Short circuit protection circuit and buck driving circuit

Abstract

The application provides a short-circuit protection circuit and a Buck driving circuit. The short-circuit protection circuit comprises a short-circuit threshold value providing circuit and a short-circuit protection signal generating circuit. The short-circuit threshold value providing circuit is used for providing a third reference voltage as a current detection resistance short-circuit protection threshold value according to an input voltage of the Buck driving circuit; the short-circuit protection signal generating circuit is used for generating a third short-circuit protection signal according to the third reference voltage and a detection voltage between the current detection resistance at a predetermined time point of each switching cycle of the Buck driving circuit. The application can provide safe and reliable short-circuit protection function.

Description

Technical Field

[0001] This application relates to the field of LED driver technology, and in particular to a short-circuit protection circuit and a Buck driver circuit. Background Technology

[0002] LED (Light Emitting Diode) lighting is widely used in daily production and life due to its advantages such as energy saving, environmental protection, and long lifespan. Based on the light-emitting principle and characteristics of LEDs, constant current sources are selected to drive LED chips. Constant current sources are generally divided into linear constant current sources and switching mode constant current sources. Switching mode constant current sources stand out due to their high efficiency and small size. Among them, the average current control mode Buck (step-down) drive circuit is widely used in medium and high power LED driving applications because of its excellent constant current accuracy and regulation rate. In current customer applications, short circuits in some components can cause system failure, resulting in open flames or even explosions, failing to meet safety regulations. Summary of the Invention

[0003] The purpose of this application is to provide a short-circuit protection circuit and a Buck drive circuit that can provide safe and reliable short-circuit protection.

[0004] One aspect of this application provides a short-circuit protection circuit. The short-circuit protection circuit is applied to a Buck drive circuit. The short-circuit protection circuit is used to provide short-circuit protection for a current-sensing resistor connected in series in the Buck drive circuit. The current-sensing resistor is used to indirectly detect the inductor current in the Buck drive circuit and generate a detection voltage proportional to the inductor current. The short-circuit protection circuit includes: a short-circuit threshold providing circuit, used to provide a third reference voltage as a short-circuit protection threshold for the current-sensing resistor based on the input voltage of the Buck drive circuit; and a short-circuit protection signal generating circuit, used to generate a third short-circuit protection signal at a predetermined time point in each switching cycle of the Buck drive circuit, based on the third reference voltage and the detection voltage across the current-sensing resistor.

[0005] Furthermore, the short-circuit threshold providing circuit includes a resistor voltage divider circuit, a voltage-to-current conversion circuit, and a threshold generation circuit. One end of the resistor voltage divider circuit is connected to the input voltage of the Buck driving circuit, and the other end is grounded. The input terminal of the voltage-to-current conversion circuit is connected to the output terminal of the resistor voltage divider circuit. The input terminal of the threshold generation circuit is connected to the output terminal of the voltage-to-current conversion circuit, and the output terminal of the threshold generation circuit is used to output the third reference voltage.

[0006] Further, the voltage-to-current conversion circuit includes a first operational amplifier, a first MOSFET, and a third resistor. The non-inverting input of the first operational amplifier is connected to the output of the resistor divider circuit, the inverting input of the first operational amplifier is connected to the source of the first MOSFET, and the output of the first operational amplifier is connected to the gate of the first MOSFET. The source of the first MOSFET is grounded through the third resistor, and the drain of the first MOSFET serves as the voltage-current converter. □ The output terminal of the current conversion circuit.

[0007] Furthermore, the threshold generation circuit includes a current mirror, a fourth resistor, and a second operational amplifier. The output terminal of the voltage-to-current conversion circuit is connected to the non-inverting input terminal of the second operational amplifier through the current mirror, and the non-inverting input terminal of the second operational amplifier is also grounded through the fourth resistor. The output terminal of the second operational amplifier is connected to the inverting input terminal of the second operational amplifier and serves as the output terminal of the threshold generation circuit.

[0008] Furthermore, the short-circuit threshold providing circuit also includes a filtering device, which is disposed between the output terminal of the resistor voltage divider circuit and the input terminal of the voltage-to-current conversion circuit. The cutoff frequency of the filtering device is set according to the noise spectrum of the input port of the Buck drive circuit.

[0009] Furthermore, the short-circuit protection signal generation circuit includes a first comparator, a short-circuit timing circuit, and a logic circuit. The non-inverting input of the first comparator is connected to the output of the short-circuit threshold providing circuit, and the inverting input of the first comparator is connected to the detection voltage. The short-circuit timing circuit is used to generate a short-circuit detection timing signal based on a clock signal and a drive signal. The logic circuit is used to generate the third short-circuit protection signal based on the comparison signal output by the first comparator, the short-circuit detection timing signal, and the drive signal.

