A PWM dimming control type TLCC drive circuit

Abstract

The present invention discloses a PWM dimming control type TLCC driving circuit, comprising a power supply, a dimming module, an over-temperature protection module and an LED load, wherein the dimming module is arranged between the power supply and the over-temperature protection module, and the dimming module comprises a transistor Q3, a current limiting resistor R3, a ground resistor R4 and a pulse width modulator PWM, wherein the base of the transistor Q3 is connected to a communication interface of the pulse width modulator PWM through the current limiting resistor R3 and is connected to a cathode loop end of the power supply through the ground resistor R4, wherein the emitter of the transistor Q3 is connected to the cathode loop end of the power supply, and can output a constant current, has the characteristic of automatic over-temperature protection, and can be dimmed as required.

Description

[Technical field]

[0002] The present invention relates to the technical field of drive circuits, and in particular to the technical field of a PWM dimming control type TLCC (Triode linear constant current) drive circuit. [Background technology]

[0004] LED lamps are recognized as the fourth generation of green light sources. They have many advantages such as high efficiency, long life, safety and environmental protection, small size, high reliability and fast response speed. The technology is mature and widely used in various fields. Since LED is a constant current workload, constant current drive is used to ensure that it always maintains a safe and stable working condition. The existing driving circuit of LED lamps usually relies on a dedicated constant current drive chip for constant current drive. Therefore, the production capacity of the product is greatly affected by the market supply of the chip, and the price of the product is also prone to change with the price increase of the chip, making it difficult to ensure stable production. The driving circuit that uses some discrete components to achieve constant current drive has problems such as complex circuit structure and high cost. In actual production, it cannot achieve the cost-effectiveness and reliability of the driving circuit using a dedicated chip.

[0005] The forward voltage VF of the LED lamp has a negative temperature characteristic, which is manifested as the VF value decreases with the increase of temperature. When the LED lamp is driven at a constant voltage, the temperature of the LED lamp increases due to the ambient temperature and self-heating, and the VF value decreases, which will cause the conduction current of the LED lamp to increase, which in turn causes the temperature of the LED to rise further and the VF value to decrease further. In terms of power, this process is a positive feedback process, which will eventually lead to thermal runaway of the LED lamp, affecting the reliability and service life of the LED lamp. In order to avoid the above problems, the over-temperature protection of the LED drive circuit has to be given priority consideration.

[0006] In addition, with the continuous innovation of LED driving technology, user needs are also changing, from the initial requirements of high brightness and low efficacy to requirements for dimming characteristics and light quality. However, LED lamps are different from traditional incandescent lamps and are not pure resistive loads. If a dimmer is directly configured for dimming, it will cause serious flickering and other problems, which need to be solved urgently. [Summary of the invention]

[0008] The purpose of the present invention is to solve the problems in the prior art and to propose a PWM dimming control type TLCC driving circuit which can output a constant current, has the characteristics of automatic over-temperature protection, and can be dimmed as needed.

[0009] To achieve the above-mentioned purpose, the present invention proposes a PWM dimming control type TLCC driving circuit, including a power supply, a dimming module, an over-temperature protection module and an LED load, wherein the dimming module is arranged between the power supply and the over-temperature protection module, and the dimming module includes a transistor Q3, a current limiting resistor R3, a ground resistor R4 and a pulse width modulator PWM, wherein the base of the transistor Q3 is connected to the communication interface of the pulse width modulator PWM through the current limiting resistor R3 and is connected to the cathode loop end of the power supply through the ground resistor R4, and the emitter of the transistor Q3 is connected to the cathode loop end of the power supply;

[0010] The pulse width modulator PWM switches the PWM signal to a suspended or low level state, and uses the transistor Q3 to turn on the over-temperature protection module, thereby conducting between the LED load and the power supply;

[0011] The pulse width modulator PWM switches the PWM signal to a high level state and uses the transistor Q3 to turn off the over-temperature protection module, thereby disconnecting the phase between the LED load and the power supply.

