Switching power supply circuitry

Abstract

The embodiment of the application discloses a switching power supply circuit system, which is applied to the technical field of electronic circuits. In the switching power supply circuit system, after a starting circuit starts a controller, the controller controls a first switch tube and a second switch tube to start conduction through a driving signal output end. In this way, after a first original side of a transformer connected with the first switch tube induces a voltage, a second original side of the transformer induces a voltage to supply power to the controller through a power supply input end of the controller. The drain electrode of the second switch tube is connected to the current detection input end of the controller, the source electrode of the second switch tube is connected to a high-voltage grounding end, and the capacitor-resistor circuit is connected between the drain electrode and the source electrode of the second switch tube. The source electrode of the first switch tube is connected between the capacitor-resistor circuit, and the current detection input end is directly short-circuited to the ground through the second switch tube. In the large-current starting process of the controller, a transient peak current is generated in the first switch tube, but the current detection input end is clamped at a low level, and the overcurrent protection is not triggered.

Description

Technical Field

[0001] This invention relates to the field of electronic circuit technology, and in particular to a switching power supply circuit system. Background Technology

[0002] Switching power supplies are indispensable core components in modern electronic devices, boasting advantages such as high efficiency, small size, and wide voltage regulation range. They primarily work by continuously switching a switching transistor on and off at extremely high frequencies (tens to hundreds of kHz), "chopping" the input DC voltage into a series of pulses. These pulses then pass through a transformer and filter circuit, ultimately restoring a stable DC voltage output.

[0003] To maintain a stable output voltage, the switching power supply circuit dynamically adjusts the pulse width (i.e., PWM pulse width modulation) through feedback control. The higher the output voltage, the narrower the pulse width, and vice versa. Summary of the Invention

[0004] This invention provides a switching power supply circuit system that prevents overcurrent protection from being accidentally triggered during the controller startup process.

[0005] This invention provides a switching power supply circuit system, including: a controller, a startup circuit, a drive circuit, and a current sampling circuit. The controller includes a power supply input terminal, a drive signal output terminal, and a current detection input terminal. The startup circuit is used to start the controller, and the startup circuit is connected to the power supply input terminal through a startup capacitor; The driving circuit includes a first switching transistor and a transformer. The gate driving terminal of the first switching transistor is connected to the driving signal output terminal, the drain of the first switching transistor is connected to the first primary side of the transformer, and the second primary side of the transformer is connected between the power supply input terminal and the high voltage ground terminal. The current sampling circuit includes a second switching transistor. The gate driving terminal of the second switching transistor is connected to the driving signal output terminal through a capacitor. The drain of the second switching transistor is connected to the current detection input terminal. The source of the second switching transistor is connected to the high voltage ground terminal. A capacitor-resistor circuit is connected between the drain and the source of the second switching transistor. The source of the first switching transistor is connected between the capacitor and resistor circuit.

[0006] As can be seen, in the switching power supply circuit system of this embodiment, after the controller is started by the startup circuit, the controller controls the first and second switching transistors to start conducting through the drive signal output terminal. Thus, a voltage is induced on the first primary side of the transformer connected to the drain of the first switching transistor, and a voltage is induced on the second primary side of the transformer to supply power to the controller through the power supply input terminal. The drain of the second switching transistor is connected to the current detection input terminal of the controller, and its source is connected to the high-voltage ground terminal. A capacitor-resistor circuit is connected between its drain and source, and the source of the first switching transistor is connected to this capacitor-resistor circuit. The current detection input terminal is directly shorted to ground through the second switching transistor. During the high-current startup process of the controller, a momentary peak current will be generated in the first switching transistor. However, even if the voltage drop across the resistor connected to the source of the first switching transistor is large, the controller will not trigger overcurrent protection because the current detection input terminal is clamped at a low level, thus shielding against false alarms. Attached Figure Description

[0007] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0008] Figure 1 This is a circuit diagram of a switching power supply circuit system provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the secondary circuit included in the switching power supply circuit system in this embodiment of the invention; Figure 3 This is a circuit diagram of another switching power supply circuit system provided in an embodiment of the present invention. Detailed Implementation

