Constant current circuit for optocoupler driving and switching power supply system

Abstract

The invention discloses a constant current circuit for optocoupler driving, and the circuit comprises a constant current source module, the input end of which is connected with a driving signal source; the anode of the photoelectric coupler module is connected with the output end of the constant current source module, and the cathode of the photoelectric coupler module is grounded; wherein the constant current source module is configured to provide constant output current for the photoelectric coupler under the action of a driving signal. The constant-current driving mode has the characteristic of inhibiting oscillation caused by sudden current change, the design of an external damping capacitor can be simplified or even eliminated, the complexity of a peripheral circuit and the element cost are reduced, and the PCB layout is more concise.

Description

Technical Field

[0001] This invention relates to the field of electronic circuit technology, and more specifically to a constant current circuit and switching power supply system for driving optocouplers. Background Technology

[0002] In modern switching power supply systems, optocouplers are commonly used as gate drive interfaces to achieve electrical isolation between the control circuit and the power circuit and to reliably drive power switching transistors (such as MOSFETs or IGBTs). Traditional driving methods include... Figure 1 As shown, the drive output pin of the control chip (such as TI's UCC28950) is directly connected to the anode of the LED in the optocoupler through a current-limiting resistor R1, while the cathode of the LED is grounded. To suppress signal ringing and noise caused by resistor current limiting and line parasitic parameters, a damping capacitor C1 is usually connected in parallel at the input of the optocoupler.

[0003] However, the aforementioned traditional solution has significant technical drawbacks: First, the current-limiting resistor R1 and the damping capacitor C1 (including unavoidable distributed capacitance and diode junction capacitance) form an RC network, which generates a charging and discharging delay when the PWM signal changes, with a time constant of [missing information]. This leads to a significant transmission delay in the output signal of the optocoupler relative to the input signal. Secondly, in multi-channel applications (such as a phase-shifted full-bridge synchronous rectification topology based on the UCC28950), the manufacturing tolerances of resistors and capacitors (e.g., resistance ±5%, capacitance ±10%) make it difficult to maintain consistent RC time constants across channels, resulting in inconsistent signal delays between channels. This delay inconsistency causes asynchronous turn-on and turn-off times of the power switches in each phase, leading to unbalanced inter-phase currents, decreased system efficiency, increased electromagnetic interference (EMI), and even affecting system loop stability, severely degrading the overall performance and control accuracy of the switching power supply. Summary of the Invention

[0004] To overcome the inherent technical defects of traditional resistor current limiting methods, such as RC delay and multi-channel inconsistency, this invention provides a...

[0005] To solve the above problems, the present invention is implemented according to the following technical solution:

[0006] In a first aspect, the present invention provides a constant current circuit for driving an optocoupler, comprising: a constant current source module, the input terminal of which is connected to a driving signal source; an optocoupler module, the anode of which is connected to the output terminal of the constant current source module, and the cathode of which is connected to ground; wherein the constant current source module is configured to provide a constant output current to the optocoupler under the action of a driving signal.

[0007] In conjunction with the first aspect, the present invention provides a first specific implementation of the first aspect. Specifically, the constant current source module includes: a first transistor, a first resistor, a light-emitting diode (LED), a second transistor, and a second resistor; the base of the first transistor is connected to the driving signal source through the first resistor; the anode of the LED is connected to a power supply, and the cathode of the LED is connected to the collector of the first transistor through a third resistor; the base of the second transistor is connected to the cathode of the LED, and the collector of the second transistor serves as the output terminal of the constant current source module and is connected to the anode of the optocoupler module; one end of the second resistor is connected to the base of the first transistor, and the other end of the second resistor is connected to the emitter of the first transistor and ground, respectively.

[0008] In conjunction with the first aspect, the present invention provides a second specific implementation of the first aspect. Specifically, the constant current source module further includes: a fourth resistor, one end of which is connected to a power supply, and the other end of which is connected to the emitter of the second transistor.

[0009] In conjunction with the first aspect, the present invention provides a third specific implementation of the first aspect. Specifically, the constant current source module further includes: a fifth resistor, which is connected to the collector of the second transistor and the anode of the optocoupler module, respectively, and the other end of the fifth resistor is connected to the cathode of the optocoupler module and ground, respectively.