[0012] Preferably, the over-temperature protection module includes a transistor Q1, a transistor Q2, a starting resistor group and a constant current resistor Rs, the collector of the transistor Q1, the base of the transistor Q2 and the collector of the transistor Q3 are connected and connected to the anode loop end of the power supply and the positive end of the LED load through the starting resistor group, the base of the transistor Q1 is connected to the emitter of the transistor Q2 and connected to the cathode loop end of the power supply through the constant current resistor Rs, the emitter of the transistor Q1 is connected to the cathode loop end of the power supply, and the negative end of the LED load is connected to the collector of the transistor Q2.

[0013] Preferably, the power supply is an alternating current power supply AC, and also includes a rectifier and filter module. The alternating current power supply AC is processed by the rectifier and filter module to generate a smooth high-voltage direct current voltage, which is then passed through a dimming module and an over-temperature protection module to power the LED load.

[0014] Preferably, the rectifier and filter module includes a rectifier bridge DB1 and a high-voltage electrolytic capacitor C1, the two AC input terminals of the rectifier bridge DB1 are respectively connected to the ACL terminal and the ACN terminal of the AC power supply AC, and the two DC output terminals of the rectifier bridge DB1 and the two connection terminals of the high-voltage electrolytic capacitor C1 are respectively connected to the LED load after the dimming control of the dimming module and the temperature rise monitoring of the over-temperature protection module.

[0015] Preferably, a wire-wound fuse resistor RF1 is further provided between the ACL terminal of the AC power source AC and an AC input terminal of the rectifier bridge DB1.

[0016] Preferably, the number of starting resistors in the starting resistor group is at least 2.

[0017] Preferably, the power supply is a direct current power supply DC, and the DC+ terminal and DC- terminal of the direct current power supply DC are connected to the LED load after being respectively controlled by a dimming module and monitored by an over-temperature protection module.

[0018] Preferably, the number of the starting resistors in the starting resistor group is at least one.

[0019] Preferably, a shunt resistor RA is connected between the collector of the transistor Q2 and the emitter of the transistor Q2.

[0020] Preferably, the TLCC driving circuit exhibits a constant current output characteristic during normal operation and the calculation formula is as follows:

[0021] ;

[0022] Among them, Iout_CC is the constant output current, Q1Vbe is the voltage between the base and the emitter of the transistor Q1, and Rs is the resistance of the constant current resistor Rs.

[0023] Beneficial effects of the present invention: the present invention can realize digital intelligent dimming control by accessing the high and low levels of the pulse width modulator PWM, thereby utilizing the adjustment of the opening angle of the transistor Q3; by arranging the transistor Q1, the transistor Q2, the starting resistor group and the constant current resistor Rs to jointly form an over-temperature protection module, while making the current flowing through the constant current resistor Rs equal to the loop current of the LED load, and making the voltage of the constant current resistor Rs equal to the voltage between the base and the emitter of the transistor Q1, thereby utilizing the characteristic that Q1Vbe is close to a fixed value, freely adjusting the resistance parameter of the constant current resistor Rs as required, realizing automatic adjustment of the constant output current, without using a dedicated constant current chip, being less affected by the price and supply of the chip, and being able to alleviate the problem of the lack of chips in the integrated circuit to a certain extent, and the overall electrical The circuit has obvious advantages, outstanding performance, low cost and high cost performance; it can utilize the inherent temperature drift characteristics of the transistor, so that when the circuit itself or the external temperature is higher than the threshold temperature of the transistor, the constant output current is reduced, and when the driving circuit is released from the abnormal temperature rise state, the normal constant output current is restored, and the whole process is repeated, thereby realizing the characteristics of automatic over-temperature protection; by setting the wire-wound fuse resistor RF1, the rectifier bridge DB1 and the high-voltage electrolytic capacitor C1, when the power supply is an alternating current power supply AC, surge interference can be limited to prevent abnormal short circuits in the circuit, and a stable high-voltage DC voltage can be generated after rectification and filtering; by setting the shunt resistor RA between the collector of the transistor Q2 and the emitter of the transistor Q2, the power consumption transfer of the transistor Q2 can be better realized, and the reliability and safety of the circuit can be further improved.

[0024] The features and advantages of the present invention will be described in detail through embodiments in conjunction with the accompanying drawings.

