CN108337774B - High-power MOSFET dimming circuit - Google Patents

Abstract

The invention discloses a high-power MOSFET dimming circuit, which is additionally provided with a grid-source overvoltage protection circuit, a MOSFET drain-source overvoltage protection and spike absorption circuit, an input overvoltage protection circuit, an output overvoltage protection circuit and an adjustable short-circuit protection control circuit on the basis of the existing dimming circuit, and adopts simple and reliable protection measures with high response speed and low cost to improve the durability of the MOSFET dimming circuit so as to solve the technical problems of fragility and narrow application range of the existing MOSFET dimming circuit.

Description

High-power MOSFET dimming circuit

Technical Field

The invention relates to the field of household and building light control, in particular to a high-power MOSFET dimming circuit for wiring-free LED dimming engineering.

Background

There are two main dimming products in the current market: leading edge thyristor dimming and trailing edge low power MOSFET dimming.

The front cut silicon controlled rectifier light-adjusting device has the advantages of high adjusting precision, high efficiency, small volume, light weight, easiness in remote control and the like, but the front cut silicon controlled rectifier light-adjusting device is only suitable for resistive and inductive responsibility, is not matched with a driver of a main stream LED lamp product in the current market, has the problems of large impact current, easiness in flickering when the light is adjusted to low brightness and the like, and becomes a difficult problem of popularization of the current wiring-free LED light-adjusting mode.

The trailing edge phase-cut MOSFET controls the dimmer and is made of a Field Effect Transistor (FET) or an Insulated Gate Bipolar Transistor (IGBT) device. The trailing edge dimming is suitable for capacitive and resistive load dimming, has no minimum load requirement, is applied to LED lighting equipment, and can realize better performance on single lighting equipment or very small load; although MOS dimming has the advantages of high adjusting precision, high efficiency, small volume, light weight, adaptability to capacitive load, easiness in remote control and the like, the driving power is not large, and at present, only a knob type single-lamp dimmer is generally manufactured, so that the MOS dimming is not suitable for the engineering field; the high-power IGBT is mainly used, the problems of high cost, large volume, large heating value, relatively complex and unstable dimming circuit and the like are solved, the high-power IGBT is rarely applied to a dimming system, a trailing edge dimming mode is not developed, and the silicon controlled dimmer still occupies most of the dimming system market.

The existing trailing edge phase-cut MOSFET control dimmer mostly adopts IGBT, but the IGBT has the advantages of high conduction voltage drop, high heat loss, high heat dissipation cost and large volume, and is not beneficial to miniaturization; meanwhile, the MOSFET device is sensitive to heat, and has the characteristic of low-resistance conduction, so that the MOSFET has high conduction resistance and becomes larger along with the increase of temperature in the working process, and the current thermal damage is easily caused by cycle increment; at present, the LED products in the market are basically capacitive products, and when the LED products work, especially in a phase-cut dimming state, peak current is very large, and when the peak current reaches a certain value, the heat of the MOSFET is very large, and a circuit cannot radiate and disperse in time, so that heat damage is caused; on the other hand, the high-current product of the MOSFET has low voltage resistance, and the voltage resistance is 600-700V generally at present. However, because the circuit power consumption environment is relatively complex, the dimming product usually generates a very high induction voltage peak >600V on a long line in a dimming state, and the breakdown and damage of the MOSFET overvoltage are very easy to cause.

Disclosure of Invention

The technical problem to be solved by the invention is to provide a MOSFET dimming circuit, which is based on the existing dimming circuit, is provided with four overvoltage protection circuits and an adjustable short-circuit protection control circuit, and adopts simple and reliable protection measures with high response speed and low cost, so that the durability of the MOSFET dimming circuit is improved, and the technical problems of fragility and narrow application range of the existing MOSFET dimming circuit are solved.