[0010] Furthermore, the short-circuit timing circuit includes a second comparator, wherein the non-inverting input of the second comparator is connected to a triangular wave signal synchronized with the clock signal, the inverting input of the second comparator is connected to a fourth reference voltage, and the output of the second comparator is used to output the short-circuit detection timing signal.

[0011] Furthermore, the duty cycle of the low level in the short-circuit detection timing signal is equal to the ratio of the amplitude of the fourth reference voltage to that of the triangular wave signal, and the period of the short-circuit detection timing signal is equal to the switching period.

[0012] Furthermore, the logic circuit includes a second AND gate and a NAND gate, wherein one input of the second AND gate is connected to the output of the short-circuit timing circuit, and the other input of the second AND gate is connected to the driving signal; the two inputs of the NAND gate are respectively connected to the output of the first comparator and the output of the second AND gate, and the output of the NAND gate is used to output the third short-circuit protection signal.

[0013] Furthermore, the short-circuit protection circuit also includes a hiccup time setting module, which is connected to the output of the NAND gate and is used to set the hiccup time of the third short-circuit protection signal.

[0014] Furthermore, the short-circuit protection circuit is also used to provide short-circuit protection for the LED and inductor in the Buck drive circuit. The short-circuit protection circuit further includes a comparator circuit and an OR gate. The input terminal of the comparator circuit is respectively connected to the detected voltage, a first reference voltage as the LED short-circuit protection threshold, and a second reference voltage as the inductor short-circuit protection threshold. The comparator circuit is used to compare the detected voltage with the first reference voltage and the second reference voltage, and output a first short-circuit protection signal and a second short-circuit protection signal. The input terminal of the OR gate is respectively connected to the first short-circuit protection signal, the second short-circuit protection signal, and the third short-circuit protection signal. The output terminal of the OR gate is used to output the short-circuit protection signal of the short-circuit protection circuit.

[0015] Another aspect of this application provides a Buck drive circuit. The Buck drive circuit includes an inductor and a short-circuit protection circuit as described above.

[0016] Furthermore, the Buck drive circuit also includes a compensator, a pulse width modulation circuit, a first AND gate, and a gate drive circuit. The compensator is used to obtain a control signal based on the difference between the detected voltage and a reference voltage of the inductor current. The pulse width modulation circuit is used to generate a PWM signal based on the control signal. The input of the first AND gate is connected to the output of the pulse width modulation circuit and the output of the short-circuit protection circuit, respectively. The input of the gate drive circuit is connected to the output of the first AND gate, and the output of the gate drive circuit is used to output a drive signal.

[0017] The short-circuit protection circuit of one or more embodiments of this application has a safe and reliable short-circuit protection function. When a short-circuit fault occurs in the current sensing resistor of the Buck drive circuit, it can detect the short-circuit fault in the current sensing resistor in a timely and accurate manner and turn off the power switch, thereby keeping the Buck drive circuit in a safe state.

[0018] The short-circuit protection circuit of one or more embodiments of this application can provide an adaptive current sensing resistor short-circuit protection threshold based on the input voltage of the Buck drive circuit. Therefore, the RCS short-circuit detection of this application is not affected by the wide input voltage range and the wide output lamp voltage range, which can meet the needs of most low-voltage DC LED driver applications and provide safe and reliable protection functions. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of a Buck drive circuit with an average current control mode in related technologies.

[0020] Figure 2 This is a schematic diagram of a short-circuit protection circuit for a Buck drive circuit in related technologies.

[0021] Figure 3 for Figure 2 The waveform diagram of the short-circuit protection circuit shown is displayed when an LED short circuit occurs.

[0022] Figure 4 for Figure 2 The waveform diagram of the short-circuit protection circuit shown is displayed when an inductive short circuit occurs.

[0023] Figure 5 This is a schematic diagram of the structure of a Buck drive circuit according to an embodiment of this application.

[0024] Figure 6 This is a schematic diagram of the structure of an RCS short-circuit protection circuit according to an embodiment of this application.

[0025] Figure 7 This is a schematic diagram of the circuit providing the short-circuit threshold according to an embodiment of this application.

[0026] Figure 8 This is a schematic diagram of the short-circuit protection signal generation circuit according to an embodiment of this application.

[0027] Figure 9 This is a schematic diagram of a short-circuit sequential circuit according to an embodiment of this application.