[0010] In conjunction with the first aspect, the present invention provides a fourth specific implementation of the first aspect, specifically, the forward voltage drop of the light-emitting diode provides a base bias voltage for the second transistor, and together with the second resistor, sets the magnitude of the constant drive current.

[0011] In conjunction with the first aspect, the present invention provides a fifth specific embodiment of the first aspect, wherein the formula for calculating the constant drive current is as follows: ;in, The forward voltage drop of the light-emitting diode is... This is the base-emitter turn-on voltage of the second transistor. The resistance value of the fourth resistor.

[0012] In conjunction with the first aspect, the present invention provides a sixth specific embodiment of the first aspect, wherein the optocoupler module includes an optocoupler, the anode of the optocoupler is connected to the collector of the second transistor, and the cathode of the optocoupler is grounded.

[0013] In conjunction with the first aspect, the present invention provides a seventh specific embodiment of the first aspect. Specifically, the constant current circuit is configured as multiple channels, each channel including a constant current source module and an optocoupler module, and the constant current source module of each channel is configured to output a constant current of the same magnitude.

[0014] Secondly, the present invention also provides a switching power supply system, including a control chip and at least one constant current circuit for driving the optocoupler, wherein the input terminal of the constant current source module is connected to the driving voltage output terminal of the control chip, and the driving power output terminal is used to provide a driving signal source.

[0015] Compared with the prior art, the beneficial effects of the present invention are:

[0016] This circuit uses a constant current source module to directly drive the optocoupler, replacing the current-limiting resistor in traditional solutions. Due to the extremely high output impedance of the constant current source, its output current does not fluctuate with rapid changes in the voltage of the downstream load (the optocoupler's LED and its parallel distributed capacitance and junction capacitance). This effectively isolates the influence of the capacitive load on the driving signal edge, allowing the optocoupler's LED current to instantaneously establish or deactivate in close accordance with the driving signal voltage, avoiding the charging and discharging process of traditional RC networks. Therefore, this solution significantly reduces signal transmission delay, achieves faster and steeper edge response, and greatly improves signal transmission bandwidth and fidelity.

[0017] Traditional solutions for optimizing waveforms and suppressing ringing often require additional adjustments and parallel damping capacitors. However, the constant current drive method of this invention inherently suppresses oscillations caused by sudden current changes, simplifying or even eliminating the need for external damping capacitors. This reduces the complexity of peripheral circuitry and component costs, resulting in a simpler PCB layout. Attached Figure Description

[0018] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings, wherein:

[0019] Figure 1 This is a circuit diagram of a conventional control chip and a gate-driven optocoupler according to the present invention.

[0020] Figure 2 This is a circuit diagram of a constant current circuit for driving an optocoupler according to the present invention.

[0021] In the diagram: 1-Constant current source module; 2-Optocoupler module. Detailed Implementation

[0022] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0023] like Figures 1-2 As shown, this invention provides a constant current circuit for driving an optocoupler.

[0024] Example 1

[0025] like Figure 2 As shown, a constant current circuit for driving an optocoupler includes: a constant current source module 1, the input terminal of which is connected to a driving signal source; and an optocoupler module 2, the anode of which is connected to the output terminal of the constant current source module 1, and the cathode of which is connected to ground; wherein the constant current source module 1 is configured to provide a constant output current to the optocoupler under the action of a driving signal.

[0026] Specifically, this invention uses a constant current source module 1 to directly drive the optocoupler module 2. Through a simple and compact layout, parasitic parameters in the signal loop are minimized, effectively suppressing ringing and oscillation at the signal edges. Therefore, this circuit can obtain a pure drive waveform without relying on traditional external damping capacitors. Since the drive current is strictly set and kept constant by the constant current source, the charge injection process required for the optocoupler to turn on has a fixed time rate. This makes its turn-on and turn-off delay times highly stable and mainly depends on the constant current value itself. The drive signal is generated by the drive signal source.

[0027] This feature brings a key advantage: by ensuring that the output current settings of the constant current source modules in each parallel drive channel are consistent, a high degree of consistency in signal transmission delay across all channels can be guaranteed. This fundamentally solves the synchronization problem caused by delay differences in multi-channel systems, laying a solid foundation for improving the control accuracy, efficiency, and reliability of systems such as multiphase switching power supplies.