In order to solve the above technical problems, the present invention provides a MOSFET dimming circuit, including: the system comprises a zero crossing detection circuit 100, a phase angle cutting power control circuit 200, a current detection circuit 300, a gate source overvoltage protection circuit 400, a MOSFET drain source overvoltage protection and peak absorption circuit 500, an input overvoltage protection circuit 600, an output overvoltage protection circuit 700 and an adjustable short-circuit protection control circuit;

The input end of the zero-crossing detection circuit 100 is connected with an alternating current power supply AC, one path of the output end of the zero-crossing detection circuit is connected with an A/D port AVC pin of the microprocessor MCU for input voltage detection, and the other path of the zero-crossing detection circuit is connected with a VPA port of the microprocessor MCU for processing a time reference coordinate point of phase control output and interrupting processing synchronous trigger signals;

The phase angle-cutting power control circuit 200 comprises a microprocessor MCU, a special optical coupler isolation driving chip U10 for a MOSFET, MOSFET tubes QA2 and QA1 and resistors RA10, RA9, RA7 and RA8; the microprocessor MCU converts the signal input by the zero crossing detection circuit into a PWM signal, outputs the PWM signal from TRGA pins and is connected to the MOSFET optocoupler isolation driving chip U10 for providing a MOSFET driving signal;

The current detection circuit 300 is connected with an IA A/D port of the microprocessor MCU through drain-source currents of MOSFET transistors Q1 and Q2, pins 3 and 4 of the Hall current sensing device UA1, pins 1 and 2, induced voltages output from a 7 th pin, resistors RA17, RA19, RA18, RA23, RA24, RA25 and RA21, a capacitor CA8 and an operational amplifier circuit U11A, U D;

The gate-source overvoltage protection circuit 400 is formed by connecting a resistor RA3 and a transient suppression diode TVSA1 in parallel; one end of the drive output 11 pin PWMout is connected to the optocoupler isolation drive chip U10, and the other end of the drive output 11 pin PWMout is connected with the sources of the connecting MOSFET transistors Q1 and Q2 and is connected with a reference zero level point COMA;

The MOSFET drain-source overvoltage protection and peak absorption circuit 500 is formed by connecting a resistor RA1 and a capacitor CA1 in parallel and connecting a bidirectional transient suppression diode DA5 in series; one end of the power supply is connected with the input of a power line, and the other end of the power supply is connected with the 1 st pin and the 2 nd pin of the Hall current sensor UA1, so that overvoltage spikes generated at a load end are eliminated, and the safety of loop voltage is ensured;

The input overvoltage protection circuit 600 consists of piezoresistors; one end of the power supply is connected with an alternating current ACL, and the other end of the power supply is connected with an alternating current zero line ACN, so that clamping of input voltage is realized, and input voltage safety is further ensured.

The output overvoltage protection circuit 700 is formed by connecting a resistor RA20 and a capacitor CA7 in parallel and connecting a bidirectional transient suppression diode DA1 in series; the two ends of the output overvoltage protection circuit are respectively connected between the output end and the zero line to form the output overvoltage protection circuit for inhibiting the output overvoltage induction voltage peak.

The adjustable protection control circuit can provide two different protection modes according to different power magnitudes and on-resistances RDS of MOSFET tubes in an actual circuit.

When the adjustable short-circuit protection control circuit is applied to low power, the RDS is generally more than 50mΩ, and the adjustable short-circuit protection control circuit 900A with an inaccurate current limit value is only selected for the adjustable protection control circuit; the circuit comprises three ends, wherein one end is connected with a 14 pin of an optical coupler isolation driving chip U10, and the other two ends are respectively connected with drain marks of MOSFET (metal oxide semiconductor field effect transistor) tubes QA1 and QA2 through fast recovery diodes; the pin 14 of the optocoupler isolation driving chip U10 provides constant bias current, and a source-drain on-voltage detection circuit of QA2 is formed by a resistor RA5, a fast recovery diode DA2 and a switching diode DA6 respectively; resistors RA6 and RA12, a fast recovery diode DA3 and a switching diode DA4 form a source-drain on-voltage detection circuit of QA 1; triode QA3, resistance RA12, RA29, RA11 form the current limit value regulating circuit; by setting the imprecise current limit value adjustable short-circuit protection control circuit 900A, abnormal large current at the load end of the circuit can be avoided, and the MOSFETs QA1 and QA2 are prevented from being damaged.