[0009] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0010] The terms “first,” “second,” “third,” “fourth,” etc. (if present) in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a particular order or sequence. It should be understood that such data can be interchanged where appropriate so that embodiments of the invention described herein can be implemented, for example, in orders other than those illustrated or described herein. Furthermore, the terms “comprising” and “having,” and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0011] This invention provides a switching power supply circuit system, the structure of which is as follows: Figure 1 As shown, it includes: a controller U1, a startup circuit, a drive circuit, and a current sampling circuit. The controller U1 includes a power supply input terminal Vcc, a drive signal output terminal OUTPUT, and a current detection input terminal CS, wherein: The startup circuit is used to start the controller U1. This startup circuit is connected to the power supply input terminal Vcc through the startup capacitor C6. The driving circuit includes a first switching transistor Q1 and a transformer T1. The gate driving terminal of the first switching transistor Q1 is connected to the driving signal output terminal OUTPUT, and the drain of the first switching transistor Q1 is connected to the first primary side 1-3 of the transformer T1. The second primary side 5-6 of the transformer T1 is connected between the power supply input terminal Vcc and the high voltage ground terminal HGND. The current sampling circuit includes a second switch Q2. The gate drive terminal of the second switch Q2 is connected to the drive signal output terminal OUTPUT through a capacitor C15. The drain of the second switch Q2 is connected to the current detection input terminal CS. The source of the second switch Q2 is connected to the high voltage ground terminal HGND. A capacitor-resistor circuit is connected between the drain and source of the second switch Q2. The source of the first switching transistor Q1 is connected between the capacitor and resistor circuit.

[0012] Specifically, the capacitor-resistor circuit connecting the drain and source of the second switching transistor Q2 can include two series resistors R29 and R30, which are connected in parallel with two series resistors R31 and R32, then connected in series with another resistor R28, and finally connected in parallel with capacitor C16. The source of the first switching transistor Q1 is connected to the midpoint of the series connection between another resistor R28 and the other four resistors R29, R30, R31, and R32.

[0013] It is understood that the controller U1 in the switching power supply circuit of this embodiment is mainly a pulse width modulation (PWM) controller. The controller primarily includes the following pins: error amplifier output (COMP), voltage feedback input (VFB), current detection input (CS), oscillator timing input (RT / CT), reference voltage input (VREF), power supply input (Vcc), drive signal output (OUTPUT), and ground (GND). This controller is generally used in switching power supply circuit systems such as AC-DC power adapters, electric vehicle chargers, and DC-DC converters.

[0014] The error amplifier output terminal COMP is connected to the high-voltage ground terminal HGND through resistor R17 and capacitor C8. The reference voltage terminal VREF is connected to the high-voltage ground terminal HGND through capacitor C8. Resistors R15 and R16 and capacitor C9 are connected in series between the reference voltage terminal VREF and the high-voltage ground terminal HGND. The oscillator timing terminal RT / CT is connected to the high-voltage ground terminal HGND through capacitor C9. The voltage feedback input terminal VFB and the ground terminal GND are both connected to the high-voltage ground terminal HGND.

[0015] The transformer T1 includes a first primary side 1-3, a second primary side 5-6, and multiple secondary sides (not shown in the figure). The first primary side 1-3 is connected to the drain of the first switching transistor Q1, and the second primary side 5-6 is connected to the drive circuit. Both the first primary side 1-3 and the second primary side 5-6 can induce voltages and output various supply voltages through multiple secondary sides, such as 5V, 15V, and 24V.

[0016] For example Figure 2 As shown ( Figure 2 (Only one of the secondary circuits is shown in the diagram). A certain secondary circuit 22-21 can output a 5V supply voltage. This secondary circuit 22-21 is connected between the ground terminal GND and the power supply output terminal P5V. To make the voltage at the power supply output terminal more stable, a circuit consisting of diodes D6 and D7, resistor R34, and capacitor C19 is connected in series between the ground terminal GND and the power supply output terminal P5V. The series-connected resistor R34 and capacitor C19 are connected in parallel with diode D6, and then in parallel with diode D7.

[0017] Furthermore, multiple capacitors and resistors are connected in parallel between the grounding terminal GND and the power supply output terminal P5V, such as capacitors C20, C21, C22, C23, C24 and C25, and resistors 35 and R36. In some parallel branches of capacitors, an inductor L1 is connected in series, that is, capacitor C23 and inductor L1 are connected in series.

