CN104168696A - Compatible LED power supply circuit - Google Patents

Abstract

The invention relates to a compatible LED power supply circuit, which comprises an alternating current connecting end, a power inductor L1, a first rectifier bridge, a second rectifier bridge, a first filter circuit, a PWM controller, an EMC circuit, a coupling transformer T1 and an LED output circuit, wherein the alternating current connecting end is connected with the power inductor L1; the alternating current connection end is connected to a primary coil of a coupling transformer T1 through a power inductor L1, a second rectifier bridge and an EMC circuit, and a secondary coil of the coupling transformer T1 is connected with the LED output circuit; the input end of the first rectifier bridge is connected with the alternating current connecting end, and the output end of the first rectifier bridge is connected with the first filter circuit; the first filter circuit is connected with a first input end of a first error amplifier of the PWM controller; the signal output of the PWM controller is connected to the second terminal of the primary winding of the coupling transformer T1. The invention can effectively adjust and match the impedance of different electronic ballasts, protect the electronic ballasts, meet the actual use and realize compatibility; in addition, the LED fluorescent lamp can be compatible with an inductive ballast and a common alternating current input, so that a real LED lamp tube replaces a traditional fluorescent lamp tube.

Description

Compatible LED power supply circuit

technical field

The invention relates to a power supply circuit of an LED lamp tube, in particular to a power supply circuit of an LED lamp tube compatible with an electronic ballast, an inductance ballast and an AC power supply.

Background technique

Traditional daylight lighting is achieved by combining fluorescent tubes and ballasts. Generally, there are two forms of magnetic ballasts plus starters, or electronic ballasts. With the popularization of the new lighting material LED, a variety of LED lamp tubes to replace fluorescent tubes gradually appear. LED lamp tubes are equipped with driving power circuits to cooperate with existing lamps and directly replace fluorescent tubes. For LED lamps that use inductive ballasts or are directly driven by alternating current, since the 50-60Hz alternating current of the mains is directly used, the power supply circuit is easy to implement. However, for LED lamps driven by electronic ballasts, since the output of electronic ballasts is high-frequency alternating current, the general frequency is 35-65kHz, and the output current is constant. If the load of the electronic ballast does not match, when the equivalent impedance of the load is higher than the impedance designed by the electronic ballast itself, the output AC voltage becomes larger; otherwise, the output AC voltage becomes smaller. Therefore, how to match the output impedance of the electronic ballast is a difficult point to be solved in the LED driving power supply circuit. There is a lack of LED tubes on the market that are compatible with different electronic ballasts. Even if they claim to be compatible, their compatibility is basically poor. That is to say, the LED lamp cannot be lit, or the electronic ballast is overheated and damaged. On the other hand, if the LED lamp tube can be directly compatible with the use of electronic ballasts, magnetic ballasts and AC drives, it will further meet the needs of actual use.

Contents of the invention

In view of the above-mentioned deficiencies in the prior art, the technical problem to be solved by the present invention is to provide a LED driving power circuit, so that the equivalent input impedance of the LED driving power circuit follows the output impedance of the electronic ballast to achieve compatibility with different electronic ballasts. device purpose.

In order to solve the above-mentioned technical problems, the technical solution adopted by the present invention is that a compatible LED power supply circuit includes an AC connection terminal, a power inductor L1, a first rectifier bridge, a second rectifier bridge, a first filter circuit, a PWM controller, and an EMC circuit , coupling transformer T1 and LED output circuit; the AC connection end is connected to the first end of the primary coil of the coupling transformer T1 through the power inductor L1, the second rectifier bridge and the EMC circuit in turn, and the secondary coil of the coupling transformer T1 is connected to the LED output circuit; The input end of the first rectifier bridge is connected to the AC connection end, and the output end of the first rectifier bridge is connected to the first filter circuit; the first filter circuit is connected to the first input end of the first error amplifier of the PWM controller, and the first error The second input terminal of the amplifier is used to connect with the first reference voltage; the signal output terminal of the PWM controller is connected with the second terminal of the primary coil of the coupling transformer T1. Such a scheme enables the pulse width of the EMC to be changed by the input ECG, thereby changing the matching impedance.

A further technical solution is that the first filtering circuit includes a resistor R5, a capacitor C6, a diode D15 and an electrolytic capacitor C7; the parallel branch of the resistor R5 and the capacitor C6 is connected between the positive output terminal and the negative output terminal of the first rectifier bridge Between, the positive output terminal of the first rectifier bridge is the VECG terminal, the negative output terminal of the first rectifier bridge is grounded; the positive output terminal of the first rectifier bridge is also connected to the anode of the diode D15, and the cathode of the diode D15 is connected to the positive terminal of the electrolytic capacitor C7 Connect, the negative electrode of the electrolytic capacitor C7 is grounded; the positive electrode of the electrolytic capacitor C7 is the VCC end, which is connected to the power supply pin of the PWM controller; the VECG end of the first filter circuit is connected to the first error amplifier of the PWM controller through a diode D17 The first input end, the VECG end, is connected to the anode of the diode D17.