Brief Description of the Drawings

[0026] Figure 1 is a structural schematic diagram of embodiment 1;

[0027] Figure 2 is a structural diagram of Embodiment 2;

[0028] Figure 3 is a schematic structural diagram of Embodiment 3;

[0029] Figure 4 It is a structural diagram of embodiment 4. [Specific implementation method]

[0031] Embodiment 1:

[0032] See also Figure 1 The present invention provides a PWM dimming control type TLCC driving circuit, comprising a power supply, a dimming module, an over-temperature protection module and an LED load, wherein the dimming module is arranged between the power supply and the over-temperature protection module, and the dimming module comprises a transistor Q3, a current limiting resistor R3, a grounding resistor R4 and a pulse width modulator PWM, wherein the base of the transistor Q3 is connected to the communication interface of the pulse width modulator PWM through the current limiting resistor R3 and is connected to the cathode loop end of the power supply through the grounding resistor R4, and the emitter of the transistor Q3 is connected to the cathode loop end of the power supply;

[0033] The pulse width modulator PWM switches the PWM signal to a suspended or low level state, and uses the transistor Q3 to turn on the over-temperature protection module, thereby conducting between the LED load and the power supply;

[0034] The pulse width modulator PWM switches the PWM signal to a high level state and uses the transistor Q3 to turn off the over-temperature protection module, thereby disconnecting the phase between the LED load and the power supply.

[0035] The over-temperature protection module includes a transistor Q1, a transistor Q2, a starting resistor group and a constant current resistor Rs. The collector of the transistor Q1, the base of the transistor Q2 and the collector of the transistor Q3 are connected and connected to the anode loop end of the power supply and the positive end of the LED load through the starting resistor group. The base of the transistor Q1 is connected to the emitter of the transistor Q2 and connected to the cathode loop end of the power supply through the constant current resistor Rs. The emitter of the transistor Q1 is connected to the cathode loop end of the power supply, and the negative end of the LED load is connected to the collector of the transistor Q2.

[0036] The power supply is an alternating current power supply AC, and also includes a rectifier and filter module. The alternating current power supply AC is processed by the rectifier and filter module to generate a stable high-voltage direct current voltage, which is then supplied to the LED load through a dimming module and an over-temperature protection module.

[0037] The rectifier and filter module includes a rectifier bridge DB1 and a high-voltage electrolytic capacitor C1. The two AC input terminals of the rectifier bridge DB1 are respectively connected to the ACL terminal and the ACN terminal of the AC power source AC. The two DC output terminals of the rectifier bridge DB1 and the two connection terminals of the high-voltage electrolytic capacitor C1 are respectively connected to the LED load after the dimming control of the dimming module and the temperature rise monitoring of the over-temperature protection module.

[0038] A wire-wound fuse resistor RF1 is also provided between the ACL terminal of the AC power source AC and an AC input terminal of the rectifier bridge DB1.

[0039] The number of the starting resistors in the starting resistor group is at least 2, namely R1 and R2.

[0040] The TLCC driving circuit exhibits a constant current output characteristic during normal operation and the calculation formula is as follows:

[0041] ;

[0042] Among them, Iout_CC is the constant output current, Q1Vbe is the voltage between the base and the emitter of the transistor Q1, and Rs is the resistance of the constant current resistor Rs.

[0043] Working process of the present invention:

[0044] The AC power supply AC is connected to the TLCC drive circuit through the ACL and ACN terminals. The wire-wound fuse resistor RF1 is used to limit surge interference. At the same time, its own fuse protection mechanism is used to prevent abnormal short circuits in the circuit. The rectifier bridge DB1 and the high-voltage electrolytic capacitor C1 are used to achieve rectification and filtering characteristics, generating a stable high-voltage DC voltage after rectification and filtering.

[0045] Subsequently, the high voltage DC voltage is divided into two paths, one of which is directly connected to the positive terminal of the LED load, and the other is connected to the collector of transistor Q1 and the base of transistor Q2 through the starting resistor R1 and the starting resistor R2, respectively, thereby providing a collector bias resistor for transistor Q1 and a base starting voltage for transistor Q2. In addition, the emitter of transistor Q1 is grounded, the base of transistor Q1 is connected to the emitter of transistor Q2 and grounded through the constant current resistor Rs, and the collector of transistor Q2 is connected to the negative terminal of the LED load, so that the switching state of transistor Q2 can be controlled by transistor Q1.