[0018] In this embodiment, the switching power supply circuit system first starts the controller U1 through the startup circuit during actual operation, and then the controller U1 drives the first switching transistor Q1 and the second switching transistor Q2 to start working. Specifically: (1) During the startup phase The startup circuit includes a rectifier bridge DQ1, filter capacitors C1, C2, C3, and C4, and a startup resistor (composed of resistors R1, R2, R3, R4, R5, and R6). Thus, the AC input voltage is rectified by the rectifier bridge DQ1 and the filter capacitors to form a DC high voltage. The DC high voltage is directly applied to the startup resistor to form a large current, which charges the startup capacitor C6. When the voltage at the power supply input terminal Vcc connected to the startup capacitor reaches the startup threshold, the internal oscillator of the controller U1 starts to operate, and begins to output a reference voltage from the reference voltage terminal VREF for use by the internal logic circuit. It also outputs PWM drive pulses through the drive signal output terminal OUTPUT to drive the first switch Q1 and the second switch Q2.

[0019] (2) The controller U1 drives the first switch Q1 and the second switch Q2 to conduct. Controller U1 outputs a drive signal through its drive signal output terminal OUTPUT to turn on the first switch Q1 and the second switch Q2, wherein: When the first switching transistor Q1 is turned on, current flows through its drain and the first primary winding 1-3 of transformer T1, inducing a voltage on the first primary winding 1-3. This allows the transformer T1 core to begin storing magnetic energy. Simultaneously, after the controller U1 starts, a voltage is also induced on the second primary winding 5-6 of transformer T1, the auxiliary winding, from the magnetic energy stored in the first primary winding 1-3. This induced voltage is rectified by diode D2 and then filtered by capacitors C6 and C7, generating a stable DC voltage that officially takes over the power supply to the controller U1's input terminal Vcc. The startup circuit automatically cuts off the power supply to the controller U1.

[0020] After the second switching transistor Q2 is turned on, the resistance between its drain and source is extremely small, so the current detection input terminal CS of the controller U1 can be directly shorted to ground.

[0021] During the high-current startup of the controller U1, the first primary winding 1-3 of the transformer T1 acts as a large inductor, generating an extremely high di / dt current spike at the moment of conduction. This current spike flows through the first switching transistor Q1, causing it to experience a large peak current (i.e., surge current). This peak current will generate an extremely high voltage drop across the sampling resistor connected in series with the source of the first switching transistor Q1. The sampling resistor connected in series with the source of the first switching transistor Q1 includes resistor R28 in the capacitor-resistor circuit connecting the drain and source of the second switching transistor Q2.

[0022] In this situation, the source of the first switching transistor Q1 is connected to the current detection input terminal CS of the controller U1 through a series sampling resistor. The current detection input terminal CS will directly sample the voltage drop. The comparator inside the controller U1 will detect the overcurrent signal, causing it to terminate the output drive signal, thus preventing the first switching transistor Q1 and the second switching transistor Q2 from starting, and consequently preventing the controller U1 from receiving power.

[0023] In this embodiment, since the drain of the second switch Q2 is connected to the current detection input terminal CS of the controller U1, and its source is connected to the high-voltage ground terminal HGND, when the second switch Q2 is turned on, it is equivalent to directly short-circuiting the current detection input terminal CS of the controller U1 to ground. At this time, even if the voltage drop across the source resistor of the first switch Q1 is large (for example, far exceeding the threshold), since the current detection input terminal CS is forcibly clamped at 0V (or extremely low level) by the second switch Q2, the comparator inside the controller U1 cannot detect the overcurrent signal. Therefore, the controller U1 will not trigger the overcurrent protection and stop outputting the drive signal (this drive signal is used to drive the first switch Q1 and the second switch Q2), and the false alarm is completely shielded.

