Output short-circuit switching cycle current limiting protection circuit and electronic transformer

Abstract

A switch-cycle current limiting protection circuit for output short circuit includes diodes D6, D5, D2, D9, D4, and D3, drive windings T2-2 and T2-3, resistors R4 and R7, transistors Q2 and Q1. This circuit prevents transistors Q2 and Q1 in the half-bridge circuit of the electronic transformer from being deeply saturated and burning out due to excessive current, thus achieving switch-cycle current limiting protection. Therefore, an electronic transformer with an output short circuit switch-cycle current limiting protection circuit can also achieve switch-cycle current limiting protection.

Description

Technical Field

[0001] This invention relates to the field of electronic transformer technology, and in particular to an output short-circuit switching cycle current limiting protection circuit and an electronic transformer having an output short-circuit switching cycle current limiting protection circuit. Background Technology

[0002] Existing electronic transformer output short-circuit protection circuits (such as...) Figure 3 As shown, when the outputs of OU1 and OUT2 are short-circuited, the overcurrent sampling voltage driven by resistor R9 is rectified through diode D10 and stored in electrolytic capacitor C8, causing transistor Q3 to conduct for 1 to 5 seconds. This results in the voltage across film capacitor C6 approaching 0 volts, meaning the starting voltage of transistor Q1 is 0 volts. Consequently, the half-bridge drive circuit cannot start within 1 to 5 seconds after the rectified voltage of rectifier bridge BD1 crosses zero, causing hiccup protection. However, before the rectified voltage crosses zero, transistors Q1 and Q2 are still working through the drive voltage and drive current of drive coil T2. There is no current limiting protection for each switching cycle. As a result, when the maximum AC voltage input at L and N terminals short-circuits the outputs of OU1 and OUT2, the drive current of drive coil T2 increases significantly. That is, the current between the base and emitter of transistors Q1 and Q2 is very large, causing transistors Q1 and Q2 to conduct deeply. The excessive switching current between the collector and emitter of transistors Q1 and Q2 burns out transistors Q1 and Q2. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art by providing an output short-circuit switching cycle current limiting protection circuit and an electronic transformer having an output short-circuit switching cycle current limiting protection circuit.

[0004] The objective of this invention is achieved through the following technical solution:

[0005] A current-limiting protection circuit for output short circuit switching cycle is provided, including diodes D6, D5, D2, D9, D4, and D3, drive windings T2-2 and T2-3, resistors R4 and R7, transistors Q2 and Q1. The anode of diode D6 is connected to the anode of diode D4, the cathode of diode D5, and the opposite terminal of drive winding T2-2. The cathode of diode D6 is connected to the collector of transistor Q2, and the cathode of diode D4 is connected to the base of transistor Q2. The positive terminal of diode D5 is connected to one end of resistor R4. The same-name terminal of drive winding T2-2 is connected to the other end of resistor R4 and the emitter of transistor Q2. The positive terminal of diode D2 is connected to the positive terminal of diode D3, the negative terminal of diode D9 and the same-name terminal of drive winding T2-3. The negative terminal of diode D2 is connected to the collector of transistor Q1. The negative terminal of diode D3 is connected to the base of transistor Q1, the positive terminal of diode D9 and one end of resistor R7. The other end of resistor R7 is connected to the emitter of transistor Q1 and the opposite-name terminal of drive winding T2-3.

[0006] The present invention also provides an electronic transformer, including a bridge rectifier BD1, a half-bridge drive circuit, and the output short-circuit switching cycle current limiting protection circuit described above. The positive and negative terminals of the mains power are respectively connected to the two input terminals of the bridge rectifier BD1, and the positive and negative output terminals of the bridge rectifier BD1 are respectively connected to the two input terminals of the half-bridge drive circuit. The half-bridge drive circuit includes an alternately conducting first switching circuit, a second switching circuit, and a transformer TR1. The first switching circuit includes the transistor Q1, and the second switching circuit includes the transistor Q2.

[0007] Preferably, the electronic transformer of the present invention further includes a starting circuit and a first short-circuit protection circuit. The starting resistor includes a resistor R1, a resistor R2, a capacitor C2, a diode D1, a resistor R3, a bidirectional diode T1, and a capacitor C6. One end of the resistor R2 is connected to the positive input terminal of the bridge rectifier BD1, one end of the resistor R1, and the collector of the transistor Q2. The other end of the resistor R2 is connected to one end of the capacitor C2, the positive terminal of the diode D1, and one end of the resistor R3. The other end of the resistor R1 is connected to the other end of the capacitor C2. The negative terminal of the diode D1 is connected to the same-name terminal of the drive winding T2-2. The other end of the resistor R3 is connected to one end of the bidirectional diode T1. The other end of the bidirectional diode T1 is connected to the base of the transistor Q1. The other end of the capacitor C6 is grounded.

