An LED color temperature adjustment circuit that effectively prevents current overshoot

Abstract

The present invention relates to an LED color temperature adjustment circuit that effectively prevents current overshoot. The circuit is connected to a cold color temperature LED and a warm color temperature LED respectively. The adjustment circuit includes an LED constant current drive circuit, a dimming control single chip, a cold color temperature drive MOSFET and a warm color temperature drive MOSFET. The LED constant current drive circuit is connected to the dimming control single chip, the cold color temperature drive MOSFET and the warm color temperature drive MOSFET respectively. The cold color temperature drive MOSFET is connected to the cold color temperature LED, and the warm color temperature drive MOSFET is connected to the warm color temperature LED. The adjustment circuit also includes a color temperature adjustment drive circuit, and the color temperature adjustment drive circuit is connected to the dimming control single chip, the cold color temperature drive MOSFET and the warm color temperature drive MOSFET respectively. Compared with the prior art, the present invention has the advantages of reducing costs and ensuring reliability.

Description

Technical Field

[0001] The invention relates to an LED color temperature adjustment circuit, in particular to an LED color temperature adjustment circuit which can effectively prevent current overshoot. Background Art

[0002] The existing mainstream mature color temperature adjustment LED driver products, the circuit is as shown in the frame Figure 1 As shown, a group of DC / DC is used to drive the cold color temperature LED and the warm color temperature LED respectively. Such a color temperature adjustment circuit has a good effect and is very reliable, but the cost of the DCDC driving circuit is very high.

[0003] There is also a low-cost color temperature adjustment LED driver product, the circuit is as shown in the frame Figure 2 As shown, the existing cold color temperature driving MOSFET 202 and the existing warm color temperature driving MOSFET 203 are driven by the PWM signal of the existing dimming control microcontroller 201 to switch the LED constant current driving circuit 200 to flow to the existing cold color temperature LED 2 204 or the existing warm color temperature LED 2 205.

[0004] Use as box Figure 2 When the product shown in the figure is used, the existing cold color temperature driving MOSFET 202 driven by the single chip PWM2 and PWM3 is turned on and the existing warm color temperature driving MOSFET 203 is turned on. Since PWM3 passes through the signal inverter 206, the inverted PWM3 signal will be delayed, which will eventually cause the following Figure 3 The conduction timing of the two MOSFETs makes the LED constant current drive circuit unloaded when the two MOSFETs are switched.

[0005] Using two PWM signals of the microcontroller to control the switching of two MOSFETs separately may also cause the LED constant current drive circuit to be unloaded when the two MOSFETs are switched because the two PWM signals are not synchronized.

[0006] Since LED drivers are generally current sources, and the characteristics of current sources are that they cannot be open-circuited, if the two MOSFETs for color temperature adjustment do not overlap during conduction, the LED constant current drive circuit will be open-circuited when the two MOSFETs are switched, causing the output voltage to rise. When the switching is completed, the other MOSFET is turned on, causing an instantaneous excessive current, which can damage the LED and MOSFET. Figure 3 If the MOSFET switching sequence is not the same, it will cause damage to the LED and MOSFET. This problem can be avoided by turning on both MOSFETs at the same time during switching. Summary of the invention

[0007] The purpose of the present invention is to overcome the defects of the prior art and provide an LED color temperature adjustment circuit which can effectively prevent current overshoot.

[0008] The purpose of the present invention can be achieved by the following technical solutions:

[0009] The invention discloses an LED color temperature adjustment circuit which effectively prevents current overshoot. The circuit is connected to a cold color temperature LED and a warm color temperature LED respectively. The adjustment circuit comprises an LED constant current drive circuit, a dimming control single chip computer, a cold color temperature drive MOSFET and a warm color temperature drive MOSFET respectively. The LED constant current drive circuit is connected to the dimming control single chip computer, the cold color temperature drive MOSFET and the warm color temperature drive MOSFET respectively. The cold color temperature drive MOSFET is connected to the cold color temperature LED, and the warm color temperature drive MOSFET is connected to the warm color temperature LED. The adjustment circuit also comprises a color temperature adjustment drive circuit which is connected to the dimming control single chip computer, the cold color temperature drive MOSFET and the warm color temperature drive MOSFET respectively.

[0010] Preferably, the color temperature adjustment driving circuit includes a signal inverter U2, an R / S trigger U1, a boost circuit, a boost delay circuit, a first totem pole circuit and a second totem pole circuit. The signal inverter U2 is connected to the R / S trigger U1 through the boost circuit and the boost delay circuit respectively, the R / S trigger U1 is connected to the cold color temperature LED through the first totem pole circuit, the R / S trigger U1 is connected to the warm color temperature LED through the second totem pole circuit, and the signal inverter U2 is connected to the dimming control microcontroller.

