Output overcurrent rapid protection restart circuit and method of non-isolated driving flyback power supply

Abstract

The invention provides an output overcurrent quick protection restart circuit and method of a non-isolated driving flyback power supply. The circuit comprises an output current acquisition circuit, an output overcurrent quick trigger circuit, a pulse isolation circuit, a protection trigger response circuit and a PWM (Pulse Width Modulation) slow start circuit, the output current acquisition circuit is used for acquiring a current signal output by the flyback high-voltage power supply and converting the current signal into a voltage signal; when the voltage signal reaches a protection voltage threshold and lasts for a time threshold, the output overcurrent quick trigger circuit is triggered; the pulse isolation circuit converts the trigger signal into a pulse signal; and the protection trigger response circuit controls the turn-off of the PWM pulse width modulation slow start circuit, and performs slow start of the power supply according to a preset time interval. Large current impact of a power circuit and the use number of power devices can be reduced to a certain extent, the reliability of a circuit system is improved, the power supply cost is controlled, the power density of the power supply is improved, and good applicability is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of output overcurrent protection of a non-isolated driven flyback high voltage power supply, and in particular relates to an output overcurrent fast protection restart circuit and method for a non-isolated driven flyback power supply. Background Art

[0002] At present, the output overcurrent protection circuit of the flyback high-voltage power supply using non-isolated drive is generally: the signal of the primary current of the converter is collected through the current detection (CS) end of the PWM controller. When the flyback converter outputs overcurrent, it detects whether the primary current collection signal of the converter reaches the protection threshold of the CS end. If the protection threshold is reached, the converter outputs constant power, and its output voltage drops to avoid further increase of the output current, thereby realizing output overcurrent protection. However, the overcurrent protection method has a slow response speed. When a super-large current narrow pulse appears on the output side, the power supply cannot be quickly shut down, which may cause overcurrent stress damage or failure of the components on the rectifier side of the converter. If the converter output overcurrent time is long, it may cause the power supply to be used overpowered for a long time, and then cause the power supply to be damaged or even burned due to heat accumulation. Therefore, in summary, the general overcurrent protection circuit of the flyback high-voltage power supply using non-isolated drive currently has a slow response speed when the load changes on the output side of the power supply are complex or the working conditions are bad, and it is not easy to realize fast and reliable protection of the circuit. Summary of the invention

[0003] The present invention provides an output overcurrent fast protection restart circuit and method for a non-isolated driven flyback power supply, aiming to solve the problem that a general overcurrent protection circuit of a flyback high-voltage power supply currently using a non-isolated drive has a slow response speed when the load on the output side of the power supply changes complexly or the working conditions are harsh, and it is difficult to achieve fast and reliable protection for the power supply.

[0004] In order to achieve the above object, the present invention adopts the following technical scheme:

[0005] The present invention provides an output overcurrent fast protection restart circuit for a non-isolated drive flyback power supply, the circuit comprising an output current acquisition circuit, an output overcurrent fast trigger circuit, a pulse isolation circuit, a protection trigger response circuit, and a PWM pulse width modulation slow start circuit; wherein:

[0006] The output current acquisition circuit is used to collect the current signal output by the flyback high-voltage power supply, and convert the current signal into a voltage signal and send it to the output overcurrent fast trigger circuit;

[0007] The output overcurrent fast trigger circuit is preset with a protection voltage threshold and a time threshold; when the voltage signal reaches the protection voltage threshold and lasts for a duration threshold, the output overcurrent fast trigger circuit is triggered and sends a trigger signal to the pulse isolation circuit;

[0008] The pulse isolation circuit is used to convert the trigger signal into a pulse signal and then transmit it to the protection trigger response circuit;

[0009] The protection trigger response circuit is used to control the shutdown of the PWM pulse width modulation slow start circuit based on the pulse signal through the single-ended drive controller of the PWM pulse width modulation slow start circuit, and to perform slow start of the power supply according to a preset time interval.

[0010] In some implementations, the output current acquisition circuit acquires the current signal output by the flyback high-voltage power supply through a current sampling resistor or a current sensor.

[0011] In some embodiments, the output current acquisition circuit converts the current signal of the current sampling resistor into a voltage signal, adjusts the ratio of the differential amplifier circuit through the differential adjustment resistor, and sets the protection voltage threshold and time threshold in combination with the trigger voltage of the output overcurrent fast trigger circuit.