[0028] Figure 10 This is a short-circuit protection timing diagram of a short-circuit protection circuit according to an embodiment of this application. Detailed Implementation

[0029] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numerals in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses consistent with some aspects of this application as detailed in the appended claims.

[0030] Figure 1 A schematic diagram of a Buck drive circuit with an average current control mode in related technologies is shown. (Example) Figure 1 As shown, in the Buck drive circuit, the current sensing resistor Rcs is used to indirectly detect the current of the inductor L and generate a detection voltage Vcs proportional to the inductor current. The detection voltage Vcs is the detection voltage across the current sensing resistor Rcs.

[0031] Short-circuit protection is a typical safety requirement. When a short circuit occurs in the LED or inductor L in the Buck drive circuit, the excessive current can be determined by measuring the voltage across the current sensing resistor Rcs connected in series in the Buck drive circuit, i.e., the sensing voltage Vcs. This triggers the short-circuit protection condition, shutting off the power switch M in the Buck drive circuit, so that the entire Buck drive circuit is in a safe and controllable state.

[0032] Figure 2 A schematic diagram of a short-circuit protection circuit 100 for a Buck drive circuit in related technologies is shown. For example... Figure 2 As shown, the difference between the detection voltage Vcs and the reference voltage Vref of the inductor current is used by the compensator 110 to obtain the control signal EA. When the Buck drive circuit is working normally, the short-circuit protection signal Protect is high. The control signal EA is used by the pulse width modulation circuit 120 and the gate drive circuit 130 to generate the drive signal DRV. Figure 1 The diagram shows the power switch M being turned on and off. In steady-state operation, Vcs = Vref, therefore, the average inductor current IL_AVG = Vcs / Rcs = Vref / Rcs. When short-circuit protection is triggered, the short-circuit protection signal Protect is low, the drive signal DRV is low, the power switch M is turned off, and the inductor current gradually decreases to 0.

[0033] Figure 3 Revealed Figure 2 The waveform diagram of the short-circuit protection circuit 100 shown is displayed when an LED short circuit occurs. (See diagram below.) Figure 3 As shown, during normal operation, the Buck drive circuit periodically generates the DRV drive signal. Figure 1The power switch M is shown to be on and off, and the detection voltage Vcs resembles a knife-edge shape. When an LED short-circuit fault occurs, the inductor current slope increases, leading to an increase in the peak inductor current. The voltage across the current sensing resistor Rcs, i.e., the detection voltage Vcs, exceeds the first reference voltage Vref1, which serves as the LED short-circuit protection threshold, for a cumulative total of 3 times. At this point, the short-circuit protection signal Protect outputs a low level, the drive signal DRV is pulled low, the power switch M is turned off, and the inductor current gradually decreases to 0. Thus, the components in the Buck drive circuit are protected.

[0034] Figure 4 Revealed Figure 2 The waveform diagram of the short-circuit protection circuit 100 shown is displayed when an inductive short circuit occurs. (See diagram below.) Figure 4 As shown, during normal operation, the Buck drive circuit periodically generates the DRV drive signal. Figure 1 The power switch M is shown to be on and off, and the detected voltage Vcs resembles a knife-edge shape. When an inductor short-circuit fault occurs and the power switch M is on, only the parasitic inductance from the wiring hinders the current change in the entire power circuit. The circuit is almost short-circuited, and the circuit current increases instantaneously. The amplitude of the detected voltage Vcs instantaneously exceeds the second reference voltage Vref2, which serves as the inductor short-circuit protection threshold. The short-circuit protection signal Protect outputs a low level and remains so, the drive signal DRV is pulled low, the power switch M is turned off, and the inductor current gradually decreases to 0. Thus, the components in the Buck drive circuit are protected.

[0035] As described above, both LED short-circuit protection and inductor short-circuit protection rely on detecting the voltage across the current sensing resistor Rcs, i.e., the detection voltage Vcs. Clearly, if the current sensing resistor Rcs is short-circuited, the voltage across it, i.e., the detection voltage Vcs, will be almost zero when an LED or inductor short-circuit fault occurs, failing to reach the short-circuit protection threshold. Therefore, it will not trigger short-circuit protection, causing both short-circuit protection functions to fail. Furthermore, if a short-circuit fault occurs in the current sensing resistor Rcs during normal operation, causing the voltage across it, i.e., the detection voltage Vcs, to consistently fail to reach the inductor current reference voltage Vref, then according to... Figure 2 The logic of the short circuit protection circuit 100 is such that the power switch M remains on, causing a short circuit in the circuit, which will inevitably lead to fire or explosion of components, ultimately resulting in safety hazards.

