CN109741711A - A kind of LED backlight adjusting circuit based on high-frequency PWM - Google Patents
A kind of LED backlight adjusting circuit based on high-frequency PWM Download PDFInfo
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- CN109741711A CN109741711A CN201910192061.5A CN201910192061A CN109741711A CN 109741711 A CN109741711 A CN 109741711A CN 201910192061 A CN201910192061 A CN 201910192061A CN 109741711 A CN109741711 A CN 109741711A
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- 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
- Y02B20/30—Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]
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Abstract
The invention discloses a kind of, and the LED backlight based on high-frequency PWM adjusts circuit, including DC/DC power supply, LED light string, switch element and constant-current source, the output end series connection of the output end, the LED light string, the switch element and the constant-current source of the DC/DC power supply, the DC/DC power supply provides common anode pole tension for LED light string, the switch element controls on-off by pwm control signal, the constant-current source is always maintained at saturation bias state in switching elements conductive and in disconnecting, it is the configuration of the present invention is simple, at low cost, there is very strong practicability.
Description
Technical field
The present invention relates to electronic technology fields.Specifically, the present invention relates to a kind of LED backlight tune based on high-frequency PWM
Economize on electricity road.
Background technique
PWM light modulation is that LED is opened and closed by PWM wave to change the turn-on time of forward current, to reach brightness tune
The effect of section.It the occasion more demanding to LED backlight such as shows in screen, PWM is needed to work with higher frequency.In high frequency
Under, the rising edge and failing edge of current waveform are very precipitous, i.e. waveform Slew Rate is higher, are just able to achieve complete PWM square wave wave
Shape.In PWM light modulation, duty ratio precision directly determines the precision of light modulation, therefore it is required that pwm control signal and PWM current signal
Duty ratio to have higher consistency.
PWM light adjusting circuit has following several at present, and has deficiency:
(1) according to the pressure drop of LED light string, the resistance R of specific resistance value is concatenated in lamp string to obtain the current value of requirement,
As shown in Figure 1.This programme obtains current waveform using the on-off of pwm control signal control switch.But because single led lamp pressure
There are errors for drop, and multiple LED series connection cause the pressure drop difference of different LED light strings larger, so such dimming mode current precision
It is low, it cannot achieve accurate light modulation.
(2) realize that PWM is dimmed by the electric current of control constant-current source offer, as shown in Figures 2 and 3.In Fig. 2, PWM control
The noninverting input of signal input operational amplifier come control constant-current source offer electric current；In Fig. 3, pwm control signal control is opened
The on-off of pass come control constant-current source offer electric current.Both circuits have the problem of following several respects:
1. requiring the bandwidth of operational amplifier and metal-oxide-semiconductor higher when realizing high-frequency PWM, increase hardware cost, circuit
Complexity increases.
2. it is required that metal-oxide-semiconductor meets high-power simultaneously and realizes high-frequency when working in linear region, in manufacturing process compared with
For difficulty, MOS transistor device type selecting range is smaller.
3. can not achieve accurately duty ratio control.Constant-current source circuit is larger since metal-oxide-semiconductor drain voltage changes, so that permanent
Current source circuit is not able to maintain saturation biasing.When controlling switch disconnection of the signal in low level, Fig. 3, the drain electrode of metal-oxide-semiconductor is disconnected
The output end on road, operational amplifier enters power rail；When control signal jumps to high level from low level, the switch in Fig. 3 is closed
When conjunction, operational amplifier needs regular hour delay just to can enter normal linear work area, this has resulted in constant-current source and has mentioned
The rising edge of the current signal of confession can generate delay compared to the rising edge of pwm control signal, generate duty cycle error.
Existing scientific and technical literature also discloses some solutions, and documents CN103150997A discloses a kind of name
The referred to as patent of invention of " LED backlight drive circuit ", documents CN102811540A disclose a kind of entitled " suitable for big
The patent of invention of the PWM adjusting control circuit of power backlight LED driver ", the two inventions are using pwm control signal control electricity
The on-off in source realizes that PWM is dimmed, and requires the bandwidth of device higher when realizing high-frequency PWM, to the dependence of the performance of device very strong,
Complexity is high.The invention that documents CN104853486A discloses a kind of entitled " a kind of light adjusting circuit based on PWM " is special
Benefit, the invention do not solve the problems, such as to generate duty cycle error because constant-current supply is not able to maintain saturation bias state.