[0012] In some embodiments, the output current acquisition circuit includes a current sampling resistor R16, a sampling filter capacitor C9, a differential adjustment resistor R12, a differential adjustment resistor R13, a differential adjustment resistor R14, a differential adjustment resistor R15, a filter capacitor C7, a filter capacitor C8, an operational amplifier, and an operational amplifier power supply current limiting protection circuit; wherein:

[0013] R16 and C9 are connected in parallel, one end of R14 is connected to the current inflow end of R16 and the other end is connected to the non-inverting end of the operational amplifier, R12 and C7 are connected in parallel, one end is connected to the non-inverting end of the operational amplifier and the other end is connected to the power supply ground Gnd2 of the operational amplifier; one end of R15 is connected to the current outflow end of R16 and the other end is connected to the inverting end of the operational amplifier, R13 and C8 are connected in parallel, one end is connected to the inverting end of the operational amplifier and the other end is connected to the output end of the operational amplifier; the operational amplifier power supply current limiting protection circuit is used for current limiting protection of the circuit.

[0014] Furthermore, the operational amplifier power supply current limiting protection circuit includes an operational amplifier power supply current limiting protection resistor R10 and a power supply filter capacitor C5, each of which has one end connected to the positive power supply terminal of the operational amplifier, and an operational amplifier power supply current limiting protection resistor R11 and a power supply filter capacitor C6, each of which has one end connected to the negative power supply terminal of the operational amplifier. The other end of R10 is connected to the circuit power supply positive terminal Vcc+, the other end of R11 is connected to the circuit power supply negative terminal Vcc-, and the other ends of C5 and C6 are connected to the power supply ground Gnd2 of the operational amplifier.

[0015] In some embodiments, the output overcurrent fast trigger circuit includes a current limiting resistor R9, a voltage stabilizing diode V4, an NPN transistor Q3, an adjustment capacitor C4, and a resistor R8; wherein:

[0016] V4 and R9 are connected in series, one end of R9 is connected to the output current collection circuit and the other end is connected to the cathode of V4, the anode of V4 is connected to the base of Q3, the emitter of Q3 is connected to the power supply ground Gnd2 of the operational amplifier, and the collector of Q3 is connected to the pulse isolation circuit; C4 and R8 are connected in parallel with one end connected to the base of Q3 and the other end connected to the emitter of Q3.

[0017] In some implementations, the pulse isolation circuit implements magnetic isolation between the primary side and the secondary side of the flyback power supply through a pulse transformer.

[0018] In some embodiments, the pulse isolation circuit includes a current limiting resistor R7, a pulse transformer T1, a diode V3, and a magnetic reset resistor R6; wherein:

[0019] One end of R7 is connected to the positive power supply terminal of the circuit, and the other end is connected to the 1st pin of T1; the 2nd pin of T1 is connected to the output overcurrent fast trigger circuit; after R6 is connected in parallel with the N2 winding of T1, the 3rd pin of T1 is connected to the anode of V3, and the 4th pin of T1 is connected to the power supply ground Gnd1 of the PWM pulse width modulator; the cathode of V3 is connected to the protection trigger response circuit; where:

[0020] Pin 1 and pin 3 of the pulse transformer T1 are the same-name terminals, and pin 2 and pin 4 are the same-name terminals.

[0021] In some implementations, the protection trigger response circuit controls the output of the PWM pulse width modulation soft start circuit to synchronize the discharge reset of the soft start circuit so as to shut down the output of the flyback high voltage power supply.

[0022] The present invention also provides an output overcurrent fast protection restart method of an output overcurrent fast protection restart circuit of a non-isolated drive flyback power supply, comprising the following steps:

[0023] S1, the output current acquisition circuit acquires the current signal output by the flyback high-voltage power supply, converts the current signal into a voltage signal and sends it to the output overcurrent fast trigger circuit;

[0024] S2, the output overcurrent fast trigger circuit presets the protection voltage threshold and time threshold; when the voltage signal reaches the protection voltage threshold and lasts for the duration threshold, the output overcurrent fast trigger circuit is triggered and sends the trigger signal to the pulse isolation circuit;

[0025] S3, the pulse isolation circuit converts the trigger signal into a pulse signal and transmits it to the protection trigger response circuit;

[0026] S4. The protection trigger response circuit controls the shutdown of the PWM pulse width modulation slow start circuit based on the pulse signal through the single-ended drive controller of the PWM pulse width modulation slow start circuit, and performs a slow start of the power supply according to a preset time interval.