[0024] Understandably, in practice, the second switch Q2 will turn on before the first switch Q1 by a preset time (e.g., tens of nanoseconds) to ensure that the current detection input CS is pulled low before the first switch Q1 turns on. Specifically: At startup, the first primary side 1-3 of transformer T1 is equivalent to a large inductor. When the first switching transistor Q1 is turned on, an extremely high current spike (di / dt is extremely large) will be generated. When this spike current flows through the sampling resistor (R28) connected in series with the source of the first switching transistor Q1, an extremely high voltage drop will be generated instantaneously.

[0025] If the second switch Q2 and the first switch Q1 are turned on simultaneously, or if the second switch Q2 is turned on later than the first switch Q1, the voltage spike generated at the instant the first switch Q1 is turned on will be immediately detected by the current detection input CS of the controller U1. The internal comparator of the controller U1 will mistakenly interpret this as an overcurrent and immediately terminate the drive signal output, causing the entire power supply to fail to start normally. Therefore, by turning on the second switch Q2 before the first switch Q1, the current detection input CS is clamped at a low position, preventing overcurrent protection from occurring.

[0026] (3) The controller U1 drives the first switch Q1 and the second switch Q2 to turn off. The controller U1 controls the first switching transistors Q1 and Q2 to turn off through the drive signal output terminal OUTPUT. When the first switching transistor Q1 is turned off, the magnetic energy stored in the transformer T1 supplies power to the controller U1 through the voltage induced by the second primary side 5-6.

[0027] When the first switch Q1 has been conducting for a preset, extremely short time (typically several hundred nanoseconds to several microseconds), the peak current it carries has decayed, and the current enters a normal rising phase. At this point, the controller U1 will control the second switch Q2 to turn off, releasing the current detection input CS and allowing it to begin normal current detection. Meanwhile, the first switch Q1 continues to conduct until the maximum on-time of the PWM cycle output at the drive signal output OUTPUT ends, at which point the controller U1 controls the first switch Q1 to turn off.

[0028] In this way, during the entire long process of the first switch Q1 being turned on, the current detection input terminal CS is shorted to ground by the second switch Q2 for only a short period of time at the beginning, while the current detection input terminal CS is not shorted to ground for the rest of the time, and overcurrent detection is performed normally.

[0029] In the above process, the gate drive terminal of the second switch Q2 is connected to the drive signal output terminal OUTPUT through a capacitor C15, which can be implemented as follows: When the drive signal output terminal OUTPUT of controller U1 outputs a high level, the voltage across capacitor C15 is 0V at the instant the output level transitions from low to high. At this moment, the voltage output from OUTPUT is fully applied to the gate of the second switch Q2 through capacitor C15, turning on Q2. Simultaneously, capacitor C15 charges through resistor R24 ​​connected to the gate of Q2. After a short time, the voltage across capacitor C15 reaches a level close to the voltage output from OUTPUT, turning off Q2 and completing the momentary turn-on. When the drive signal output terminal OUTPUT of controller U1 outputs a low level, the voltage across capacitor C15 discharges through OUTPUT and pins 2-3 of diode D4, bringing the voltage across capacitor C15 back to 0V, preparing for the next PWM pulse output from OUTPUT.

[0030] Another function of diode D4 is to prevent reverse voltage at the drive signal output terminal OUTPUT, thus protecting the switching transistor.

[0031] Furthermore, in a specific embodiment, to achieve slow on and fast off of the switching power supply, the gate drive terminal of the first switching transistor Q1 is connected to the drive signal output terminal OUTPUT of the controller U1 through a resistor R26 and a diode D3 connected in parallel. The parallel diode D3 branch also includes another resistor R25. Specifically: (1) During the slow-start process of the switching power supply When the OUTPUT output of the drive signal of controller U1 is high, current flows through resistor R26 to charge the gate capacitance of the first switching transistor Q1. At this time, diode D4 is reverse biased (i.e., the cathode voltage is higher than the anode voltage) and is in the off state, not participating in the charging. In this case, the charging time constant of the gate capacitance of the first switching transistor Q1 is ≈ R26 × Ciss. The resistance value of resistor R26 is chosen to be moderately large, so that the gate voltage of the first switching transistor Q1 rises more slowly, and the drain current rise rate (di / dt) is reduced, thereby suppressing high-frequency radiation and ringing at the moment of conduction, i.e., electromagnetic interference (EMI).