Summary of the invention
The present invention is to provide that a kind of current precision is high, PWM duty cycle essence to overcome deficiency existing for above-mentioned background technique
Degree is high, component bandwidth requirement is low, High-current output when parts selection range is wide, structure is simple, lower-cost is based on high frequency
The LED backlight regulating circuit of PWM.
To realize the purpose, the present invention adopts the following technical scheme:
A kind of LED backlight adjusting circuit based on high-frequency PWM, which is characterized in that including DC/DC power supply, LED light string, open
Close element and constant-current source, the output end of the DC/DC power supply, the LED light string, the switch element and the constant-current source it is defeated
Outlet series connection, the DC/DC power supply provide common anode pole tension for LED light string, and the switch element is controlled logical by pwm control signal
Disconnected, the constant-current source is always maintained at saturation bias state in switching elements conductive and in disconnecting.
Preferably, in switching elements conductive, the cathode of the LED light string can be connected with the output end of the constant-current source, institute
The anode for stating LED light string can be connected with the output end of the DC/DC power supply.
Preferably, the constant-current source may include metal-oxide-semiconductor, operational amplifier and resistance, the operational amplifier it is in the same direction defeated
Enter end and input relevant to the electric current that the constant-current source provides reference voltage Vref, the reverse input end of the operational amplifier and
The source electrode of the metal-oxide-semiconductor and one end of resistance are electrically connected, the other end of resistance ground connection, the operational amplifier it is defeated
Outlet is connected with the grid of metal-oxide-semiconductor, and the drain electrode of the metal-oxide-semiconductor is connected with the output end of the constant-current source, in the switch element
The drain electrode of the MOS pipe inputs metal-oxide-semiconductor bias voltage when disconnection.
Preferably, the constant-current source may include diode D1, the drain electrode phase of the cathode and the metal-oxide-semiconductor of the diode D1
Even, the anode input diode bias voltage Vd of the diode D1.
Preferably, the diode D1 reversely ends in the switching elements conductive, inputs the sun of the diode D1
The diode bias voltage Vd of pole be less than cathode voltage of the LED light string in the switching elements conductive, described two
Pole pipe D1 forward conduction when the switch element disconnects.
Preferably, the metal-oxide-semiconductor bias voltage for the drain electrode for inputting the metal-oxide-semiconductor when the switch element disconnects can be big
Difference between the grid voltage of the metal-oxide-semiconductor and the threshold voltage of the grid of the metal-oxide-semiconductor.
Preferably, the resistance of the reference voltage Vref, the resistance of the noninverting input of the operational amplifier is inputted
The relational expression between electric current I that value R and the constant-current source provide can are as follows: Vref=R × I.
The present invention controls signal by high-frequency PWM using keeping the constant-current source of saturation bias state to provide high-precision current
The on-off of control switch element SW obtains PWM current waveform.Constant-current source is not controlled the shadow of signal by high-frequency PWM in the present invention
It rings, therefore the component bandwidth requirement in constant-current source is low, greatly reduces hardware cost.
The present invention inputs metal-oxide-semiconductor biased electrical by the drain electrode when the switch element SW is disconnected in the metal-oxide-semiconductor of constant-current source
Pressure makes constant-current source keep saturation bias state, maintains linear characteristic.When switch element SW is disconnected, metal-oxide-semiconductor bias voltage is added in
In the drain electrode of metal-oxide-semiconductor, so that the output end of operational amplifier U1 is not entered power rail, solve in prior art in PWM
The hopping edge for controlling signal generates duty ratio mistake due to operational amplifier needs are switched to linear work area from nonlinear operation area
The problem of difference.
It is the configuration of the present invention is simple, at low cost, there is very strong practicability.
Through the following description and in conjunction with the attached drawings, the present invention will become more fully apparent, these attached drawings are used to explain the present invention
Embodiment.