When applied to high power, RDS is typically less than 50mΩ, in order to avoid that the actual bias value of the circuit exceeds the range that the device can withstand, resulting in circuit damage. An accurate current limit value adjustable short-circuit protection control circuit 900B can be additionally arranged on the basis. The method utilizes the current induction voltage output by the 7 th pin VO of a Hall current accurate induction device UA1 to respectively pass through RA33 to a positive peak comparator consisting of an operational amplifier U11C, resistors RA30 and RA34 and pass through RA28 to a negative peak comparator consisting of an operational amplifier U11B, resistors RA37 and RA38, and the accurate control limit value is set through the circuit voltage of the two comparators;

as a further aspect of the present invention, the MOSFET tubes QA1, QA2 are selected to meet the following key parameter requirements:

a) According to specific rated current Io specification requirements, selecting MOSFETs with different Iar specification values: iar is greater than or equal to Io;

b) The MOSFET drain current Id is selected according to the applicable peak current Ip range, where Ip is of the value specification: id is more than or equal to Ip;

c)VDSS≥600V；

d)MOSFET dv/dt≥50V/ns；

e) The power consumption umbrella curve meets the current ID > ISHORT short-circuit protection current of a 10 mu s safety voltage current curve 580V;

f)IDSS≦50μA；

The Iar, io, id, ip and VDSS, ID, ISHORT, IDSS are avalanche current of the MOSFET, rated current of the dimmer, drain current of the MOSFET, peak current, drain-source voltage, drain current, short-circuit protection current and saturated drain-source current respectively.

The selection of the parameters can fully utilize the characteristics of the device and ensure the switching performance by combining the circuit of the invention;

as a further aspect of the present invention, the circuit further includes an output end high-frequency filter circuit 800 formed by connecting an inductance L2 to a UA1 st leg 2 and an output end, and connecting two ends of a capacitor CA11 between the UA1 st leg 2 and a zero line, respectively;

The invention provides a MOSFET dimming circuit, which can realize the matching performance of an LED dimming lamp which cannot be realized relative to the front-edge dimming of a silicon controlled rectifier by arranging four overvoltage protection circuits and an adjustable short-circuit protection circuit, avoid flickering and low-power limitation, and keep the characteristics of high front-edge dimming adjustment precision, high efficiency, small volume, light weight, easiness in remote control of wiring-free LED dimming and the like; meanwhile, the MOSFET dimming circuit can effectively protect devices to work in a safety range by utilizing the innovative boundary-adjustable short-circuit protection circuit and overvoltage protection measures; the error action is avoided through the tolerance reset setting of the chip, the power application range is effectively expanded, and larger power dimming, higher reliability and device utilization efficiency can be realized.

Drawings

The invention is further described below with reference to the drawings and examples.

Fig. 1 is a circuit diagram of an embodiment of the present invention.

Fig. 2 is a circuit diagram of a second embodiment of the present invention.

Detailed Description

The following description of specific embodiments is provided for the purpose of illustrating the invention by way of example and not for the purpose of limiting the invention by way of the accompanying drawings.

The invention includes two different embodiments

Embodiment one:

as shown in fig. 1, the operational amplifiers U5B and U5D, the voltage transformer TA, the resistors R11, R8, R9, R12, R17, R18, R23, R24, R25, R26, R29, and the capacitors C14 and C15 form a zero-crossing detection circuit 100. The alternating current power supply is connected through a terminal DZA, is connected with the TA input end of a voltage transformer through resistors R26 and R29, is connected with a matching resistor R28 and a coupling resistor R23 through a coupling output end, is connected with the U5B operational amplifier input pin 5 through a resistor R25 after being subjected to high-frequency filtering through a capacitor C14, is output from the 7 th pin after being amplified, and is sent to the A/D port AVC pin of a microprocessor MCU in the phase angle cutting power control circuit 200 through a resistor R12 to be used for input voltage calculation and power calculation application parameters; the other path is sent to the 12-pin input of the operational amplifier U5D through the resistor R18, and the comparator formed by the resistor R27 and the capacitor C15, wherein the resistor R27 is connected with the pins of the resistor R18 and the resistor 13; when the potential of the 12 pin input U5D exceeds the midpoint level 2.5V input by the 13 pin, outputting a high level from the 14 pin of U5D, otherwise, when the potential of the 12 pin input U5D is lower than the midpoint level input by the 13 pin, outputting a zero level from the 14 pin of U5D, and converting the 14 pin output level of U5D once when the input alternating current crosses zero once; the 14-pin output signal of U5D is sent to the VPA port of microprocessor MSP430FR6972IPMR in phase cut power control circuit 200; the zero-crossing detection circuit 100 has the characteristics of accurate zero-crossing detection and strong anti-interference capability; the MCU of the present invention may be of the type commonly used in the art, and is not limited to the specific model used in the embodiments.

