CN108966403B - Conversion type constant current LED driver - Google Patents

Conversion type constant current LED driver Download PDF

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CN108966403B
CN108966403B CN201710387184.5A CN201710387184A CN108966403B CN 108966403 B CN108966403 B CN 108966403B CN 201710387184 A CN201710387184 A CN 201710387184A CN 108966403 B CN108966403 B CN 108966403B
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current
inductor
duty cycle
constant current
voltage
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CN108966403A (en
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萧韦俊
江岳桦
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Taiwan Semiconductor Manufacturing Co TSMC Ltd
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Taiwan Semiconductor Manufacturing Co TSMC Ltd
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
    • H05B45/30—Driver circuits
    • H05B45/37—Converter circuits
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B20/00—Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps
    • Y02B20/40—Control techniques providing energy savings, e.g. smart controller or presence detection

Abstract

The invention discloses a conversion type constant current LED driver, which is provided with an energy transmission unit, an LED module, a power transistor, a resistor and a control unit, wherein the control unit is provided with a driving unit for generating a driving voltage signal and a duty cycle determining unit for determining a duty cycle of the driving voltage signal, the duty cycle determining unit determines a charging time of a reference current to an external capacitor according to a current time length of the duty cycle and determines a discharging time of a discharging current to the external capacitor according to an inductor discharging time to generate a comparison voltage, a next time length of the duty cycle is generated according to a comparison operation of the comparison voltage and a sawtooth voltage, and the discharging current is in direct proportion to an average value of an inductor charging state signal.