[0046] For the LED load, the current flows from its positive terminal to the negative terminal, then flows through the collector of transistor Q2 to the emitter of transistor Q2, and finally connects to the ground through the constant current resistor Rs to form a complete electrical circuit. At this time, the loop current of the LED load is equal to the current flowing through the constant current resistor Rs. Because the two ends of the constant current resistor Rs are connected to the base of transistor Q1 and the emitter of transistor Q1 respectively, the voltage of the constant current resistor Rs is equal to the voltage between the base of transistor Q1 and the emitter of transistor Q1, that is, Q1Vbe. As we all know, Vbe is the characteristic voltage of the transistor and is close to a fixed value, such as 0.6~0.7V for silicon tubes and 0.2~0.3V for germanium tubes. Therefore, by adjusting the resistance parameters of the constant current resistor Rs, the constant output current of the TLCC drive circuit can be adjusted. Taking Q1Vbe as 0.6V, the calculation formula of the constant output current Iout_CC is as follows:

[0047] ;

[0048] Among them, Iout_CC is the constant output current, Q1Vbe is the voltage between the base and the emitter of the transistor Q1, and Rs is the resistance of the constant current resistor Rs.

[0049] During operation, the TLCC drive circuit presents a constant current output characteristic, and the transistor Q1 constantly detects the temperature rise to achieve the function of automatic over-temperature protection. The principle of automatic over-temperature protection is as follows:

[0050] The transistor has an inherent temperature drift characteristic, that is, when the circuit itself or the external temperature is higher than the threshold temperature of the transistor, the Vbe of the transistor gradually decreases as the temperature rises. In other words, when the transistor Q1 detects that the temperature is too high, Q1Vbe will decrease accordingly, so that the current of the constant current resistor Rs is pulled down, thereby reducing Iout_CC; when the TLCC drive circuit is relieved of the abnormal temperature rise state, Q1Vbe returns to normal, so that the voltage detected at both ends of the constant current resistor Rs returns to normal, thereby achieving the set constant current state, and the whole process repeats itself.

[0051] In the dimming module, the emitter of the transistor Q3 is grounded, and the base of the transistor Q3 is connected to the communication interface of the pulse width modulator PWM through the current limiting resistor R3 on the one hand, and is grounded through the ground resistor R4 on the other hand to resist interference, and the collector of the transistor Q3 is respectively connected to one end of the starting resistor group, the collector of the transistor Q1, and the base of the transistor Q2.

[0052] When dimming is required, when the pulse width modulator PWM switches the PWM signal to a suspended or low level state, the transistor Q3 is not started, the collector of the transistor Q3 is regarded as a suspended invalid state, and the drive circuit realizes a 100% constant current setting output; when the pulse width modulator PWM switches the PWM signal to a high level state, the Vbe of the transistor Q3 is turned on, so that the collector of the transistor Q3 to the emitter of the transistor Q3 is grounded, so that the base of the transistor Q2 is regarded as grounded through the collector of the transistor Q3, forcing the transistor Q2 to turn off, so that the LED load cannot form a normal working circuit, and finally the whole system is in standby. In addition, in the standby state, the standby power consumption circuit is the ground circuit of the start-up resistor R1 and the start-up resistor R2. Since the resistance values ​​of the start-up resistor R1 and the start-up resistor R2 are relatively large, the standby power consumption is extremely low and can be ignored. In summary, the high and low levels of the pulse width modulator PWM can be connected, so as to adjust the opening angle of the transistor Q3 to realize digital intelligent dimming control.

[0053] Embodiment 2:

[0054] See also Figure 2 A shunt resistor is connected between the collector of the transistor Q2 and the emitter of the transistor Q2.

[0055] The rest is the same as in the first embodiment.

[0056] The shunt resistor RA added in parallel between the collector and emitter of transistor Q2 in the TLCC drive circuit has a unique shunt and power consumption function, which can divide the circuit from the positive end of the LED load to the negative end of the LED load into two paths. One of the two currents flows directly through the collector of transistor Q2 to the emitter of transistor Q2, while the other current flows to the emitter of transistor Q2 after flowing through the shunt resistor RA. The two currents are finally gathered together at the emitter of transistor Q2, and then connected to the base of transistor Q1, forming a loop to the ground through the constant current resistor Rs.

