CN112867207A

CN112867207A - High-linearity TRIAC dimming compatible LED driving circuit

Info

Publication number: CN112867207A
Application number: CN202110188945.0A
Authority: CN
Inventors: 雷建明
Original assignee: Nanjing Vocational University of Industry Technology NUIT
Current assignee: Nanjing Vocational University of Industry Technology NUIT
Priority date: 2021-02-19
Filing date: 2021-02-19
Publication date: 2021-05-28
Anticipated expiration: 2041-02-19
Also published as: CN112867207B

Abstract

The invention discloses a high-linearity TRIAC dimming compatible LED driving circuit, which adopts a gallium nitride-based high electron mobility transistor (GaN HEMT) and a driving circuit thereof to replace a traditional silicon-based MOSFET and realizes a MHz high-frequency working environment. The frequency is greatly improved, so that the values of a filter capacitor and an inductor can be reduced, the impact current and the current oscillation in a circuit can be greatly reduced, and the TRIAC dimming compatibility is improved. By adopting the chip FB pin voltage linear regulation technology and the voltage compensation technology, high linearity in the LED dimming process is realized. In addition, the MCU intelligent control module is used for detecting a conduction angle, providing a compensation signal for a FB pin of the chip, and controlling the disconnection of the dummy load, so that the loss caused by the connection of the dummy load is effectively reduced under the condition that the conduction current is greater than the TRIAC starting ignition current.

Description

High-linearity TRIAC dimming compatible LED driving circuit

Technical Field

The invention relates to the field of LED driving, in particular to a high-linearity TRIAC dimming compatible LED driving circuit.

Background

TRIAC dimmers, which can adjust the effective value of the input ac voltage and thus the brightness of the LED output, were originally used for incandescent lamp dimming. Incandescent lamps exhibit purely resistive characteristics and may be suitable for TRIAC dimming. The solid-state LED lighting of the new generation is actually a low-voltage diode, and in order to obtain high driving efficiency, a nonlinear high-frequency constant-current switching power supply is generally required to supply power. However, the non-linearity of high frequency constant current switching power supplies makes them difficult to be compatible with TRIAC dimmers.

Due to the inertia of the market, the TRIAC silicon controlled rectifier dimming mode still exists in a large quantity, and therefore, the design of the dimming driving circuit makes the compatibility of the LED lamp and the TRIAC dimmer very significant. In order to obtain good control feeling, the linearity of dimming is generally required to be high, namely the linearity of the current passing through the LED load and the effective voltage value after phase switching of the thyristor is one-to-one. However, in the case of LEDs, the non-linear characteristics of the LEDs are not easily linear in a dynamic dimming process, and moreover, non-monotonic power variation and dimming delay occur, and discontinuous light sensation variation such as flickering, jumping, and shaking of the LEDs may occur. This is a critical issue that needs to be addressed urgently.

All the existing TRIAC dimming schemes only monitor phase angles and do not monitor output current, and under the condition that the compatibility of a TRIAC dimmer and an LED is not ideal, the linearity that the current passing through an LED load and the effective voltage value after phase cutting of a silicon controlled rectifier are one-to-one cannot be ensured, non-monotonic power change and dimming delay can occur, and even the phenomena of flickering, jumping and shaking of the LED can occur.

The switching signal frequency in the PWM scheme in the present TRIAC dimming scheme is typically around 100kHz due to the frequency limitation caused by the large parasitic capacitance of the silicon-based MOSFET device. The low driving frequency causes the non-linearity problem of the input current of the driving converter to be more prominent, thereby affecting the working state of the TRIAC dimmer.

Disclosure of Invention

The invention aims to provide a high-linearity TRIAC dimming compatible LED driving circuit, wherein a GaN HEMT device is used as a power switch tube and applied to the LED driving circuit, and a corresponding high-speed voltage mode pulse width modulator and a driving chip are matched to increase the driving frequency to several MHz; meanwhile, the FB pin voltage linear regulation and the FB pin voltage compensation of the chip are adopted, so that the LED driving control chip does not need a special dimming compatible control chip, high linearity in the LED dimming process is realized, and the current passing through the LED load is ensured to correspond to the effective value of the input voltage in real time.

