Short-circuit protection circuit with dual-mode sampling

Abstract

The utility model discloses a short-circuit protection circuit with dual-mode sampling. The short-circuit protection circuit comprises a comparator U1, an MOS tube Q2, a voltage sampling circuit and a current sampling circuit. The output end of the comparator U1 is connected with the control end of the MOS tube Q2 and outputs a signal SCP to the main control circuit, and the input end of the MOS tube Q2 is connected with the PWM end of the main control circuit; the input end of the voltage sampling circuit is connected with the drain electrode of the dimming MOS tube Q1, and the output end of the voltage sampling circuit is connected with the positive input end of the comparator U1; the input end of the current sampling circuit is connected with the source electrode of the dimming MOS tube Q1, and the output end of the current sampling circuit is connected with the positive input end of the comparator U1; the phenomenon that the dimming MOS tube is repeatedly switched on and off under peak current generated by short circuit is avoided, and the phenomenon that short circuit is not protected during dimming and minimum adjustment is also avoided, so that the dimming MOS tube Q1 with output protection is achieved, normal output can be self-recovered when short circuit is canceled, and an LED driving power supply does not need to be restarted.

Description

Technical Field

[0001] The utility model relates to the field of LED switch power supply, in particular to a short circuit protection circuit with dual-mode sampling. Background Art

[0002] At present, LED dimming power supplies and switching power supplies are widely used in the market. LED dimming power supplies account for a large share in the market. Most of the short-circuit protection circuits use a single current sampling mode for protection. In the case of output short circuit, whether the current is amplified by an operational amplifier and then triggered by protection or the current is compared by a comparator and then triggered by protection, the following problems will occur in the single current sampling mode:

[0003] 1. When the output is short-circuited, the short-circuit signal will be repeatedly triggered (such as Figure 3 As shown in the figure, the output dimming MOS tube keeps switching repeatedly at the moment of short circuit. The instantaneous current is very large during short circuit, so the output dimming MOS tube keeps switching repeatedly under the great impact of the circuit, making the dimming MOS tube easy to be damaged;

[0004] 2. When the dimming is turned down and short-circuited, the current also decreases. After the short-circuit, the short-circuit signal fails to reach the trigger point. Therefore, when the dimming is turned down, the short-circuit fails to protect, and the dimming MOS tube can only be resisted by its own stress. Over time, the dimming MOS tube will also be damaged.

[0005] Therefore, there is an urgent need for a short-circuit protection circuit with dual-mode sampling to solve the above problems. Utility Model Content

[0006] The utility model aims to solve at least one of the technical problems existing in the prior art. To this end, the utility model proposes a short-circuit protection circuit with dual-mode sampling.

[0007] An embodiment of the utility model solves the technical problem by adopting a technical solution: a short-circuit protection circuit with dual-mode sampling, including a comparator U1 and a MOS tube Q2, and also including a voltage sampling circuit and a current sampling circuit;

[0008] The negative input terminal of the comparator U1 is connected to the reference voltage Vref, the power supply terminal of the comparator U1 is connected to the voltage source VCC, and the ground terminal of the comparator U1 is connected to the GND terminal;

[0009] The output end of the comparator U1 is connected to the control end of the MOS tube Q2 and outputs a signal SCP to the main control circuit. The input end of the MOS tube Q2 is connected to the PWM end of the main control circuit. The output end of the MOS tube Q2 is connected to the GND end.

[0010] The input end of the voltage sampling circuit is connected to the drain of the dimming MOS tube Q1, and the output end is connected to the positive input end of the comparator U1;

[0011] The input end of the current sampling circuit is connected to the source of the dimming MOS tube Q1 , and the output end is connected to the positive input end of the comparator U1 .

[0012] As one of the preferred embodiments of the utility model, the voltage sampling circuit includes a voltage regulator tube Z1, a resistor R6, a resistor R8 and a resistor R10. One end of the voltage regulator tube Z1 is connected to the drain of the dimming MOS tube Q1, and the other end of the voltage regulator tube Z1 is connected to one end of the resistor R8 and one end of the resistor R10 respectively through the resistor R6. The other end of the resistor R8 is connected to the positive input end of the comparator U1, and the other end of the resistor R10 is connected to the GND end.

