Isolated power supply output voltage regulating circuit

Abstract

The utility model discloses an isolation type power supply output voltage adjusting circuit, comprising an MCU control circuit, a switch power supply output circuit, an optical coupling isolation circuit, a signal processing circuit and a PWM conversion circuit, the MCU control circuit is connected with the input end of the optical coupling isolation circuit and shares a signal ground with the input end of the optical coupling isolation circuit; the output end of the optocoupler isolation circuit is connected with the input end of the signal processing circuit, the output end of the signal processing circuit is connected with the input end of the PWM conversion circuit, the output end of the PWM conversion circuit is connected with the switching power supply output circuit, and the output end of the switching power supply output circuit is further connected with the MCU control circuit. The beneficial effects of the utility model are that by adding the optocoupler isolation circuit, the signal processing circuit and the PWM conversion circuit, isolation control is realized, the circuit safety is high, and the reliability is high; and the digital signal is used for voltage regulation, so that the influence of noise can be reduced to the greatest extent.

Description

Technical Field

[0001] The utility model relates to the technical field of switching power supplies, in particular to an isolated power supply output voltage regulating circuit. Background Art

[0002] With the continuous expansion of electrical equipment, the conventional single output voltage of the switching power supply can no longer meet the requirements of diversified usage scenarios. Some occasions require the same power supply equipment to have different output voltages. Most switching power supplies have output voltage regulation functions. The currently commonly used voltage regulation circuits have the following problems:

[0003] First, use a mechanical potentiometer adjustment solution, such as Figure 1 The circuit structure is simple and the cost is low. Because the initial resistance of the potentiometer is uncertain, it needs to be manually adjusted to the required output voltage. The changes of the internal mechanical contacts in harsh environments such as vibration, high and low temperatures cause the output resistance to drift. The output voltage adjustment has low accuracy and a narrow adjustment range. It is only used in power supply equipment with low cost requirements and good environment.

[0004] Second, use a non-isolated digital circuit regulation solution, such as Figure 2 . The circuit uses the MCU control circuit to output an adjustable output voltage reference, which is directly connected to the output voltage adjustment terminal of the switching power supply, adjusts the current flowing into or out of the adjustment terminal, and indirectly adjusts the impedance of the upper and lower voltage divider of the internal reference source of the switching power supply, thereby achieving the purpose of adjusting the output voltage. This circuit can achieve high-precision output voltage regulation through the feedback circuit, but the power supply ground of the MCU control circuit must be connected to the output ground of the switching power supply at a single point, that is, a non-isolated connection method is used. Due to the large fundamental or multiple harmonic interference of the switching power supply output noise, this connection method is easy to interfere with the normal operation of the MCU circuit, and in various transient states (startup, shutdown or fault moment), there are high requirements for the voltage stability of the MCU control circuit output, otherwise it is easy to cause the output voltage to be out of control. In order to ensure the output voltage accuracy, this connection method is only suitable for one MCU circuit to control one switching power supply output. In situations where multiple output voltages are isolated from each other and need to be adjusted, multiple MCU control circuits are required, which is costly. Utility Model Content

[0005] In view of the defects in the prior art, the purpose of the utility model is to provide an isolated power supply output voltage regulation circuit.

[0006] The technical solution adopted by the utility model is: an isolated power supply output voltage regulation circuit, including an MCU control circuit and a switching power supply output circuit; the isolated power supply output voltage regulation circuit also includes an optocoupler isolation circuit, a signal processing circuit and a PWM conversion circuit, the MCU control circuit is connected to the input end of the optocoupler isolation circuit and shares a signal ground, the output end of the optocoupler isolation circuit is connected to the input end of the signal processing circuit, the output end of the signal processing circuit is connected to the input end of the PWM conversion circuit, the output end of the PWM conversion circuit is connected to the switching power supply output circuit, and the output end of the switching power supply output circuit is also connected to the MCU control circuit, for feeding back the output voltage signal to the MCU control circuit.