[0027] Compared with the prior art, the output overcurrent fast protection restart circuit and method of a non-isolated drive flyback power supply of the present invention has the following beneficial effects:

[0028] The invention discloses an output overcurrent fast protection restart circuit of a non-isolated driven flyback power supply, the circuit includes an output current acquisition circuit, an output overcurrent fast trigger circuit, a pulse isolation circuit, a protection trigger response circuit, and a PWM pulse width modulation slow start circuit; wherein: the output current acquisition circuit is used to acquire the current signal output by the flyback high-voltage power supply, and convert the current signal into a voltage signal and then send it to the output overcurrent fast trigger circuit; the output overcurrent fast trigger circuit is preset with a protection voltage threshold and a time threshold; when the voltage signal reaches the protection voltage threshold and lasts for a duration threshold, the output overcurrent fast trigger circuit is triggered and the trigger signal is sent to the pulse isolation circuit; the pulse isolation circuit is used to convert the trigger signal into a pulse signal and then transmit it to the protection trigger response circuit; the protection trigger response circuit is used to control the shutdown of the PWM pulse width modulation slow start circuit based on the pulse signal through the single-ended drive controller of the PWM pulse width modulation slow start circuit, and perform a slow start of the power supply according to a preset time interval. Based on the above, the invention aims at the problem of output overcurrent of a flyback high-voltage power supply using a non-isolated drive, and proposes a flyback high-voltage power supply output overcurrent fast protection restart circuit with a simple structure, high reliability, fast response speed, and autonomous shutdown and restart of the power supply after overcurrent. Based on the output overcurrent protection requirements of a non-isolated driven flyback high-voltage power supply under complex load changes or harsh working conditions, the present invention proposes an output overcurrent fast protection restart circuit, which is composed of several functional circuits such as an output current acquisition circuit, an output overcurrent fast trigger circuit, a pulse isolation circuit, a protection trigger response circuit, and a PWM pulse width modulation slow start circuit. It can quickly respond to the current above a certain threshold output by the non-isolated driven flyback high-voltage power supply (the larger the current, the faster the response time), and perform power supply shutdown and restart adjustment, thereby avoiding the large current impact of the flyback high-voltage power supply output short-circuit overcurrent on the power supply itself and the primary bus, and realizing reliable control of the flyback high-voltage power supply output discharge current. By adopting the circuit of the present invention, the large current impact of the power circuit can be reduced to a certain extent, thereby reducing the number of power devices used, and improving the reliability of the entire circuit system, which has relatively important practical significance for improving the power density, reliability and cost of controlling the power supply. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The drawings in the specification are used to provide further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0030] Figure 1It is a schematic diagram of the overall architecture of an output overcurrent fast protection restart circuit in an output overcurrent fast protection restart circuit and method for a non-isolated drive flyback power supply of the present invention;

[0031] Figure 2 The present invention provides a schematic diagram of the principles of an output current acquisition circuit, an output overcurrent fast trigger circuit, a pulse isolation circuit, a protection trigger response circuit, and a PWM pulse width modulation slow start circuit in an output overcurrent fast protection restart circuit and method of a non-isolated drive flyback power supply. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0033] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0035] In the description of the embodiments of the present invention, it should be noted that if the terms "upper", "lower", "horizontal", "inner", etc. indicate an orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the invention is usually placed when in use, it is only for the convenience of describing the present invention and simplifying the description, and does 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. In addition, the terms "first", "second", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0036] In addition, if the term "horizontal" appears, it does not mean that the component must be absolutely horizontal, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", which does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0037] In the description of the embodiments of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal connection of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0038] For the fast overcurrent protection and restart mechanism of non-isolated drive flyback power supply, through the carefully designed circuit architecture, it can realize fast monitoring of power supply output current, overcurrent protection triggering, signal isolation, protection response execution and soft start recovery after fault, so as to ensure the stability and reliability of the power supply system.

