PWM chopping dimming self-locking short-circuit protection circuit

Abstract

The invention discloses a PWM (Pulse Width Modulation) chopping dimming self-locking short-circuit protection circuit, aiming at solving the technical problem that an MOS (Metal Oxide Semiconductor) tube is easy to damage when a load is short-circuited in the existing PWM chopping dimming circuit. The current flowing through the load is detected in real time through the sampling resistor, and the self-locking protection unit is driven after the current is amplified by the operational amplifier. When the load is detected to be short-circuited, the self-locking unit locks the G-pole level of the MOS tube, so that the MOS tube is continuously turned off, and the MOS tube is prevented from being damaged by large current under the condition of short circuit. Meanwhile, the circuit is simple in design and easy to integrate, can be widely applied to various PWM dimming circuit occasions, and has an efficient short-circuit protection function.

Description

Technical Field

[0001] The present invention relates to a PWM dimming circuit, and more particularly to a PWM chopping dimming circuit with a self-locking short-circuit protection function for preventing the circuit from being damaged in a short-circuit state. Background Art

[0002] With the development of lighting technology, users' demand for the dimming and color-tuning functions of lighting fixtures has increased, and PWM chopping dimming has become the mainstream application method. However, in the prior art, when the load is short-circuited, the chopping MOS transistor is easily damaged due to excessive pulse current. Especially at the moment of short circuit, the energy stored in the output capacitor of the constant voltage source or constant current source will be instantaneously released, generating a current exceeding the bearing capacity of the MOS transistor, thereby causing device damage. The prior art lacks effective short-circuit protection measures, especially in complex chopping circuits, and the protection mechanism is more difficult in the case of multiple outputs. Summary of the Invention

[0003] The purpose of the present invention is to provide a PWM chopping dimming self-locking short-circuit protection circuit to solve the problems raised in the above background art.

[0004] To achieve the above purpose, the present invention provides the following technical solutions:

[0005] A PWM chopping dimming self-locking short-circuit protection circuit, the circuit comprising: a constant voltage source or a constant current source for providing a stable voltage or current to the load; a PWM chopping unit including at least one dimming circuit controlled by a MOS transistor, the G pole of the MOS transistor being controlled by a PWM signal for adjusting the brightness of the load; a sampling resistor located between the constant voltage source or constant current source and the PWM chopping unit for detecting the total current flowing through the PWM chopping unit; an operational amplifier connected across the sampling resistor for amplifying the sampled voltage signal; a self-locking short-circuit protection unit connected to the output of the operational amplifier, which triggers and locks the MOS transistor in the off state when detecting a load short circuit to prevent the MOS transistor from being damaged in the case of a short circuit.

[0006] Preferably, the self-locking short-circuit protection unit includes: a triode Q5, the base of which is connected to the sampled voltage signal after filtering and amplification, the emitter is grounded, and the collector is connected to the G pole of the MOS transistor; a triode Q4 forming a self-locking structure with Q5, when Q5 conducts, pulling down the base voltage of Q4 to make Q4 conduct and further maintaining the conducting state of Q5; a voltage dividing network including resistors R4 and R5 for generating a bias voltage to maintain the conducting state of Q4 when Q5 conducts.

[0007] Preferably, an RC filter circuit is further included between the sampling resistor and the operational amplifier, and the RC filter circuit is used to filter out high-frequency noise and interference signals in the sampled voltage.

[0008] Preferably, the RC filter circuit includes R7 and C3 in series, with C3 grounded. One end of R7 is connected to the positive terminal of the sampling resistor, and the other end is connected to the positive input terminal of the operational amplifier.

[0009] Preferably, the self-locking short-circuit protection unit further includes a light-emitting diode LED for indicating the short-circuit state when a load short-circuit is detected. The light-emitting diode is connected to the collector of the triode Q4, and when Q4 conducts, the LED emits light.