[0007] Preferably, the optical coupling isolation circuit includes an optical coupler, and the optical coupler is a high-speed switching optical coupler.

[0008] Preferably, the signal processing circuit is a signal inversion circuit, and the signal output by the optocoupler is inverted by the signal inversion circuit and then transmitted to the subsequent PWM conversion circuit.

[0009] Preferably, the signal processing circuit includes a current limiting resistor, and the signal output by the optocoupler is directly transmitted to the PWM conversion circuit of the subsequent stage through the current limiting resistor.

[0010] Preferably, the PWM conversion circuit includes a capacitor C2, a capacitor C3, a TVS tube Z1 and a chip N2;

[0011] The VCC terminal of the chip N2 is grounded through the capacitor C2, the output terminal of the chip N2 is grounded through the capacitor C3, and the TVS tube Z1 is connected in parallel with the capacitor C3.

[0012] Preferably, the chip N2 adopts GP8101S, and the PWM terminal of the chip N2 serves as the input terminal of the PWM conversion circuit.

[0013] Preferably, the anode of the TVS tube Z1 is grounded, and the cathode of the TVS tube Z1 is connected to the output end of the chip N2.

[0014] The beneficial effects of the utility model are embodied in: by adding optocoupler isolation, signal processing and PWM conversion circuits on the basis of existing non-isolated digital circuits, isolation control is realized, and the duty cycle of the PWM signal output by the MCU control circuit is used to adjust the output voltage of the power supply, and digital signals are used for voltage regulation instead of analog signals, which can minimize the impact of noise; making the circuit of this solution highly safe, anti-interference and stable. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the specific implementation of the utility model or the technical solution in the prior art, the following is a brief introduction to the drawings required for the specific implementation or the prior art description. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, each element or part is not necessarily drawn according to the actual scale.

[0016] Figure 1 A circuit schematic diagram of a mechanical potentiometer adjustment solution provided in the prior art;

[0017] Figure 2 A circuit schematic diagram of a non-isolated digital circuit adjustment solution provided by the prior art;

[0018] Figure 3 A principle block diagram of an isolated power supply output voltage regulation circuit provided by an embodiment of the utility model;

[0019] Figure 4 A connection diagram of an isolated power supply output voltage regulation circuit provided by an embodiment of the utility model;

[0020] Figure 5 A connection diagram of another isolated power supply output voltage regulation circuit provided by an embodiment of the utility model;

[0021] Figure 6 A connection diagram for controlling the output voltage of a multi-way switching power supply provided in an embodiment of the utility model. DETAILED DESCRIPTION

[0022] The following embodiments of the technical solution of the utility model are described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the utility model, and are therefore only used as examples, and cannot be used to limit the protection scope of the utility model.

[0023] It should be noted that, unless otherwise specified, the technical terms or scientific terms used in this application should have the common meanings understood by technicians in the field to which the utility model belongs.

[0024] like Figures 3 to 5As shown, an isolated power supply output voltage regulation circuit provided by an embodiment of the present invention includes an MCU control circuit and a switching power supply output circuit; the isolated power supply output voltage regulation circuit also includes an optocoupler isolation circuit, a signal processing circuit and a PWM conversion circuit, the MCU control circuit is connected to the input end of the optocoupler isolation circuit and shares a signal ground, the output end of the optocoupler isolation circuit is connected to the input end of the signal processing circuit, the output end of the signal processing circuit is connected to the input end of the PWM conversion circuit, the output end of the PWM conversion circuit is connected to the switching power supply output circuit, and the output end of the switching power supply output circuit is also connected to the MCU control circuit, for feeding back the output voltage signal to the MCU control circuit.

[0025] In this embodiment, the MCU control circuit is used to output a PWM waveform with a fixed amplitude and a fixed frequency, and the duty cycle of the waveform can be adjusted from 0 to 100%. R1 is a current limiting resistor. At the same time, the MCU control circuit receives the output feedback to sample the output voltage signal Vo-sample (i.e., the feedback in the figure), and then adjusts the duty cycle of the PWM signal through feedback control, thereby further improving the output voltage accuracy.