[0013] As one of the preferred embodiments of the utility model, a short circuit protection circuit with dual-mode sampling further includes a capacitor C3, one end of the capacitor C3 is connected to the other end of the resistor R8, and the other end of the capacitor C3 is connected to the GND end.

[0014] As one of the preferred embodiments of the present utility model, the current sampling circuit includes a resistor R4, one end of the resistor R4 is connected to the source of the dimming MOS tube Q1, and the other end of the resistor R4 is connected to the positive input end of the comparator U1.

[0015] As one of the preferred embodiments of the present utility model, a short circuit protection circuit with dual-mode sampling further includes a reference voltage module connected to the negative input terminal of the comparator U1 and the voltage source VCC respectively, for generating a reference voltage Vref.

[0016] As one of the preferred embodiments of the utility model, the reference voltage module includes resistors R2-R3 and capacitors C1-C2, one end of the resistor R3 is respectively connected to the voltage source VCC and one end of the capacitor C2, the other end of the resistor R3 is respectively connected to the negative input end of the comparator U1, one end of the capacitor C1 and one end of the resistor R2, the other end of the capacitor C1, the other end of the capacitor C2 and the other end of the resistor R2 are connected to the GND end.

[0017] As one of the preferred embodiments of the utility model, a short-circuit protection circuit with dual-mode sampling also includes a resistor R5, a resistor R7 and a resistor R9, one end of the resistor R5 is connected to the voltage source VCC, the other end of the resistor R5 is respectively connected to the output end of the comparator U1, one end of the resistor R7 and one end of the resistor R9, the other end of the resistor R7 is connected to the control end of the MOS tube Q2, and the other end of the resistor R9 outputs a signal SCP.

[0018] The beneficial effects of the utility model are as follows: a short-circuit protection circuit with dual-mode sampling includes a comparator U1, a MOS tube Q2, a voltage sampling circuit and a current sampling circuit; the negative input terminal of the comparator U1 is connected to a reference voltage Vref, the power supply terminal of the comparator U1 is connected to a voltage source VCC, and the ground terminal of the comparator U1 is connected to a GND terminal; the output terminal of the comparator U1 is connected to a control terminal of the MOS tube Q2 and outputs a signal SCP to a main control circuit, the input terminal of the MOS tube Q2 is connected to a PWM terminal of the main control circuit, and the output terminal of the MOS tube Q2 is connected to a GND terminal; the voltage sampling circuit ...; the input terminal of the MOS tube Q2 is connected to a PWM terminal of the main control circuit, and the output terminal of the MOS tube Q2 is connected to a GND terminal; the voltage sampling circuit is connected to a reference voltage Vref, the power supply terminal of the comparator U1 is connected to a voltage source VCC, and the ground terminal of the comparator U1 is connected to a GND terminal; the output terminal of the comparator U1 is connected to The input end of the voltage sampling circuit is connected to the drain of the dimming MOS tube Q1, and the output end is connected to the positive input end of the comparator U1; the input end of the current sampling circuit is connected to the source of the dimming MOS tube Q1, and the output end is connected to the positive input end of the comparator U1; when the short-circuit protection of the dual-mode sampling is used, the dimming MOS tube will not switch repeatedly under the peak current generated by the short circuit, and the short circuit will not be unprotected when the dimming is adjusted to the minimum, thereby protecting the output dimming MOS tube, and the normal output can be restored when the short circuit is cancelled, and there is no need to restart the LED drive power supply. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0020] Figure 1 This is a principle block diagram of an LED dimming power supply;

[0021] Figure 2 A circuit schematic diagram of a short-circuit protection circuit with dual-mode sampling;

[0022] Figure 3 This is the waveform diagram of the output in the single current sampling mode when the output is short-circuited;

[0023] Figure 4 The figure is a waveform diagram of the output of a short-circuit protection circuit with dual-mode sampling when the output is short-circuited. DETAILED DESCRIPTION

[0024] This section will describe in detail the specific embodiments of the utility model. The preferred embodiments of the utility model are shown in the accompanying drawings. The purpose of the accompanying drawings is to supplement the description of the text part of the specification with graphics, so that people can intuitively and vividly understand each technical feature and the overall technical solution of the utility model, but it cannot be understood as a limitation on the protection scope of the utility model.