[0028] In contrast, in traditional resistor-based current limiting schemes, the current-limiting resistor, along with unavoidable parasitic capacitance or an external damping capacitor, forms an RC circuit. Its delay time ( The signal is directly affected by the manufacturing tolerances of the resistors and capacitors themselves (such as ±5% resistance tolerance and ±10% capacitance tolerance). In multi-channel systems, these minute component differences accumulate and amplify into significant signal delay deviations between channels, causing the turn-on and turn-off times of the power switches in each phase to be out of sync. This leads to a series of problems such as phase-to-phase current imbalance, overall efficiency reduction, and increased electromagnetic interference (EMI).

[0029] This invention eliminates the dependence of delay time on resistor and capacitor parameters by employing constant current drive. The constant current source itself has stable output characteristics and is minimally affected by component parameter variations, thus eradicating the inter-channel delay dispersion introduced by inconsistent RC parameters in traditional solutions. This not only ensures precise synchronization timing but also simplifies peripheral circuit design and improves the system's stability and robustness under different operating conditions.

[0030] In a preferred embodiment, the constant current source module 1 includes: a first transistor, a first resistor, a light-emitting diode (LED), a second transistor, and a second resistor; the base of the first transistor is connected to the driving signal source through the first resistor; the anode of the LED is connected to a power supply, and the cathode of the LED is connected to the collector of the first transistor through a third resistor; the base of the second transistor is connected to the cathode of the LED, and the collector of the second transistor serves as the output terminal of the constant current source module 1 and is connected to the anode of the optocoupler module 2; one end of the second resistor is connected to the base of the first transistor, and the other end of the second resistor is connected to the emitter of the first transistor and ground, respectively.

[0031] Specifically, the first transistor (e.g., an NPN transistor) acts as a switch controlled by the drive signal source (e.g., a PWM pin of a control chip). When the drive signal is high, the first transistor is saturated and turned on, its collector potential is pulled low, thereby forward-biased LED1 and establishing a stable reference voltage across it. The second transistor (e.g., a PNP transistor) is connected in series with the light-emitting diode of the optocoupler to form a constant current output electrode in the form of an emitter follower (or common base), through which a constant output current flows through the emitter of the second transistor (i.e., through the anode of the optocoupler U1).

[0032] More preferably, the constant current source module 1 further includes: a fourth resistor, one end of which is connected to a power supply, and the other end of which is connected to the emitter of the second transistor.

[0033] Specifically, a fourth resistor is added. Subsequently, the emitter of the second transistor is no longer directly connected to the power supply VCC, but is instead connected to VCC through a fourth resistor. The fourth resistor... The introduction of this technology increases the total current flowing through the emitter of the second transistor (i.e., the optocoupler drive current). The sum of the base current of the second transistor and the base current of the third transistor produces a voltage drop across the fourth resistor. This voltage drop, together with the reference voltage established by the LED, allows for more precise setting and stabilization. Specifically, the base voltage of the second transistor Reference voltage established by LED Determine (ignoring the voltage drop across R3), its emitter voltage Therefore, the current flowing through the fourth resistor (approximately...) ) can be derived from the formula Setting and estimation are performed. This structure reduces the dependence on the second transistor. The sensitivity to parameter drift improves the stability of the output current at different temperatures. Fourth resistor As a series impedance between the power supply VCC and the drive circuit, it limits the maximum transient current, providing buffer protection for the second transistor and optocoupler. Output current. Still supported by a stable reference voltage and precision resistors (Fourth resistor) setting, maintaining constant characteristics. The switching delay of the optocoupler remains constant. The decisions are highly repeatable.

[0034] In a multi-channel system, it is only necessary to ensure the reference voltage of each channel. With precision resistors Matching the resistance value of the fourth resistor ensures a high degree of consistency between the current and delay across channels, fundamentally solving the synchronization problem. Simultaneously, the high impedance characteristic of the constant current drive effectively suppresses the effects of parasitic capacitance, eliminating the need for an external damping capacitor. By adjusting the resistance value of the fourth resistor, it can more flexibly adapt to different power supply voltages (VCC), ensuring that the drive current remains constant even at higher VCC values. It can still be precisely limited to a safe and appropriate range, increasing the flexibility of circuit design.