[0039] like Figure 1 As shown, the present invention proposes an output overcurrent fast protection restart circuit for a non-isolated drive flyback power supply, the circuit includes an output current acquisition circuit, an output overcurrent fast trigger circuit, a pulse isolation circuit, a protection trigger response circuit, and a PWM pulse width modulation slow start circuit; wherein:

[0040] The output current acquisition circuit is used to collect the current signal output by the flyback high-voltage power supply, and convert the current signal into a voltage signal and send it to the output overcurrent fast trigger circuit;

[0041] The output overcurrent fast trigger circuit is preset with a protection voltage threshold and a time threshold; when the voltage signal reaches the protection voltage threshold and lasts for a duration threshold, the output overcurrent fast trigger circuit is triggered and sends a trigger signal to the pulse isolation circuit;

[0042] The pulse isolation circuit is used to convert the trigger signal into a pulse signal and then transmit it to the protection trigger response circuit;

[0043] The protection trigger response circuit is used to control the shutdown of the PWM pulse width modulation slow start circuit based on the pulse signal through the single-ended drive controller of the PWM pulse width modulation slow start circuit, and to perform slow start of the power supply according to a preset time interval.

[0044] The present invention uses a current sampling resistor or a current sensor to collect the output current of a flyback high-voltage power supply and converts it into a voltage signal, which is the basis for subsequent protection judgment. The present invention presets a protection voltage threshold and a time threshold. When the converted voltage signal exceeds the protection voltage threshold and the duration reaches the time threshold, the trigger circuit is activated and an overcurrent protection signal is issued. The present invention realizes magnetic isolation of the signal through components such as a pulse transformer, ensures electrical isolation between the primary side (input side) and the secondary side (output side), and improves the safety and reliability of the system. After receiving the overcurrent protection pulse signal, the protection trigger response circuit quickly shuts off the power supply output by controlling the single-ended drive controller of the PWM pulse width modulation slow start circuit to prevent damage caused by excessive current. In actual working conditions, the single-ended drive controller can be selected but not limited to UC1845. At the same time, the power supply is slowly started according to a preset time interval to reduce the current impact when starting again.

[0045] The output overcurrent fast protection restart circuit and method of a non-isolated drive flyback power supply proposed by the present invention are further described in detail below through specific embodiments.

[0046] Output current acquisition circuit: The output current of the flyback high-voltage power supply is collected through a current sampling resistor (or current sensor), the current signal is converted into a voltage signal, and sent to the output overcurrent fast trigger circuit;

[0047] Output overcurrent fast trigger circuit: This circuit receives the output current sampling signal. When the flyback high-voltage power supply has an output overcurrent, the output current sampling signal reaches the protection threshold voltage and lasts for a period of time (the time is set according to the needs and can reach μs level at the fastest). Then, the circuit is triggered and the trigger signal is sent to the pulse isolation circuit.

[0048] Pulse isolation circuit: This circuit receives the overcurrent protection trigger signal, converts the signal into a pulse signal, transmits it to the protection trigger response circuit, and realizes magnetic isolation between the primary and secondary sides of the flyback power supply through a pulse transformer;

[0049] Protection trigger response circuit: This circuit receives a pulse signal, controls the output of the PWM pulse width modulation circuit to shut down, and synchronizes the discharge reset of the slow start circuit, thereby shutting down the output of the flyback high voltage power supply;

[0050] PWM pulse width modulation slow start circuit: The PWM pulse width modulator COMP terminal (the output terminal of the internal error amplifier) ​​is controlled by the protection response circuit and the slow start circuit, so as to realize the soft start of the power supply after a period of time (the time is set according to the demand) when the output of the flyback high-voltage power supply is overcurrent, and the flyback high-voltage power supply restores the output state before the overcurrent.

[0051] In the present invention, the output overcurrent fast protection restart circuit based on the non-isolated drive flyback power supply includes an output current acquisition circuit, an output overcurrent fast trigger circuit, a pulse isolation circuit, a protection trigger response circuit, and a PWM pulse width modulation slow start circuit, and its working mechanism is as follows:

[0052] like Figure 1 and Figure 2 As shown, in the present invention, the output current acquisition circuit is composed of a current sampling resistor R16, a sampling filter capacitor C9, four differential adjustment resistors, namely a differential adjustment resistor R12, a differential adjustment resistor R13, a differential adjustment resistor R14 and a differential adjustment resistor R15, two filter capacitors, namely a filter capacitor C7 and a filter capacitor C8, an operational amplifier, operational amplifier power supply current limiting protection resistors R10 and R11 and power supply filter capacitors C5 and C6.