A high-linearity TRIAC dimming compatible LED driving circuit comprises a dimming input module, an ignition module, a bridge rectifier and filter module, a DC/DC converter, a dummy load module, a PWM control module, a switch tube driving module, an MCU intelligent control module, an FB pin voltage linear adjusting module and an FB pin compensation module which are mutually coupled, wherein a high-frequency switching device Q3 is further connected between the DC/DC converter and the switch tube driving module.

Preferably, the dimming input module comprises a TRIAC dimmer and a fuse resistor RF1 connected in series before the TRIAC dimmer on the ac input L line.

Preferably, the ignition module comprises a capacitor C1 and a resistor R1 connected in series with the capacitor C1.

Preferably, the bridge stack and the filter module comprise a rectifier bridge BR1 and a pi filter circuit composed of an inductor L1, an inductor L2, a capacitor C2 and a capacitor C3 which are connected in series.

Preferably, the DC/DC converter consists of an inductor L3, an electrolytic capacitor C4, a diode D4 and an LED load, and a single-stage non-isolated suspension type buck-boost circuit is adopted in a power topology.

Preferably, the dummy load module includes a GaN depletion type NMOS transistor Q2, the NMOS transistor Q2 is in a normally open state, and the resistor R3 is connected in series to the NMOS transistor Q2.

Preferably, the PWM control module is a high-speed voltage mode pulse width modulator, and is composed of a chip of a model UCC 25705;

the inside of the switching tube driving module is a driving chip SI8271GB which provides gate driving for a high-frequency switching device.

Preferably, the MCU intelligent control module comprises a conduction angle detection, dummy load module switch control and current comparison functional block;

there are mainly two input signals: the current and the LED load current signal after the TRAIC dimmer chopping;

two paths of output signals: one path of the control dummy load module is disconnected, and the other path of the FB pin linear regulation module compensates signals.

Preferably, the effective value of the input voltage of the FB pin linear regulating module is detected by the module, and the voltage signal sent to the FB pin of the UCC25705 in the PWM modulating module is linearly changed according to the change of the detected voltage value, so as to linearly control the duty ratio of PWM and the magnitude of the LED output current.

Preferably, the FB pin compensation module comprises a resistor R14 and a resistor R15 which are connected between the base of the PNP transistor Q1 in the FB pin linear regulation module and the current comparison functional block in the MCU intelligent control module, and a capacitor C8 is connected between the resistor R14 and the resistor R15.

The invention has the advantages that:

1. the GaN HEMT device is used as a power switch tube and applied to an LED drive circuit, and is matched with a corresponding high-speed voltage mode pulse width modulator and a drive chip, so that the drive frequency is increased to several MHz. Meanwhile, due to the use of the high-frequency switching device HEMT, the switching loss correlation is greatly reduced compared with that of a conventional silicon-based MOS tube. The frequency is improved, so that the requirements on inductance and electrolytic capacitance values in a power topology are reduced, the corresponding device has a smaller volume, and the requirements on application design of a driver, such as miniaturization, thinness and high efficiency, can be met;

2. the FB pin voltage linear regulation of the chip is adopted, the sampling of the effective value of the input alternating current signal is realized by building a pure analog control circuit, and the FB pin voltage of the control chip is linearly regulated correspondingly, so that the switching condition of the power switching tube is controlled, and the output voltage linearly changes according to the effective value of the input voltage. Due to the addition of the linear adjusting circuit, the LED driving control chip does not need a special dimming compatible control chip but only needs a common control chip, so that the model selection space of the chip is expanded, and the cost of the chip is reduced; and FB pin voltage compensation is adopted, and the input effective value is compared with the LED load current through the MCU intelligent control module, so that the chip pin voltage is linearly compensated in real time, high linearity in the LED dimming process is realized, and the current passing through the LED load is ensured to correspond to the input voltage effective value in real time.