[0035] In a preferred embodiment, the constant current source module 1 further includes a fifth resistor, which is connected to the collector of the second transistor and the anode of the optocoupler module, respectively, and the other end of the fifth resistor is connected to the cathode of the optocoupler module and ground, respectively.

[0036] Specifically, the fifth resistor is connected in series in the main current path between the constant current output stage (the collector of the second transistor) and the load (the light-emitting diode). A current-dependent current is generated across the fifth resistor, which is related to the drive current. proportional voltage drop ( This voltage signal can be used as a current monitoring point to monitor the operating status of the drive circuit in real time (e.g., to confirm whether the constant current source has started normally and whether the current value is stable), without affecting the constant current drive characteristics of the main circuit.

[0037] In a preferred embodiment, the forward voltage drop of the light-emitting diode provides a base bias voltage for the second transistor, and together with the second resistor, sets the magnitude of the constant drive current.

[0038] Specifically, this circuit utilizes the forward voltage drop of the light-emitting diode inside the optocoupler ( This serves as a stable reference voltage source. This voltage drop is applied between the base and emitter of the second transistor (typically a current-setting transistor), establishing a bias condition for the second transistor. The current flowing through the second resistor (i.e., the set current of the constant current source) acts as a reference voltage source. ) by this voltage ( Divide by the resistance of the second resistor ( ) decision, that is .because For a specific type of LED, this is a relatively stable parameter; therefore, the magnitude of the constant drive current is mainly determined by… Precise settings.

[0039] This approach directly utilizes the characteristics of the LED itself to set the drive current, eliminating the need for an additional precision voltage reference (such as a bandgap reference) or complex bias circuitry. This ensures a constant drive current in a simple and low-cost manner.

[0040] In a preferred embodiment, the formula for calculating the constant drive current is: ;in, The forward voltage drop of the light-emitting diode is... This is the base-emitter turn-on voltage of the second transistor. The resistance value of the fourth resistor.

[0041] Specifically, this invention creatively utilizes the forward voltage drop of the light-emitting diode (LED1) of the optocoupler itself. This voltage serves as a reference voltage source. While driving the LED, it also biases the second transistor in the constant current source circuit and interacts with the fourth resistor (i.e., the current setting resistor). This constitutes a simple current setting network.

[0042] More specifically, its working principle and advantages lie in: due to the output current Ultimately, a relatively stable voltage difference is achieved. With a high-precision resistor The ratio is determined by this. Therefore, the present invention preferably uses the fourth resistor. Precision resistors are selected. This makes the constant current value extremely insensitive to voltage fluctuations from the upstream drive signal source, resulting in a very high power supply rejection ratio. Regardless of how the input drive voltage varies within a reasonable range, the optocoupler can obtain a highly stable drive current. This stability fundamentally ensures the linearity, repeatability, and long-term reliability of signal transmission.

[0043] Compared with traditional technologies: In traditional resistor current limiting schemes, the drive current directly depends on the ratio of the power supply voltage to the resistance value ( The current fluctuates linearly with the power supply voltage. Even with a constant current source constructed from a simple transistor, its reference voltage often depends directly or indirectly on the power supply voltage, resulting in limited anti-interference capability. Both of these traditional methods are susceptible to power supply fluctuations, leading to unstable drive current, which in turn causes the operating point of the optocoupler's current transfer ratio (CTR) to drift, ultimately degrading the quality and consistency of the drive signal.

[0044] More specifically, the light-emitting diode of this invention can be of any color, but a red light-emitting diode is more preferably selected in this invention. In this scheme, the red light-emitting diode (LED1) plays two key roles simultaneously: firstly, as the signal transmitting unit of the optocoupler, and secondly, as the built-in reference voltage source of the constant current source. Its forward voltage drop is 1.8V to 2.0V. The red LED provides a suitable and remarkably stable voltage reference for the constant current source's bias circuit within its normal operating current range. Experimental results show that the voltage stability of the red LED under its normal operating current is superior to that of a typical Zener diode within the same voltage range. This directly means that the constant drive current set based on this voltage has higher accuracy and temperature stability, ensuring signal transmission consistency from the source. While providing a stable reference voltage, the red LED's luminescence naturally serves as a visual indicator of the circuit's operating status, facilitating system debugging and status monitoring. This achieves a perfect integration of the two functions of providing a reference voltage and indicating operating status, eliminating the complexity and cost of adding additional status indicators.