A further technical solution is that the first filtering circuit also includes a voltage stabilizing diode ZD4; the voltage stabilizing diode ZD4 is connected between the VECG terminal and the diode D15, the cathode of the voltage stabilizing diode ZD4 is connected to the VECG terminal, and the voltage stabilizing diode ZD4 is connected to the VECG terminal. The anode of ZD4 is connected to the anode of diode D15. Such a solution can be applied to the compatibility between the preheating start type and the instant start type. For the preheating start type, the PWM controller is not powered until the voltage reaches the starting voltage.

A further technical solution is a signal isolation circuit; the signal isolation circuit includes a switch tube Q6, a resistor R9, a resistor R10 and a diode D16; the source of the switch tube Q6 is grounded, and the resistor R9 is connected to the source and gate of the switch tube Q6 between the poles; the gate of the switching tube Q6 is also connected to the VECG terminal; the drain of the switching tube Q6 is connected to the standard reference voltage terminal through the resistor R10; the drain of the switching tube Q6 is also connected to the anode of the diode D16, and the cathode of the diode D16 Connect to the first input of the first error amplifier. Such a solution can prevent the VECG terminal signal from affecting the pulse width modulation of the PWM controller when a non-ECG is connected.

A further technical solution is to further include a frequency selection voltage divider circuit and a charging power supply circuit; the frequency selection voltage divider circuit includes a capacitive part; the power inductor L1 is connected in series between the positive end of the AC connection end and the second rectifier bridge The AC connection end is connected to the first rectifier bridge through a frequency-selective voltage divider circuit, and the capacitive part is connected to the positive end of the AC connection end; the coupling transformer T1 also includes a second secondary coil, which is connected to the second secondary coil The charging power supply circuit is connected, the charging power supply circuit is provided with a power supply output terminal, and the power supply output terminal is connected to the power supply pin of the PWM controller; the current detection voltage terminal of the LED output circuit is connected to the second input of the second error amplifier of the PWM controller Terminal, the first input terminal of the second error amplifier is used to connect with the second reference voltage. Such a solution enables the PWM controller to perform pulse width modulation in different ways according to different input starters, and is fully compatible with the use of CCG, AC and ECG.

A further technical solution is that the charging circuit includes a diode D7, a switch tube Q2, a transistor Q3, a voltage regulator diode ZD3, a voltage regulator diode ZD6, a diode D9, a diode D10, an electrolytic capacitor C4, an electrolytic capacitor C5, a resistor R3 and a resistor R6; the anode of the diode D7 is connected to the first end of the primary coil of the coupling transformer T1, the cathode of the diode D7 is connected to the cathode of the Zener diode ZD3, the anode of the Zener diode ZD3 is connected to the drain of the switching tube Q2 through the resistor R3, and the switch The gate of the transistor Q2 is connected to the collector of the transistor Q3, the source of the switching transistor Q2 is connected to the anode of the electrolytic capacitor C5, and the emitter of the transistor Q3 is grounded; the base of the transistor Q3 is connected to the anode of the Zener diode ZD6 through the resistor R6 ; The cathode of the Zener diode ZD6 is connected to the cathode of the diode D9; the anode of the diode D9 is connected to the first end of the second secondary coil of the coupling transformer T1, and the second end of the second secondary coil is grounded; the cathode of the diode D9 is also It is connected to the anode of diode D10, the cathode of diode D10 is also connected to the positive pole of electrolytic capacitor C5, the negative pole of electrolytic capacitor C5 is grounded, the positive pole of electrolytic capacitor C4 is connected to the anode of diode D10, and the negative pole of electrolytic capacitor C4 is grounded.

Preferably, the frequency-selective voltage dividing circuit further includes an inductive part forming a voltage dividing circuit with a capacitive part; the capacitive part is a capacitor CS1, and the inductive part is a transformer LS1; one end of the capacitor CS1 is connected to the AC connection end The positive end is connected, the other end of the capacitor CS1 is connected to one end of the primary coil of the transformer LS1, and the other end of the primary coil of the transformer LS1 is connected to the negative end of the AC connection end; the two ends of the secondary coil of the transformer LS1 are respectively connected to the first The input terminal of a rectifier bridge; the capacitance value of capacitor CS1 is not more than 0.3μF; the inductance value of the primary coil of transformer LS1 is 0.3mH-6mH.

The preferred technical solution is also that the capacitive part is a capacitor CS2; the frequency selection voltage divider circuit also includes a capacitor CS3; one end of the capacitor CS2 is connected to the positive end of the AC connection end, and the other end of the capacitor CS2 is connected to the first rectifier bridge One input end of the capacitor CS3; one end of the capacitor CS3 is connected to the other input end of the first rectifier bridge, and the other end of the capacitor CS3 is connected to the negative end of the AC connection end.