[0025] In the description of the present utility model, the meaning of "more than" is more than two, "greater than", "less than", "exceed" etc. are understood to exclude the number itself, and "above", "below", "within" etc. are understood to include the number itself. If there is a description of "first" or "second", it is only used for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0026] In the description of the present invention, it should be understood that descriptions involving orientation, such as up, down, front, back, left, right, etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0027] In the present invention, unless otherwise clearly defined, the words "set", "install", "connect" and the like should be understood in a broad sense, for example, they can be directly connected or indirectly connected through an intermediate medium; they can be fixedly connected or detachably connected or integrally formed; they can be mechanically connected; they can be the internal connection of two elements or the interaction relationship between two elements. Those skilled in the art can reasonably determine the specific meanings of the above words in the present invention in combination with the specific content of the technical solution.

[0028] Reference Figure 1 The utility model provides an LED power supply, including an EMI filter circuit 50, an AC-DC circuit 60, a dimming drive circuit 70, a main control circuit 30, a dimming circuit 80 and a dimming MOS tube Q1. The input end of the EMI filter circuit 50 is connected to the live wire L and the neutral wire N, the output end of the EMI filter circuit 50 is connected to the input end of the AC-DC circuit 60, the output end of the AC-DC circuit 60 is respectively connected to the dimming drive circuit 70 and the positive electrode of the load LED, the dimming drive circuit 70 is respectively connected to the main control circuit 30 and the gate of the dimming MOS tube Q1, the drain of the dimming MOS tube Q1 is connected to the negative electrode of the load LED, the source of the dimming MOS tube Q1 is connected to the GND end, and the dimming circuit 80 is respectively connected to the dimmer 80 and the main control circuit 30.

[0029] When the system is powered on, the AC current enters the EMI filter circuit 50 through the live wire L and the neutral wire N, and is rectified into direct current through the rectifier bridge. When the AC-DC circuit 60 is working stably, since the voltage outer loop feedback is taken from the primary auxiliary winding, and the ratio of the voltage after rectification of the primary auxiliary winding to the voltage of the secondary winding is equal to the ratio of their number of turns, and the ratio of the voltage after rectification of the primary auxiliary winding to the voltage of the secondary auxiliary winding is equal to the ratio of their number of turns, a stable voltage source V+ and a voltage source VCC will appear. The voltage source V+ serves as the energy input of the subsequent dimming drive circuit 70, and the voltage source VCC serves as the energy input of the main control circuit 30. At the same time, the AC current also serves as the dimming The dimmer 90 is powered. When the dimmer 90 operates dimming, the dimmer 90 outputs a signal to the dimming circuit 80. At this time, the dimming circuit 80 outputs a signal to the main control circuit 30 after processing. Then the main control circuit 30 outputs a PWM signal to the dimming drive circuit 70 according to the size of the dimmer 90 signal. The dimming drive circuit 70 then outputs a drive signal to change the duty cycle of the dimming MOS tube Q1 according to the size of the PWM signal. At this time, the voltage source V+ normally flows through the positive electrode of the load LED, and then flows into the drain of the dimming MOS tube Q1 through the negative electrode of the load LED, and then passes through the source of the dimming MOS tube Q1, enters the resistor R1 and then forms a loop to the GND end, thereby realizing dimming.

[0030] Reference Figure 1-2 The utility model also provides a short-circuit protection circuit with dual-mode sampling, which is applied to the above-mentioned LED power supply. The short-circuit protection circuit includes a comparator U1, a MOS tube Q2, a voltage sampling circuit 10 and a current sampling circuit 20; the negative input terminal of the comparator U1 is connected to the reference voltage Vref, the power supply terminal of the comparator U1 is connected to the voltage source VCC, and the ground terminal of the comparator U1 is connected to the GND terminal; the output terminal of the comparator U1 is connected to the control terminal of the MOS tube Q2 and outputs a signal SCP to the main control circuit 30, the input terminal of the MOS tube Q2 is connected to the PWM terminal of the main control circuit 30, and the output terminal of the MOS tube Q2 is connected to the GND terminal; the input terminal of the voltage sampling circuit 10 is connected to the drain of the dimming MOS tube Q1, and the output terminal is connected to the positive input terminal of the comparator U1; the input terminal of the current sampling circuit 20 is connected to the source of the dimming MOS tube Q1, and the output terminal is connected to the positive input terminal of the comparator U1.