[0045] Traditional precision constant current sources or voltage reference circuits typically require dedicated reference voltage chips (such as bandgap references) or complex current mirrors (current mirror sources) composed of multiple transistors. This invention achieves equivalent or even superior high-stability constant current drive using only a common, low-cost red LED, along with a small number of resistors and transistors. This completely eliminates the need for dedicated reference chips or complex mirror circuits, simplifying the circuit topology, reducing PCB footprint, and significantly lowering overall material costs and supply chain complexity, making it particularly beneficial for large-scale production applications. This specific choice deeply aligns with the core objective of this invention: "eliminating RC delay and ensuring multi-channel consistency." A stable The reference voltage directly determines the formula: The accuracy of the red LED is enhanced by its excellent voltage stability, allowing for more precise setting of the constant current value for each channel. Its low cost makes it possible to use a single LED as a reference for each channel, thus achieving top-tier inter-channel current matching and delay consistency at the system level in an economical way. The key optimization of this invention is the selection of a red LED with a specific forward voltage drop as the core reference device. It integrates high-performance constant current drive, status indication, and cost control in a simple, efficient, and economical manner, demonstrating the outstanding advantages of this invention in terms of engineering practicality, superior performance, and economy.

[0046] In a preferred embodiment, the optocoupler module 2 includes an optocoupler, the anode of which is connected to the collector of the second transistor, and the cathode of which is grounded.

[0047] Specifically, the collector of the second transistor serves as the final output node of the constant current source module, and its output current ( The current is directly injected into the positive terminal of the LED inside the optocoupler. The cathode of the LED is directly grounded, forming a clear, low-impedance current path. This simple connection ensures that the constant drive current generated by the constant current source can flow almost entirely and without loss through the LED, thus achieving the most direct and effective drive. Because the positive terminal of the LED is connected to the constant current output point (the collector of the second transistor), and its cathode is grounded, the forward voltage drop across the LED is... This is utilized by the bias circuit of the second transistor in the constant current source (i.e., to provide the base bias voltage for the second transistor). This connection forms a self-biasing loop, which is the structural basis for the circuit to automatically and stably operate at a certain constant current point.

[0048] In a preferred embodiment, the constant current circuit is configured with multiple channels, each channel including one constant current source module 1 and one optocoupler module 2, and the constant current source module 1 of each channel is configured to output a constant current of the same magnitude.

[0049] Specifically, the constant current source modules of each channel are precisely configured to output the same constant current. They use the same type of LED with the same forward voltage drop characteristics as the internal reference and are paired with precisely set resistors to ensure the drive current from the first channel to the Nth channel. It exhibits extremely low dispersion. The "matching" of this current source takes precedence over "absolute accuracy," and is more critical for the synchronization performance of multiphase systems. It directly ensures that all optocoupler LEDs operate under identical current conditions, thus making their turn-on and turn-off dynamic processes highly consistent.

[0050] In traditional multi-channel schemes, the random tolerances of the current-limiting resistors and parasitic capacitances in each channel lead to different RC time constants, resulting in delay deviations that are difficult to calibrate. This invention eliminates this deviation mechanism at its source through a multi-channel constant-current drive scheme. Because the drive current is constant and consistent, the switching delay of the optocoupler itself (primarily dependent on carrier transit time, whose dispersion is much smaller than the difference in RC constants) becomes the main component of the delay, and this difference is typically minimal and predictable. Therefore, this embodiment can reduce the transmission delay difference between channels to near the theoretical lower limit of the optocoupler's own parameter dispersion, providing a circuit-level guarantee for achieving perfect multiphase synchronization (such as in full-bridge, interleaved parallel, and other topologies).

[0051] The constant current circuit for optocoupler driving described in this invention fundamentally revolutionizes the driving method of optocouplers, thus its application range is extremely wide. With its core characteristic of "providing a constant driving current," this circuit can be applied to any electronic circuit and system that requires signal isolation, transmission, or level conversion using optocouplers.