MCU, MOSFET opto-coupler isolation drive chip U10, resistance RA7, RA8, RA9, RA10, isolation drive control circuit that electric capacity EA1, CA4 constitute. And the MCU receives the zero crossing signal as the time of the phase control output to calculate a reference coordinate point and interrupt processing synchronous trigger signal, and the control program operation of each half period is triggered when the zero crossing occurs. When the MCU receives a dimming instruction, a CLOSA pin of the MCU outputs a high level, the MCU carries out operation according to the control instruction, the current state and the setting, and an alternating current corner cut PWM signal synchronous with a zero crossing signal is output from a TRGA port of the MCU; the PWM signal is coupled and output to the 1 st pin PWM+ port input of the MOSFET optocoupler isolation driving chip U10 through the connected resistors RA10 and RA9, the PWM driving signal matched with the MOSFET is output from the 11 pin PWMout port through the internal coupling driving of the U10, and then the PWM driving signal is coupled to the grid electrodes of the MOSFET transistors QA1 and QA2 through RA7 and RA8 so as to drive the on/off of the QA1 and QA 2. Capacitors EA1 and CA4 are power supply filter capacitors of U10; in this embodiment, the optocoupler isolation driving chip is an a316J chip, but is not limited thereto.

The drain electrode of the N-channel power MOSFET QA2 is connected with the input end of the alternating current line, the source electrode of the QA2 is connected with the source electrode of the MOSFET QA1, and is connected with a reference zero level point COMA; the drain electrode of the MOSFET QA1 is connected with the 3 rd IP-4 th IP-pin of a Hall current sensor UA1 (A712 or A714 is selected in the present example) as an input signal, and the 1 rd IP+ pin and the 2 nd IP+ pin of the UA1 are connected with an inductor L2 to form a power control switch main loop; the alternating current can be reliably cut off or conducted no matter in positive and negative half cycles, and the accurate digital front edge/back edge cut angle dimming control of the alternating current power supply is achieved; in this embodiment, the hall current sensor is a712 or a714 chip, but is not limited thereto.

When the short-circuit protection alarm is triggered, a low-level alarm signal output by ERR at the 6 th pin of U10 is coupled to OVERA pins of an MCU of the microprocessor through RA 14. In general, if the load is a linear pure resistive load, the protection action is proper, but if the load is a capacitive load, for example, when a plurality of LED lamps are connected, the initial power-on impact current is large due to the power rectification filter capacitor of the driver, the protection can be triggered, but when the load works normally, the current is not large, and the problem of misjudgment exists; for this reason, the VPA pin level of the microprocessor MCU is set for each conversion, and the OVERA pins of the MCU are detected once; if the detection level is high, resetting the protection counter; once the OVERA th pin of the MCU detects the low level of the protection trigger, the protection counter is added with 1, whether the counter is smaller than a certain value is judged, if so, the 5 th pin of the U10 is pulled up after the CLOSA th pin of the MCU is pulled down by 1us, and the U10 is reset; otherwise, judging that the circuit is short, starting a timer, outputting a low level by the TRGA pin of the microprocessor MCU within a timing time, keeping the CLOSA pin unchanged, not resetting U10, driving in a protection locking state, outputting the TRGA pin of the microprocessor MCU according to a normal state after timing is finished, triggering a zero crossing point, resetting a protection counter, pulling down the CLOSA pin by 1us, pulling up, and resetting U10. The protection of avoiding misjudging short circuit by the load of the capacitive load or other thermosensitive devices is achieved, and meanwhile, the protection can be realized when faults occur rapidly and reliably, and the damage of the MOSFET devices Q1 and Q2 due to the short circuit is avoided. The capacitive load and other nonlinear loads are ensured, and limit large current can be generated at intervals in the transient process, so that the damage of devices is avoided, and the application range is effectively widened.