[0031] As a preferred embodiment of the voltage sampling circuit 10, the voltage sampling circuit 10 includes a voltage regulator tube Z1, a resistor R6, a resistor R8 and a resistor R10. One end of the voltage regulator tube Z1 is connected to the drain of the dimming MOS tube Q1, and the other end of the voltage regulator tube Z1 is connected to one end of the resistor R8 and one end of the resistor R10 respectively through the resistor R6. The other end of the resistor R8 is connected to the positive input terminal of the comparator U1, and the other end of the resistor R10 is connected to the GND terminal. As a preferred embodiment of the current sampling circuit 20, the current sampling circuit 20 includes a resistor R4. One end of the resistor R4 is connected to the source of the dimming MOS tube Q1, and the other end of the resistor R4 is connected to the positive input terminal of the comparator U1.

[0032] The working principle of the short-circuit protection circuit is as follows:

[0033] 1. When the output is not short-circuited:

[0034] The voltage source V+ normally flows through the positive electrode of the load LED, then flows into the drain of the dimming MOS tube Q1 through the negative electrode of the load LED, and then enters the resistor R1 through the source of the dimming MOS tube Q1 to form a loop at the GND end; ①: Current sampling mode, when current flows through the resistor R1, there is a voltage difference between the two ends of the resistor. At this time, the voltage difference signal is Ics, which enters the positive input end of the comparator U1 after passing through the resistor R4. At this time, the positive input end of the comparator U1 is less than the reference voltage Vref, so the output end of the comparator U1 outputs a low signal, the MOS tube Q2 is not turned on, and the signal SCP is low. Enter the main control circuit 30 without any processing; ②: voltage sampling mode, when it works normally without short circuit, the dimming MOS tube Q1 is in the on state, so the drain signal Vd of the dimming MOS tube Q1 is low, passes through the voltage regulator tube Z1 and then through the resistor R6 and R10 to enter the resistor R8, and enters the positive input end of the comparator U1. At this time, the voltage at the positive input end of the comparator U1 is less than the reference voltage Vref, so the output end of the comparator U1 outputs a low signal, the MOS tube Q2 is not turned on, the signal SCP is low, and enters the main control circuit 30 without any processing;

[0035] 2. When the output is fully loaded and short-circuited:

[0036] It is equivalent to a short circuit at both ends of the load LED. At this time, the drain of the dimming MOS tube Q1 instantly generates a spike current, and the dimming MOS tube Q1 is still in the turn-on stage. The spike current flows through the dimming MOS tube Q1 through the resistor R1 to the GND end; ① Current sampling mode, a spike current flows through the resistor R1, so a spike voltage Ics is generated. At this time, the spike voltage Ics enters the positive input end of the comparator U1 through the resistor R4. At this time, the voltage at the positive input end of the comparator U1 is greater than the reference voltage Vref. The output end of the comparator U1 outputs a high signal, which enters the gate of the MOS tube Q2 through the resistor R7. At this time, the MOS tube Q2 is turned on , pull down the PWM end, at this time the dimming drive circuit 70 does not output the drive signal, and the dimming MOS tube Q1 is not turned on; ② voltage sampling mode, after the current sampling mode, the dimming MOS tube Q1 is in the off state, the drain signal Vd of the dimming MOS tube Q1 = voltage source V+, passes through the voltage regulator tube Z1 and then through the resistor R6 and the resistor R10 for voltage division and enters the resistor R8, and enters the positive input end of the comparator U1. At this time, the voltage at the positive input end of the comparator U1 is greater than the reference voltage Vref, and the output end of the comparator U1 outputs a high signal, the MOS tube Q2 is turned on, the signal SCP is high, and enters the main control circuit 30 for short-circuit hiccup mode processing.