[0052] The working principle of the constant current circuit for optocoupler driving described in this invention is as follows: when the driving signal turns on the first transistor, the light-emitting diode (LED1) is lit, and the forward voltage drop of the light-emitting diode (LED1) ( A negative reference voltage, with the +5 power rail as a reference, is established at the base of the second transistor, thereby turning on the second transistor and generating a collector current. The second transistor The magnitude of the voltage drop across the fourth resistor affects the voltage across the second transistor, thus changing the emitter voltage. The total voltage across the second transistor (Veb) plus the voltage across the fourth resistor is related to the voltage supplied by the light-emitting diode (LED1). A dynamic comparison is performed, and the comparison result determines the second transistor's... The size of the second transistor. The size directly determines the second transistor. The size is such that the second transistor is in a real-time linear adjustment state. Because the output current is constant... By the fourth resistor The pressure drop across the two ends determines the value, and its calculation formula is as follows: ;

[0053] in, It is the forward voltage drop of the light-emitting diode (LED1). It is the base-emitter voltage of the second transistor. Because... and Both are relatively stable PN junction voltage drops, therefore the output current Highly stable. This is the emitter-base turn-on voltage of the second transistor (approximately 0.7V). The constant current value can be set by selecting the value of the second resistor (R2). The VF of the red LED is supplied by the light-emitting diode (LED1), replacing the traditional mirror diode or Zener diode solution. The light-emitting diode (LED1) also serves as the second transistor. It increases the reference voltage and also serves as an indicator light for pulse signal output.

[0054] Example 2

[0055] A switching power supply system includes a control chip and at least one constant current circuit for optocoupler driving. The input terminal of the constant current source module 1 is connected to the drive voltage output terminal of the control chip, and the drive power output terminal is used to provide a drive signal source.

[0056] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Therefore, any modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A constant current circuit for driving an optocoupler, characterized in that, include: A constant current source module, wherein the input terminal of the constant current source module is connected to a drive signal source; An optocoupler module, wherein the anode of the optocoupler module is connected to the output terminal of the constant current source module, and the cathode of the optocoupler module is connected to ground; The constant current source module is configured to provide a constant output current to the optocoupler under the action of a drive signal.

2. The constant current circuit for driving an optocoupler according to claim 1, characterized in that, The constant current source module includes: A first transistor, a first resistor, a light-emitting diode, a second transistor, and a second resistor; The base of the first transistor is connected to the drive signal source through the first resistor; The positive terminal of the light-emitting diode is connected to the power supply, and the negative terminal of the light-emitting diode is connected to the collector of the first transistor through a third resistor; The base of the second transistor is connected to the negative terminal of the light-emitting diode, and the collector of the second transistor is connected to the anode of the optocoupler module as the output terminal of the constant current source module. One end of the second resistor is connected to the base of the first transistor, and the other end of the second resistor is connected to the emitter of the first transistor and ground, respectively.

3. The constant current circuit for driving an optocoupler according to claim 2, characterized in that, The constant current source module also includes: A fourth resistor, one end of which is connected to a power supply, and the other end of which is connected to the emitter of the second transistor.

4. The constant current circuit for optical coupling drive according to claim 2, characterized in that, The constant current source module also includes: The fifth resistor is connected to the collector of the second transistor and the anode of the optocoupler module, respectively, and the other end of the fifth resistor is connected to the cathode of the optocoupler module and ground, respectively.

5. The constant current circuit for optical coupling drive according to claim 3, characterized in that, The forward voltage drop of the light-emitting diode provides the base bias voltage for the second transistor, and together with the second resistor, sets the magnitude of the constant drive current.

6. The constant current circuit for optocoupler driving according to claim 5, characterized in that, The formula for calculating the constant drive current is: ； in, The forward voltage drop of the light-emitting diode is... This is the base-emitter turn-on voltage of the second transistor. The resistance value of the fourth resistor.

7. The constant current circuit for optocoupler driving according to claim 6, characterized in that, The optocoupler module includes an optocoupler, the anode of which is connected to the collector of the second transistor, and the cathode of which is grounded.

8. The constant current circuit for optocoupler driving according to claim 7, characterized in that, The constant current circuit is configured with multiple channels, each channel containing a constant current source module and an optocoupler module, and the constant current source module of each channel is configured to output a constant current of the same magnitude.

9. A switching power supply system, characterized in that, It includes a control chip and at least one constant current circuit for optocoupler driving as described in any one of claims 1 to 8, wherein the input terminal of the constant current source module is connected to the drive voltage output terminal of the control chip, and the drive power output terminal is used to provide a drive signal source.

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