In the phase-cut power control circuit 200, when the MOSFET transistors Q1 and Q2 are turned on, load current is input from the 3 rd IP-, 4 th IP-pins of the current-sensing hall device UA1, the 1th ip+, 2ip+ pins are output, and the induced voltage generated by flowing through the current-sensing hall device UA1 is output from the 7 th pin VO of the UA 1. One path of voltage VIA1 output from the 7 th pin VO of UA1 is transmitted to the 2 nd pin reverse input end of the operational amplifier integrated chip U11A through a resistor RA17 to be input, and RA23 is connected between the 1 st output end and the 2 nd pin reverse input end of the U11A in a bridging mode to form a proportional amplifier. The output voltage VIA1 is amplified by the operational amplifier U11A and is output from the 1 st pin output end of the U11A. the signal output from U11A is input from the 12 th pin positive input end of the operational amplifier U11D through a resistor RA19, amplified by the operational amplifier U11D and output from the 14 th pin output end. The signal output from U11D is sent to the A/D input port IA of the microprocessor MCU through the resistor RA18, A/D detection sampling is carried out, accurate value of current detection is carried out, voltage detection value is combined, the work rate is judged through MCU operation, and normal output or constant low level over-power protection is carried out through TRGA control of the MCU. The 14-pin DESAT of the MOSFET drive control integrated chip U10 is connected with a capacitor CA5 and a resistor RA11, and the other end of the resistor RA11 is respectively connected with resistors RA5, RA6 and RA12; RA5 is connected with a fast recovery diode DA2, DA2 is connected with the drain electrode of a MOSFET (metal oxide semiconductor field effect transistor) QA2, and a source drain conduction voltage drop detection circuit of QA2 is formed; RA6 is connected with a fast recovery diode DA3, and the other end of RA6 is connected with the drain electrode of a MOSFET (metal oxide semiconductor field effect transistor) tube QA1 to form a source drain conduction voltage drop detection circuit of QA 1; the positive end of the switching diode DA4 is connected with the middle connection point of RA6 and DA3, the positive end of the switching diode DA6 is connected with the middle connection point of RA5 and DA2, the negative end of the switching diode DA4 and DA6 are connected with the base electrode of the triode QA3 together, and a resistor RA29 is connected between the base electrode and the collector electrode of QA3 in parallel; The other end of RA12 is connected with the emitter of QA3, and forms a voltage limit value adjustable gate circuit with a constant current source in the 14 feet of U10; the non-precision short-circuit current adjustable protection control circuit 900A is formed by matching a constant level comparator in the pin 14 of the U10 and a MOSFET driving gate latch controller circuit. When the 1 st pin of the U10 inputs the high level, the microprocessor MCU outputs the 5 th pin RST connected with the U10 through the CLOSA pin. When the voltage is at a high level, U10 drives QA1 and QA2 to be started through 11 feet PWMout, meanwhile, 14 th feet DESAT outputs 0.25mA constant current, the current provides DA2 forward bias current through R11 and part of the current through RA5, drain-source voltage difference of QA2 is detected through drain electrode to source electrode of QA2, and QA3 base level is provided through DA 6; A part of the positive bias current of DA3 is provided through RA6, drain-to-source voltage difference of QA1 is detected through drain-to-source of QA1, and base level of QA3 is provided through DA 4; due to the unidirectional conduction characteristics of the diodes DA4, DA6, the base level of QA3 is at the same potential as the drain higher potential of QA1, QA 2. The current consumption of the voltage drop detection circuit portion, the maximum current is about i1= (7-0.7-0.25×ra11)/(RA 5+ra 6)/(RA 5×ra 6) =5.48/50k=0.11 mA (the calculation formula is based on the threshold level 7V of the currently used device internal comparator, and a set of external matching design parameters, not limited to the selection parameters); Another fraction of the current is at a minimum of about i2=0.25-I1, stepped down by RA12 (lowest voltage drop vra12=i2×ra 12), to the emitter of QA3, to the collector, back to COMA; the minimum total voltage v2=0.25×ra11+i2×ra12 from the emitter of the 14 pins DESAT to QA3 of U10, then the voltage v14=v2+0.7+vds of the 14 pins of U10 is constant when the circuit parameters are determined, the voltage drop V2 is constant, the size of the VU14 varies with the size of VDS, vds=rds×io, RDS is determined by the selected components, so the size of V14 directly reflects the size of IO; When the load end has abnormal heavy current, drain-source opening voltage drops VDS of QA1 and QA2 are increased, and when the U10 recognizes that the load end has abnormal short-circuit current through a constant voltage comparator in a 14-pin DESAT, the 11 pin of the U10 is pulled down through an internal latch circuit, so that a rapid hardware protection function is achieved; CA5 plays a role in filtering out transient interference pulses; and meanwhile, the alarm level is output from the 6 th pin of the U10 and is output to the OVERA th pin of the MCU through the RA14 to inform the MCU of abnormality.