[0036] In view of this, this application provides an improved short-circuit protection circuit that can be used to short-circuit protect the current sensing resistor Rcs in the Buck drive circuit.

[0037] The short-circuit protection circuit and Buck drive circuit of this application will now be described in detail with reference to the accompanying drawings. Unless otherwise specified, the features of the following embodiments and implementations can be combined with each other.

[0038] Figure 5 A schematic diagram of the structure of a Buck drive circuit 200 according to an embodiment of this application is shown. Figure 5 As shown, a Buck drive circuit 200 according to one embodiment of this application includes a compensator 210, a pulse width modulation circuit 220, a first AND gate AND1, a gate drive circuit 230, and a short-circuit protection circuit (not labeled).

[0039] The compensator 210 can obtain a control signal EA based on the difference between the detected voltage Vcs and the reference voltage Vref of the inductor current.

[0040] The input terminal of the pulse width modulation circuit 220 is connected to the output terminal of the compensator 210. The pulse width modulation circuit 220 can generate a PWM signal based on the control signal EA output by the compensator 210.

[0041] The inputs of the first AND gate AND1 are connected to the outputs of the pulse width modulation circuit 220 and the short-circuit protection circuit, respectively. The output of the short-circuit protection circuit is used to output the short-circuit protection signal Protect.

[0042] The input terminal of the gate drive circuit 230 is connected to the output terminal of the first AND gate AND1, and the output terminal of the gate drive circuit 230 is used to output the drive signal DRV.

[0043] When no short-circuit fault occurs in the Buck drive circuit 200, the short-circuit protection signal Protect output by the short-circuit protection circuit is high, i.e., "1". When the short-circuit protection signal Protect output by the short-circuit protection circuit is "1", the control signal EA generates the drive signal DRV through the pulse width modulation circuit 220 and the gate drive circuit 230 to drive the power switch M to turn on and off normally.

[0044] When a short circuit fault occurs in the Buck drive circuit 200, the short circuit protection signal Protect output by the short circuit protection circuit is low, i.e., "0", thereby pulling the output of the first AND gate AND1 low, i.e., "0". At this time, the PWM signal output by the pulse width modulation circuit 220 is essentially shielded, and the drive signal DRV output by the gate drive circuit 230 is pulled low by the short circuit protection signal Protect, thereby turning off the power switch and providing short circuit protection for the Buck drive circuit 200.

[0045] The short-circuit protection circuit of this application may include a current sensing resistor (RCS) short-circuit protection circuit 300, which can provide short-circuit protection for the current sensing resistor Rcs connected in series in the Buck drive circuit 200. Figure 6 A schematic diagram of the structure of an RCS short-circuit protection circuit 300 according to an embodiment of this application is shown. Figure 6 As shown, the RCS short-circuit protection circuit 300 is applied to the Buck drive circuit 200, which may include a short-circuit threshold providing circuit 310 and a short-circuit protection signal generating circuit.

[0046] The short-circuit threshold providing circuit 310 can provide a third reference voltage Vref3 as the short-circuit protection threshold of the current sensing resistor (RCS) based on the input voltage Vin of the Buck drive circuit 200.

[0047] The short-circuit protection signal generation circuit can generate a third short-circuit protection signal Protect3 at a predetermined time point in each switching cycle of the Buck drive circuit 200, based on the third reference voltage Vref3 and the detection voltage Vcs.

[0048] The RCS short-circuit protection circuit 300 of this application provides an adaptive third reference voltage Vref3 based on the input voltage Vin of the Buck drive circuit 200 by setting a short-circuit threshold providing circuit 310. By comparing the third reference voltage Vref3 with the detection voltage Vcs at a predetermined time point in each switching cycle, a short-circuit fault in the current sensing resistor Rcs is detected, and a third short-circuit protection signal Protect3 is generated. The function of short-circuit protection for the current sensing resistor Rcs can be realized through the third short-circuit protection signal Protect3.

[0049] Figure 7 A schematic diagram of the structure of a short-circuit threshold providing circuit 310 according to an embodiment of this application is shown. Figure 7 As shown, in some embodiments, the short-circuit threshold providing circuit 310 of this application may include a resistor voltage divider circuit 311, a voltage-to-current conversion circuit 312, and a threshold generating circuit 313.

[0050] One end of the resistor voltage divider circuit 311 is connected to the input voltage Vin of the Buck driver circuit 200, and the other end is grounded. The resistor voltage divider circuit 311 includes a first resistor R1 and a second resistor R2 connected in series. One end of the first resistor R1 is connected to the input voltage Vin of the Buck driver circuit 200, and the other end of the first resistor R1 is connected to one end of the second resistor R2, serving as the output terminal of the resistor voltage divider circuit 311. The other end of the second resistor R2 is grounded.