[0011] Preferably, the boost circuit includes a transistor Q9 and a transistor Q10, which are used to boost the 3.3V signal to 15V and output it to the R / S trigger U1.

[0012] Preferably, the base of the transistor Q9 is connected to the signal inverter U2 via the resistor R16, the emitter is connected to the R1 pin of the R / S trigger U1, and the collector is grounded.

[0013] Preferably, the transistor Q10 is connected to the signal inverter U2 via the resistor R17, the emitter is connected to the R2 pin of the R / S trigger U1, and the collector is grounded.

[0014] Preferably, the boost delay circuit includes a transistor Q11 and a transistor Q12, which are used to boost the 3.3V signal to 15V and delay the output signal, and output it to the R / S trigger U1.

[0015] Preferably, the base of the transistor Q11 is connected to the signal inverter U2 via a resistor R18, and the base is grounded via a capacitor C3, the emitter is connected to the S1 pin of the R / S trigger U1, and the collector is grounded.

[0016] Preferably, the base of the transistor Q12 is connected to the signal inverter U2 via a resistor R19, and the base is grounded via a capacitor C4, the emitter is connected to the S2 pin of the R / S trigger U1, and the collector is grounded.

[0017] Preferably, the first totem pole circuit comprises a transistor Q1 and a transistor Q3, the base of the transistor Q1 is connected to the base of the transistor Q3, the emitter of the transistor Q1 is connected to the emitter of the transistor Q3 and then connected to the cold color temperature driving MOSFET Q4;

[0018] The second totem pole circuit includes a transistor Q5 and a transistor Q7, the base of the transistor Q5 is connected to the base of the transistor Q7, the emitter of the transistor Q5 is connected to the emitter of the transistor Q7 and then connected to the warm color temperature driving MOSFET Q8.

[0019] Preferably, the cold color temperature driving MOSFET Q4 is output through the inductor L1 and the diode D1;

[0020] The warm color temperature driving MOSFET Q8 is output through the inductor L2 and the diode D2.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] 1) Compared with the product using two-channel DCDC to drive LED, the technical solution of the present invention has lower cost, but the effect is equivalent and the reliability is guaranteed;

[0023] 2) Compared with the simple product of using two MOSFETs to drive the LED, the technical solution of the present invention has a small increase in cost, but will not cause damage to the LED;

[0024] 3) The technical solution of the present invention can reduce costs, ensure reliability, and achieve higher dimming and color temperature adjustment accuracy, which will be very competitive compared with similar products on the market. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic diagram of an existing two-channel DCDC driving LED;

[0026] Figure 2 This is a schematic diagram of using two MOSFETs to drive an LED.

[0027] Figure 3 Switching timing diagram for existing MOSFET;

[0028] Figure 4 It is a structural schematic diagram of the present invention;

[0029] Figure 5 A specific circuit diagram of the present invention;

[0030] Figure 6 This is a switching timing diagram of the present invention.

[0031] 100 is AC / DC, 101 is an existing dimming control microcontroller, 102 is a cold color temperature driving DCDC, 103 is a warm color temperature driving DCDC, 104 is an existing cold color temperature LED, and 105 is an existing warm color temperature LED;

[0032] 200 is an existing LED constant current drive circuit, 201 is an existing dimming control single chip microcomputer 2, 202 is an existing cold color temperature drive MOSFET, 203 is an existing warm color temperature drive MOSFET, 204 is an existing cold color temperature LED 2, 205 is an existing warm color temperature LED 2, and 206 is a signal inverter;

[0033] 300 is an LED constant current drive circuit, 301 is a dimming control microcontroller, 302 is a color temperature adjustment drive circuit, 303 is a cold color temperature drive MOSFET, 304 is a warm color temperature drive MOSFET, 305 is a cold color temperature LED, and 306 is a warm color temperature LED. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0035] like Figure 4As shown, an LED color temperature adjustment circuit that effectively prevents current overshoot is connected to a cold color temperature LED 305 and a warm color temperature LED 306 respectively. The adjustment circuit includes an LED constant current drive circuit 300, a dimming control microcontroller 301, a cold color temperature drive MOSFET 303 and a warm color temperature drive MOSFET 304. The LED constant current drive circuit 300 is connected to the dimming control microcontroller 301, the cold color temperature drive MOSFET 303 and the warm color temperature drive MOSFET 304 respectively. The cold color temperature drive MOSFET 303 is connected to the cold color temperature LED 305, and the warm color temperature drive MOSFET 304 is connected to the warm color temperature LED 306. The adjustment circuit also includes a color temperature adjustment drive circuit 302, which is connected to the dimming control microcontroller 301, the cold color temperature drive MOSFET 303 and the warm color temperature drive MOSFET 304 respectively.

