the zero-voltage control signal is used to determine whether to turn off the second power transistor. The LED control circuit with stable illuminance according to claim 7, wherein the voltage conversion unit has a voltage level converter, the voltage level converter is electrically connected to the zero voltage detector and the second power transistor, and the zero voltage The zero-voltage control signal output by the voltage detector is converted to a voltage level by the voltage level converter and then sent to the second power transistor. The LED control circuit for stable illuminance according to claim 8, wherein the voltage conversion unit has a delay unit, the delay unit is electrically connected to the modulation control unit and the first power transistor, and the delay unit receives the modulation control unit and delaying the modulation control signal, and the delay unit transmits the delayed modulation control signal to the first power transistor.

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