Detailed description of the invention
Fig. 1 is the schematic diagram that the first LED backlight adjusts circuit in the prior art；
Fig. 2 is the schematic diagram that second of LED backlight adjusts circuit in the prior art；
Fig. 3 is the schematic diagram that the third LED backlight adjusts circuit in the prior art；
Fig. 4 is the schematic diagram of the embodiment of the present invention.
Specific embodiment
Embodiment 1, as shown in figure 4, it includes a DC/DC power supply, one that the LED backlight based on high-frequency PWM, which adjusts circuit,
1, switch element SW of LED light string and a constant-current source 22, it is the output end of the DC/DC power supply, the LED light string 1, described
The output end of switch element SW and the constant-current source 2 is sequentially connected in series.The switch element SW is logical by high-frequency PWM control signal control
Disconnected, the constant-current source 2 is always maintained at saturation bias state in switch element SW is connected and disconnects, and the DC/DC power supply is LED
Lamp string 1 provides common anode pole tension, and the anode of the LED light string 1 is connected with the output end of the DC/DC power supply.In the switch
The cathode of the LED light string 1 is connected with the output end of the constant-current source 2 when element SW conducting.
The constant-current source 2 includes diode D1, metal-oxide-semiconductor, operational amplifier U1 and resistance R, the operational amplifier U1's
Noninverting input inputs reference voltage Vref relevant to the electric current I that the constant-current source 2 provides, the reference voltage Vref, institute
State the relational expression between the electric current I that resistance R and the constant-current source 2 provide are as follows:
Vref=R × I --- formula 1.
The reverse input end of the operational amplifier U1 and one end of the source electrode of the metal-oxide-semiconductor and resistance R are electrically connected,
The resistance R other end ground connection, the output end of the operational amplifier U1 are electrically connected with the grid of metal-oxide-semiconductor, the leakage of the metal-oxide-semiconductor
Pole is connected with the output end of the constant-current source 2, and the drain electrode of the metal-oxide-semiconductor is electrically connected with the cathode of the diode D1, and described two
The anode input diode bias voltage Vd of pole pipe D1.
When switch element SW conducting, the diode bias voltage Vd is less than the cathode electricity of the LED light string 1
Pressure, the diode D1 reversely end.When the switch element SW is disconnected, the diode D1 forward conduction, described in input
The metal-oxide-semiconductor bias voltage of the drain electrode of metal-oxide-semiconductor be greater than the metal-oxide-semiconductor grid voltage and the metal-oxide-semiconductor threshold voltage of the grid it
Between difference, the metal-oxide-semiconductor bias voltage is equal to the diode bias voltage Vd and subtracts the forward conduction of the diode D1
Pressure drop.The threshold voltage of the grid of the metal-oxide-semiconductor is metal-oxide-semiconductor performance parameter itself.
The circuit design of the present embodiment first has to the electric current of the offer of the constant-current source 2 according to the parameter setting of LED light string 1
I, the electric current I that the resistance value of resistance R and constant-current source 2 provide, which is substituted into formula 1, can be obtained the value of the reference voltage Vref, then root
The claimed range of the diode bias voltage Vd can be obtained according to the parameter of the diode D1 and the metal-oxide-semiconductor.
In actual operation, when the switch element SW is connected, the constant-current source 2 exports constant high precision electro to the present embodiment
Stream, the LED light string 1 is bright, and the diode D1 reversely ends；When the switch element SW is disconnected, the LED light string 1 is gone out,
The diode D1 forward conduction, the diode bias voltage Vd are added in after the forward conduction voltage drop of diode D1 partial pressure
In the drain electrode of metal-oxide-semiconductor, so that constant-current source 2 is kept saturation bias state, maintain linear characteristic.