A further technical solution is to further include a second signal isolation circuit, the second signal isolation circuit includes a diode D18 and a Zener diode ZD7; the first filter circuit is connected to the first error amplifier of the PWM controller through a diode D17. One input terminal, wherein the cathode of the diode D17 is connected to the first input terminal of the first error amplifier; the cathode of the voltage stabilizing diode ZD7 is connected to the anode of the diode D17, the anode of the voltage stabilizing diode ZD7 is connected to the anode of the diode D18, and the anode of the diode D18 The cathode is connected to the first input of the second error amplifier. In such a scheme, even if the maximum pulse width Dmax of the PWM controller is not set, the PWM output pulse width D is not affected by the second error amplifier.

A further technical solution is to further include a protection circuit; the protection circuit includes a resistor R1, a resistor R7, a resistor R8, a transistor Q5, a Zener diode ZD1, a switch tube Q1 and a capacitor C2; the series branch connection of the resistor R7 and the resistor R8 Between the positive output terminal of the EMC circuit and the reference terminal; the base of the transistor Q5 is connected to the node of the resistor R7 and the resistor R8; the emitter of the transistor Q5 is connected to the reference terminal of the EMC circuit; the collector of the transistor Q5 is connected to the switching tube The gate of Q1; the source of the switching tube Q1 is connected to the reference terminal of the EMC circuit, the drain of the switching tube Q1 is grounded; the anode of the Zener diode ZD1 is connected to the emitter of the transistor Q5, and the cathode of the Zener diode ZD1 is connected to the transistor The collector of Q5; the collector of transistor Q5 is also connected to the positive output terminal of the EMC circuit through the resistor R1; one end of the capacitor C2 is connected to the positive output terminal of the EMC circuit, and the other end of the capacitor C2 is grounded.

The compatible LED power supply circuit of the present invention can effectively adjust and match the impedance of different electronic ballasts, protect the electronic ballasts and meet the actual use, and realize compatibility; in addition, it can also be compatible with inductive ballasts and ordinary AC input, realizing real LED tubes replace traditional fluorescent tubes.

Description of drawings

Fig. 1 is a schematic circuit diagram of the first embodiment of the compatible LED power supply circuit of the present invention.

Fig. 2 is a schematic circuit diagram of the second embodiment of the compatible LED power supply circuit of the present invention.

Figure 3 is a schematic diagram of the input voltage of the electronic ballast.

Fig. 4 is a schematic diagram of the input voltage of the magnetic ballast or alternating current.

Fig. 5 is a schematic diagram of the input voltage of the preheating start type magnetic ballast.

Detailed ways

Below in conjunction with accompanying drawing and specific embodiment the present invention will be described in further detail

As shown in Figure 1, the first embodiment of the compatible LED power supply circuit of the present invention includes AC connection terminals (positive terminal LA1, positive terminal LA2, negative terminal RA1 and negative terminal RA2), power inductor L1, a first rectifier Bridge (Diode D11, Diode D12, Diode D13, and Diode D14), Second Rectifier Bridge (Diode D1, Diode D2, Diode D3, and Diode D4), First Filter Circuit, PWM Controller, EMC Circuit, Coupling Transformer T1, and LED output circuit. The AC connection end is connected to the first end of the primary coil of the coupling transformer T1 through the power inductor L1, the second rectifier bridge and the EMC circuit in turn, specifically, the positive end LA1 of the AC connection end is connected to the first end of the power inductor L1 through the fuse F3. terminal, the positive terminal LA2 is connected to the positive terminal LA1 through the fuse F1; the power inductor L1 is connected to the input positive terminal of the EMC circuit through the second rectifier bridge, the input of the EMC circuit is connected to the negative output terminal of the second rectifier bridge, and the second rectifier A capacitor C1 is also connected between the positive output terminal of the bridge (the node of diode D1 and diode D2 ) and the negative output terminal; the positive output terminal of the EMC circuit is connected to the first terminal of the primary coil of the coupling transformer T1. The secondary coil of the coupling transformer T1 is connected to the LED output circuit. Specifically, in this embodiment, the LED output circuit includes a diode D8, an electrolytic capacitor C3 and a resistor R4. The anode of the diode D8 is connected to the first coil of the secondary coil of the coupling transformer T1. Terminal, the second terminal of the secondary coil of the coupling transformer is grounded; the anode of the electrolytic capacitor C3 is connected to the cathode of the diode D8, and the negative pole of the electrolytic capacitor C3 is grounded; the positive pole of the electrolytic capacitor C3 is the VO terminal, which is used to connect with the anode of the LED light string ; The cathode of the electrolytic capacitor C3 is connected to the first end of the resistor R4, and the second end of the resistor R4 is the current detection voltage end (that is, the IO end) of the LED output circuit, which is also used to connect with the cathode of the LED light string; wherein the coupling transformer The second end of the primary coil of T1 and the first end of the secondary coil have the same name. The current detection voltage terminal of the LED output circuit is connected to the second input terminal (positive input terminal in this embodiment) of the second error amplifier EA2 of the PWM controller, and the first input terminal (negative input terminal) of the second error amplifier EA2 ) is used to connect with the second reference voltage REF2. Through the power supply of the coupling transformer T1, the electrolytic capacitor C3 is charged to a stable voltage, thereby realizing the power supply to the LED light string; it should be noted that the LED output circuit is not considered in the scope of the present invention, and only one method for realizing the LED power supply output is proposed here. The method is not intended to limit the present invention, and other forms and functions of LED output circuits can be used in actual implementation.