[0032] (2) During the fast-shutdown process of the switching power supply When the drive signal output terminal OUTPUT of controller U1 outputs a low level, diode D4 is forward biased at this time. The charge stored in the gate capacitor of the first switching transistor Q1 is forward-biased through diode D4 and resistor R25 and flows directly to the drive signal output terminal OUTPUT. The impedance of this path is extremely low, consisting only of the diode's on-resistance and the resistance of resistor R25. As a result, the gate voltage of the first switching transistor Q1 drops quickly, its drain current drops at a high rate (di / dt), and the turn-off loss is small.

[0033] Furthermore, to stabilize the output voltage of controller U1 and prevent excessive voltage from being supplied to the first switching transistor Q1, a Zener diode D5 is connected between the gate drive terminal of the first switching transistor Q1 and the high-voltage ground terminal HGND. Specifically: When the high-level signal output from the OUTPUT terminal of the controller U1 is applied to the gate drive terminal of the first switching transistor Q1, the regulated voltage of the Zener diode D5 is greater than the normal gate voltage of the first switching transistor Q1. At this time, the Zener diode D5 is reverse-biased and cut off, equivalent to an open circuit. Under these circumstances, the gate voltage of the first switching transistor Q1 rises and falls normally, and the first switching transistor Q1 switches normally.

[0034] When the gate voltage of the first switching transistor Q1 exceeds the preset range of the Zener diode D5, Zener diode D5 undergoes avalanche breakdown, and current begins to flow from its gate to the high-voltage grounding transistor HGND of the controller U1. This current clamps the gate voltage of the first switching transistor Q1, stabilizing it within the aforementioned preset range and preventing the gate voltage from rising further. Subsequently, when the gate voltage falls back below the preset range, Zener diode D5 automatically turns off, and the drive circuit returns to normal.

[0035] Furthermore, to provide passive clamping protection for the drive signal output terminal OUTPUT of controller U1, suppress ringing and negative voltage spikes on the output drive signal, and protect the output stage of controller U1 from damage, the drive signal output terminal OUTPUT is connected to the common terminal 3 of diode array D4 through capacitor C15. Two resistors R26 and R27 are connected in series between the other two terminals 12 of diode array D4. One terminal 2 of diode array D4 is connected to the high-voltage ground terminal HGND. The drive signal output terminal is connected to the gate drive terminal of the first switching transistor Q1 through a resistor. Specifically: Capacitor C15 can AC couple the PWM drive signal (including ringing) of the drive signal output terminal OUTPUT of controller U1 to the common terminal 3 of diode array D4.

[0036] In one scenario, when the PWM drive signal experiences a large negative ringing (e.g., below -0.5V), the voltage at common terminal 3 is momentarily pulled down. If the voltage falls below a certain threshold, one diode in the diode array D4 conducts forward (from common terminal 3 to terminal 2), thus clamping the voltage at common terminal 3 firmly to a certain threshold. This is equivalent to limiting the negative voltage spike at the drive signal output terminal OUTPUT of controller U1 to a safe range near that threshold, preventing the parasitic transistors in the output stage of controller U1 from being falsely triggered or damaged.

[0037] In another scenario, when a positive overshoot voltage occurs at the drive signal output terminal OUTPUT, this positive voltage raises the potential of the common terminal 3, one diode in the diode array D4 is reverse-biased and cut off, and the bias voltage difference of the other diode (from one terminal 1 to the common terminal 3) decreases or even reverse-biases, providing no discharge path, and the diode array D4 does not intervene in the positive overshoot.

[0038] As can be seen, in the switching power supply circuit system of this embodiment, after the controller is started by the startup circuit, the controller controls the first and second switching transistors to start conducting through the drive signal output terminal. Thus, a voltage is induced on the first primary side of the transformer connected to the drain of the first switching transistor, and a voltage is induced on the second primary side of the transformer to supply power to the controller through the power supply input terminal. The drain of the second switching transistor is connected to the current detection input terminal of the controller, and its source is connected to the high-voltage ground terminal. A capacitor-resistor circuit is connected between its drain and source, and the source of the first switching transistor is connected to this capacitor-resistor circuit. The current detection input terminal is directly shorted to ground through the second switching transistor. During the high-current startup process of the controller, a momentary peak current will be generated in the first switching transistor. However, even if the voltage drop across the resistor connected to the source of the first switching transistor is large, the controller will not trigger overcurrent protection because the current detection input terminal is clamped at a low level, thus shielding against false alarms.