The following are a kind of design of physical circuit of the present embodiment, the electric current I that the constant-current source 2 provides is 100mA, the electricity
Resistance R be 10 Ω, according to formula 1 can calculate the reference voltage Vref be 1V；The DC/DC supply voltage is 40V, the height
The frequency of frequency pwm control signal is 100KHz, duty ratio 50%；The reverse withstand voltage of the diode D1 is 100V, described
The forward conduction voltage drop of diode D1 is 0.5V；The LED light string 1 includes 10 concatenated LED lamp beads, when the constant-current source 2
When the 100mA electric current I of offer is by the LED light string 1, the forward conduction voltage drop of every LED lamp bead is 3V, the LED
The forward conduction voltage drop of lamp string 1 is 30V；The threshold voltage of the grid of the metal-oxide-semiconductor is 2.9V, and the GS voltage of the metal-oxide-semiconductor is 3V,
Diode bias voltage Vd=5V is set.
When switch element SW conducting, the 100mA electric current I that the constant-current source 2 provides is described by the LED light string 1
The cathode voltage (drain voltage of the namely described metal-oxide-semiconductor) of LED light string 1 subtracts described equal to the DC/DC supply voltage
The cathode voltage 10V of the forward conduction voltage drop of LED light string 1, i.e. 40V-30V=10V, LED light string 1 at this time is greater than two pole
Pipe bias voltage Vd, diode D1 cut-off, therefore the diode bias voltage Vd will not be added in the drain electrode of metal-oxide-semiconductor.At this time
The constant-current source 2 forms the electric current of 100mA, that is, the high level of PWM current waveform in the LED light string 1.
When switch element SW is disconnected, the LED light string 1 and the drain electrode of the metal-oxide-semiconductor are disconnected, the positive guide of diode D1
Logical, the MOS pipe bias voltage for inputting the drain electrode of the metal-oxide-semiconductor is equal to the diode bias voltage Vd and subtracts diode D1's
Forward conduction voltage drop, i.e. 5V-0.5V=4.5V；The source voltage of the metal-oxide-semiconductor is equal with the reference voltage Vref, described
The source voltage that the grid voltage of metal-oxide-semiconductor is equal to the metal-oxide-semiconductor adds the GS voltage of the metal-oxide-semiconductor, i.e. 1V+3V=4V is described
Difference between the grid voltage of metal-oxide-semiconductor and the threshold voltage of the grid of the metal-oxide-semiconductor is 1.1V.The metal-oxide-semiconductor bias voltage is big
Difference between the grid voltage of the metal-oxide-semiconductor and the threshold voltage of the grid of the metal-oxide-semiconductor, therefore disconnected in switch element SW
Shi Suoshu constant-current source 2 still maintains saturation bias state, maintains linear characteristic, and the electric current in the LED light string 1 is 0 at this time,
The namely low level of PWM current waveform.The switch element SW is controlled signal control on-off repeatedly by high-frequency PWM, in LED
The alternate PWM current waveform of height is formed in lamp string 1.The parameter of the circuit devcie of the present embodiment is not limited to this above one kind.
Combining most preferred embodiment above, invention has been described, but the invention is not limited to implementations disclosed above
Example, and various modifications, equivalent combinations according to the essence of the present invention should be covered.
Claims (7)
1. a kind of LED backlight based on high-frequency PWM adjusts circuit, which is characterized in that including DC/DC power supply, LED light string, switch
Element and constant-current source, the output of the output end, the LED light string, the switch element and the constant-current source of the DC/DC power supply
End series connection, the DC/DC power supply provide common anode pole tension for LED light string, and the switch element is controlled logical by pwm control signal
Disconnected, the constant-current source is always maintained at saturation bias state in switching elements conductive and in disconnecting.
2. a kind of LED backlight based on high-frequency PWM according to claim 1 adjusts circuit, which is characterized in that in switch member
The cathode of the LED light string is connected with the output end of the constant-current source when part conducting.
3. a kind of LED backlight based on high-frequency PWM according to claim 1 or 2 adjusts circuit, which is characterized in that described
Constant-current source includes metal-oxide-semiconductor, operational amplifier and resistance, and the noninverting input input of the operational amplifier is mentioned with the constant-current source
The relevant reference voltage Vref of the electric current of confession, the source electrode and resistance of the reverse input end of the operational amplifier and the metal-oxide-semiconductor
One end be electrically connected, the other end of resistance ground connection, the grid phase of the output end and metal-oxide-semiconductor of the operational amplifier
Even, the drain electrode of the metal-oxide-semiconductor is connected with the output end of the constant-current source, the leakage of the metal-oxide-semiconductor when the switch element disconnects
Pole inputs metal-oxide-semiconductor bias voltage.