The input end of the first rectifier bridge (ie, the node of the diode D11 and the diode D13 , the node of the diode D12 and the diode D14 ) is connected to the AC connection end. Specifically, the present invention also includes a frequency-selective voltage-divider circuit, the frequency-selective voltage-divider circuit includes a capacitive part, in this embodiment, the capacitive part is capacitor CS1, and the inductive part is transformer LS1; One end of CS1 is connected to the positive end of the AC connection end (specifically, the positive end LA1 and the positive end LA2 connected to the fuse F3), the other end of the capacitor CS1 is connected to one end of the primary coil P of the transformer LS1, and the transformer LS1 The other end of the primary coil P is connected to the negative terminal of the AC connection terminal (the negative terminal RA1 and the negative terminal RA2 connected to the fuse F2); the two ends of the secondary coil S of the transformer LS1 are respectively connected to the input terminals of the first rectifier bridge. The capacitance value of the capacitor CS1 is not greater than 0.3μF; the inductance value of the primary coil of the transformer LS1 is 0.3mH-6mH. When the input is ECG (electronic ballast), the AC frequency generally reaches 35KHz-65KHz, as shown in Figure 3, under high-frequency AC, the impedance of the capacitive part, that is, the capacitor CS1, is very small, while the inductive part, that is, the transformer LS1 The impedance of the primary coil P of the transformer LS1 is relatively large, so the secondary coil S of the transformer LS1 can obtain a large partial voltage of the input voltage; on the other hand, when the input is CCG (inductive ballast) or ordinary current, its AC frequency is market Electricity is about 50Hz, as shown in Figure 4, which belongs to low-frequency alternating current. The impedance of capacitor CS1 is relatively large, while the impedance of the primary coil P of transformer LS1 is relatively small, so the voltage obtained on the secondary coil S of transformer LS1 It will be much smaller than the voltage obtained by ECG input. With this scheme, the type of input voltage can be judged, whether the input is ECG or CCG/AC; on the other hand, when the input is ECG, the input voltage can be selected by frequency division Voltage division circuit, so the frequency selection voltage division circuit also has the function of detecting the input voltage of ECG. In the case where there is no need for high-frequency judgment (only for ECG) and the detection accuracy of the input ECG voltage is low, the setting of the frequency selection and voltage divider circuit can be cancelled.

The output terminal of the first rectifier bridge is connected with the first filter circuit; specifically, the first filter circuit includes resistor R5, capacitor C6, diode D15 and electrolytic capacitor C7; the parallel branch of resistor R5 and capacitor C6 is connected to the first Between the positive output terminal of the rectifier bridge (the node of diode D11 and diode D12) and the negative output terminal (the node of diode D13 and diode D14), the positive output terminal of the first rectifier bridge is the VECG terminal (obtaining the detected ECG input voltage Transformed voltage), the negative output terminal of the first rectifier bridge is grounded; the positive output terminal of the first rectifier bridge is also connected to the anode of the diode D15, the cathode of the diode D15 is connected to the positive pole of the electrolytic capacitor C7, and the negative pole of the electrolytic capacitor C7 is grounded The anode of the electrolytic capacitor C7 is a VCC end, which is connected to the power supply pin of the PWM controller; the VECG end of the first filter circuit is connected to the first input end of the first error amplifier EA1 of the PWM controller through a diode D17 (this implementation For example, the negative input terminal), the VECG terminal is connected to the anode of the diode D17. The second input terminal (positive input terminal) of the first error amplifier EA2 is used to connect with the first reference voltage REF1; the signal output terminal of the PWM controller (that is, the PWM terminal in the figure) is connected to the second Specifically, the signal output terminal is connected to the gate of a switching transistor Q4, the source of the switching transistor Q4 is grounded, and the drain is connected to the second end of the primary coil of the coupling transformer T1. After the first filter circuit obtains the ECG input voltage, the saturated electrolytic capacitor C7 supplies power to the PWM controller to make the PWM controller work. For warm-up electronic ballasts, as shown in Figure 5, the input voltage will be at a low value at the beginning, and it will generally increase to a stable working voltage after about 500ms. In this case, a Zener diode ZD4 can be connected in series between the VECG terminal and the diode D15, wherein the cathode of the Zener diode ZD4 is connected to the VECG terminal, and the anode of the Zener diode ZD4 is connected to the anode of the diode D15. During the warm-up period (that is, during the low voltage period), since the Zener diode ZD4 has no reverse conduction, the electrolytic capacitor C7 is not charged, and the PWM controller is not powered to start. After the voltage stabilizes to the working voltage, the Zener diode ZD4 conducts reversely. PWM control obtains power supply; for instant-start electronic ballasts (that is, without warm-up time), the input voltage will not affect the start-up of the PWM controller even if the Zener diode ZD4 conducts in reverse when it is turned on, because the instant-start type can be realized Compatibility between electronic ballasts and warm start type electronic ballasts.