[0053] Among them, the current sampling resistor R16 and the sampling filter capacitor C9 are connected in parallel; one end of the differential adjustment resistor R14 is connected to the current inflow end of the current sampling resistor R16, and the other end is connected to the non-inverting end of the operational amplifier; after the differential adjustment resistor R12 and the filter capacitor C7 are connected in parallel, one end is connected to the non-inverting end of the operational amplifier, and the other end is connected to the power supply ground Gnd2 of the operational amplifier; one end of the differential adjustment resistor R15 is connected to the current outflow end of the current sampling resistor R16, and the other end is connected to the inverting end of the operational amplifier; after the differential adjustment resistor R13 and the filter capacitor C8 are connected in parallel, one end is connected to the inverting end of the operational amplifier, and the other end is connected to the output end of the operational amplifier. One end of the operational amplifier power supply current limiting protection resistor R10 is connected to the circuit power supply positive terminal Vcc+, and the other end is connected to the positive power supply terminal of the operational amplifier; one end of the operational amplifier power supply current limiting protection resistor R11 is connected to the circuit power supply negative terminal Vcc-, and the other end is connected to the negative power supply terminal of the operational amplifier; one end of the power supply filter capacitor C5 is connected to the positive power supply terminal of the operational amplifier, and the other end is connected to the power supply ground Gnd2 of the operational amplifier; one end of the power supply filter capacitor C6 is connected to the negative power supply terminal of the operational amplifier, and the other end is connected to the power supply ground Gnd2 of the operational amplifier.

[0054] In the present invention, the output current acquisition circuit converts the current I flowing through the sampling resistor R16 into a voltage signal. The ratio of the differential amplifier circuit can be adjusted by adjusting the size of the resistors R12, R13, R14, and R15, and the output overcurrent protection threshold is set in combination with the trigger voltage of the subsequent output overcurrent fast trigger circuit.

[0055] In the present invention, the output overcurrent fast trigger circuit: the output overcurrent fast trigger circuit is composed of a current limiting resistor R9, a voltage stabilizing diode V4, an NPN transistor Q3 (trigger transistor), an adjustment capacitor C4 and a resistor R8.

[0056] Among them, one end of the current limiting resistor R9 is connected to the output end of the output current acquisition circuit operational amplifier, and the other end is connected to the cathode of the voltage-stabilizing diode V4; the voltage-stabilizing diode V4 is connected in series with the current limiting resistor R9, and the anode of the voltage-stabilizing diode V4 is connected to the base of the transistor Q3; the emitter of the transistor Q3 is connected to the power supply ground Gnd2 of the operational amplifier; the collector of the transistor Q3 is connected to the 2nd foot of the pulse isolation transformer T1 in the pulse isolation circuit; the regulating capacitor C4 is connected in parallel with the resistor R8, one end of which is connected to the base of the transistor Q3, and the other end is connected to the emitter of the transistor Q3, that is, the power supply ground Gnd2 of the operational amplifier.

[0057] The reverse breakdown voltage of the voltage zener diode V4 and the Vbe voltage of the transistor Q3 when it is turned on together constitute the trigger voltage; the current limiting resistor R9 limits the size of the breakdown current when the voltage zener diode V4 is reversely broken down to avoid damage to V4, and at the same time forms an RC voltage integration circuit with the capacitor C4, and the protection trigger time is adjusted by adjusting the size of R9 and C4; when the transistor Q3 is turned on, the N1 winding of the pulse transformer T1 generates a pulse current, and the resistor R7 in the pulse isolation circuit is the current limiting resistor at the moment of Q3 turning on. When the output voltage of the current acquisition circuit of the front stage is greater than the trigger voltage, the voltage zener diode V4 reversely breaks down, the capacitor C4 charges, the Vbe voltage of the transistor Q3 gradually increases, the Vce voltage gradually decreases, the current flowing through the N1 winding of the pulse transformer gradually increases, and the voltage of the N1 winding gradually increases; when the output overcurrent disappears, the output voltage of the front stage operational amplifier is less than the trigger voltage, the transistor Q3 is turned off, and the current flowing through the N1 winding of the pulse transformer gradually decreases to zero. This process causes the pulse transformer to generate a pulse signal.

[0058] In the present invention, the pulse isolation circuit is composed of a current limiting resistor R7, a pulse transformer T1, a diode V3 and a magnetic reset resistor R6.

[0059] Among them, one end of the current limiting resistor R7 is connected to the positive power supply terminal Vcc+ of the circuit, and the other end is connected to the 1st pin of the pulse transformer T1; the 2nd pin of the pulse transformer T1 is connected to the collector of the transistor Q3 in the output overcurrent fast trigger circuit; after the magnetic reset resistor R6 is connected in parallel with the N2 winding of the pulse transformer T1, the 3rd pin of the pulse transformer T1 is connected to the anode of the diode V3, and the 4th pin of the pulse transformer T1 is connected to the power supply ground Gnd1 of the PWM pulse width modulator; the cathode of the diode V3 is connected to one end of the current limiting resistor R17 in the protection trigger response circuit. The 1st and 3rd pins of the pulse transformer T1 are the same-named terminals, and the 2nd and 4th pins are the same-named terminals.