[0051] The input terminal of the voltage-to-current conversion circuit 312 is connected to the output terminal of the resistor divider circuit 311. In some embodiments, the voltage-to-current conversion circuit 312 includes a first operational amplifier AMP1, a first MOSFET M1, and a third resistor R3. The first MOSFET M1 is an NMOS transistor. The non-inverting input terminal of the first operational amplifier AMP1 is connected to the output terminal of the resistor divider circuit 311, the inverting input terminal of the first operational amplifier AMP1 is connected to the source of the first MOSFET M1, and the output terminal of the first operational amplifier AMP1 is connected to the gate of the first MOSFET M1. The source of the first MOSFET M1 is grounded through the third resistor R3, and the drain of the first MOSFET M1 serves as the output terminal of the voltage-to-current conversion circuit 312.

[0052] The input terminal of the threshold generation circuit 313 is connected to the output terminal of the voltage-to-current conversion circuit 312, and the output terminal of the threshold generation circuit 313 can be used to output the third reference voltage Vref3.

[0053] In some embodiments, the threshold generation circuit 313 includes a current mirror 3130, a fourth resistor R4, and a second operational amplifier AMP2. The output of the voltage-to-current conversion circuit 312 can be connected to the non-inverting input of the second operational amplifier AMP2 via the current mirror 3130. The current mirror 3130 is used to mirror the current signal output by the voltage-to-current conversion circuit 312. Furthermore, the non-inverting input of the second operational amplifier AMP2 is grounded via the fourth resistor R4; the output of the second operational amplifier AMP2 is connected to its inverting input and serves as the output of the threshold generation circuit 313. The second operational amplifier AMP2 constitutes a voltage follower, enabling voltage following and enhancement, improving voltage stability, and providing a stable third reference voltage Vref3.

[0054] In one embodiment, the current mirror 3130 may include a second MOSFET M2 and a third MOSFET M3. Both the second MOSFET M2 and the third MOSFET M3 are PMOS transistors. The gate of the second MOSFET M2 is connected to the gate of the third MOSFET M3. The sources of both the second MOSFET M2 and the third MOSFET M3 are connected to a power supply voltage Vcc. The drain of the second MOSFET M2 is shorted to its gate, and the drain of the second MOSFET M2 is connected to a voltage - □ The output terminal of the current conversion circuit 312 and the drain of the third MOSFET M3 serve as the output terminal of the current mirror 3130.

[0055] In some embodiments, the short-circuit threshold providing circuit 310 of this application may further include a filter device 314. The filter device 314 is disposed between the output terminal of the resistor divider circuit 311 and the input terminal of the voltage-to-current conversion circuit 312. The cutoff frequency of the filter device 314 can be set according to the noise spectrum of the input port of the Buck drive circuit 200. When noise exists in the input voltage Vin of the Buck drive circuit 200, the user can set the cutoff frequency of the filter device 314 according to the input noise spectrum, thereby ensuring the robustness of the RCS short-circuit protection function and guaranteeing the anti-interference performance generated by the third reference voltage Vref3.

[0056] The output voltage of the resistor divider circuit 311 is V0, and the low-frequency gain of the filter device 314 is maintained at G. The voltage obtained after passing through the filter device 314 is V1. Therefore, V1 = G * V0. When G = 1, we can obtain V1 = Vin * R2 / (R1 + R2). The voltage-to-current conversion circuit 312 uses the "virtual short and virtual open" of the first operational amplifier AMP1 to limit the source voltage of the first MOSFET M1 to V1, and uses the third resistor R3 to convert the voltage into current, so that the current flowing through the third resistor R3 is V1 / R3. The first MOSFET M1 and the third resistor R3 are connected in series, so the current flowing through the first MOSFET M1 is also V1 / R3. A current mirror with a 1:N ratio is formed by the second MOSFET M2 and the third MOSFET M3. Therefore, the current flowing through the second MOSFET M2 is equal to V1 / R3, and the current flowing through the third NMOS transistor M3 is N*V1 / R3. Therefore, the voltage V2 across the fourth resistor R4 is R4*N*V1 / R3. After passing through the voltage follower formed by the second operational amplifier AMP2, the third reference voltage Vref3 can be obtained: V2 = R4*N*V1 / R3. Therefore, the third reference voltage Vref3 = Vin*G*R2*R4*N / [(R1+R2)*R3].