3. The MCU intelligent control module is adopted to detect the conduction angle and control the disconnection of the dummy load, so that the loss caused by the connection of the dummy load is effectively reduced under the condition that the conduction current is greater than the TRIAC starting ignition current;

4. meanwhile, the single-stage non-isolated suspension type buck-boost circuit is adopted in the power topology, compared with the problems of complex circuits, excessive application devices, low efficiency and large size in a double-stage driving scheme, the single-stage scheme has high circuit conversion efficiency, simplifies peripheral application circuits, reduces the number of components and reduces the size of a driver, and is easy to control, high in efficiency and high in constant current precision. Meanwhile, the number of the magnetic elements is reduced, the influence of parasitic capacitance and inductance parameters is reduced, and the circuit operation under high frequency is ensured. The design requirement of LED dimming driving is met.

Drawings

FIG. 1 is a schematic circuit diagram of the present invention;

FIG. 2 is a schematic diagram of an exemplary simulation of the present invention;

101, a dimming input module, 102, an ignition module, 103, a bridge stack and filter module, 104, a DC/DC converter, 105, a dummy load module, 106, a PWM control module, 107, a switching tube driving module, 108, an MCU intelligent control module, 109, an FB pin voltage linear regulation module, 110 and an FB pin compensation module.

Detailed Description

In order to make the technical means, the creation characteristics, the achievement purposes and the effects of the invention easy to understand, the invention is further described with the specific embodiments.

As shown in fig. 1 to 2, a high-linearity TRIAC dimming compatible LED driving circuit includes a dimming input module 101, an ignition module 102, a bridge stack and filter module 103, a DC/DC converter 104, a dummy load module 105, a PWM control module 106, a switching tube driving module 107, an MCU intelligent control module 108, an FB pin voltage linearity adjusting module 109, and an FB pin compensation module 110, which are coupled to each other, wherein a high-frequency switching device Q3 is further connected between the DC/DC converter 104 and the switching tube driving module 107.

The dimming input module 101 comprises a TRIAC dimmer and a fuse resistor RF1 connected in series before the TRIAC dimmer on the ac input L-line.

The ignition module 102 includes a capacitor C1 and a resistor R1 in series with the capacitor C1.

The bridge stack and filter module 103 comprises a rectifier bridge BR1 and a pi filter circuit composed of an inductor L1, an inductor L2, a capacitor C2 and a capacitor C3 which are connected in series.

The DC/DC converter 104 consists of an inductor L3, an electrolytic capacitor C4, a diode D4 and an LED load, and a single-stage non-isolated suspension type buck-boost circuit is adopted in a power topology.

The dummy load module 105 includes a GaN depletion type NMOS transistor Q2, the NMOS transistor Q2 is in a normally open state, and a resistor R3 is connected in series to the NMOS transistor Q2.

The PWM control module 106 is a high-speed voltage mode pulse width modulator, and is composed of a chip of a model UCC 25705;

the inside of the switching driving module 107 is a driving chip SI8271GB for providing gate driving for the high frequency switching device.

The MCU intelligent control module 108 comprises a conduction angle detection, dummy load module switch control and current comparison functional block;

two paths of output signals: one way controls the dummy load module 105 to be switched off, and one way FB pin linear adjusting module 109 compensates signals.

The effective value of the input voltage of the FB pin linear adjustment module 109 is detected by the module, and the voltage signal sent to the FB pin of the UCC25705 in the PWM modulation module 106 is linearly changed according to the change of the detected voltage value, so as to linearly control the PWM duty cycle and the magnitude of the LED output current.

The FB pin compensation module 110 comprises a resistor R14 and a resistor R15 connected between the base of the PNP transistor Q1 in the FB pin linear adjustment module 109 and the current comparison functional block in the MCU intelligent control module 108, and a capacitor C8 connected between the resistor R14 and the resistor R15.