[0060] The pulse transformer T1 is controlled by the transistor Q3 in the output overcurrent fast trigger circuit. The on and off of the transistor Q3 causes the pulse transformer to generate a pulse signal and transmit it to the protection trigger response circuit. After the transistor Q3 is turned off, the magnetic reset resistor R6 completes the magnetic reset of the pulse transformer, and the ground wire isolation between the power supply ground Gnd2 of the operational amplifier and the power supply ground Gnd1 of the PWM pulse width modulator is achieved through the pulse transformer T1, that is, the primary and secondary ground wire isolation.

[0061] In the present invention, the protection trigger response circuit is composed of a current limiting resistor R17, an anti-interference capacitor C3, a resistor R5, an NPN transistor Q2 (protection trigger response transistor) and a current limiting resistor R4.

[0062] Among them, one end of the current limiting resistor R17 is connected to the cathode of the transistor V3 in the pulse isolation circuit, and the other end is connected to the base of the transistor Q2; after the anti-interference capacitor C3 is connected in parallel with the resistor R5, one end is connected to the base of the transistor Q2, and the other end is connected to the emitter of the transistor Q2, that is, the power supply ground Gnd1 of the PWM pulse width modulator; one end of the current limiting resistor R4 is connected to the COMP end of the PWM controller in the PWM pulse width modulation slow start circuit, and the other end is connected to the collector of the transistor Q2.

[0063] The function of the anti-interference capacitor C3 is to filter out high-frequency interference signals to avoid false protection actions caused by interference signals, so its capacitance should not be too large to avoid affecting the protection response time. The current limiting resistors R17 and R4 limit the size of the transient current when the transistor Q2 is turned on to avoid overcurrent in the transistor.

[0064] When overcurrent is triggered, transistor Q2 receives the pulse signal and turns on, the voltage at the COMP terminal of the PWM controller changes from a high level to a low level, the diode V2 turns on, the capacitor C1 discharges, the PWM controller has no output, and the flyback power supply is turned off; when the pulse signal disappears, the transistor Q2 turns off, the PWM controller starts slowly, and the power supply returns to the output state before the overcurrent.

[0065] In the present invention, the PWM pulse width modulation slow start circuit is composed of a PNP transistor Q1, a diode V1, a diode V2, a resistor R1, a resistor R2, a resistor R3, a capacitor C1, a capacitor C2, a PWM pulse width modulator and its peripheral circuits. It should be noted that the peripheral circuits are designed according to the specific requirements of the power supply. Figure 2 No specific description is given in the article.

[0066] Among them, one end of the resistor R1 is connected to the cathode of the diode V1, and the other end is connected to the Vref end of the PWM pulse width modulator; the anode of the diode V1 is connected to the common end of the capacitor C1 and the resistor R3; one end of the resistor R2 is connected to the Vref end of the PWM pulse width modulator, and the other end is connected to the anode of the diode V1; one end of the capacitor C1 is connected to the anode of the diode V1, and the other end is connected to the power supply ground Gnd1 of the PWM pulse width modulator; one end of the resistor R3 is connected to the anode of the diode V1, and the other end is connected to the base of the transistor Q1; the capacitor C2 is connected in parallel with the diode V2, the cathode of the diode V2 is connected to the COMP end of the PWM pulse width modulator, and the anode of the diode V2 is connected to the base of the transistor Q1; the emitter of the transistor Q1 is connected to the COMP end of the PWM pulse width modulator, and the collector of the transistor Q1 is connected to the power supply ground Gnd1 of the PWM pulse width modulator.

[0067] When the power supply starts or the overcurrent protection is triggered, the voltage at the COMP terminal of the PWM pulse width modulator and the initial terminal of capacitor C1 is 0 or less than the normal working voltage. At this time, the Vref terminal starts to charge capacitor C1 through resistor R2, and the transistor Q1 is turned on. After the voltage at the COMP terminal slowly rises to its normal working voltage, the power supply is slowly started. Under steady-state working conditions, the voltage difference between the Vref terminal and the COMP terminal of the PWM pulse width modulator is applied to resistors R2 and R3, and the diode V2 is turned on to avoid large reverse voltages at the b and e poles of the transistor; when the power supply is turned off, that is, when the PWM pulse width modulator is powered off, the capacitor C1 is quickly discharged to the Vref terminal through the diode V1 and the resistor R1 (the resistance of the resistor R1 is much smaller than that of the resistor R2). The slow start time of the power supply can be adjusted by adjusting the parameters of C1, R2, and R3.

