A circuit for compensating for temperature drift of an optocoupler in a switching power supply
By introducing an NTC thermistor into the switching power supply system to compensate for the temperature drift of the optocoupler, the loop difference problem caused by the temperature drift of the optocoupler is solved, and the stability and response speed of the switching power supply at different temperatures are improved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- JIANGSU ZHAONENG ELECTRONICS
- Filing Date
- 2025-08-22
- Publication Date
- 2026-07-24
AI Technical Summary
Temperature drift of optocouplers in switching power supply systems causes significant differences in loop performance at high, normal, and low temperatures, affecting system stability and response speed.
A compensation circuit is adopted, which includes an output voltage sampling circuit, a voltage loop control circuit, an optocoupler, a temperature compensation circuit, and a PWM control chip. The NTC thermistor is used to compensate for the current transfer ratio drift of the optocoupler at different temperatures, and the loop is stabilized by adjusting the current of the photodiode.
It achieves basic consistency of the switching power supply loop under different temperatures, improves system stability and response speed, simplifies circuit design and reduces costs.
Smart Images
Figure CN224555466U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to the field of switching power supplies, and in particular to a circuit for compensating for the temperature drift of optocouplers in a switching power supply. Background Technology
[0002] In primary-secondary isolated switching power supply circuits, optocouplers are typically used at the output of the voltage loop control circuit to transfer current from the secondary side to the primary side, while also providing primary-secondary isolation. Optocouplers play a crucial role in the stability of switching power supply systems, especially their current transfer ratio (CTR), which directly affects the gain and stability of the switching power supply loop. Switching power supplies typically operate in environments between -40°C and +85°C, and sometimes even between -55°C and +100°C. The CTR value of optocouplers is easily affected by temperature, a phenomenon commonly known as temperature drift. At high temperatures, the CTR value decreases, the loop crossover frequency decreases, the switching power supply system becomes more sensitive to environmental noise, ripple increases, and the response speed slows down. At low temperatures, the CTR value increases, the loop crossover frequency increases, the gain decreases, directly leading to output voltage overshoot or oscillation. Because of the high and low temperature characteristics of optocouplers, the loop of switching power supplies varies greatly in high temperature, normal temperature and low temperature environments. Switching power supply R&D personnel always have to spend a lot of effort on loop debugging to ensure the loop at low temperature and take into account the dynamic response at high temperature.
[0003] To address the aforementioned problems, this invention provides a circuit for compensating for the temperature drift of optocouplers in a switching power supply. Utility Model Content
[0004] The technical problem solved by this utility model is to provide a circuit for compensating for the temperature drift of optocouplers in a switching power supply.
[0005] The technical solution adopted by this utility model to solve the above-mentioned technical problems is as follows: a circuit for compensating for the temperature drift of an optocoupler in a switching power supply. The circuit includes an output voltage sampling circuit, a voltage loop control circuit, an optocoupler (hereinafter referred to as: optocoupler), a temperature compensation circuit, and a PWM control chip. The input of the output voltage sampling circuit is connected to the positive output terminal of the switching power supply, and the output is connected to the input terminal of the voltage loop control circuit. The output of the voltage loop control circuit is connected to the anode of the light-emitting diode on the input side of the optocoupler. The cathode of the light-emitting diode is connected to the temperature compensation circuit. The collector on the output side of the optocoupler is connected to a power supply port of the PWM control chip, and the emitter is connected to a feedback port of the PWM control chip. The temperature compensation circuit includes a first resistor, a second resistor, and an NTC thermistor. One end of the first resistor is connected to the cathode of the photodiode on the input side of the optocoupler, and the other end is connected in series with the second resistor and then grounded. The NTC thermistor is connected in parallel with the second resistor.
[0006] Furthermore, in another connection method of the compensation line, the second resistor is connected in series with the NTC thermistor and then in parallel with the first resistor. One end of the first resistor is connected to the cathode of the photodiode on the input side of the optocoupler, and the other end is grounded.