[0057] Figure 8 A schematic diagram of a short-circuit protection signal generation circuit according to an embodiment of this application is disclosed. (Refer to reference...) Figure 6 and Figure 8 As shown, in some embodiments, the short-circuit protection signal generation circuit may include a first comparator COMP1, a short-circuit timing circuit 320, and a logic circuit 330.

[0058] One input of the first comparator COMP1 is connected to the output of the short-circuit threshold providing circuit 310, and is used to input the third reference voltage Vref3 output by the short-circuit threshold providing circuit 310. The other input of the first comparator COMP1 is connected to the detection voltage Vcs. Specifically, the non-inverting input of the first comparator COMP1 is connected to the output of the short-circuit threshold providing circuit 310, and the inverting input of the first comparator COMP1 is connected to the detection voltage Vcs. When the detection voltage Vcs is lower than the third reference voltage Vref3, the first comparator COMP1 outputs a high level; conversely, when the detection voltage Vcs is higher than the third reference voltage Vref3, the first comparator COMP1 outputs a low level.

[0059] Figure 9 A schematic diagram of a short-circuit sequential circuit 320 according to an embodiment of this application is shown. Figure 9 As shown, the short-circuit timing circuit 320 can generate a short-circuit detection timing signal TRS based on the clock signal Clock and the drive signal DRV. In some embodiments, the short-circuit timing circuit 320 includes a second comparator COMP2. The non-inverting input of the second comparator COMP2 is connected to a triangular wave signal synchronized with the clock signal Clock, the amplitude of which is Vc. The inverting input of the second comparator COMP2 is connected to a fourth reference voltage Vref4. When the level of the fourth reference voltage Vref4 is higher than the amplitude Vc of the triangular wave, the second comparator COMP2 outputs a low level; conversely, when the level of the fourth reference voltage Vref4 is lower than the amplitude Vc of the triangular wave, the second comparator COMP2 outputs a high level. The output of the second comparator COMP2 is used to output the short-circuit detection timing signal TRS. The duty cycle of the low level in the short-circuit detection timing signal TRS is equal to the ratio of the fourth reference voltage Vref4 to the amplitude of the triangular wave signal, i.e., M = Vref4 / Vc. The period of the short-circuit detection timing signal TRS is equal to the switching period Tsw of the Buck drive circuit 200. Therefore, the low level time of the short-circuit detection timing signal TRS is M*Tsw.

[0060] When designing the Buck drive circuit 200, the third reference voltage Vref3 can be made to equal Vin * Vref * M / K. Combining this with the above, we can obtain G * R2 * R4 * N / [(R1 + R2) * R3] = Vref * M / K, where Vref is the reference voltage for the inductor current, and M is... Figure 8 The duty cycle of the low level of the short-circuit detection timing signal TRS in the circuit is K, which is a constant. Generally, let K = VLED / n, where n is the ripple coefficient of the inductor current and VLED is the output voltage of the LED.

[0061] Logic circuit 330 can generate a third short-circuit protection signal Protect3 based on the comparison signal output from the first comparator COMP1, the short-circuit detection timing signal TRS, and the drive signal DRV. For example... Figure 8 As shown, in some embodiments, logic circuit 330 may include a second AND gate AND2 and a NAND gate NAND.

[0062] One input of the second AND gate AND2 is connected to the output of the short-circuit timing circuit 320, i.e., the output of the second comparator COMP2; the other input of the second AND gate AND2 is connected to the drive signal DRV.

[0063] When the drive signal DRV is low, the output of the second AND gate AND2 will be low regardless of whether the short-circuit detection timing signal TRS is high or low. Therefore, the RCS short-circuit fault detection function can be disabled.

[0064] The two inputs of the NAND gate are connected to the output of the first comparator COMP1 and the output of the second AND gate AND2, respectively. The output of the NAND gate is used to output the third short-circuit protection signal Protect3.

[0065] In some embodiments, the RCS short-circuit protection circuit of this application may further include a hiccup time setting module 340. The hiccup time setting module 340 is connected to the output of the NAND gate and is used to set the hiccup time of the third short-circuit protection signal Protect3. The RCS short-circuit protection circuit 300 can maintain the RCS short-circuit protection function of the Buck drive circuit 200 at this hiccup time. After the hiccup time has elapsed, the Buck drive circuit 200 will attempt to automatically restart to recover.