[0008] Preferably, the electronic transformer of the present invention further includes a first short-circuit protection circuit, which includes sampling resistors R8 and R9, rectifier diode D10, energy storage capacitor C8, resistors R6 and R5, and transistor Q3. One end of resistor R9 is connected to the voltage output terminal of the first switching circuit and one end of resistor R8, and the other end of resistor R9 is connected to the negative terminal of energy storage capacitor C8. The other end of resistor R8 is connected to the positive terminal of diode D10, and the negative terminal of diode D10 is connected to the positive terminal of energy storage capacitor C8 and one end of resistor R6. The other end of resistor R6 is connected to one end of resistor R5 and the base of transistor Q3. The emitter of transistor Q3 is grounded, and the collector of transistor Q3 is connected to one end of capacitor C6 and the base of transistor Q1.

[0009] Preferably, the half-bridge drive circuit further includes a drive winding T2-1, with the opposite-named terminal of the drive winding T2-1 connected to the emitter of the transistor Q2, and the same-named terminal of the drive winding T2-1 connected to the opposite-named terminal of the primary winding of the transformer.

[0010] Preferably, the first switching circuit further includes a freewheeling diode D11, with the anode of diode D11 connected to the emitter of transistor Q1 and the cathode of diode D11 connected to the collector of transistor Q1. The second switching circuit further includes a freewheeling diode D7, with the anode of diode D7 connected to the emitter of transistor Q2 and the cathode of diode D7 connected to the collector of transistor Q2.

[0011] Preferably, the half-bridge drive circuit further includes a capacitor C3, which is connected between the collector of transistor Q2 and the corresponding terminal of transformer TR1.

[0012] Preferably, the half-bridge drive circuit further includes a freewheeling diode D12, with the positive terminal of diode D12 grounded and the negative terminal of diode D12 connected to the primary winding of transformer TR1.

[0013] Preferably, the output short-circuit switching cycle current limiting protection circuit further includes a capacitor C7, which is connected between ground and the same-name terminal of the primary winding of transformer TR1.

[0014] Preferably, the half-bridge drive circuit further includes a freewheeling diode D8, the negative terminal of which is connected to the collector of transistor Q1, and the positive terminal of which is connected to the primary winding of transformer TR1.

[0015] The beneficial effects of this invention are as follows: This invention provides an output short-circuit cycle-by-cycle current limiting protection circuit, comprising diodes D6, D5, D2, D9, D4, and D3. The anode of diode D6 is connected to the anode of diode D4 and the cathode of diode D5. The cathode of diode D6 is connected to the collector of transistor Q2. The cathode of diode D4 is connected to the base of transistor Q2 and the anode of diode D5. The anode of diode D2 is connected to the anode of diode D3 and the cathode of diode D9. The cathode of diode D2 is connected to the collector of transistor Q1. The anode of diode D3 is connected to the base of transistor Q1 and the anode of diode D9. This circuit prevents the transistors in the half-bridge circuit of the electronic transformer from deep saturation and burnout due to excessive current, thus achieving cycle-by-cycle current limiting protection. Therefore, an electronic transformer with an output short-circuit cycle-by-cycle current limiting protection circuit can also achieve cycle-by-cycle current limiting protection. Attached Figure Description

[0016] The invention will be further illustrated with reference to the accompanying drawings, but the embodiments in the drawings do not constitute any limitation on the invention. For those skilled in the art, other drawings can be obtained based on the following drawings without any creative effort.

[0017] Figure 1 This is a circuit diagram of an output short-circuit switch-by-switch current limiting protection circuit according to the present invention.

[0018] Figure 2 This is a circuit diagram of an electronic transformer with an output short-circuit switching cycle current limiting protection circuit according to the present invention.

[0019] Figure 3 This is a circuit diagram of an existing electronic transformer.

[0020] The image includes:

[0021] Half-bridge drive circuit 1, first switching circuit 11, second switching circuit 12, first short-circuit protection circuit 2, start-up circuit 3, output short-circuit cycle-by-cycle current limiting protection circuit 4. Detailed Implementation

[0022] The present invention will be further described in conjunction with the following embodiments.