The short-circuit protection current can be set through parameters of source-drain resistance RDS, RA11 and RA12 of the MOS tube; the protection circuit has the characteristics of simplicity and reliability, and high response speed; however, since the current detection depends on the on-resistance RDS of the MOSFET, the smaller the RDS is, the larger the action discreteness of the protection current threshold along with the deviation of the VZ parameter of the device is; because the VZ value is 7+/-0.5V, when the output control power reaches more than 2000W, the maximum deviation reaches more than 20A when RDS is less than 0.025 omega, and the deviation is very large; in addition to the MOSFET device parameter tolerance, the deviation value easily exceeds the device bearable range, and the risk of protection failure increases. The current protection circuit can be used alone, typically when the MOSFET selected for Q1, Q2 has an RDS >50mΩ. Otherwise, an accurate limit value adjustable protection control circuit is added.

The transient suppression diode TVSA and the resistor RA3 are connected in parallel to form a gate-source overvoltage protection circuit 400, one end of which is connected with the pin U10, and the other end of which is connected with the sources of QA1 and QA2 and with a reference zero level point COMA. The gate-source overvoltage protection circuit 400 ensures that the Vgs voltage is within specification and is not broken down by the overvoltage.

The resistor RA1 is connected in parallel with the capacitor CA1 and then connected in series with the bidirectional transient suppression diode DA5, and two ends of the DA5 are respectively connected with an alternating current line input end and a1 st pin 2 of the UA1 to form a MOSFET drain-source overvoltage peak absorption circuit 600; in the trailing edge dimming state, when QA1 and QA2 are switched from on to off, the voltage between the drain and source pins of QA1 and QA2 is changed greatly due to the line inductance, when the voltage exceeds the threshold voltage of DA5 (bidirectional TVS is selected), DA5 is conducted to charge CA1, CA1 discharges through RA1 when the voltage is lower than the threshold voltage of DA5, overvoltage spikes between the drain and source pins of QA1 and QA2 are eliminated, and the situation that the drain and source pins of MOSFET tubes QA1 and QA2 are damaged by overvoltage impact breakdown is ensured.

The two ends of the piezoresistor ZNRA are connected between the on-line power supply input and the zero line to form an input overvoltage protection 600; when the input voltage exceeds the threshold voltage of the piezoresistor ZNRA, ZNRA is conducted, the input voltage is clamped in the threshold voltage, the input voltage is ensured to be safe, and the MOSFET is protected.

The resistor RA20 and the capacitor CA7 are connected in parallel and then connected with the bidirectional transient suppression diode DA1 in series, and the two ends of the resistor RA20 and the capacitor CA7 are respectively connected with an output end and a zero line end to form an output overvoltage protection circuit 900; when the voltage of the liability terminal is lower than the DA1 threshold voltage, CA7 discharges through RA20 to ensure the safety of loop voltage and eliminate overvoltage peak generated by the load terminal. The dimming loop is jointly protected through multiple dimensions, and overvoltage dangerous spike voltage on the input end, the output end and the MOSFET is absorbed, so that safe application is ensured.

The dimming circuit shown in fig. 1 further includes a high-frequency filter circuit 800 for filtering the high-frequency interference of the load end, where an inductor L2 of the circuit is connected to the 1 st pin 2 of UA1 and the output end, and two ends of a capacitor CA11 are respectively connected between the 1 st pin 2 of UA1 and the zero line;

in order to further ensure the switching performance and fully utilize the device characteristics, QA1 and QA2 can be selected to meet the following key parameter requirements:

a) According to specific rated current Io specification requirements, selecting MOSFETs with different avalanche current Iar specification values: iar is greater than or equal to Io;

b) The MOSFET drain current Id is selected according to the applicable peak current Ip range, where Ip is of the value specification: id is more than or equal to Ip;

c) The VDSS drain-source voltage is more than or equal to 600V;

d) The MOSFET switching speed dv/dt is more than or equal to 50V/ns;

e) The power consumption umbrella curve meets the current ID > ISHORT short-circuit protection current of a 10 mu s safety voltage current curve 580V;

f) IDSS zero gate voltage drain current is less than or equal to 50 μa.