[0066] Figure 10 A short-circuit protection timing diagram of a short-circuit protection circuit according to an embodiment of this application is disclosed. (Refer to reference...) Figure 10 The two inputs of the second AND gate, AND2, are connected to the short-circuit detection timing signal TRS and the drive signal DRV of the Buck driver circuit 200, respectively. When both the short-circuit detection timing signal TRS and the drive signal DRV are high, the second AND gate, AND2, outputs a high level; otherwise, it outputs a low level. The two inputs of the NAND gate, NAND, are connected to the output of the second AND gate, AND2, and the output of the first comparator, COMP1, respectively. When both the output levels of the second AND gate, AND2, and the first comparator, COMP1, are high, the NAND gate, NAND, outputs a low level; otherwise, it outputs a high level. The output signal of the NAND gate, NAND, is the third short-circuit protection signal, Protect3. (Refer to reference...) Figure 5When the third short-circuit protection signal Protect3 is low, the drive signal DRV is pulled low, and therefore the power switch is turned off.

[0067] The short-circuit protection circuit of this application can also be used to provide short-circuit protection for the LEDs and inductors in the Buck drive circuit 200. (Continue to refer to...) Figure 5 In some embodiments, the short-circuit protection circuit further includes a comparator circuit 240 and an OR gate 250.

[0068] The input terminals of the comparator circuit 240 are respectively connected to the detection voltage Vcs, the first reference voltage Vref1 which serves as the LED short-circuit protection threshold, and the second reference voltage Vref2 which serves as the inductor short-circuit protection threshold. The comparator circuit 240 can compare the detection voltage Vcs with the first reference voltage Vref1 and the second reference voltage Vref2 respectively, and output the corresponding first short-circuit protection signal Protect1 and the second short-circuit protection signal Protect2.

[0069] The inputs of OR gate 250 are respectively connected to the first short-circuit protection signal Protect1, the second short-circuit protection signal Protect2, and the third short-circuit protection signal Protect3; the output of OR gate 250 is connected to one input of the first AND gate AND1, and is used to output the short-circuit protection signal Protect of the short-circuit protection circuit. When any one of the short-circuit protection signals Protect1, Protect2, and Protect3 is low, the short-circuit protection signal Protect output by OR gate 250 will also be low, thereby pulling the drive signal DRV low and turning off the power switch.

[0070] The short-circuit protection circuit of this application can detect the short-circuit fault of the current sensing resistor in a timely and accurate manner when a short-circuit fault occurs in the Buck drive circuit 200 in the average current control mode, and turn off the power switch transistor, thereby keeping the Buck drive circuit 200 in a safe state.

[0071] The short-circuit protection circuit of this application can provide an adaptive current sensing resistor short-circuit protection threshold (i.e., the third reference voltage) based on the input voltage Vin of the Buck driver circuit 200. Therefore, this RCS short-circuit detection is not affected by the wide input voltage Vin range and the wide output lamp voltage range, which can meet the needs of most low-voltage DC LED driver applications and provide safe and reliable protection functions.

[0072] The short-circuit protection circuit and Buck drive circuit provided in the embodiments of this application have been described in detail above. Specific examples have been used to illustrate the short-circuit protection circuit and Buck drive circuit of the embodiments of this application. The descriptions of the embodiments above are only for helping to understand the core ideas of this application and are not intended to limit this application. It should be noted that for those skilled in the art, several improvements and modifications can be made to this application without departing from the spirit and principles of this application, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A short-circuit protection circuit, applied to a Buck drive circuit, characterized in that, The short-circuit protection circuit includes: A short-circuit threshold providing circuitry is used to provide a third reference voltage as a short-circuit protection threshold for the current sensing resistor, based on the input voltage of the Buck drive circuit. A short-circuit protection signal generation circuit is used to generate a third short-circuit protection signal at a predetermined time point in each switching cycle of the Buck drive circuit, based on the third reference voltage and the detected voltage across the current sensing resistor.

2. The short-circuit protection circuit as described in claim 1, characterized in that, The short-circuit threshold providing circuit includes a resistor voltage divider circuit, a voltage-to-current conversion circuit, and a threshold generation circuit, wherein... One end of the resistor voltage divider circuit is connected to the input voltage of the Buck drive circuit, and the other end is grounded; The input terminal of the voltage-to-current conversion circuit is connected to the output terminal of the resistor divider circuit; The input terminal of the threshold generation circuit is connected to the output terminal of the voltage-to-current conversion circuit, and the output terminal of the threshold generation circuit is used to output the third reference voltage.