Working principle: The saturation current of the power inductor L1 is greater than the peak current flowing through the power inductor L1. The inductance of the power inductor L1 generally takes a value of 0.1-1mH.

When CCG or AC is input, because the frequency is as low as 50/60Hz, the equivalent impedance of the power inductor L1 is very small, which is almost equivalent to a short circuit and has no effect on the circuit.

When ECG is input, because the frequency is as high as 35-65kHz, the equivalent impedance on the power inductor L1 is between tens to hundreds of ohms. At this point, take

IECG≈ICS1+IL1

(In the above formula, IECG is the effective value of the output current of the ECG design, ICS1 is the effective value of the current flowing through the capacitor CS1, and IL1 is the effective value of the current flowing through the power inductor L1) so that the input equivalent impedance of the LED lamp It matches the output impedance of ECG design, making the designed LED lamp compatible with ECG. According to the ECG output characteristics, if IECG>ICS1+IL1, the ECG output voltage VOECG increases; if IECG<ICS1+IL1, the ECG output voltage VOECG decreases. The internal equivalent structure diagram of the PWM controller is shown in the figure. The FB signal terminal of the PWM controller outputs a 20-100kHz PWM signal through the current drive module of the PWM controller to drive the switching tube Q4 on and off. When the FB signal When the voltage rises, the PWM pulse width D decreases; otherwise, the PWM pulse width D increases.

When the detection signal through capacitor CS1 and transformer LS1 is rectified and filtered, it becomes the detection signal VECG of the output voltage VOECG of the electronic ballast (that is, the voltage on the WECG terminal, VECG is proportional to VOECG, and the specific proportional relationship is related to the circuit device. parameter correlation), VECG is input to the first error amplifier through the diode D17, compared with the first reference reference voltage REF1, and then amplified to output the FB signal through a diode.

During this process:

FB↓=>D↑=>IL1↑=>ICS1+IL1↑=>VOECG↓=>VECG↓=>FB↑=>D↓=>IL1↓=>ICS1+IL1↓=>VOECG↑=>VECG↑ =>FB↓

In this way, a closed feedback loop is formed, and the input equivalent impedance of the LED light tube can match different equivalent impedances for different ECGs to achieve the purpose of being compatible with ECGs. When the PWM is set to the maximum pulse width Dmax, the current detection voltage IO of the LED light string is still lower than the reference voltage REF2, that is, "EA2->EA2+", then the second error amplifier EA2 has no output, and the IO signal has no effect on the FB signal, and thus has no effect on the FB signal. PWM output pulse width D has no effect.

When the input is CCG or AC, the second error amplifier EA2 works normally,

During this process:

FB↓＝>D↑＝>IO↑＝>FB↑＝>D↓＝>IO↓＝>FB↓

Thus, a closed feedback loop is formed, so that the working current of the LED light string can be effectively controlled.

Further, the present invention also includes a signal isolation circuit; the signal isolation circuit includes a switch tube Q6, a resistor R9, a resistor R10 and a diode D16; the source of the switch tube Q6 is grounded, and the resistor R9 is connected to the source and gate of the switch tube Q6 between the poles; the gate of the switching tube Q6 is also connected to the VECG terminal; the drain of the switching tube Q6 is connected to the standard reference voltage terminal REF through the resistor R10; the drain of the switching tube Q6 is also connected to the anode of the diode D16, and the drain of the diode D16 The cathode is connected to the first input terminal of the first error amplifier EA1.

The sum of the first reference voltage REF1 and the forward conduction voltage of the diode D16 is set to be much smaller than the standard reference voltage REF. When the input is CCG or AC, VECG is close to 0, and the switching tube Q6 is cut off.

REF passes through resistor R10 and diode D16 to the negative input terminal of the first error amplifier EA1, and its voltage value is higher than the first reference reference voltage REF1, that is, “EA1->EA1+”, then the first error amplifier EA1 has no output, and the VECG signal is PWM output pulse width D has no effect.