[0039] In a specific embodiment, such as Figure 3 As shown, the switching power supply circuit system also includes a feedback circuit, which is connected to the error amplifier output terminal COMP of the controller U1, and is used to supply the power supply voltage (such as the one mentioned above) through either secondary side of the transformer T1. Figure 2 The 5V supply voltage shown is used to adjust the signal output from the COMP terminal of the error amplifier. Specifically, the feedback circuit includes: A voltage regulator U2 and an optocoupler OP1 are connected. The reference terminal of the voltage regulator U2 is connected to a capacitor-resistor circuit between the power supply output terminal P5V and the ground terminal GND. The anode of the voltage regulator U2 is connected to the ground terminal GND. The cathode of the voltage regulator U2, the light-emitting diode (LED) in the optocoupler OP1, and the resistor R18 are connected to the power supply output terminal P5V. The phototransistor in the optocoupler OP1 is connected between the error amplifier output terminal COMP of the controller U1 and the high-voltage ground terminal HGND. A capacitor C10 is connected in parallel across the phototransistor.

[0040] Specifically, the capacitor-resistor circuit connected to the reference terminal of the voltage regulator U2 can include three parallel branches: capacitor C14; resistors R21, R22, and R23 connected in series; and resistors R19 and R20 connected in series, along with capacitors C12 and C13. In addition, capacitor C11 is connected in parallel across resistor R20 and capacitor C12. The reference terminal of the voltage regulator U2 is connected to the midpoint of two of the parallel branches, which is one end of capacitor C11.

[0041] In this way, when the feedback circuit adjusts the signal output from the COMP terminal of the error amplifier, specifically: The power supply voltage output from the P5V power supply output terminal is divided by the capacitor and resistor circuit and then connected to the reference terminal of the voltage regulator U2. Under normal operation, the voltage at the reference terminal of the voltage regulator U2 will be stabilized near a reference voltage.

[0042] When the power supply voltage output at the P5V power supply output terminal changes, the voltage change will be reflected at the reference terminal of the voltage regulator U2. The voltage regulator U2 will drive the cathode current to increase or decrease according to the relationship between the voltage divided by the capacitor and resistor circuit and the reference voltage.

[0043] The change in cathode current will change the current of the LED in optocoupler OP1, which will cause the current output across the phototransistor in optocoupler OP1 to change accordingly, thereby changing the voltage output of the error amplifier COMP. For example, when the current output of optocoupler OP1 decreases, the voltage output of the error amplifier COMP increases, and when the current output of optocoupler OP1 increases, the voltage output of the error amplifier COMP is pulled down.

[0044] The controller U1 compares the voltage output from the error amplifier's COMP terminal with the voltage at the current detection input CS terminal, adjusting the PWM duty cycle accordingly. For example, a higher COMP output voltage allows for a larger peak current and a larger duty cycle, while a lower COMP output voltage results in a smaller duty cycle. The PWM duty cycle, in turn, determines the driving of the first switch Q1 and the second switch Q2, thus enabling precise voltage regulation at the transformer's secondary power supply output.

[0045] The switching power supply circuit system provided by the embodiments of the present invention has been described in detail above. Specific examples have been used to illustrate the principle and implementation of the present invention. The description of the above embodiments is only for the purpose of helping to understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation and application scope based on the idea of ​​the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A switching power supply circuit system, characterized in that, include: The system includes a controller, a startup circuit, a drive circuit, and a current sampling circuit. The controller includes a power supply input terminal, a drive signal output terminal, and a current detection input terminal. The startup circuit is used to start the controller, and the startup circuit is connected to the power supply input terminal through a startup capacitor; The driving circuit includes a first switching transistor and a transformer. The gate driving terminal of the first switching transistor is connected to the driving signal output terminal, the drain of the first switching transistor is connected to the first primary side of the transformer, and the second primary side of the transformer is connected between the power supply input terminal and the high voltage ground terminal. The current sampling circuit includes a second switching transistor. The gate driving terminal of the second switching transistor is connected to the driving signal output terminal through a capacitor. The drain of the second switching transistor is connected to the current detection input terminal. The source of the second switching transistor is connected to the high voltage ground terminal. A capacitor-resistor circuit is connected between the drain and the source of the second switching transistor. The source of the first switching transistor is connected between the capacitor and resistor circuit.