The specific implementation mode and principle are as follows:

as shown in fig. 1, the dimming input module 101 is characterized in that an ac input L line is connected in series with a fuse resistor RF1 instead of a fuse and an input lead, and provides an insertion impedance for suppressing current oscillation while playing a role of a fuse, so that the TRIAC dimming effect can be improved, and the space utilization rate can be improved; the ignition module 102 prevents the TRIAC dimmer from being difficult to maintain and extinguishing during the starting moment, when the TRAIC is about to start, the capacitor C1 in the ignition module can realize a pulse starting current as the ignition current to trigger the dimmer, and simultaneously, a resistor R1 is connected in series with the capacitor C1 to play a role of damping oscillation.

The bridge rectifier and filter module 103 is rectified by a rectifier bridge BR1 to convert the ac power into "steamed bread" waves. The pi filter circuit composed of L1, L2, C2, and C3 can suppress EMI noise. The DC/DC converter 104 is composed of a high-frequency switching device HEMT Q3, an inductor L3, an electrolytic capacitor C4, a diode D4 and an LED load, and a single-stage non-isolated suspension type buck-boost circuit is adopted in a power topology. The power topology enables efficient conversion of input energy to LED output energy. And the adoption of the isolated circuit topology reduces the number of magnetic elements, reduces the influence of parasitic capacitance and inductance parameters and is beneficial to the circuit work under high frequency. The working mode is a DCM mode, and high PF value and low THD can be realized. Meanwhile, due to the use of the high-frequency switch device HEMT, the switching loss is greatly reduced compared with that of a conventional silicon-based MOS tube. The frequency is increased to several megahertz which can not be achieved by a common MOS tube, the requirements on the inductance L3 and the electrolytic capacitor C4 are reduced, the size of a corresponding device is smaller, and the application design requirements of a driver for miniaturization, lightness, thinness and high efficiency can be met.

The dummy load module 105 comprises a GaN depletion type NMOS transistor Q2 and is in a normally open state, after the Q2 is conducted, the current passing through the TRIAC dimmer is extracted through a resistor R3, and when the TRIAC is started, the conduction current is ensured to be larger than the conduction ignition current, so that the normal work of the dimmer is ensured; the turn-off of Q2 is determined by the MCU control signal input from the gate.

The UCC25705 of the chip in the PWM control module 106 is a high-speed voltage mode pulse width modulator, and the frequency of the output pulse can be determined by setting the resistance capacitance values of the RC and DISCH pins. After passing through the linear adjusting module, the current input to the FB pin is sent to the input end of the internal PWM comparator through the internal partial pressure of the chip, and according to the result of the comparator, the chip can change the duty ratio of the PWM signal output by the OUT pin, so that the switching condition of the HEMT power switching tube is controlled. Meanwhile, the UCC25705 of the intra-module chip can limit the current one by one pulse period, only peak current control is needed, and constant-voltage closed-loop control is not needed; the detection voltage obtained from the end of the current detection resistor R13 is input to the ILIM pin of the chip, and when the detection voltage exceeds 200mV, the internal PWM latch can be reset at high speed through a 25ns response path in the chip, so that overcurrent protection is realized. The switching tube driving module 107 is internally provided with a driving chip SI8271GB for providing gate driving for the HEMT. The chip is an isolated chip, VDDI and GNDI are power supply pins and grounding pins of an input end respectively, and VDD and GND are power supply pins and grounding pins of a driving end respectively. After being limited by the resistor R9, Vin pin receives the digital driving control PWM signal transmitted by the upper stage. VO + is transmitted to a pull-up voltage of a grid electrode of the HEMT through R10, VO-is transmitted to a pull-down voltage through R11, and the switch of the HEMT is controlled.