[0023] This embodiment describes an electronic transformer with an output short-circuit switching cycle current limiting protection circuit, such as... Figure 1As shown, the output short-circuit cycle-by-cycle current limiting protection circuit 4 includes diodes D6, D5, D2, D9, Schottky diodes D4 and D3, drive windings T2-2 and T2-3, resistors R4 and R7, transistors Q2 and Q1. The anode of diode D6 is connected to the anode of diode D4, the cathode of diode D5, and the opposite-name terminal of drive winding T2-2. The cathode of diode D6 is connected to the collector of transistor Q2. The cathode of diode D4 is connected to the base of transistor Q2, the anode of diode D5, and one end of resistor R4. The same-name terminal of drive winding T2-2 is connected to the other end of resistor R4 and the emitter of transistor Q2.

[0024] The positive terminal of diode D2 is connected to the positive terminal of diode D3, the negative terminal of diode D9, and the same-name terminal of drive winding T2-3. The negative terminal of diode D2 is connected to the collector of transistor Q1. The negative terminal of diode D3 is connected to the base of transistor Q1, the positive terminal of diode D9, and one end of resistor R7. The other end of resistor R7 is connected to the emitter of transistor Q1 and the opposite-name terminal of drive winding T2-3.

[0025] This embodiment also provides an electronic transformer, such as Figure 2 As shown, the circuit includes a bridge rectifier BD1, a half-bridge drive circuit 1, and the aforementioned output short-circuit switching cycle current limiting protection circuit 4. The positive and negative terminals of the mains power are connected to the two input terminals of the bridge rectifier BD1, and the positive and negative output terminals of the bridge rectifier BD1 are connected to the two input terminals of the half-bridge drive circuit 1, respectively. The half-bridge drive circuit 1 includes an alternately conducting first switching circuit 11, a second switching circuit 12, and a transformer TR1. The first switching circuit 11 includes the transistor Q1, and the second switching circuit 12 includes the transistor Q2.

[0026] Preferably, the electronic transformer of the present invention further includes a starting circuit 3 and a first short-circuit protection circuit 2. The starting resistor includes a resistor R1, a resistor R2, a capacitor C2, a diode D1, a resistor R3, a bidirectional diode T1, and a capacitor C6. One end of the resistor R2 is connected to the positive input terminal of the bridge rectifier BD1, one end of the resistor R1, and the collector of the transistor Q2. The other end of the resistor R2 is connected to one end of the capacitor C2, the positive terminal of the diode D1, and one end of the resistor R3. The other end of the resistor R1 is connected to the other end of the capacitor C2. The negative terminal of the diode D1 is connected to the same-name terminal of the drive winding T2-2. The other end of the resistor R3 is connected to one end of the bidirectional diode T1. The other end of the bidirectional diode T1 is connected to the base of the transistor Q1. The other end of the capacitor C6 is grounded. The function of the diode D1 is to discharge the capacitor C6 when the transistor Q2 is turned on.

[0027] Preferably, the electronic transformer of the present invention further includes a first short-circuit protection circuit 2. The first short-circuit protection circuit 2 includes sampling resistors R8 and R9, rectifier diode D10, energy storage capacitor C8, resistors R6 and R5, and transistor Q3. One end of resistor R9 is connected to the voltage output terminal of the first switching circuit 11 and one end of resistor R8. The other end of resistor R9 is connected to the negative terminal of energy storage capacitor C8. The other end of resistor R8 is connected to the positive terminal of diode D10. The negative terminal of diode D10 is connected to the positive terminal of energy storage capacitor C8 and one end of resistor R6. The other end of resistor R6 is connected to one end of resistor R5 and the base of transistor Q3. The emitter of transistor Q3 is grounded. The collector of transistor Q3 is connected to one end of capacitor C6 and the base of transistor Q1.

[0028] Preferably, the half-bridge drive circuit 1 further includes a drive winding T2-1, with the opposite-named end of the drive winding T2-1 connected to the emitter of the transistor Q2, and the same-named end of the drive winding T2-1 connected to the opposite-named end of the primary winding of the transformer.

[0029] Preferably, the first switching circuit 11 further includes a freewheeling diode D11, the anode of which is connected to the emitter of transistor Q1, and the cathode of which is connected to the collector of transistor Q1. When transistor Q1 is turned off, diode D7 freewheels. The second switching circuit 12 further includes a freewheeling diode D7, the anode of which is connected to the emitter of transistor Q2, and the cathode of which is connected to the collector of transistor Q2. When transistor Q2 is turned off, diode D11 freewheels.