[0010] Preferably, the short-circuit protection unit further includes a plurality of diodes respectively connected between the G poles of the MOS transistors and the collector of the triode Q5. When Q5 conducts, the diodes clamp the G pole voltage of the MOS transistors to a low level, thereby turning off all the MOS transistors.

[0011] Preferably, the gain of the operational amplifier can be adjusted by adjusting the resistance values of resistors R9 and R11 to meet the short-circuit protection requirements under different load conditions.

[0012] Preferably, an RC filter circuit is further included at the input and output terminals of the operational amplifier to further remove the noise in the signal and ensure the sensitivity and accuracy of the short-circuit protection.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0014] 1. For this PWM chopper dimming self-locking short-circuit protection circuit, by placing a sampling circuit on the low side of the chopping unit to detect the total operating current, regardless of the actual circuit of the chopping unit, the circuit does not need to be changed. Therefore, this circuit can be used as a short-circuit protection module and applied to various PWM chopper dimming occasions that require short-circuit protection.

[0015] 2. For this PWM chopper dimming self-locking short-circuit protection circuit, an analog operational amplifier is used to process the sampling signal. It can amplify a weak signal to a signal that the subsequent self-locking circuit can handle, and at the same time, it can increase the input impedance to ensure the progress and consistency of sampling. Meanwhile, its response speed is extremely fast, and it can turn off the MOS transistor within a few microseconds, avoiding the continuous increase of the surge current generated by the short circuit and ultimately exceeding the current capacity of the MOS transistor, resulting in damage to the MOS transistor.

[0016] 3. For this PWM chopper dimming self-locking short-circuit protection circuit, when the load short-circuit triggers the protection, the self-locking circuit locks the GATE of the chopping MOS transistor to a low level, avoiding repeated short-circuit phenomena in a short time and resulting in damage to the MOS transistor. Description of the Drawings

[0017] Figure 1The logic circuit diagram of the constant voltage source or constant current source and the PWM chopping unit for the PWM chopping dimming self-locking short-circuit protection circuit of the present invention;

[0018] Figure 2 The overall logic circuit diagram of the PWM chopping dimming self-locking short-circuit protection circuit of the present invention. Specific embodiments

[0019] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0020] Please refer to Figure 1 - Figure 2 as shown, a technical solution provided by the present invention:

[0021] A PWM chopping dimming self-locking short-circuit protection circuit, the circuit includes: a constant voltage source or a constant current source, used to provide a stable voltage or current for the load; a PWM chopping unit, including at least one dimming circuit controlled by a MOS tube, the G pole of the MOS tube is controlled by a PWM signal, used to adjust the brightness of the load; a sampling resistor, located between the constant voltage source or the constant current source and the PWM chopping unit, used to detect the total current flowing through the PWM chopping unit; an operational amplifier, connected to both ends of the sampling resistor, used to amplify the sampling voltage signal; a self-locking short-circuit protection unit, connected to the output end of the operational amplifier, when detecting a load short circuit, the self-locking unit triggers and locks the MOS tube in the off state to prevent the MOS tube from being damaged in case of a short circuit.