[0037] The dual-mode sampling short-circuit circuit will not cause the comparator U1 output to repeatedly output high and low signals. After the current sampling mode, PWM is pulled down, and then after the voltage mode sampling, PWM is pulled down. At this time, the comparator U1 is always in a high signal after a high and low signal (such as Figure 4 As shown in the figure), MOS tube Q2 is in the conduction stage and keeps pulling down the PWM signal, thereby protecting the dimming MOS tube Q1.

[0038] After the short circuit is cancelled, the voltage Ics does not generate a spike, the drain signal Vd of the dimming MOS tube Q1 is ≠ the voltage source V+, the voltage at the positive input terminal of the comparator U1 is less than the reference voltage Vref, and the output terminal of the comparator U1 outputs a low signal. At this time, PWM outputs normally, which is equivalent to self-recovery to normal output after the short circuit is cancelled, and there is no need to restart the LED power supply.

[0039] 3. When dimming is adjusted to minimum short circuit:

[0040] It is equivalent to a short circuit at both ends of the load LED. At this time, the peak current generated by the drain of the dimming MOS tube Q1 fails to reach the protection trigger point, and the dimming MOS tube Q1 is still in the turn-on stage. The peak current flows through the dimming MOS tube Q1 through the resistor R1 to the GND end; in the current sampling mode, a peak current flows through the resistor R1, generating a peak voltage Ics, so the peak voltage fails to reach the voltage that triggers the protection. At this time, Ics enters the positive input terminal of the comparator U1 through the resistor R4. The voltage at the positive input terminal of the comparator U1 is less than the reference voltage Vref, and the output terminal of the comparator U1 The output is a low signal, the MOS tube Q2 is not turned on, and the PWM output is normal; at this time, the voltage sampling mode is entered, and the drain signal Vd of the dimming MOS tube Q1 = the voltage source V+, passes through the voltage regulator tube Z1 and then through the resistor R6 and the resistor R10 for voltage division and enters the resistor R8, and enters the positive input terminal of the comparator U1. At this time, the voltage at the positive input terminal of the comparator U1 is greater than the reference voltage Vref, and the output terminal of the comparator U1 outputs a high signal, the MOS tube Q2 is turned on, and the signal SCP is high, and enters the main control circuit 30 for short-circuit hiccup mode processing, thereby protecting the dimming MOS tube Q1.

[0041] After the short circuit is cancelled, the drain signal Vd of the dimming MOS tube Q1 is ≠ the voltage source V+, the voltage at the positive input terminal of the comparator U1 is less than the reference voltage Vref, and the output terminal of the comparator U1 outputs a low signal. At this time, PWM outputs normally, which is equivalent to self-recovery to normal output after the short circuit is cancelled, and there is no need to restart the LED power supply.

[0042] In some embodiments, a short-circuit protection circuit with dual-mode sampling also includes a reference voltage module 40 connected to the negative input terminal of the comparator U1 and the voltage source VCC, respectively, for generating a reference voltage Vref; as a preferred embodiment of the reference voltage module 40, the reference voltage module 40 includes resistors R2-R3 and capacitors C1-C2, one end of the resistor R3 is respectively connected to the voltage source VCC and one end of the capacitor C2, the other end of the resistor R3 is respectively connected to the negative input terminal of the comparator U1, one end of the capacitor C1 and one end of the resistor R2, the other end of the capacitor C1, the other end of the capacitor C2 and the other end of the resistor R2 are connected to the GND terminal, and the voltage source VCC generates the reference voltage Vref after voltage division by the resistor R3 and the resistor R2.

[0043] In some embodiments, a short circuit protection circuit with dual-mode sampling further includes a capacitor C3, one end of the capacitor C3 is connected to the other end of the resistor R8, and the other end of the capacitor C3 is connected to the GND end; the capacitor C2 is a filter capacitor at the power supply end of the comparator U1.

[0044] In some embodiments, a short-circuit protection circuit with dual-mode sampling further includes a resistor R5, a resistor R7, and a resistor R9, one end of the resistor R5 is connected to a voltage source VCC, the other end of the resistor R5 is respectively connected to an output end of a comparator U1, one end of the resistor R7, and one end of the resistor R9, the other end of the resistor R7 is connected to a control end of a MOS tube Q2, and the other end of the resistor R9 outputs a signal SCP.