Description

Conversion type constant current LED driver
Technical Field
The invention relates to a conversion type constant current LED driver.
Background
Referring to fig. 1, fig. 1 is a block diagram of a conventional conversion type constant current LED driver in the prior art. As shown in fig. 1, the switching type constant current LED driver has a power conversion control unit 10, an LED module 20 and a resistor 30.
The power conversion control unit 10 is used for controlling the voltage V across the resistor 30XAdjusting a duty cycle to convert an input DC voltage VINIs converted into an output constant current IOTo drive the LED module 20.
However, there is still room for improvement in response speed and stability of the conventional switching constant current LED driver.
To solve the foregoing problems, there is a need in the art for a novel switched constant current LED driver.
Disclosure of Invention
An aspect of the present invention is to provide a switching type constant current LED driver, which can generate a duty cycle in a duty cycle feedback manner to quickly stabilize an output current at a predetermined current value, and the predetermined current value can be set by an external resistor.
Another aspect of the present invention is to provide a switching type constant current LED driver, which can determine the next time period of a duty cycle according to an inductor charging state signal, the current time period of the duty cycle and an inductor discharging time.
To achieve the above object, a switched constant current LED driver is then proposed, having:
an energy transmission unit having an inductor, a diode and a capacitor for converting an input dc voltage into an output constant current, wherein the diode provides a discharge current by discharging an accumulated energy of the inductor, the capacitor provides the output constant current by providing an auxiliary current to cooperate with the discharge current, and the energy transmission unit has a sensing circuit for providing an inductor discharge state signal of the inductor;
the LED module is connected with the energy transmission unit to receive the output constant current;
the power transistor is provided with a control end, a channel input end and a channel output end, the control end is connected with a driving voltage signal, and the channel input end is connected with the energy transmission unit;
a resistor connected between the channel output end and a reference ground to generate an inductance charging state signal; and
a control unit having a duty cycle determining unit and a driving unit, the driving unit being configured to generate the driving voltage signal, and the duty cycle determining unit being configured to determine a duty cycle of the driving voltage signal, wherein the duty cycle determining unit determines a charging time of a first current to an external capacitor according to a current time duration of the duty cycle and determines a discharging time of a second current to the external capacitor according to an inductor discharging time to generate a comparison voltage, and generates a next time duration of the duty cycle according to a comparison operation of the comparison voltage and a sawtooth voltage, the first current being directly proportional to a reference voltage, the second current being directly proportional to an average value of the inductor charging status signal, and the inductor discharging time being determined according to the inductor discharging status signal.
In one embodiment, the control unit has a first transconductance amplifier for generating the first current according to the reference voltage, and a second transconductance amplifier for generating the second current according to the average value of the inductor charge state signal.
In one embodiment, the first transconductance amplifier and/or the second transconductance amplifier has a current mirror circuit.
In one embodiment, the control unit has a comparator for determining the inductor discharge time according to a comparison result of the inductor discharge state signal and a predetermined voltage.
In one embodiment, the power transistor is an N-type MOSFET.
Drawings
Fig. 1 is a block diagram of a conventional switching constant current LED driver.
Fig. 2 is a block diagram of an embodiment of a switched constant current LED driver according to the present invention.
Fig. 3a is a circuit diagram of an embodiment of an energy transmission unit of fig. 2.
Fig. 3b is a circuit diagram of another embodiment of an energy transmission unit of fig. 2.
Fig. 4 is a circuit diagram of an embodiment of a control unit of fig. 2.
Detailed Description
In order that the objects, technical solutions and advantages of the present invention will become more apparent, the present invention will be further described in detail with reference to the accompanying drawings in conjunction with the following specific embodiments.
Referring to fig. 2, fig. 2 is a block diagram of an embodiment of a conversion type constant current LED driver according to the invention. As shown in fig. 2, the switching type constant current LED driver includes an energy transmission unit 100, an LED module 110, a power transistor 120, a resistor 130, a control unit 140, and a capacitor 150.
The energy transmission unit 100 has an inductor, a diode and a capacitor for converting an input DC voltage VINIs converted into an output constant current IOWherein the diode provides a discharge current by discharging an accumulated energy of the inductor, the capacitor provides the output constant current by providing an auxiliary current combined with the discharge current, and the energy transmission unit has a sensing circuit for providing an inductor discharge state signal V of the inductordis。
The LED module 110 is connected with the energy transmission unit 100 to receive the output constant current IO。
The power transistor 120 may be an N-typeA MOSFET (metal-oxide-semiconductor field effect transistor) having a control terminal, a channel input terminal and a channel output terminal, the control terminal being connected with a driving voltage signal VGConnected, the channel input is connected to the energy transfer unit 100.
The resistor 130 has a resistance RCSAnd is connected between the channel output terminal and a reference ground to generate an inductor charging state signal VCS。
Referring to fig. 3a, fig. 3a is a circuit diagram of an embodiment of the energy transmission unit 100 of fig. 2. As shown in fig. 3a, the energy transfer unit 100 has an inductor 101, a diode 102 and a capacitor 103, wherein one end of the inductor 101 is connected to the dc voltage VINThe other end is connected to the anode of the diode 102 and the channel of the power transistor 120, and the cathode of the diode 102 is connected to the capacitor 103 and the LED module 110.