[0036] The color temperature adjustment driving circuit 302 includes a signal inverter U2, an R / S trigger U1, a boost circuit, a boost delay circuit, a first totem pole circuit and a second totem pole circuit. The signal inverter U2 is connected to the R / S trigger U1 through the boost circuit and the boost delay circuit respectively. The R / S trigger U1 is connected to the cold color temperature LED 305 through the first totem pole circuit. The R / S trigger U1 is connected to the warm color temperature LED 306 through the second totem pole circuit. The signal inverter U2 is connected to the dimming control microcontroller 301.

[0037] The boost circuit includes transistors Q9 and Q10, which are used to boost the 3.3V signal to 15V and output it to the R / S trigger U1. The base of the transistor Q9 is connected to the signal inverter U2 through the resistor R16, the emitter is connected to the R1 pin of the R / S trigger U1, and the collector is grounded. The transistor Q10 is connected to the signal inverter U2 through the resistor R17, the emitter is connected to the R2 pin of the R / S trigger U1, and the collector is grounded.

[0038] The boost delay circuit includes a transistor Q11 and a transistor Q12, which are used to boost the 3.3V signal to 15V and delay the output signal, and output it to the R / S trigger U1. The base of the transistor Q11 is connected to the signal inverter U2 through a resistor R18, and the base is grounded through a capacitor C3, the emitter is connected to the S1 pin of the R / S trigger U1, and the collector is grounded. The base of the transistor Q12 is connected to the signal inverter U2 through a resistor R19, and the base is grounded through a capacitor C4, the emitter is connected to the S2 pin of the R / S trigger U1, and the collector is grounded.

[0039] The first totem pole circuit includes a transistor Q1 and a transistor Q3, the base of the transistor Q1 is connected to the base of the transistor Q3, the emitter of the transistor Q1 is connected to the emitter of the transistor Q3 and then connected to the cold color temperature driving MOSFET Q4; the second totem pole circuit includes a transistor Q5 and a transistor Q7, the base of the transistor Q5 is connected to the base of the transistor Q7, the emitter of the transistor Q5 is connected to the emitter of the transistor Q7 and then connected to the warm color temperature driving MOSFET Q8.

[0040] The cold color temperature driving MOSFET Q4 is output through the inductor L1 and the diode D1; the warm color temperature driving MOSFET Q8 is output through the inductor L2 and the diode D2.

[0041] The specific principles are as follows:

[0042] In the present invention, a single PWM signal and a logic circuit are used to control the switching of two MOSFETs, so that the switching of the MOSFETs will not be affected by the PWM signal asynchronism problem caused by two different PWM outputs of the single-chip microcomputer.

[0043] After receiving the digital instruction, the dimming control microcontroller 301 sends a PWM1 signal to adjust the output current of the LED constant current drive circuit 300; sends a PWM2 signal to adjust the proportion of the output current of the LED constant current drive circuit 300 distributed to the cold color temperature LED 305 and the warm color temperature LED 306, so as to adjust the color temperature.

[0044] The color temperature adjustment drive circuit in the present invention uses only one PWM2 signal control, and then passes through the reverse signal of the signal inverter U2. The 3.3V signal is boosted to 15V through Q9 and Q10, and output to the R1 and R2 pins of the R / S trigger U1; Q11 and Q12 can boost the 3.3V signal to 15V and can also delay the output signal, and output it to the S1 and S2 pins of the R / S trigger U1. This design can delay the generation of the falling edges of the two output signals of the Q1 and Q2 pins of the R / S trigger U1. The signals output by the Q1 and Q2 pins drive the cold color temperature drive MOSFET Q4 and the warm color temperature drive MOSFET Q8 through the current gains of the two sets of totem pole circuits Q1, Q3 and Q5, Q7. Finally, the conduction switching timing of the cold color temperature drive MOSFET Q4 and the warm color temperature drive MOSFET Q8 is as follows: Figure 6 As shown. There will be overlap when the two MOSFETs switch, and the overlapping conduction may cause a slight deviation in color temperature adjustment, which can be corrected. The overlap time △t when the two MOSFETs switch can be adjusted by adjusting the parameters of R18, C3 and R19, C4.