[0007] Furthermore, the output voltage sampling line includes a third resistor, a fourth resistor, a fifth resistor, and a first capacitor. One end of the third resistor is connected to the positive output terminal of the switching power supply, and the other end is connected to ground after being connected in series with the fourth resistor. The fifth resistor is connected in series with the first capacitor and then in parallel with the third resistor.
[0008] Furthermore, the voltage loop control circuit includes an error amplifier, a voltage regulator, a sixth resistor, a seventh resistor, an eighth resistor, a second capacitor, and a third capacitor. The positive input terminal of the error amplifier is connected to the voltage divider connection point of the third and fourth resistors in the output voltage sampling circuit. The negative input terminal of the error amplifier is connected to one end of the sixth resistor. The other end of the sixth resistor is connected to one end of the seventh resistor and the inverting terminal of the voltage regulator. The positive terminal of the voltage regulator is grounded. The other end of the seventh resistor is connected to the power supply port of the error amplifier. The output of the error amplifier is connected to the anode of the light-emitting diode on the input side of the optocoupler. One end of the eighth resistor is connected to one end of the third capacitor and the positive input terminal of the error amplifier. The other end is connected in series with the second capacitor and then connected to the other end of the third capacitor and the output of the error amplifier.
[0009] The technical advantages achieved by this utility model compared to existing designs are as follows:
[0010] The circuit for compensating for the temperature drift of the optocoupler provided by this utility model uses an NTC thermistor to compensate for the drift of the optocoupler's CTR at different temperatures, so that the loop of the switching power supply is basically consistent in high temperature, normal temperature and low temperature environments. The circuit is simple, easy to implement and low in cost. Attached Figure Description
[0011] Figure 1 This is a schematic diagram of the circuit structure for compensating for the temperature drift of the optocoupler in the switching power supply provided by this utility model;
[0012] Figure 2 This is a schematic diagram of another circuit structure for compensating for the temperature drift of the optocoupler in the switching power supply provided by this utility model. Detailed Implementation
[0013] The embodiments of the circuit of this utility model are given below with reference to the accompanying drawings to illustrate the technical solution of this utility model in detail.
[0014] by Figure 1 For example, the route is illustrated. Figure 1It includes an output voltage sampling line 10, a voltage loop control line 20, an optocoupler U1 (abbreviated as: optocoupler), a temperature compensation line 30, and a PWM control chip. The input of line 10 is connected to the positive output terminal Vout+ of the switching power supply, and the output is connected to the input terminal of line 20. The output of line 20 is connected to the anode of the light-emitting diode on the input side of optocoupler U1. The cathode of the light-emitting diode is connected to line 30. The collector on the output side of optocoupler is connected to a power supply port Vref of the PWM control chip, and the emitter is connected to a feedback port FB of the PWM control chip. Line 30 includes a first resistor R1, a second resistor R2, and an NTC thermistor. One end of R1 is connected to the cathode of the photodiode on the input side of U1, and the other end is connected in series with R2 and then grounded. The NTC thermistor is connected in parallel with R2.
[0015] The output voltage sampling line 10 includes a third resistor R3, a fourth resistor R4, a fifth resistor R5, and a first capacitor C1. One end of R3 is connected to the positive output terminal Vout+ of the switching power supply, and the other end is connected to ground after being connected in series with R4. R5 is connected in series with C1 and then in parallel with R3.
[0016] The voltage loop control circuit 20 includes an error amplifier IC1, a voltage regulator IC2, a sixth resistor R6, and a seventh resistor R7. The positive input terminal IN+ of IC1 is connected to the voltage divider connection point of R3 and R4 in circuit 10. The negative input terminal IN- of IC1 is connected to one end of R6. The other end of R6 is connected to one end of R7 and the inverting terminal of IC2. The positive terminal of IC2 is grounded. The other end of R7 is connected to the power supply port of IC1. The output of IC1 is connected to the anode of the light-emitting diode on the input side of U1.