During a turn-on period T of the power transistor 120ONThe voltage across the inductor 101 is approximately equal to VIN(ii) a When the power transistor 120 is turned off, the inductor 101 is in a discharging period TdisThe pressure is about equal to (V)IN-VD-VLED) In which V isDIs the bias voltage of the diode 102, VLEDIs the bias voltage of the LED module 110. Because the inductor 101 is in the conducting period TONThe accumulated energy is equal to the discharge period TdisThe released energy outputs a constant current IOEqual to the period T of the inductor 101 during dischargedisAverage value of the supplied current, and thus, a constant current I is outputOThe derivation can be as follows:
VIN×TON+(VIN-VD-VLED)×Tdis＝0 (1)
Figure BDA0001306201430000041
Figure BDA0001306201430000042
Figure BDA0001306201430000043
Figure BDA0001306201430000044
Figure BDA0001306201430000045
wherein E isINRepresenting the time during which a transition period T occursSEnergy accumulated in the internal inductor 101, EOUTRepresents the transition period TSEnergy, I, released by the internal inductor 1011Represents the charging current, I, of the inductor 1012Representing the discharge current, V, of the inductor 101CS，AVGSignal V representing the state of charge of the inductorCSAverage value of (a).
If a charging current source (with a current value of V) is designed inside the control unit 140REF×gm1) To be in the conducting period TONCharging the capacitor 150 and designing a discharging current source (with a current value of V)CS，AVG×gm2) To be in the discharge period TdisDischarging the capacitor 150, at steady state,
VCS，AVG×gm2×Tdis＝VREF×gm1×TON(7)
Figure BDA0001306201430000046
that is, the present invention enables the designer to obtain the desired output constant current I by only changing the resistance of the resistor 130O。
Referring to fig. 3b, fig. 3b is a circuit diagram of another embodiment of the energy transmission unit 100 of fig. 2. As shown in fig. 3b, the energy transfer unit 100 has an inductor 101, a diode 102 and a capacitor 103, wherein one end of the inductor 101 is connected to the dc voltage VINThe other end of the diode 102 is connected to the anode of the diode 102 and the channel of the power transistor 120, and the cathode of the diode 102 is connected to the cathode of the power transistorConnected to the capacitor 103 and the LED module 110.
During a turn-on period T of the power transistor 120ONThe voltage across the inductor 101 is approximately equal to VIN(ii) a When the power transistor 120 is turned off, the inductor 101 is in a discharging period TdisThe cross pressure born by the device is about equal to (-V)D-VLED) In which V isDIs the bias voltage of the diode 102, VLEDIs the bias voltage of the LED module 110. Because the inductor 101 is in the conducting period TONThe accumulated energy is equal to the discharge period TdisThe released energy outputs a constant current IOEqual to the period T of the inductor 101 during dischargedisAverage value of the supplied current, and thus, a constant current I is outputOThe derivation can be as follows:
VIN×TON+(-VD-VLED)×Tdis＝0 (1)
Figure BDA0001306201430000051
Figure BDA0001306201430000052
Figure BDA0001306201430000053
Figure BDA0001306201430000054
Figure BDA0001306201430000055
wherein E isINRepresenting the time during which a transition period T occursSEnergy accumulated in the internal inductor 101, EOUTRepresents the transition period TSEnergy, I, released by the internal inductor 1011Representing the charging current of the inductor 101, 12Representing the discharge current, V, of the inductor 101CS，AVGSignal V representing the state of charge of the inductorCSAverage value of (a).
If a charging current source (with a current value of V) is designed inside the control unit 140REF×gm1) To be in the conducting period TONCharging the capacitor 150 and designing a discharging current source (with a current value of V)CS，AVG×gm2) To be in the discharge period TdisDischarging the capacitor 150, at steady state,
VCS，AVG×gm2×Tdis＝VREF×gm1×TON(7)
Figure BDA0001306201430000056
that is, the present invention enables the designer to obtain the desired output constant current I by only changing the resistance of the resistor 130O。
Referring to fig. 4, fig. 4 is a circuit diagram of an embodiment of the control unit 140 of fig. 2. As shown in fig. 4, the control unit 140 has a first transconductance amplifier 141, a switch 142, an integrating circuit 143, a second transconductance amplifier 144, a switch 145, a comparator 146, a discharge time detecting circuit 147 and a driving unit 148, wherein the first transconductance amplifier 141, the switch 142, the integrating circuit 143, the second transconductance amplifier 144, the switch 145, the comparator 146 and the discharge time detecting circuit 147 form a duty cycle determining unit. The driving unit 148 is used for generating the driving voltage signal VGAnd the duty cycle determining unit is used for determining the driving voltage signal VGA period of responsibility (i.e. T)ON) Wherein the duty cycle determining unit determines the duty cycle (i.e. T)ON) A current time length of the switch 142 to determine a first current IC1A charging time for the external capacitor 150, and a discharging time according to an inductor (i.e. T)dis) Determining the on-time of the switch 145 to determine a second current IC2A discharge time of the external capacitor 150 to generate a comparison voltage VCMP(ii) a The first current IC1And a reference voltage VREFIs proportional to the reference voltage V by the first transconductance amplifier 141REFProceed a firstThe second current I is generated by transductive amplification operationC2And the inductance charging state signal VCSAn average value V ofCS，AVGIs proportional to the average value V and is measured by the second transconductance amplifier 144CS，AVGPerforming a second transconductance amplification operation to generate the second transconductance amplification signal, and the integration circuit 143 is used for amplifying the inductor charging state signal VCSPerforming an average operation to generate the average value VCS，AVG(ii) a And a comparator 146 for comparing the comparison voltage VCMPAnd a sawtooth voltage VSAWA comparison operation is performed to generate the duty cycle (i.e., T)ON) The next length of time. In addition, the discharge time detection circuit 147 is used for detecting the discharge time according to the inductor discharge state signal VdisAnd a predetermined voltage (T) to determine the inductor discharge timedis). In addition, the first transconductance amplifier 141 and/or the second transconductance amplifier 144 may have a current mirror circuit.
Through the design disclosed in the foregoing, the present invention has the following advantages:
1. the switching type constant current LED driver can generate a duty cycle in a duty cycle feedback mode so as to enable the output current to be quickly stabilized at a preset current value, and the preset current value can be set by an external resistor.
2. The conversion type constant current LED driver can determine the next time length of a duty cycle according to an inductor charging state signal, the current time length of the duty cycle and inductor discharging time.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (4)