The present invention also includes a charging power supply circuit. The coupling transformer T1 also includes a second secondary coil connected to the charging power supply circuit. pin connection. Specifically, the charging circuit includes a diode D7, a switch tube Q2, a transistor Q3, a Zener diode ZD3, a Zener diode ZD6, a diode D9, a diode D10, an electrolytic capacitor C4, an electrolytic capacitor C5, a resistor R3 and a resistor R6; the diode D7 The anode of the diode D7 is connected to the first end of the primary coil of the coupling transformer T1, the cathode of the diode D7 is connected to the cathode of the Zener diode ZD3, the anode of the Zener diode ZD3 is connected to the drain of the switching tube Q2 through the resistor R3, and the gate of the switching tube Q2 pole is connected to the collector of transistor Q3, the source of switch tube Q2 is connected to the positive pole of electrolytic capacitor C5, and the emitter of transistor Q3 is grounded; the base of transistor Q3 is connected to the anode of Zener diode ZD6 through resistor R6; Zener diode The cathode of ZD6 is connected to the cathode of diode D9; the anode of diode D9 is connected to the first end of the second secondary coil of coupling transformer T1, and the second end of the second secondary coil is grounded; the cathode of diode D9 is also connected to the diode D10. The anode is connected, the cathode of the diode D10 is also connected to the positive pole of the electrolytic capacitor C5, the negative pole of the electrolytic capacitor C5 is grounded, the positive pole of the electrolytic capacitor C4 is connected to the anode of the diode D10, and the negative pole of the electrolytic capacitor C4 is grounded. When the input is CCG or AC, if the input voltage is low, the output voltage of the EMC circuit is also low at this time, and the Zener diode ZD3 will not conduct in reverse, so there will be no start-up voltage provided to the power supply lead of the PWM controller. pin, the PWM controller does not work;

When the normal voltage is input, the Zener diode ZD3 conducts reversely, the switch tube Q2 conducts, the output voltage of the EMC circuit charges the electrolytic capacitor C5 through the diode D7, the Zener diode ZD3, the resistor R3, and the switch tube Q2, and the electrolytic capacitor C5 When the voltage value reaches the starting voltage of the PWM controller, the PWM controller starts to work. Then the PWM has a pulse width output, and then the induced voltage of the second secondary coil of the coupling transformer T1 is rectified by the diode D9, filtered by the electrolytic capacitor C4, and then sent to the power supply pin of the PWM controller through the diode D10. After startup, the Zener diode ZD6 conducts in reverse, and the transistor Q3 is turned on accordingly, pulling the gate voltage of the switching tube Q2 to close to 0V, so that the switching tube Q2 is turned off. That is, when the PWM controller is started, it is powered by the starting circuit composed of diode D7, Zener diode ZD3, resistor R3, switch tube Q2, resistor R2, and Zener diode ZD5. After starting, the second secondary coil of the coupling transformer T1 passes through the diode The rectification filter circuit composed of D9, electrolytic capacitor C4, diode D10, and electrolytic capacitor C5 supplies power; when the lamp input is ECG, the power supply voltage of the PWM controller is obtained by rectifying the secondary coil S of the transformer LS1 through the first rectifier bridge , control cleverly.

The present invention also includes a protection circuit; the protection circuit includes a resistor R1, a resistor R7, a resistor R8, a transistor Q5, a Zener diode ZD1, a switching tube Q1 and a capacitor C2; the series branch of the resistor R7 and the resistor R8 is connected to the EMC circuit Between the positive output terminal and the reference terminal; the base of transistor Q5 is connected to the node of resistor R7 and resistor R8; the emitter of transistor Q5 is connected to the reference terminal of the EMC circuit; the collector of transistor Q5 is connected to the gate of switching tube Q1 ; The source of the switching tube Q1 is connected to the reference terminal of the EMC circuit, and the drain of the switching tube Q1 is grounded; the anode of the Zener diode ZD1 is connected to the emitter of the transistor Q5, and the cathode of the Zener diode ZD1 is connected to the collector of the transistor Q5 The collector of the transistor Q5 is also connected to the positive output terminal of the EMC circuit through the resistor R1; one end of the capacitor C2 is connected to the positive output terminal of the EMC circuit, and the other end of the capacitor C2 is grounded. When the circuit is abnormal, the voltage output from the ECG to the lamp is rectified by the second rectifier bridge (diode D1-diode D4), then filtered by the capacitor C1, then passed through the EMC circuit, divided by the resistor R7 and the resistor R8, once the voltage is divided When the voltage is greater than the junction conduction voltage of the transistor Q5, the transistor Q5 is turned on, the gate voltage of the switching tube Q1 is pulled down by the transistor Q5, and the switching tube Q1 is turned off, thereby achieving the purpose of protecting the downstream circuit of the switching tube Q1 and the ECG.