[0022] Such as Figure 1As shown in the figure, the present invention provides a PWM chopper dimming self-locking short-circuit protection circuit, which includes a constant voltage source or a constant current source, a PWM chopper unit, and a control unit. The constant voltage source or the constant current source provides stable electrical energy for the circuit. The output current passes through the filter capacitor C1 to ensure the stability of the power supply, and then enters the PWM chopper unit. In the PWM chopper unit, there are multiple MOS transistors (Q1, Q2, Q3) and load resistors (R1, R2, R3). The G pole of each MOS transistor receives a PWM signal through the control unit for control. When the PWM signal is at a high level, the MOS transistor is turned on and the load works; when the PWM signal is at a low level, the MOS transistor is turned off and the current is interrupted. By adjusting the duty cycle of the PWM signal, the magnitude of the current flowing through the load can be accurately controlled, thereby realizing the adjustment of the brightness of the lamp. The control unit generates PWM signals with different frequencies and duty cycles according to the externally input brightness requirements, and controls the on and off of Q1, Q2, and Q3 through PWM1, PWM2, and PWM3 respectively, thereby realizing multi-channel dimming. When the constant voltage source or the constant current source provides energy for the chopper dimming unit, the current enters the dimming unit from one port and returns to the power supply from another port. No matter how complex the dimming circuit is, the total current is equal to the magnitude of the current flowing through this two-terminal network. Therefore, the working state of the load can be judged by monitoring this total current. On the basis of this embodiment, it can be further combined with Figure 2 to implement a short-circuit protection mechanism. When a load short-circuit is detected, the circuit will lock the off state of the MOS transistor through the sampling resistor and the operational amplifier, cut off the current, and prevent the short-circuit from damaging the MOS transistor and other components.

[0023] As Figure 2 shown in the figure, a sampling resistor RS1 is connected in series at the low end from the constant voltage source or the constant current source to the PWM chopper unit of the PWM chopper dimming self-locking short-circuit protection circuit of the present invention for detecting the current flowing through the load. One end of the sampling resistor RS1 is connected to the constant voltage source or the constant current source, and the other end is connected to the low end of the PWM chopper unit. The total current flowing through the PWM chopper unit generates a voltage signal through RS1, and the voltage signal is filtered by the RC filter composed of the resistor R7 and the capacitor C3 to eliminate high-frequency interference. The filtered signal enters the non-inverting input terminal of the operational amplifier U2. The inverting input terminal of the operational amplifier U2 is grounded through the resistor R9, and the gain of the operational amplifier is determined by the ratio of the resistor R9 and the resistor R11, thereby adjusting the gain of the circuit to adapt to different working current ranges. The bypass capacitor C2 is used to stabilize the power supply of the operational amplifier to ensure that the power supply fluctuation does not affect the circuit performance.

[0024] When the load is working normally, the current remains within the set range; while when the load experiences a short circuit, the current flowing through the sampling resistor RS1 increases sharply, causing the sampling voltage signal to rise. This voltage signal passes through an RC filter and enters the non-inverting input terminal of the operational amplifier U2. After being amplified by U2, it passes through an RC filter composed of resistor R8 and capacitor C4 and enters the base of the triode Q5. If the sampling voltage signal exceeds the set threshold of 0.7V, Q5 conducts. After Q5 conducts, the voltage at its collector drops, triggering the voltage division network composed of R4 and R5, thereby increasing the base bias voltage of Q4. Q4 conducts, further pulling down the base voltage of Q5, forming a self-locking structure.

[0025] At this time, the light-emitting diode LED1 conducts and emits light, indicating that the circuit has entered the short-circuit protection state. The conduction of Q4 allows the control current to continuously pass through R6 and the base of Q5, ensuring that Q5 remains conducting, thereby locking the protection circuit. At the same time, the collector of the triode Q5 is connected to the G poles of each MOS transistor (Q1, Q2, Q3) through diodes D1, D2, and D3. After Q5 conducts, it pulls down the cathode voltage of these diodes, clamping the G pole voltage of the MOS transistors to a low level, and the MOS transistors quickly turn off, cutting off the current to prevent damage to the MOS transistors caused by the short circuit.

[0026] After the short-circuit protection is triggered, the circuit enters a self-locking state. The self-locking circuit will remain locked even after the short circuit is removed until the device is powered off. Specifically, after the self-locking circuit is triggered, Q5 and Q4 form a self-locking structure, maintaining the circuit in the locked state, ensuring that the G pole level of the MOS transistors is continuously clamped to a low level, and the MOS transistors cannot conduct, preventing the load current from passing through the circuit again. Even if the short-circuit fault is eliminated, the circuit will not automatically return to the normal working state. Only after the device is powered off and all circuit power supplies are cut off will the circuit return to the initial state. After being powered on again, the PWM chopper dimming circuit resumes normal operation, the short-circuit protection mechanism is released, and the circuit starts dimming work again.