[0057] Among them, since the voltage of the constant current resistor Rs is equal to the voltage between the base of the transistor Q1 and the emitter of the transistor Q1, the added shunt resistor RA does not affect the constant current effect of the TLCC circuit. The shunt resistor RA connected in parallel between the collector of the transistor Q2 and the emitter of the transistor Q2 has a very significant function of shunting and dividing power consumption, which can better realize the power consumption transfer of the transistor Q2 and further improve the reliability and safety of the circuit. In addition, when outputting low current constant current, such as in output applications below 10mA, the shunt resistor RA can be omitted.

[0058] Embodiment three:

[0059] See also Figure 3The present invention provides a PWM dimming control type TLCC driving circuit, comprising a power supply, a dimming module, an over-temperature protection module and an LED load, wherein the dimming module is arranged between the power supply and the over-temperature protection module, and the dimming module comprises a transistor Q3, a current limiting resistor R3, a grounding resistor R4 and a pulse width modulator PWM, wherein the base of the transistor Q3 is connected to the communication interface of the pulse width modulator PWM through the current limiting resistor R3 and is connected to the cathode loop end of the power supply through the grounding resistor R4, and the emitter of the transistor Q3 is connected to the cathode loop end of the power supply;

[0060] The pulse width modulator PWM switches the PWM signal to a suspended or low level state, and uses the transistor Q3 to turn on the over-temperature protection module, thereby conducting between the LED load and the power supply;

[0061] The pulse width modulator PWM switches the PWM signal to a high level state and uses the transistor Q3 to turn off the over-temperature protection module, thereby disconnecting the phase between the LED load and the power supply.

[0062] The over-temperature protection module includes a transistor Q1, a transistor Q2, a starting resistor group and a constant current resistor Rs. The collector of the transistor Q1, the base of the transistor Q2 and the collector of the transistor Q3 are connected and connected to the anode loop end of the power supply and the positive end of the LED load through the starting resistor group. The base of the transistor Q1 is connected to the emitter of the transistor Q2 and connected to the cathode loop end of the power supply through the constant current resistor Rs. The emitter of the transistor Q1 is connected to the cathode loop end of the power supply, and the negative end of the LED load is connected to the collector of the transistor Q2.

[0063] The power supply is a direct current power supply DC, and the DC+ terminal and DC- terminal of the direct current power supply DC are connected to the LED load after being dimmed by a dimming module and monitored by an over-temperature protection module.

[0064] The number of the starting resistors in the starting resistor group is at least one.

[0065] The TLCC driving circuit exhibits a constant current output characteristic during normal operation and the calculation formula is as follows:

[0066] ;

[0067] Among them, Iout_CC is the constant output current, Q1Vbe is the voltage between the base and the emitter of the transistor Q1, and Rs is the resistance of the constant current resistor Rs.

[0068] The working process and the principle of automatic over-temperature protection are the same as those of the first embodiment.

[0069] Embodiment 4:

[0070] See also Figure 4 A shunt resistor is connected between the collector of the transistor Q2 and the emitter of the transistor Q2.

[0071] The rest is the same as in Example 3.

[0072] The present invention can realize digital intelligent dimming control by accessing the high and low levels of the pulse width modulator PWM, thereby utilizing the adjustment of the opening angle of the transistor Q3; by arranging the transistor Q1, the transistor Q2, the starting resistor group and the constant current resistor Rs to jointly form an over-temperature protection module, the current flowing through the constant current resistor Rs is equal to the loop current of the LED load, and the voltage of the constant current resistor Rs is equal to the voltage between the base and the emitter of the transistor Q1, thereby utilizing the characteristic that Q1Vbe is close to a fixed value, freely adjusting the resistance parameter of the constant current resistor Rs as required, and realizing automatic adjustment of the constant output current, without using a dedicated constant current chip, and being less affected by the price and supply of the chip, and being able to alleviate the problem of lack of chips in the integrated circuit to a certain extent, and having obvious overall circuit advantages. , outstanding performance, low cost, and high cost performance; it can utilize the inherent temperature drift characteristics of the transistor, so that when the circuit itself or the external temperature is higher than the threshold temperature of the transistor, the constant output current is reduced, and when the driving circuit is released from the abnormal temperature rise state, the normal constant output current is restored, and the whole process is repeated, thereby realizing the characteristics of automatic over-temperature protection; by setting the wire-wound fuse resistor RF1, the rectifier bridge DB1 and the high-voltage electrolytic capacitor C1, when the power supply is an alternating current power supply AC, surge interference can be limited to prevent abnormal short circuits in the circuit, and a stable high-voltage DC voltage after rectification and filtering can be generated; by setting the shunt resistor RA between the collector of the transistor Q2 and the emitter of the transistor Q2, the power consumption transfer of the transistor Q2 can be better realized, and the reliability and safety of the circuit can be further improved.