Fig. 2 shows the second embodiment of the present invention, and the difference with the above-mentioned first embodiment is that the capacitive portion is a capacitor CS2; the frequency selection voltage divider circuit also includes a capacitor CS3; one end of the capacitor CS2 Connect the positive end of the AC connection end, the other end of the capacitor CS2 is connected to one input end of the first rectifier bridge; one end of the capacitor CS3 is connected to the other input end of the first rectification bridge, and the other end of the capacitor CS3 is connected to the negative end of the AC connection end . In this embodiment, the capacitance value of capacitor CS2 is much larger than the capacitance value of capacitor CS3. Although capacitor CS3 is a capacitor, which is a capacitive device in essence, its capacitance value is much smaller than that of capacitor CS2 used in conjunction with it. On the circuit, the purpose of voltage division detection is also realized, and its working principle is the same as that of the above-mentioned first embodiment. In addition, the capacitance values of the capacitor CS2 and the capacitor CS3 can be equivalent, or the capacitor CS3 can be omitted, and the capacitor CS2 can be set separately (or only the capacitor CS1 can be set without the transformer LS1), so that the capacitor CS2 can also form a voltage divider with the resistor R5. The voltage division can also be obtained; however, the shunting effect on the frequency-selective voltage division is not as good as the matching effect of the capacitor CS1 and the transformer LS1 in the first embodiment above. Transformer LS1 and capacitor CS1 are connected in series as a load for ECG output, so that part of the output current of ECG flows through this load, effectively reducing the current flowing through the frequency selection and voltage dividing circuit, that is, reducing the loss of rectifier tubes D1-D4 , thereby reducing the loss of the entire circuit and improving power efficiency.

On the other hand, this embodiment also includes a second signal isolation circuit, the second signal isolation circuit includes a diode D18 and a Zener diode ZD7; the first filter circuit is connected to the first error amplifier EA1 of the PWM controller through a diode D17 The first input terminal (negative input terminal) of the diode D17, wherein the cathode of the diode D17 is connected to the first input terminal of the first error amplifier EA1; the cathode of the Zener diode ZD7 is connected to the anode of the diode D17, and the anode of the Zener diode ZD7 is connected to the diode The anode of D18 is connected, and the cathode of diode D18 is connected to the first input terminal (negative input terminal) of the second error amplifier EA2. Set the current detection voltage IO of the LED light string to still be less than VECG minus the reverse voltage regulation of the Zener diode ZD7, and then subtract the forward voltage of the diode D18, then there is "EA2->EA2+", then the second error amplifier EA2 has no Output, the IO signal has no effect on the PWM output pulse width D. At this time, even if the maximum pulse width Dmax of the PWM is not set, the PWM output pulse width D is not affected by the second error amplifier EA2. This second signal isolation circuit can also be applied to the above-mentioned first embodiment.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the scope of the present invention. within the scope of protection.

Claims (10)

1. compatible type LED power circuit, is characterized in that: comprise and exchange link, power inductance L1, the first rectifier bridge, the second rectifier bridge, the first filter circuit, PWM controller, EMC circuit, coupling transformer T1 and LED output circuit; Exchange link is connected to the primary coil of coupling transformer T1 successively first end by power inductance L1, the second rectifier bridge and EMC circuit, the secondary coil of coupling transformer T1 connects LED output circuit; The input of the first rectifier bridge is connected with interchange link, and the output of the first rectifier bridge is connected with the first filter circuit; The first filter circuit is connected with the first input end of the first error amplifier of PWM controller, and the second input of the first error amplifier is for being connected with the first reference voltage; The signal output part of PWM controller is connected with the second end of the primary coil of coupling transformer T1.

2. compatible type LED power circuit according to claim 1, is characterized in that: described the first filter circuit comprises resistance R 5, capacitor C 6, diode D15 and electrochemical capacitor C7; The parallel branch of resistance R 5 and capacitor C 6 is connected between the positive output end and negative output terminal of the first rectifier bridge, and the positive output end of the first rectifier bridge is VECG end, the negative output terminal ground connection of the first rectifier bridge; The positive output end of the first rectifier bridge is also connected to the anode of diode D15, and the negative electrode of diode D15 is connected with the positive pole of electrochemical capacitor C7, the minus earth of electrochemical capacitor C7; The just very VCC end of electrochemical capacitor C7, is connected with the energization pins of PWM controller; The VECG end of the first filter circuit is connected to the first input end of the first error amplifier of PWM controller by a diode D17, the anodic bonding of VECG end and diode D17.

3. compatible type LED power circuit according to claim 2, is characterized in that: described the first filter circuit also comprises voltage stabilizing didoe ZD4; Described voltage stabilizing didoe ZD4 is connected between VECG end and diode D15, and the negative electrode of voltage stabilizing didoe ZD4 is connected with VECG end, the anodic bonding of the anode of voltage stabilizing didoe ZD4 and diode D15.

4. compatible type LED power circuit according to claim 3, is characterized in that: signal isolation circuit; Described signal isolation circuit comprises switching tube Q6, resistance R 9, resistance R 10 and diode D16; The source ground of switching tube Q6, resistance R 9 is connected between the source electrode and grid of switching tube Q6; The grid of switching tube Q6 is also connected to VECG end; The drain electrode of switching tube Q6 is connected to canonical reference voltage end by resistance R 10; The drain electrode of switching tube Q6 is also connected to the anode of diode D16, and the negative electrode of diode D16 is connected to the first input end of the first error amplifier.