2. The switching power supply circuit system as described in claim 1, characterized in that, The capacitor-resistor circuit includes: two series resistors, which are connected in parallel with the two series resistors, then connected in series with another resistor, and then connected in parallel with a capacitor; The source of the first switch is connected to the midpoint of the series connection between the other resistor and the other four resistors.

3. The switching power supply circuit system as described in claim 1, characterized in that, The startup circuit generates a large current to charge the startup capacitor. When the voltage at the input terminal of the power supply reaches the startup threshold, the controller outputs a drive pulse through the drive signal output terminal to drive the first and second switching transistors.

4. The switching power supply circuit system as described in claim 3, characterized in that, When the first switch is turned on, a voltage is induced on the first primary side and the second primary side, and a DC voltage is generated on the voltage induced on the second primary side to supply power to the power supply input terminal. When the second switch is turned on, the current detection input terminal of the controller is shorted to ground; In this configuration, the second switch is turned on before the first switch.

5. The switching power supply circuit system as described in claim 4, characterized in that, When the first switch is turned off, the controller is powered by the voltage induced on the second primary side. After the first switch has been on for a preset time, the controller controls the second switch to turn off, so that the current detection input terminal can perform current detection.

6. The switching power supply circuit system according to any one of claims 1 to 5, characterized in that, The gate drive terminal of the first switching transistor is connected to the drive signal output terminal through a resistor and a diode connected in parallel, and the diode branch connected in parallel includes another resistor; When the controller outputs a high level, current flows through the parallel-connected resistor to charge the gate capacitance of the first switching transistor, and the diode is in the off state. When the drive signal output terminal of the controller outputs a low level, the charge stored in the gate capacitor of the first switching transistor flows to the drive signal output terminal through the diode and another resistor in the diode branch.

7. The switching power supply circuit system according to any one of claims 1 to 5, characterized in that, A Zener diode is connected between the gate drive terminal of the first switching transistor and the high-voltage ground terminal; When the gate voltage of the first switch exceeds the preset range of the Zener diode's voltage regulation value, the gate voltage of the first switch will be clamped and stabilized within the preset range.

8. The switching power supply circuit system according to any one of claims 1 to 5, characterized in that, The switching power supply circuit system also includes a diode array; The drive signal output terminal is connected to the common terminal of the diode array through a capacitor, and two resistors are connected in series between the other two terminals of the diode array. One end of the diode array is connected to the high voltage ground terminal.

9. The switching power supply circuit system according to any one of claims 1 to 5, characterized in that, The controller also includes an error amplifier output terminal, and the switching power supply circuit system also includes a feedback circuit, which is used to adjust the signal output by the error amplifier output terminal by the power supply voltage output from any secondary side of the transformer; The feedback circuit includes a voltage regulator and an optocoupler. The reference terminal of the voltage regulator is connected to another capacitor-resistor circuit, which is connected between the power supply output terminal and the ground terminal. The anode of the voltage regulator is connected to the ground terminal, and the cathode of the voltage regulator is connected to the light-emitting diode and resistor in the optocoupler. The phototransistor in the optocoupler is connected between the error amplifier output terminal and the high voltage ground terminal of the controller, and a capacitor is connected in parallel across the two ends of the phototransistor.

10. The switching power supply circuit system as described in claim 9, characterized in that, The power supply voltage output from the power supply output terminal is connected to the reference terminal of the voltage regulator after being divided by the other capacitor-resistor circuit. The voltage regulator drives the cathode current to increase or decrease according to the relationship between the voltage divided by the other capacitor-resistor circuit and the reference voltage. The change in the cathode current alters the current of the light-emitting diode in the optocoupler, causing a change in the current output across the phototransistor in the optocoupler, thereby changing the voltage output at the output terminal of the error amplifier. The controller compares the voltage output from the error amplifier with the voltage at the current detection input and adjusts the duty cycle of the drive signal.

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