4. a kind of LED backlight based on high-frequency PWM according to claim 3 adjusts circuit, which is characterized in that the constant current
Source includes diode D1, and the cathode of the diode D1 is connected with the drain electrode of the metal-oxide-semiconductor, the anode input of the diode D1
Diode bias voltage Vd.
5. a kind of LED backlight based on high-frequency PWM according to claim 4 adjusts circuit, which is characterized in that two pole
Pipe D1 reversely ends in the switching elements conductive, diode D1 forward conduction when the switch element disconnects.
6. a kind of LED backlight based on high-frequency PWM according to claim 3 adjusts circuit, which is characterized in that opened described
The metal-oxide-semiconductor bias voltage for closing the drain electrode that the metal-oxide-semiconductor is inputted when element disconnects is greater than grid voltage and the institute of the metal-oxide-semiconductor
State the difference between the threshold voltage of the grid of metal-oxide-semiconductor.
7. a kind of LED backlight based on high-frequency PWM according to claim 3 adjusts circuit, which is characterized in that described in input
The electricity that the reference voltage Vref of the noninverting input of operational amplifier, the resistance value R of the resistance and the constant-current source provide
Flow the relational expression between I are as follows: Vref=R × I.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201910192061.5A CN109741711A (en) | 2019-03-14 | 2019-03-14 | A kind of LED backlight adjusting circuit based on high-frequency PWM |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201910192061.5A CN109741711A (en) | 2019-03-14 | 2019-03-14 | A kind of LED backlight adjusting circuit based on high-frequency PWM |
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| CN109741711A true CN109741711A (en) | 2019-05-10 |
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| Application Number | Title | Priority Date | Filing Date |
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| CN201910192061.5A Pending CN109741711A (en) | 2019-03-14 | 2019-03-14 | A kind of LED backlight adjusting circuit based on high-frequency PWM |
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| CN201680231U (en) * | 2010-03-17 | 2010-12-22 | Bcd半导体制造有限公司 | LED backlight driving device of LCD |
| CN102026442A (en) * | 2009-09-11 | 2011-04-20 | 艾沃特有限公司 | Adaptive switch mode led driver |
| CN103874296A (en) * | 2014-03-21 | 2014-06-18 | 武汉精测电子技术股份有限公司 | LED constant-current driving circuit of multi-path self-adaptive loads |
| CN107635322A (en) * | 2017-10-27 | 2018-01-26 | 国网山东省电力公司商河县供电公司 | A kind of Dimmable LED constant-current drive circuit |
| CN207781160U (en) * | 2017-12-04 | 2018-08-28 | 广州视源电子科技股份有限公司 | A kind of LED light bar, backlight module, liquid crystal display die set and terminal device |
| US20180332678A1 (en) * | 2017-05-12 | 2018-11-15 | Apple Inc. | Led driver gate clamp systems and methods |
-
2019
- 2019-03-14 CN CN201910192061.5A patent/CN109741711A/en active Pending
Patent Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102026442A (en) * | 2009-09-11 | 2011-04-20 | 艾沃特有限公司 | Adaptive switch mode led driver |
| CN201680231U (en) * | 2010-03-17 | 2010-12-22 | Bcd半导体制造有限公司 | LED backlight driving device of LCD |
| CN103874296A (en) * | 2014-03-21 | 2014-06-18 | 武汉精测电子技术股份有限公司 | LED constant-current driving circuit of multi-path self-adaptive loads |
| US20180332678A1 (en) * | 2017-05-12 | 2018-11-15 | Apple Inc. | Led driver gate clamp systems and methods |
| CN107635322A (en) * | 2017-10-27 | 2018-01-26 | 国网山东省电力公司商河县供电公司 | A kind of Dimmable LED constant-current drive circuit |
| CN207781160U (en) * | 2017-12-04 | 2018-08-28 | 广州视源电子科技股份有限公司 | A kind of LED light bar, backlight module, liquid crystal display die set and terminal device |
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Application publication date: 20190510 |