[0045] L1, D1 and L2, D2 can eliminate the current spikes when Q4 and Q8 are switched, protecting the LEDs.

[0046] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. An LED color temperature adjustment circuit for effectively preventing current overshoot, the circuit being connected to a cold color temperature LED (305) and a warm color temperature LED (306) respectively, the adjustment circuit comprising an LED constant current drive circuit (300), a dimming control single chip computer (301), a cold color temperature drive MOSFET (303) and a warm color temperature drive MOSFET (304), the LED constant current drive circuit (300) being connected to the dimming control single chip computer (301), the cold color temperature drive MOSFET (303) and the warm color temperature drive MOSFET (304) respectively, the cold color temperature drive MOSFET (303) being connected to the cold color temperature LED (305), the warm color temperature drive MOSFET (304) being connected to the warm color temperature LED (306), characterized in that: The adjustment circuit further comprises a color temperature adjustment driving circuit (302), and the color temperature adjustment driving circuit (302) is respectively connected to the dimming control single chip computer (301), the cold color temperature driving MOSFET (303) and the warm color temperature driving MOSFET (304); The color temperature adjustment driving circuit (302) comprises a signal inverter U2, an R / S trigger U1, a boost circuit, a boost delay circuit, a first totem pole circuit and a second totem pole circuit; the signal inverter U2 is connected to the R / S trigger U1 through the boost circuit and the boost delay circuit respectively; the R / S trigger U1 is connected to a cold color temperature LED (305) through the first totem pole circuit; the R / S trigger U1 is connected to a warm color temperature LED (306) through the second totem pole circuit; and the signal inverter U2 is connected to a dimming control single chip computer (301); The boost circuit includes transistors Q9 and Q10, which are used to boost the 3.3V signal to 15V and output it to the R / S trigger U1; the boost delay circuit includes transistors Q11 and Q12, which are used to boost the 3.3V signal to 15V and delay the output signal, and output it to the R / S trigger U1; The first totem pole circuit includes a transistor Q1 and a transistor Q3, the base of the transistor Q1 is connected to the base of the transistor Q3, the emitter of the transistor Q1 is connected to the emitter of the transistor Q3 and then connected to the cold color temperature driving MOSFETQ4; The second totem pole circuit includes a transistor Q5 and a transistor Q7, the base of the transistor Q5 is connected to the base of the transistor Q7, the emitter of the transistor Q5 is connected to the emitter of the transistor Q7 and then connected to the warm color temperature driving MOSFETQ8; The color temperature adjustment driving circuit uses only one PWM2 signal control, and then through the reverse signal of the signal inverter U2, the 3.3V signal is boosted to 15V through Q9 and Q10, and output to the R1 and R2 pins of the R / S trigger U1; Q11 and Q12 boost the 3.3V signal to 15V and also delay the output signal, output to the S1 and S2 pins of the R / S trigger U1, so that the falling edge of the two output signals of the Q1 and Q2 pins of the R / S trigger U1 is delayed, and the signals output from the Q1 and Q2 pins drive the cold color temperature drive MOSFET Q4 and the warm color temperature drive MOSFET Q8 through the current gains of the two sets of totem pole circuits Q1, Q3 and Q5, Q7.

2. The LED color temperature adjustment circuit for effectively preventing current overshoot according to claim 1, characterized in that: The base of the transistor Q9 is connected to the signal inverter U2 through the resistor R16, the emitter is connected to the R1 pin of the R / S trigger U1, and the collector is grounded.

3. The LED color temperature adjustment circuit for effectively preventing current overshoot according to claim 1, characterized in that: The transistor Q10 is connected to the signal inverter U2 via the resistor R17, the emitter is connected to the R2 pin of the R / S trigger U1, and the collector is grounded.

4. The LED color temperature adjustment circuit for effectively preventing current overshoot according to claim 1, characterized in that: The base of the transistor Q11 is connected to the signal inverter U2 through the resistor R18, and the base is grounded through the capacitor C3, the emitter is connected to the S1 pin of the R / S trigger U1, and the collector is grounded.

5. The LED color temperature adjustment circuit for effectively preventing current overshoot according to claim 1, characterized in that: The base of the transistor Q12 is connected to the signal inverter U2 through the resistor R19, and the base is grounded through the capacitor C4, the emitter is connected to the S2 pin of the R / S trigger U1, and the collector is grounded.

6. The LED color temperature adjustment circuit for effectively preventing current overshoot according to claim 1, characterized in that: The cold color temperature driving MOSFET Q4 is output through the inductor L1 and the diode D1; The warm color temperature driving MOSFET Q8 is output through the inductor L2 and the diode D2.

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