The Iar, io, id, ip and VDSS, ID, ISHORT, IDSS are avalanche current, rated current of the dimmer, drain current, peak current, drain-source voltage, drain current, short-circuit protection current and saturated drain-source current of the MOSFET respectively.

Embodiment two:

Referring to fig. 2, in the second embodiment, on the basis of the first embodiment, an accurate current limit value adjustable short-circuit protection control circuit 900B is added, and the circuit is used in a high-power MOSFET device circuit.

One end of the accurate current limit value adjustable short-circuit protection control circuit 900B is connected with a UA 17 pin, and the other end is connected to the grid electrode of the QA3 through an optocoupler chip UA 2. Specifically, the current induction voltage VIA1 is output from 7 pins of UA1, enters the reverse input end of U11B through RA28, the positive input end of 5 th pin of op-amp U11B is connected with a resistor divider formed by connecting resistors RA37, RA38 and capacitor CA9 through RA26, and the bias level VP1 (usually set to a value lower than the intermediate potential) is provided to form a negative peak detection comparator; when VIA1 is less than VP1, the output end of the 7 th pin of U11B outputs high level, and is coupled to the first pin of UA2 through RA27 and DA 8; the current induction voltage VIA1 is output from the pin 7 VO of the UA1, the other path enters the positive input end of the U11C through the RA33, the 9 th pin reverse input end of the operational amplifier U11C is connected with a resistor divider formed by connecting resistors RA30 and RA34 and a capacitor CA10 through RA31, and the provided bias level VP2 (which is usually set to be higher than the value of the intermediate potential) forms a positive peak detection comparator; when VIA1 is larger than VP2, the output end of the 8 th pin of U11 outputs high level, and is connected with DA7 through a resistor RA32, and DA7 is connected with the 1 st pin of the optocoupler chip UA 2; when the high potential is input by the No. 1 pin of UA2, the No. 3 pin is driven by the UA2 optocoupler to output the high potential, the base potential of QA3 is pulled up, the comparator connected with the DESAT of the No. 14 pin of U10 is triggered to output the high potential, the U10 is triggered to output protection inhibition and alarm, the protection can be triggered timely whenever the current exceeding the set value occurs, and otherwise, the normal operation is realized. The circuit can realize accurate short-circuit current limit setting because the Hall current sensor has high precision and the voltage limit value can be accurately regulated through the two bias voltage dividing resistors, thereby effectively ensuring the accurate and reliable protection of the short-circuit current of the high-power dimming product of the MOSFET with low RDS.

The foregoing is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way.

Claims (7)

1. A MOSFET dimming circuit comprising: zero crossing detection circuit, phase cut angle power control circuit, current detection circuit, characterized by still includes: the system comprises a grid source overvoltage protection circuit, a MOSFET drain source overvoltage protection and spike absorption circuit, an input overvoltage protection circuit, an output overvoltage protection circuit and an adjustable short-circuit protection control circuit;

The input end of the zero-crossing detection circuit is connected with an alternating current power supply AC, one path of the output end is connected with an A/D port AVC pin of the microprocessor MCU for input voltage detection, and the other path of the output end is connected with a VPA port of the MCU for processing a time reference coordinate point of phase control output and interrupting processing synchronous trigger signals;

The phase angle-cutting power control circuit comprises the MCU, a MOSFET optocoupler isolation driving chip U10, MOSFET tubes QA2 and QA1, a resistor and a capacitor; the MCU converts the signal input by the zero crossing detection circuit into a PWM signal, outputs the PWM signal from TRGA pins and is connected to the MOSFET optocoupler isolation driving chip U10 for driving the MOSFET;