[0030] Preferably, the half-bridge drive circuit 1 further includes a capacitor C3, which is connected between the collector of transistor Q2 and the corresponding terminal of transformer TR1.

[0031] Preferably, the half-bridge drive circuit 1 further includes a freewheeling diode D12, with the positive terminal of diode D12 grounded and the negative terminal of diode D12 connected to the same-name terminal of the primary winding of transformer TR1, and D12 serving as a freewheeling diode.

[0032] Preferably, the output short-circuit switching cycle current limiting protection circuit 4 further includes a capacitor C7, which is connected between ground and the same-name terminal of the primary winding of transformer TR1.

[0033] Preferably, the half-bridge drive circuit 1 further includes a freewheeling diode D8, the negative terminal of which is connected to the collector of transistor Q1, and the positive terminal of which is connected to the same-name terminal of the primary winding of transformer TR1. D8 serves as a freewheeling diode.

[0034] In this embodiment, T1 is a bidirectional trigger diode, F1 is a fuse, BD1 is a bridge rectifier, T2 is a drive coil, R1, R2, R3, R4, R5, R6, R7, R8, and R9 are resistors, D1, D2, D5, D6, D7, D8, D9, D10, D11, and D12 are fast recovery diodes, D3 and D4 are Schottky diodes, Q1, Q2, and Q3 are transistors, C2, C3, C5, C6, and C7 are film capacitors, TR1 is a transformer, and C5 is a filter capacitor.

[0035] The working principle of this embodiment is as follows:

[0036] With the maximum AC voltage input at terminals L and N, after the half-bridge drive circuit 1 starts working normally, the induced voltage and current across the windings T2-3 and T2-2 of the T2 drive coil in half-bridge drive circuit 1 alternately pass through Schottky diodes D3 and D4, causing transistors Q1 and Q2 to conduct alternately. The induced voltage and current across the windings T2-3 and T2-2 of the T2 drive coil alternately pass through fast recovery diodes D9 and D5 and resistors R7 and R4, causing transistors Q1 and Q2 to cut off alternately. When the output terminals OU1 and OUT2 are short-circuited, the current flowing through transformer TR1 and the winding T2-1 of the T2 drive coil increases instantaneously. At this time, the cycle-by-cycle current limiting protection circuit responds first: the induced voltage and current across the windings T2-3 and T2-2 of the T2 drive coil... As the current increases, the current between the base and emitter of transistors Q1 and Q2 increases, and the current between the collector and emitter switching currents of transistors Q1 and Q2 also increases. This reduces the voltage between the emitter and collector of transistors Q2 and Q1. When the voltage between the emitter and collector of transistors Q1 and Q2 decreases to approximately 0.3 volts, the fast recovery diodes D2 and D6 pull the voltage low, clamping the induced voltage across the windings T2-3 and T2-2 of the T2 drive coil to approximately 1.1V. Therefore, the current between the base and emitter of transistors Q1 and Q2 no longer increases, and the current between the collector and emitter switching currents of transistors Q1 and Q2 also no longer increases. Transistors Q1 and Q2 will not burn out due to excessive current, achieving instantaneous, cycle-by-cycle current limiting protection. Based on this, if the short circuit persists, the first short circuit protection circuit is activated: the continuous overcurrent sampling voltage on resistor R9 is rectified by diode D10, stored in electrolytic capacitor C8, and after a short delay, turns on transistor Q3. After Q3 turns on, it pulls the voltage across capacitor C6 down to near 0 volts, thereby making the start-up voltage of transistor Q1 0 volts, and thus stopping the entire half-bridge drive circuit from working and entering the hiccup protection state.