5. compatible type LED power circuit according to claim 1, is characterized in that: also comprise frequency-selecting bleeder circuit and charging circuit; Described frequency-selecting bleeder circuit comprises capacitive portion; Described power inductance L1 is series between the anode and the second rectifier bridge that exchanges link; Described interchange link is connected to the first rectifier bridge by frequency-selecting bleeder circuit, and capacitive portion is connected with the anode that exchanges link; Described coupling transformer T1 also comprises second subprime coil, and this second subprime coil is connected with charging circuit, and charging circuit is provided with power supply output, and this power supply output is connected with the energization pins of PWM controller; The current detection voltage end of LED output circuit is connected to the second input of the second error amplifier of PWM controller, and the first input end of this second error amplifier is for being connected with the second reference voltage.

6. compatible type LED power circuit according to claim 5, is characterized in that: described charging circuit comprises diode D7, switching tube Q2, transistor Q3, voltage stabilizing didoe ZD3, voltage stabilizing didoe ZD6, diode D9, diode D10, electrochemical capacitor C4, electrochemical capacitor C5, resistance R 3 and resistance R 6; The anode of diode D7 is connected with the first end of coupling transformer T1 primary coil, the negative electrode of diode D7 is connected with the negative electrode of voltage stabilizing didoe ZD3, the anode of voltage stabilizing didoe ZD3 is connected to the drain electrode of switching tube Q2 by resistance R 3, the grid of switching tube Q2 is connected with the collector electrode of transistor Q3, the source electrode of switching tube Q2 is connected to the positive pole of electrochemical capacitor C5, the grounded emitter of transistor Q3; The base stage of transistor Q3 is connected to the anode of voltage stabilizing didoe ZD6 by resistance R 6; The negative electrode of voltage stabilizing didoe ZD6 is connected to the negative electrode of diode D9; The anode of diode D9 is connected with the first end of the second subprime coil of coupling transformer T1, the second end ground connection of second subprime coil; The negative electrode of diode D9 also with the anodic bonding of diode D10, the negative electrode of diode D10 is also connected to the positive pole of electrochemical capacitor C5, the minus earth of electrochemical capacitor C5, the anodic bonding of the positive pole of electrochemical capacitor C4 and diode D10, the minus earth of electrochemical capacitor C4.

7. compatible type LED power circuit according to claim 5, is characterized in that: described frequency-selecting bleeder circuit also comprises the perceptual portion with capacitive portion composition bleeder circuit; Described capacitive portion is capacitor C S1, and described perceptual portion is instrument transformer LS1; One end of capacitor C S1 is connected with the anode that exchanges link, and the other end of capacitor C S1 is connected with one end of the primary coil of instrument transformer LS1, and the other end of the primary coil of instrument transformer LS1 is connected to the negative terminal that exchanges link; The secondary coil two ends of instrument transformer LS1 are connected respectively to the input of the first rectifier bridge; The capacitance of capacitor C S1 is not more than 0.3 μ F; The inductance value of the primary coil of instrument transformer LS1 is 0.3mH-6mH.

8. compatible type LED power circuit according to claim 5, is characterized in that: described capacitive portion is capacitor C S2; Described frequency-selecting bleeder circuit also comprises capacitor C S3; One end of capacitor C S2 and the anode that exchanges link, the other end of capacitor C S2 is connected to an input of the first rectifier bridge; One end of capacitor C S3 is connected to another input of the first rectifier bridge, and the capacitor C S3 other end is connected to the negative terminal that exchanges link.

9. compatible type LED power circuit according to claim 5, is characterized in that: also comprise secondary signal buffer circuit, described secondary signal buffer circuit comprises diode D18 and voltage stabilizing didoe ZD7; The first filter circuit is connected to the first input end of the first error amplifier of PWM controller by a diode D17, wherein the negative electrode of diode D17 is connected with the first input end of the first error amplifier; The negative electrode of voltage stabilizing didoe ZD7 is connected to the anode of diode D17, the anodic bonding of the anode of voltage stabilizing didoe ZD7 and diode D18, and the negative electrode of diode D18 is connected to the first input end of the second error amplifier.

10. compatible type LED power circuit according to claim 1, is characterized in that: also comprise protective circuit; Described protective circuit comprises resistance R 1, resistance R 7, resistance R 8, transistor Q5, voltage stabilizing didoe ZD1, switching tube Q1 and capacitor C 2; The series arm of resistance R 7 and resistance R 8 is connected between the positive output end and reference edge of EMC circuit; The base stage of transistor Q5 is connected to the node of resistance R 7 and resistance R 8; The emitter of transistor Q5 is connected to the reference edge of EMC circuit; The collector electrode of transistor Q5 is connected to the grid of switching tube Q1; The source electrode of switching tube Q1 is connected to the reference edge of EMC circuit, the grounded drain of switching tube Q1; The anodic bonding of voltage stabilizing didoe ZD1 is to the emitter of transistor Q5, and the negative electrode of voltage stabilizing didoe ZD1 is connected to the collector electrode of transistor Q5; The collector electrode of transistor Q5 is also by being connected to the positive output end of EMC circuit by resistance R 1; One end of capacitor C 2 is connected to the positive output end of EMC circuit, the other end ground connection of capacitor C 2.