[0027] This design ensures that after a short-circuit event occurs, the circuit can effectively lock the protection state, avoiding secondary damage to components caused by repeated short circuits in a short period of time. At the same time, since the circuit can only be reset after the device is completely powered off, the reliability of the system is further improved, ensuring that after a short circuit is detected, the protection mechanism remains effective until manual intervention or the device is powered on again.

[0028] The foregoing has shown and described the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments, and the above embodiments and the descriptions in the specification are only preferred examples of the present invention and are not used to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of the present invention claimed is defined by the appended claims and their equivalents.

Claims

1. A PWM chopper dimming self-locking short-circuit protection circuit, characterized in that, The circuit includes: a constant voltage source or a constant current source for providing a stable voltage or current to the load; a PWM chopping unit including at least one dimming circuit controlled by a MOS transistor, the G pole of the MOS transistor being controlled by a PWM signal for adjusting the brightness of the load; a sampling resistor located between the constant voltage source or the constant current source and the PWM chopping unit for detecting the total current flowing through the PWM chopping unit; an operational amplifier connected across the sampling resistor for amplifying the sampled voltage signal; a self-locking short-circuit protection unit connected to the output end of the operational amplifier. When a load short circuit is detected, the self-locking unit triggers and locks the MOS transistor in the off state to prevent the MOS transistor from being damaged in case of a short circuit.

2. The PWM chopper dimming self-locking short-circuit protection circuit according to claim 1, wherein The self-locking short-circuit protection unit includes: a triode Q5, the base of which is connected to the sampled voltage signal after filtering and amplification, the emitter being grounded, and the collector being connected to the G pole of the MOS transistor; a triode Q4 forming a self-locking structure with Q5. When Q5 conducts, it pulls down the base voltage of Q4 to make Q4 conduct, further maintaining the conducting state of Q5; a voltage dividing network including resistors R4 and R5 for generating a bias voltage to maintain the conducting state of Q4 when Q5 conducts.

3. The PWM chopper dimming self-locking short-circuit protection circuit according to claim 2, characterized in that, An RC filtering circuit is further included between the sampling resistor and the operational amplifier. The RC filtering circuit is used to filter out high-frequency noise and interference signals in the sampled voltage.

4. The PWM chopper dimming self-locking short-circuit protection circuit according to claim 3, wherein, The RC filtering circuit includes R7 and C3 in series, C3 being grounded, one end of R7 being connected to the positive end of the sampling resistor, and the other end being connected to the positive input terminal of the operational amplifier.

5. The PWM chopper dimming self-locking short-circuit protection circuit according to any one of claims 1 to 4, characterized in that, The self-locking short-circuit protection unit further includes a light-emitting diode LED for indicating the short-circuit state when a load short circuit is detected. The light-emitting diode is connected to the collector of the triode Q4. When Q4 conducts, the LED emits light.

6. The PWM chopper dimming self-locking short-circuit protection circuit according to claim 5, characterized in that, Multiple diodes are further included in the short-circuit protection unit, which are respectively connected between the G poles of the respective MOS transistors and the collector of the triode Q5. When Q5 conducts, the diodes clamp the G pole voltage of the MOS transistors to a low level, thereby turning off all the MOS transistors.

7. The PWM chopper dimming self-locking short-circuit protection circuit according to claim 6, characterized in that, The gain of the operational amplifier can be adjusted by adjusting the resistance values of resistors R9 and R11 to meet the short-circuit protection requirements under different load conditions.

8. The PWM chopper dimming self-locking short-circuit protection circuit according to any one of claims 1 to 7, characterized in that, An RC filtering circuit is further included at the input and output terminals of the operational amplifier for further removing noise in the signal and ensuring the sensitivity and accuracy of short-circuit protection.

Images