1. A switched constant current LED driver, having:
an energy transmission unit having an inductor, a diode and a capacitor for converting an input dc voltage into an output constant current, wherein the diode provides a discharge current by discharging an accumulated energy of the inductor, the capacitor provides the output constant current by providing an auxiliary current for combining with the discharge current, and the energy transmission unit has a sensing circuit for providing an inductor discharge state signal of the inductor;
the LED module is connected with the energy transmission unit to receive the output constant current;
the power transistor is provided with a control end, a channel input end and a channel output end, the control end is connected with a driving voltage signal, and the channel input end is connected with the energy transmission unit;
a resistor connected between the channel output end and a reference ground to generate an inductance charging state signal; and
a control unit having a duty cycle determining unit and a driving unit, the driving unit being configured to generate the driving voltage signal, and the duty cycle determining unit being configured to determine a duty cycle of the driving voltage signal, wherein the duty cycle determining unit determines a charging time of a first current to an external capacitor according to a current time duration of the duty cycle and a discharging time of a second current to the external capacitor according to an inductor discharging time to generate a comparison voltage, and generates a next time duration of the duty cycle according to a comparison operation of the comparison voltage and a sawtooth voltage, the first current being directly proportional to a reference voltage, the second current being directly proportional to an average value of the inductor charging status signal, and the inductor discharging time being determined according to the inductor discharging status signal;
the control unit has a first transconductance amplifier for generating the first current according to the reference voltage, and a second transconductance amplifier for generating the second current according to the average value of the inductor charging state signal.
2. The switched constant current LED driver of claim 1, wherein the first transconductance amplifier and/or the second transconductance amplifier has a current mirror circuit.
3. The converted constant current LED driver of claim 1, wherein the control unit comprises a comparator for determining the inductor discharge time according to a comparison of the inductor discharge state signal and a predetermined voltage.
4. The switched mode constant current LED driver of claim 1, wherein said power transistor is an N-type MOSFET.
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Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN201349353Y (en) * 2009-01-19 2009-11-18 冠捷投资有限公司 Double-dimming backlight source drive device
CN103108437A (en) * 2011-11-15 2013-05-15 昂宝电子（上海）有限公司 Light-emitting diode (LED) illuminating system and method for constant-current control in various operation modes
CN103858328A (en) * 2011-09-30 2014-06-11 皇家飞利浦有限公司 Active capacitor circuit
TWM496905U (en) * 2014-11-21 2015-03-01 Anwell Semiconductor Corp LED driving circuit with improved performance and utilization rate
TW201526699A (en) * 2013-12-18 2015-07-01 Univ Lunghwa Sci & Technology Single-stage SEPIC LED driver with PFC function
TW201531149A (en) * 2014-01-17 2015-08-01 Immense Advance Technology Corp PWM controller capable of adjusting output current ripple by resistor and LED driving circuit
TW201603633A (en) * 2014-07-02 2016-01-16 盛群半導體股份有限公司 LED backlight driving device
TWM518453U (en) * 2014-08-01 2016-03-01 Anwell Semiconductor Corp LED dimming circuit of front-end power factor correction

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN201349353Y (en) * 2009-01-19 2009-11-18 冠捷投资有限公司 Double-dimming backlight source drive device
CN103858328A (en) * 2011-09-30 2014-06-11 皇家飞利浦有限公司 Active capacitor circuit
CN103108437A (en) * 2011-11-15 2013-05-15 昂宝电子（上海）有限公司 Light-emitting diode (LED) illuminating system and method for constant-current control in various operation modes
TW201526699A (en) * 2013-12-18 2015-07-01 Univ Lunghwa Sci & Technology Single-stage SEPIC LED driver with PFC function
TW201531149A (en) * 2014-01-17 2015-08-01 Immense Advance Technology Corp PWM controller capable of adjusting output current ripple by resistor and LED driving circuit
TW201603633A (en) * 2014-07-02 2016-01-16 盛群半導體股份有限公司 LED backlight driving device
TWM518453U (en) * 2014-08-01 2016-03-01 Anwell Semiconductor Corp LED dimming circuit of front-end power factor correction
TWM496905U (en) * 2014-11-21 2015-03-01 Anwell Semiconductor Corp LED driving circuit with improved performance and utilization rate

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