[0068] In summary, the present invention provides a non-isolated drive flyback power supply output overcurrent rapid protection restart circuit and method, which can quickly respond to the current above a certain threshold of the power supply output, and perform power supply shutdown and restart adjustment, thereby avoiding the large current impact of the flyback high-voltage power supply output short-circuit overcurrent on the power supply itself and the primary bus, and realizing reliable control of the flyback high-voltage power supply output discharge current. The application of the present invention does not conflict with the conventional primary side overcurrent protection (CS end protection) of the flyback power supply, so through the application of the present invention, the overcurrent protection with dual thresholds and dual response times of the primary and secondary sides of the flyback power supply can be realized, further improving the reliability of the power supply. The present invention improves on the output current acquisition circuit and pulse width modulation circuit that must be used in general power supplies, adds an output overcurrent fast trigger circuit, a pulse isolation circuit, a protection trigger response circuit and a power-on slow start circuit, and avoids the power supply from being impacted by current by using a small number of pulse transformers, diodes, triodes, resistors, capacitors and other devices, thereby reducing the number of high-power devices used in the power supply, controlling the cost of the circuit, and improving the safety, reliability and automation of the circuit system. The circuit not only realizes overcurrent protection, but also reduces the current impact at startup through a slow start mechanism, plays a comprehensive protective role on the power supply and the load, and has better practical value.

[0069] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any ordinary technician in the industry can smoothly implement the present invention as shown in the specification and described above. However, any equivalent changes, modifications and evolutions made by technicians familiar with the profession without departing from the scope of the technical solution of the present invention using the technical content disclosed above are all equivalent embodiments of the present invention. At the same time, any equivalent changes, modifications and evolutions made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the technical solution of the present invention.

Claims

1. The output overcurrent fast protection restart circuit of the non-isolated drive flyback power supply is characterized in that: The circuit includes an output current acquisition circuit, an output overcurrent fast trigger circuit, a pulse isolation circuit, a protection trigger response circuit, and a PWM pulse width modulation slow start circuit; wherein: The output current acquisition circuit is used to acquire the current signal output by the flyback high-voltage power supply, and convert the current signal into a voltage signal and then send it to the output overcurrent fast trigger circuit; The output overcurrent fast trigger circuit is preset with a protection voltage threshold and a time threshold; when the voltage signal reaches the protection voltage threshold and lasts for a duration of the protection voltage threshold, the output overcurrent fast trigger circuit is triggered and sends a trigger signal to the pulse isolation circuit; The pulse isolation circuit is used to convert the trigger signal into a pulse signal and then transmit it to the protection trigger response circuit; The protection trigger response circuit is used to control the shutdown of the PWM pulse width modulation slow start circuit based on the pulse signal through the single-ended drive controller of the PWM pulse width modulation slow start circuit, and perform the slow start of the power supply according to the preset time interval.

2. The output overcurrent fast protection restart circuit of the non-isolated drive flyback power supply according to claim 1, characterized in that: The output current acquisition circuit acquires the current signal output by the flyback high-voltage power supply through a current sampling resistor or a current sensor.

3. The output overcurrent fast protection restart circuit of the non-isolated drive flyback power supply according to claim 2, characterized in that: The output current acquisition circuit converts the current signal of the current sampling resistor into a voltage signal, adjusts the ratio of the differential amplifier circuit through the differential adjustment resistor, and sets the protection voltage threshold and time threshold in combination with the trigger voltage of the output overcurrent fast trigger circuit.