[0017] The negative terminal IN- of IC1 is a stable reference voltage. Due to the virtual short and virtual open characteristics of the error amplifier input, the voltage of IN+ equals the voltage of IN-. Based on the output voltage value, the resistance values of R3 and R4 are determined. The output voltage of IC1 is supplied to the input side of U1. Current flows through the input-side LED, and this current is transferred to the output side by the optocoupler's photoelectric characteristics. The PWM control chip adjusts the duty cycle based on the current signal input at the FB port. The optocoupler's current transfer ratio (CTR) increases at low temperatures, resulting in a larger output current; conversely, the CTR decreases at high temperatures, resulting in a smaller output current. This leads to significant differences in the switching power supply loop under high, normal, and low temperatures. In a conventional circuit, position 30 is occupied by a regular resistor. In this invention, an NTC thermistor (negative temperature coefficient thermistor) is introduced. Its resistance increases at low temperatures, reducing the current flowing through the photodiode on the input side of U1 and offsetting the drift of the optocoupler's CTR at low temperatures. At high temperatures, the resistance of the NTC thermistor decreases, increasing the current flowing through the photodiode on the input side of U1 and offsetting the drift of the optocoupler's CTR at high temperatures. Thus, the current transmitted to the output side of U1 is not significantly different at high, normal, and low temperatures, resulting in a basically consistent loop in the switching power supply at various temperatures.
[0018] While specific embodiments of this utility model have been described above, those skilled in the art should understand that these are merely illustrative examples, and various changes or modifications can be made to these embodiments without departing from the principles and essence of this utility model. Therefore, the scope of protection of this utility model is defined by the appended claims.
Claims
1. A circuit for compensating for temperature drift of an optocoupler in a switching power supply, the circuit comprising an output voltage sampling circuit, a voltage loop control circuit, an optocoupler (hereinafter referred to as "optocoupler"), a temperature compensation circuit, and a PWM control chip, wherein the input of the output voltage sampling circuit is connected to the positive output terminal of the switching power supply, and the output is connected to the input terminal of the voltage loop control circuit; the output of the voltage loop control circuit is connected to the anode of a light-emitting diode (LED) on the input side of the optocoupler; the cathode of the LED is connected to the temperature compensation circuit; the collector of the output side of the optocoupler is connected to a power supply port of the PWM control chip, and the emitter is connected to a feedback port of the PWM control chip, characterized in that... The temperature compensation circuit includes a first resistor, a second resistor, and an NTC thermistor. One end of the first resistor is connected to the cathode of the photodiode on the input side of the optocoupler, and the other end is connected in series with the second resistor and then grounded. The NTC thermistor is connected in parallel with the second resistor.
2. The circuit for compensating for optocoupler temperature drift in a switching power supply as described in claim 1, characterized in that, In another connection method of the temperature compensation circuit, the second resistor is connected in series with the NTC thermistor and then in parallel with the first resistor. One end of the first resistor is connected to the cathode of the photodiode on the input side of the optocoupler, and the other end is grounded.
3. The circuit for compensating for optocoupler temperature drift in a switching power supply as described in claim 1, characterized in that, The output voltage sampling line includes a third resistor, a fourth resistor, a fifth resistor, and a first capacitor. One end of the third resistor is connected to the positive output terminal of the switching power supply, and the other end is connected to ground after being connected in series with the fourth resistor. The fifth resistor is connected in series with the first capacitor and then in parallel with the third resistor.
4. The circuit for compensating for optocoupler temperature drift in a switching power supply as described in claim 1, characterized in that, The voltage loop control circuit includes an error amplifier, a voltage regulator, a sixth resistor, a seventh resistor, an eighth resistor, a second capacitor, and a third capacitor. The positive input terminal of the error amplifier is connected to the voltage divider connection point of the third and fourth resistors in the output voltage sampling circuit. The negative input terminal of the error amplifier is connected to one end of the sixth resistor. The other end of the sixth resistor is connected to one end of the seventh resistor and the inverting terminal of the voltage regulator. The positive terminal of the voltage regulator is grounded. The other end of the seventh resistor is connected to the power supply port of the error amplifier. The output of the error amplifier is connected to the anode of the light-emitting diode on the input side of the optocoupler. One end of the eighth resistor is connected to one end of the third capacitor and the positive input terminal of the error amplifier. The other end is connected in series with the second capacitor and then connected to the other end of the third capacitor and the output of the error amplifier.