[0037] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A current-limiting protection circuit for output short circuit switching cycle, characterized in that: The half-bridge drive circuit includes diodes D6, D5, D2, D9, D4, and D3; drive windings T2-2 and T2-3; resistors R4 and R7; and transistors Q2 and Q1. The anode of diode D6 is connected to the anode of diode D4, the cathode of diode D5, and the opposite terminal of drive winding T2-2. The cathode of diode D6 is connected to the collector of transistor Q2. The cathode of diode D4 is connected to the base of transistor Q2, the anode of diode D5, and one end of resistor R4. The same-named terminal of drive winding T2-2 is connected to the other end of resistor R4 and the emitter of transistor Q2. The positive terminal of diode D2 is connected to the positive terminal of diode D3, the negative terminal of diode D9, and the same-name terminal of drive winding T2-3. The negative terminal of diode D2 is connected to the collector of transistor Q1. The negative terminal of diode D3 is connected to the base of transistor Q1, the positive terminal of diode D9, and one end of resistor R7. The other end of resistor R7 is connected to the emitter of transistor Q1 and the opposite-name terminal of drive winding T2-3. The half-bridge drive circuit also includes a drive winding T2-1, with the opposite-named end of the drive winding T2-1 connected to the emitter of the transistor Q2, and the same-named end of the drive winding T2-1 connected to the opposite-named end of the primary winding of the transformer. The secondary winding of the transformer is the output terminal.

2. An electronic transformer, characterized in that: The device includes a bridge rectifier BD1, a half-bridge drive circuit, and the output short-circuit switching cycle current limiting protection circuit as described in claim 1. The positive and negative terminals of the mains power are respectively connected to the two input terminals of the bridge rectifier BD1, and the positive and negative output terminals of the bridge rectifier BD1 are respectively connected to the two input terminals of the half-bridge drive circuit. The half-bridge drive circuit includes an alternately conducting first switching circuit, a second switching circuit, and a transformer TR1. The first switching circuit includes the transistor Q1, and the second switching circuit includes the transistor Q2.

3. An electronic transformer as described in claim 2, characterized in that: It also includes a startup circuit and a first short-circuit protection circuit. The startup resistor includes resistor R1, resistor R2, capacitor C2, diode D1, resistor R3, bidirectional diode T1, and capacitor C6. One end of resistor R2 is connected to the positive input terminal of bridge rectifier BD1, one end of resistor R1, and the collector of transistor Q2. The other end of resistor R2 is connected to one end of capacitor C2, the positive terminal of diode D1, and one end of resistor R3. The other end of resistor R1 is connected to the other end of capacitor C2. The negative terminal of diode D1 is connected to the same-name terminal of drive winding T2-2. The other end of resistor R3 is connected to one end of bidirectional diode T1. The other end of bidirectional diode T1 is connected to the base of transistor Q1. The other end of capacitor C6 is grounded.

4. An electronic transformer as described in claim 3, characterized in that: It also includes a first short-circuit protection circuit, which includes sampling resistors R8 and R9, rectifier diode D10, energy storage capacitor C8, resistors R6 and R5, and transistor Q3. One end of resistor R9 is connected to the voltage output terminal of the first switching circuit and one end of resistor R8. The other end of resistor R9 is connected to the negative terminal of energy storage capacitor C8. The other end of resistor R8 is connected to the positive terminal of diode D10. The negative terminal of diode D10 is connected to the positive terminal of energy storage capacitor C8 and one end of resistor R6. The other end of resistor R6 is connected to one end of resistor R5 and the base of transistor Q3. The emitter of transistor Q3 is grounded. The collector of transistor Q3 is connected to one end of capacitor C6 and the base of transistor Q1.

5. An electronic transformer as described in claim 2, characterized in that: The first switching circuit further includes a freewheeling diode D11, with the anode of diode D11 connected to the emitter of transistor Q1 and the cathode of diode D11 connected to the collector of transistor Q1. The second switching circuit further includes a freewheeling diode D7, with the anode of diode D7 connected to the emitter of transistor Q2 and the cathode of diode D7 connected to the collector of transistor Q2.

6. An electronic transformer as described in claim 2, characterized in that: The half-bridge drive circuit also includes a capacitor C3, which is connected between the collector of transistor Q2 and the corresponding terminal of transformer TR1.

7. An electronic transformer as described in claim 6, characterized in that: The half-bridge drive circuit also includes a freewheeling diode D12, with the positive terminal of diode D12 grounded and the negative terminal of diode D12 connected to the same-name terminal of the primary winding of transformer TR1.

8. An electronic transformer as described in claim 2, characterized in that: The output short-circuit switching cycle current limiting protection circuit also includes capacitor C7, which is connected between ground and the same-name terminal of the primary winding of transformer TR1.

9. An electronic transformer as described in claim 8, characterized in that: The half-bridge drive circuit also includes a freewheeling diode D8, the negative terminal of which is connected to the collector of transistor Q1, and the positive terminal of which is connected to the primary winding of transformer TR1.

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