[0045] The utility model has the advantages that: when the short-circuit protection is realized through dual-mode sampling, the dimming MOS tube will not switch repeatedly under the peak current generated by the short circuit, and there will be no phenomenon of short-circuit failure protection when the dimming is adjusted to the minimum, thereby protecting the output dimming MOS tube Q1, and at the same time, the normal output can be restored when the short circuit is cancelled, and there is no need to restart the LED drive power supply.

[0046] Of course, the present invention is not limited to the above-mentioned embodiments, and technicians familiar with the field may make equivalent modifications or substitutions without violating the spirit of the present invention. These equivalent modifications and substitutions are all included in the scope defined by the claims of this application.

Claims

1. A short-circuit protection circuit with dual-mode sampling, comprising a comparator U1 and a MOS tube Q2, characterized in that: It also includes a voltage sampling circuit (10) and a current sampling circuit (20); The negative input terminal of the comparator U1 is connected to the reference voltage Vref, the power supply terminal of the comparator U1 is connected to the voltage source VCC, and the ground terminal of the comparator U1 is connected to the GND terminal; The output end of the comparator U1 is connected to the control end of the MOS tube Q2 and outputs a signal SCP to the main control circuit (30); the input end of the MOS tube Q2 is connected to the PWM end of the main control circuit (30); and the output end of the MOS tube Q2 is connected to the GND end; The input end of the voltage sampling circuit (10) is connected to the drain of the dimming MOS tube Q1, and the output end is connected to the positive input end of the comparator U1; The input end of the current sampling circuit (20) is connected to the source of the dimming MOS tube Q1, and the output end is connected to the positive input end of the comparator U1.

2. A short-circuit protection circuit with dual-mode sampling according to claim 1, characterized in that: The voltage sampling circuit (10) comprises a voltage regulator tube Z1, a resistor R6, a resistor R8 and a resistor R10; one end of the voltage regulator tube Z1 is connected to the drain of the dimming MOS tube Q1; the other end of the voltage regulator tube Z1 is connected to one end of the resistor R8 and one end of the resistor R10 respectively via the resistor R6; the other end of the resistor R8 is connected to the positive input end of the comparator U1; and the other end of the resistor R10 is connected to the GND end.

3. A short circuit protection circuit with dual mode sampling according to claim 2, characterized in that: It also includes a capacitor C3, one end of the capacitor C3 is connected to the other end of the resistor R8, and the other end of the capacitor C3 is connected to the GND end.

4. The short-circuit protection circuit with dual-mode sampling according to claim 1, characterized in that: The current sampling circuit (20) comprises a resistor R4, one end of the resistor R4 is connected to the source of the dimming MOS tube Q1, and the other end of the resistor R4 is connected to the positive input end of the comparator U1.

5. The short-circuit protection circuit with dual-mode sampling according to claim 1, characterized in that: It also includes a reference voltage module (40) connected to the negative input terminal of the comparator U1 and the voltage source VCC respectively, and is used to generate the reference voltage Vref.

6. The short-circuit protection circuit with dual-mode sampling according to claim 5, characterized in that: The reference voltage module (40) comprises resistors R2-R3 and capacitors C1-C2, one end of the resistor R3 is respectively connected to a voltage source VCC and one end of the capacitor C2, the other end of the resistor R3 is respectively connected to a negative input end of the comparator U1, one end of the capacitor C1 and one end of the resistor R2, the other end of the capacitor C1, the other end of the capacitor C2 and the other end of the resistor R2 are connected to a GND end.

7. The short-circuit protection circuit with dual-mode sampling according to claim 1, characterized in that: It also includes a resistor R5, a resistor R7 and a resistor R9, one end of the resistor R5 is connected to the voltage source VCC, the other end of the resistor R5 is respectively connected to the output end of the comparator U1, one end of the resistor R7 and one end of the resistor R9, the other end of the resistor R7 is connected to the control end of the MOS tube Q2, and the other end of the resistor R9 outputs a signal SCP.

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