4. The output overcurrent fast protection restart circuit of the non-isolated drive flyback power supply according to claim 1, characterized in that: The output current acquisition circuit includes a current sampling resistor R16, a sampling filter capacitor C9, a differential adjustment resistor R12, a differential adjustment resistor R13, a differential adjustment resistor R14, a differential adjustment resistor R15, a filter capacitor C7, a filter capacitor C8, an operational amplifier, and an operational amplifier power supply current limiting protection circuit; wherein: R16 and C9 are connected in parallel, one end of R14 is connected to the current inflow end of R16 and the other end is connected to the non-inverting end of the operational amplifier, R12 and C7 are connected in parallel, one end is connected to the non-inverting end of the operational amplifier and the other end is connected to the power supply ground Gnd2 of the operational amplifier; one end of R15 is connected to the current outflow end of R16 and the other end is connected to the inverting end of the operational amplifier, R13 and C8 are connected in parallel, one end is connected to the inverting end of the operational amplifier and the other end is connected to the output end of the operational amplifier; the operational amplifier power supply current limiting protection circuit is used for current limiting protection of the circuit.

5. The output overcurrent fast protection restart circuit of the non-isolated drive flyback power supply according to claim 4, characterized in that: The operational amplifier power supply current limiting protection circuit includes an operational amplifier power supply current limiting protection resistor R10 and a power supply filter capacitor C5, each of which has one end connected to the positive power supply terminal of the operational amplifier, and an operational amplifier power supply current limiting protection resistor R11 and a power supply filter capacitor C6, each of which has one end connected to the negative power supply terminal of the operational amplifier. The other end of R10 is connected to the circuit power supply positive terminal Vcc+, the other end of R11 is connected to the circuit power supply negative terminal Vcc-, and the other ends of C5 and C6 are connected to the power supply ground Gnd2 of the operational amplifier.

6. The output overcurrent fast protection restart circuit of the non-isolated drive flyback power supply according to claim 1, characterized in that: The output overcurrent fast trigger circuit includes a current limiting resistor R9, a voltage stabilizing diode V4, an NPN transistor Q3, an adjustment capacitor C4 and a resistor R8; wherein: V4 and R9 are connected in series, one end of R9 is connected to the output current collection circuit and the other end is connected to the cathode of V4, the anode of V4 is connected to the base of Q3, the emitter of Q3 is connected to the power supply ground Gnd2 of the operational amplifier, and the collector of Q3 is connected to the pulse isolation circuit; C4 and R8 are connected in parallel with one end connected to the base of Q3 and the other end connected to the emitter of Q3.

7. The output overcurrent fast protection restart circuit of the non-isolated drive flyback power supply according to claim 1, characterized in that: The pulse isolation circuit realizes magnetic isolation between the primary side and the secondary side of the flyback power supply through a pulse transformer.

8. The output overcurrent fast protection restart circuit of the non-isolated drive flyback power supply according to claim 1, characterized in that: The pulse isolation circuit includes a current limiting resistor R7, a pulse transformer T1, a diode V3 and a magnetic reset resistor R6; wherein: One end of R7 is connected to the positive power supply terminal of the circuit, and the other end is connected to the 1st pin of T1; the 2nd pin of T1 is connected to the output overcurrent fast trigger circuit; after R6 is connected in parallel with the N2 winding of T1, the 3rd pin of T1 is connected to the anode of V3, and the 4th pin of T1 is connected to the power supply ground Gnd1 of the PWM pulse width modulator; the cathode of V3 is connected to the protection trigger response circuit; where: Pin 1 and pin 3 of the pulse transformer T1 are the same-name terminals, and pin 2 and pin 4 are the same-name terminals.

9. The output overcurrent fast protection restart circuit of the non-isolated drive flyback power supply according to claim 1, characterized in that: The protection trigger response circuit controls the output of the PWM pulse width modulation slow start circuit to synchronize the discharge reset of the slow start circuit so as to shut down the output of the flyback high voltage power supply.

10. The output overcurrent fast protection restart method of the output overcurrent fast protection restart circuit of the non-isolated drive flyback power supply according to any one of claims 1 to 9, characterized in that: The steps include: S1, the output current acquisition circuit acquires the current signal output by the flyback high-voltage power supply, converts the current signal into a voltage signal and sends it to the output overcurrent fast trigger circuit; S2, the output overcurrent fast trigger circuit presets the protection voltage threshold and time threshold; when the voltage signal reaches the protection voltage threshold and lasts for the duration threshold, the output overcurrent fast trigger circuit is triggered and sends the trigger signal to the pulse isolation circuit; S3, the pulse isolation circuit converts the trigger signal into a pulse signal and transmits it to the protection trigger response circuit; S4. The protection trigger response circuit controls the shutdown of the PWM pulse width modulation slow start circuit based on the pulse signal through the single-ended drive controller of the PWM pulse width modulation slow start circuit, and performs a slow start of the power supply according to a preset time interval.

Images