[0073] The above embodiments are intended to illustrate the present invention, not to limit the present invention. Any solution that is a simple transformation of the present invention belongs to the protection scope of the present invention.

Claims

1. A PWM dimming control type TLCC driving circuit, characterized in that: It includes a power supply, a dimming module, an over-temperature protection module and an LED load, wherein the dimming module is arranged between the power supply and the over-temperature protection module, and the dimming module includes a transistor Q3, a current limiting resistor R3, a ground resistor R4 and a pulse width modulator PWM, wherein the base of the transistor Q3 is connected to the communication interface of the pulse width modulator PWM through the current limiting resistor R3 and is connected to the cathode loop end of the power supply through the ground resistor R4, and the emitter of the transistor Q3 is connected to the cathode loop end of the power supply; The pulse width modulator PWM switches the PWM signal to a suspended or low level state, and uses the transistor Q3 to turn on the over-temperature protection module, thereby conducting between the LED load and the power supply; The pulse width modulator PWM switches the PWM signal to a high level state and uses the transistor Q3 to turn off the over-temperature protection module, thereby disconnecting the phase between the LED load and the power supply; The over-temperature protection module includes a transistor Q1, a transistor Q2, a starting resistor group and a constant current resistor Rs, the collector of the transistor Q1, the base of the transistor Q2 and the collector of the transistor Q3 are connected to the anode loop end of the power supply and the positive end of the LED load through the starting resistor group, the base of the transistor Q1 is connected to the emitter of the transistor Q2 and is connected to the cathode loop end of the power supply through the constant current resistor Rs, the emitter of the transistor Q1 is connected to the cathode loop end of the power supply, and the negative end of the LED load is connected to the collector of the transistor Q2; The power supply is an alternating current power supply AC, and also includes a rectifier and filter module. The alternating current power supply AC is processed by the rectifier and filter module to generate a stable high-voltage direct current voltage, and then passes through a dimming module and an over-temperature protection module to supply power to the LED load; The rectifier and filter module includes a rectifier bridge DB1 and a high-voltage electrolytic capacitor C1. The two AC input terminals of the rectifier bridge DB1 are respectively connected to the ACL terminal and the ACN terminal of the AC power source AC. The two DC output terminals of the rectifier bridge DB1 and the two connection terminals of the high-voltage electrolytic capacitor C1 are respectively connected to the LED load after the dimming control of the dimming module and the temperature rise monitoring of the over-temperature protection module. A shunt resistor RA is connected between the collector of the transistor Q2 and the emitter of the transistor Q2.

2. A PWM dimming control type TLCC driving circuit as claimed in claim 1, characterized in that: A wire-wound fuse resistor RF1 is also provided between the ACL terminal of the AC power source AC and an AC input terminal of the rectifier bridge DB1.

3. A PWM dimming control type TLCC driving circuit as claimed in claim 2, characterized in that: The number of the starting resistors in the starting resistor group is at least 2.

4. A PWM dimming control type TLCC driving circuit as claimed in claim 1, characterized in that: The power supply is a direct current power supply DC, and the DC+ terminal and DC- terminal of the direct current power supply DC are connected to the LED load after being dimmed by a dimming module and monitored by an over-temperature protection module.

5. A PWM dimming control type TLCC driving circuit as claimed in claim 4, characterized in that: The number of the starting resistors in the starting resistor group is at least one.

6. A PWM dimming control type TLCC driving circuit according to any one of claims 1 to 5, characterized in that: The TLCC driving circuit exhibits a constant current output characteristic during normal operation and the calculation formula is as follows: Among them, Iout_CC is the constant output current, Q1Vbe is the voltage between the base and the emitter of the transistor Q1, and Rs is the resistance of the constant current resistor Rs.

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