3. The short-circuit protection circuit as described in claim 2, characterized in that, The voltage-to-current conversion circuit includes a first operational amplifier, a first MOSFET, and a third resistor, wherein... The non-inverting input of the first operational amplifier is connected to the output of the resistor divider circuit, the inverting input of the first operational amplifier is connected to the source of the first MOS transistor, and the output of the first operational amplifier is connected to the gate of the first MOS transistor. The source of the first MOS transistor is grounded through the third resistor, and the drain of the first MOS transistor serves as the output of the voltage-to-current conversion circuit.

4. The short-circuit protection circuit as described in claim 2, characterized in that, The threshold generation circuit includes a current mirror, a fourth resistor, and a second operational amplifier, wherein, The output terminal of the voltage-to-current conversion circuit is connected to the non-inverting input terminal of the second operational amplifier through the current mirror, and the non-inverting input terminal of the second operational amplifier is also grounded through the fourth resistor; the output terminal of the second operational amplifier is connected to the inverting input terminal of the second operational amplifier and serves as the output terminal of the threshold generation circuit.

5. The short-circuit protection circuit as described in claim 2, characterized in that, The short-circuit threshold providing circuit also includes a filtering device, which is disposed between the output terminal of the resistor divider circuit and the input terminal of the voltage-to-current conversion circuit. The cutoff frequency of the filtering device is set according to the noise spectrum of the input port of the Buck drive circuit.

6. The short-circuit protection circuit as described in claim 1, characterized in that, The short-circuit protection signal generation circuit includes a first comparator, a short-circuit timing circuit, and logic circuits. The non-inverting input of the first comparator is connected to the output of the short-circuit threshold providing circuit, and the inverting input of the first comparator is connected to the detection voltage. The short-circuit timing circuit is used to generate a short-circuit detection timing signal based on the clock signal and the drive signal; The logic circuit is used to generate the third short-circuit protection signal based on the comparison signal output by the first comparator, the short-circuit detection timing signal, and the drive signal.

7. The short-circuit protection circuit as described in claim 6, characterized in that, The short-circuit sequential circuit includes a second comparator, wherein... The non-inverting input of the second comparator is connected to a triangular wave signal synchronized with the clock signal, the inverting input of the second comparator is connected to a fourth reference voltage, and the output of the second comparator is used to output the short-circuit detection timing signal.

8. The short-circuit protection circuit as described in claim 7, characterized in that, The duty cycle of the low level in the short-circuit detection timing signal is equal to the ratio of the amplitude of the fourth reference voltage to that of the triangular wave signal, and the period of the short-circuit detection timing signal is equal to the switching period.

9. The short-circuit protection circuit as described in claim 6, characterized in that, The logic circuit includes a second AND gate and a NAND gate, wherein... One input of the second AND gate is connected to the output of the short-circuit timing circuit, and the other input of the second AND gate is connected to the driving signal; The two inputs of the NAND gate are respectively connected to the output of the first comparator and the output of the second AND gate, and the output of the NAND gate is used to output the third short-circuit protection signal.

10. The short-circuit protection circuit as described in claim 9, characterized in that, It also includes a hiccup time setting module, which is connected to the output of the NAND gate and is used to set the hiccup time of the third short-circuit protection signal.

11. The short-circuit protection circuit as described in any one of claims 1 to 10, characterized in that, The short-circuit protection circuit is also used to protect the LEDs and inductors in the Buck drive circuit from short circuits. The short-circuit protection circuit further includes a comparator circuit and an OR gate. The input terminals of the comparison circuit are respectively connected to the detection voltage, the first reference voltage as the LED short-circuit protection threshold, and the second reference voltage as the inductor short-circuit protection threshold. The comparison circuit is used to compare the detection voltage with the first reference voltage and the second reference voltage respectively, and output the first short-circuit protection signal and the second short-circuit protection signal. The input terminals of the OR gate are respectively connected to the first short-circuit protection signal, the second short-circuit protection signal and the third short-circuit protection signal, and the output terminal of the OR gate is used to output the short-circuit protection signal of the short-circuit protection circuit.

12. A Buck drive circuit, characterized in that, Includes inductors and short-circuit protection circuits as described in any one of claims 1 to 11.

13. The Buck drive circuit as described in claim 12, characterized in that, It also includes a compensator, a pulse width modulation circuit, a first AND gate, and a gate drive circuit, wherein, The compensator is used to obtain a control signal based on the difference between the detected voltage and the reference voltage of the inductor current; The pulse width modulation circuit is used to generate a PWM signal based on the control signal; The input terminals of the first AND gate are respectively connected to the output terminal of the pulse width modulation circuit and the output terminal of the short circuit protection circuit; The input terminal of the gate driving circuit is connected to the output terminal of the first AND gate, and the output terminal of the gate driving circuit is used to output a driving signal.

Images