The MCU intelligent control module 108 includes the conduction angle detection, dummy load module on-off control, and current comparison function blocks. There are mainly two input signals: the current and the LED load current signal after the TRAIC dimmer chopping; two paths of output signals: one path of the control dummy load is disconnected, and the other path of the FB pin compensates signals. Detecting a conduction angle: the voltage chopped by the TRAIC dimmer is input to the MCU through sampling, a zero-crossing signal is obtained through processing, the zero-crossing signal containing conduction angle information is input to the phase angle measuring module, and a zero clearing signal of the counter and a reading trigger signal of the phase angle register are obtained through processing of the zero processing module. The counter counts the high level of the zero-crossing signal from zero clearing (quantifies the size of the line voltage conduction angle); the conduction angle of the controlled silicon can be judged quickly and effectively;

and (3) false load module switch control: the dummy load is connected in a state that the conduction current is unstable when the TRAIC is initially started and in a state that the conduction current ratio is smaller when the conduction angle is smaller, the conduction current of the silicon controlled rectifier is raised, so that the conduction current of the normal work of the TRAIC silicon controlled rectifier is larger than the holding current. According to the result of the conduction angle detection function module, when the conduction angle reaches a certain value (taking the conduction angle of 15 degrees as an example), and the conduction current can be more stably larger than the holding current, in order to reduce the power consumption caused by the connection of the dummy load, the module can disconnect the connection of the dummy load by switching off the internal Q2 of the dummy load;

the current comparison module inside the MCU: and the LED load current signal is input into the MCU, and is subjected to data acquisition and conversion by the internal ADC module, and then is compared with the current effective value chopped by the TRAIC dimmer in real time by using the voltage comparator inside the MCU. When the deviation ratio of the LED load current to the rear input value of the dimmer is large and exceeds a set deviation value (taking 5% as an example), the MCU outputs an FB pin compensation signal, and the FB pin compensation signal is divided by resistors R14 and R15 and supplemented to the base of a transistor Q1 which is in linear conduction. And the MCU is utilized to realize feedback, namely, the FB pin input is compensated in real time according to the sampled LED load current, and the PWM signal sent to the power switch tube is controlled. The dimming linearity of the dimming circuit is ensured in real time.

The effective value of the input voltage of the FB pin voltage linear regulating module 109 is detected by the module, and the voltage signal sent to the FB pin of the UCC25705 in the PWM modulating module is linearly changed according to the change of the detected voltage value, so as to linearly control the duty ratio of PWM and the magnitude of the LED output current;

the specific implementation process comprises the following steps: the alternating current subjected to phase cutting by the TRIAC dimmer is rectified by D1 and D2 and then sent to the end of a resistor R4, is subjected to voltage division by resistors R4 and R5, is subjected to current limiting by a diode D3 and a resistor R7, and then is sent to the base of a triode Q1; the Q1 is in a linear conducting state, and the conducting current of the Q1 is transmitted to the FB pin through the resistor R8 after the input voltage is detected to be in a linear change by the base. Wherein, effective value collection of voltage is realized through C5 charging and discharging and the resistor R6.

The digital signal output by the FB pin compensation module 110 after MCU current comparison is sent to the base of the PNP transistor Q1 in the 109 module via R14, C8, and R15, and the FB pin voltage of the chip is affected by controlling the magnitude of the Q1 base current.

As shown in fig. 2, for comparison of the present dimming driving scheme with other dimming driving:

(1) degree of linearity

The comparison shows that under the combined action of the high-frequency driving frequency of several MHz and the linear compensation of the load current under the control of the FB pin and the MCU;

the dimming driving of the scheme can realize the linear relation of the one-to-one correspondence of the conduction phase angle and the LED load current, and solves the problem of LED flicker caused by the change fluctuation of the LED load current when the conduction angle is changed in other dimming driving schemes.

(2) Dimming range

The comparison shows that under the action of the dummy load module controlled by the MCU to be switched in, the load current can be changed within the range of 0 to 100 percent of the conduction angle. Namely, when the conduction angle is small, the normal work of the dimmer can be ensured, the LED is driven to work normally, and the phenomenon that the TRIAC dimmer cannot work normally due to insufficient conduction current in other driving schemes is avoided, so that the available conduction angle range is sacrificed.