The current detection circuit flows in through pins 3 and 4 of a Hall current sensing device UA1 by drain-source currents of MOSFET transistors Q1 and Q2, flows out through pins 1 and 2, and the induced voltage is output from a 7 th pin of the Hall current sensing device and is connected to an IA A/D port of the MCU through a resistor, a capacitor and an operational amplifier circuit;

the grid source overvoltage protection circuit is formed by connecting a resistor RA3 and a transient suppression diode TVSA1 in parallel; one end of the drive output 11 pin PWMout of the optocoupler isolation drive chip U10 is connected, and the other end of the drive output 11 pin PWMout is connected with the source electrodes of the MOSFET transistors Q1 and Q2 and is connected with a reference zero level point COMA;

The MOSFET drain-source overvoltage protection and peak absorption circuit is formed by connecting a resistor RA1 and a capacitor CA1 in parallel and then connecting a bidirectional transient suppression diode DA5 in series; one end of the Hall current sensor UA1 is connected with the input of a power line, and the other end of the Hall current sensor UA1 is connected with the 1 st pin 2;

the input overvoltage protection circuit consists of a piezoresistor; one end of the power supply is connected with an alternating current input ACL, and the other end of the power supply is connected with an alternating current zero line ACN, so that clamping of input voltage is realized;

The output overvoltage protection circuit is formed by connecting a resistor RA20 and a capacitor CA7 in parallel and connecting a bidirectional transient suppression diode DA1 in series; the two ends of the power supply are respectively connected between the output end and the zero line;

The adjustable short-circuit protection control circuit comprises an imprecise current limit value adjustable short-circuit protection control circuit; the circuit comprises three ends, wherein one end of the three ends is connected with a 14 pin of the optocoupler isolation driving chip U10, and the other two ends of the three ends are respectively connected with the leak marks of the MOSFET tubes QA1 and QA2 through fast recovery diodes; the constant bias current provided by the pin U10 of the optocoupler isolation driving chip is respectively passed through a resistor RA5, a fast recovery diode DA2 and a switching diode DA6 to form a source-drain on-voltage detection circuit of QA 2; the resistor RA6 and the fast recovery diode DA3, and the switching diode DA4 form a source-drain on-voltage detection circuit of QA 1; transistor QA3, resistors RA12, RA29, RA11 constitute a short-circuit current limit adjustment circuit.

2. The MOSFET dimming circuit according to claim 1, wherein the MOSFET tubes QA1, QA2 select the following parameters:

a) Iar is equal to or greater than Io, wherein Iar is MOSFET avalanche current and Io is dimmer rated current;

b) Id.gtoreq.ip, where Id is MOSFET drain current and Ip is peak current

C) VDSS is greater than or equal to 600V, wherein VDSS is the drain-source voltage of the MOSFET;

d) The MOSFET switching speed dv/dt is more than or equal to 50V/ns;

e) The power consumption umbrella curve meets the current ID > ISHORT of a 10 mu s safety voltage current curve 580V, wherein ID is MOSFET drain current, and ISHORT is short-circuit protection current;

f) IDSS is less than or equal to 50 μa, where IDSS is the MOSFET saturated drain-source current.

3. The MOSFET dimming circuit of claim 1, further comprising an output high frequency filter circuit comprising an inductance L2 and a capacitance CA 11; the inductance L2 is connected with the No. 1 and No. 2 pin of the UA1 and the output end, and two ends of the capacitor CA11 are respectively connected between the No. 1 and No. 2 pin of the UA1 and the zero line.

4. The MOSFET dimming circuit of claim 1, wherein the adjustable short circuit protection control circuit further comprises an accurate current limit adjustable short circuit protection control circuit; one end of the accurate current limit value adjustable short-circuit protection control circuit is connected with the 7 th pin of a Hall current accurate sensing device UA1, and the accurate current limit value adjustable short-circuit protection control circuit is respectively connected with a positive peak value comparator consisting of an operational amplifier U11C, resistors RA30 and RA34 through RA33 and a negative peak value comparator consisting of an operational amplifier U11B, resistors RA37 and RA38 through RA 28; the output end of the operational amplifier U11B, U C is connected with the base electrode of the QA3 through an optocoupler chip UA 2.

5. The MOSFET dimmer circuit of claim 1, wherein the microprocessor is an MSP430FR6972IPMR chip.

6. The MOSFET dimming circuit of claim 1, wherein the optocoupler isolation driver chip is an a316J chip.

7. The MOSFET dimmer circuit of claim 1, wherein the hall current sensor is an a712 or a714 die.