Based on the above, the GaN HEMT device is applied to an LED drive circuit as a power switch tube, and is matched with a corresponding high-speed voltage mode pulse width modulator and a drive chip to increase the drive frequency to several MHz; meanwhile, the FB pin voltage linear regulation and the FB pin voltage compensation of the chip are adopted, so that the LED driving control chip does not need a special dimming compatible control chip, high linearity in the LED dimming process is realized, and the current passing through the LED load is ensured to correspond to the effective value of the input voltage in real time.

It will be appreciated by those skilled in the art that the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The embodiments disclosed above are therefore to be considered in all respects as illustrative and not restrictive. All changes which come within the scope of or equivalence to the invention are intended to be embraced therein.

Claims

1. The high-linearity TRIAC dimming compatible LED driving circuit is characterized by comprising a dimming input module (101), an ignition module (102), a bridge stack and filter module (103), a DC/DC converter (104), a dummy load module (105), a PWM control module (106), a switching tube driving module (107), an MCU intelligent control module (108), an FB pin voltage linearity adjusting module (109) and an FB pin compensation module (110) which are mutually coupled, wherein a high-frequency switching device Q3 is further connected between the DC/DC converter (104) and the switching tube driving module (107).

2. A high linearity TRIAC dimming compatible LED driver circuit as claimed in claim 1, wherein: the dimming input module (101) comprises a TRIAC dimmer and a fuse resistor RF1 connected in series before the TRIAC dimmer on an alternating current input L line.

3. A high linearity TRIAC dimming compatible LED driver circuit as claimed in claim 1, wherein: the ignition module (102) includes a capacitor C1 and a resistor R1 in series with the capacitor C1.

4. A high linearity TRIAC dimming compatible LED driver circuit as claimed in claim 1, wherein: the bridge stack and filter module (103) comprises a rectifier bridge BR1 and a pi filter circuit which is composed of an inductor L1, an inductor L2, a capacitor C2 and a capacitor C3 which are connected in series.

5. A high linearity TRIAC dimming compatible LED driver circuit as claimed in claim 1, wherein: the DC/DC converter (104) consists of an inductor L3, an electrolytic capacitor C4, a diode D4 and an LED load, and a single-stage non-isolated suspension type buck-boost circuit is adopted in a power topology.

6. A high linearity TRIAC dimming compatible LED driver circuit as claimed in claim 1, wherein: the dummy load module (105) comprises a GaN depletion type NMOS transistor Q2, the NMOS transistor Q2 is in a normally open state, and a resistor R3 is connected to the NMOS transistor Q2 in series.

7. A high linearity TRIAC dimming compatible LED driver circuit as claimed in claim 1, wherein: the PWM control module (106) is a high-speed voltage mode pulse width modulator and is composed of a chip with the model of UCC 25705;

the inside of the switch driving module (107) is provided with a driving chip SI8271GB for providing gate driving for a high-frequency switching device.

8. A high linearity TRIAC dimming compatible LED driver circuit as claimed in claim 1, wherein: the MCU intelligent control module (108) comprises a conduction angle detection, dummy load module switch control and current comparison functional block;

two paths of output signals: and one path of control dummy load module (105) is disconnected, and one path of FB pin linear regulation module (109) compensates signals.

9. A high linearity TRIAC dimming compatible LED driver circuit as claimed in claim 1, wherein: the effective value of the input voltage of the FB pin linear regulation module (109) is detected by the FB pin linear regulation module, and the voltage signal sent to the FB pin of the UCC25705 in the PWM modulation module (106) is linearly changed according to the change of the detected voltage value, so that the duty ratio of PWM and the magnitude of LED output current are linearly controlled.

10. A high linearity TRIAC dimming compatible LED driver circuit as claimed in claim 1, wherein: the FB pin compensation module (110) comprises a resistor R14 and a resistor R15 which are connected between the base of a PNP transistor Q1 in the FB pin linear regulation module (109) and a current comparison functional block in the MCU intelligent control module (108), and a capacitor C8 is connected between the resistor R14 and the resistor R15 in parallel.