[0026] Reference Figure 4 , the circuit is composed of optocoupler N1 and resistor R7. To ensure the consistency of the optocoupler input and output waveforms, duty cycle and phase, the optocoupler of this circuit should choose a high-speed switching optocoupler, such as Toshiba's TLP2362, TLP2358, etc. The optocoupler secondary power supply is connected to the +5V voltage provided by the subsequent chip N2. When the MCU control circuit provides a high level, the optocoupler is turned on, and the optocoupler secondary collector output provides a low level of 0-0.3V; when the MCU control circuit provides a low level, the optocoupler is cut off, and resistor R7 provides a +5V high level for the secondary collector output.

[0027] In application, in order to improve the flexibility of application, the signal processing circuit has two signal processing modes: positive and negative, specifically including:

[0028] The first type (i.e. Figure 4 ), the signal processing circuit is a signal inversion circuit, the signal output by the optocoupler is inverted by the signal inversion circuit and then transmitted to the PWM conversion circuit of the subsequent stage; that is, the signal output by the optocoupler is inverted by a circuit composed of resistor R2, resistor R3, resistor R4, resistor R6, capacitor C4, and transistor V1, and then connected to the input of the subsequent chip N2. This method is negative logic control, and the PWM signal input duty cycle D output by the MCU control circuit is inversely proportional to the output voltage Vo of the switching power supply. The relationship between Vch and the duty cycle D is:

[0029] V ch =5×D

[0030] The second type (i.e. Figure 5 ), the signal processing circuit includes a current limiting resistor (i.e., R5 in the figure), and the signal output by the optocoupler is directly transmitted to the PWM conversion circuit of the subsequent stage through the current limiting resistor; that is, the optocoupler output signal is directly connected to the input of the subsequent chip N2 through the resistor R5. This mode is positive logic control, that is, the PWM signal input duty cycle D output by the MCU control circuit is proportional to the output voltage Vo of the switching power supply, and the relationship between Vch and the duty cycle D is:

[0031] V ch =5×(1-D).

[0032] It should be noted that since positive and negative logic control cannot be selected at the same time, resistor R5 and the signal inversion circuit cannot be used at the same time; Figure 4 and Figure 5 The difference lies in the difference of the signal processing circuits.

[0033] Furthermore, the PWM conversion circuit includes a capacitor C2, a capacitor C3, a TVS tube Z1 and a chip N2;

[0034] The VCC terminal of the chip N2 is grounded through the capacitor C2, the output terminal of the chip N2 is grounded through the capacitor C3, and the TVS tube Z1 is connected in parallel with the capacitor C3; wherein the PWM terminal of the chip N2 serves as the input terminal of the PWM conversion circuit; the anode of the TVS tube Z1 is grounded, and the cathode of the TVS tube Z1 is connected to the output terminal of the chip N2.

[0035] The model of the chip N2 is GP8101S, which realizes PWM signal input with a duty cycle change of 0-100%, and linearly converts it into an analog voltage output Vch of 0-5V. The analog voltage enters the voltage adjustment Trim terminal of the subsequent switching power supply to adjust the output voltage of the switching power supply. The VCC power supply range of the chip N2 is 9-36V. The chip N2 provides a +5V power supply voltage, which can power the secondary side of the front-end optocoupler isolation circuit and the signal processing circuit; the TVS tube Z1 provides surge and electrostatic protection for the conversion circuit and the Trim terminal circuit of the switching power supply.

[0036] Switching power supply output circuit. This circuit is a commonly used voltage regulation circuit for switching power supplies, consisting of resistors Ra1, Ra2, and Ra3, and the internal control chip reference voltage is Vref.

[0037] Because isolation control is used in the solution, one MCU control circuit can control multiple power outputs. The connection method is as follows: Figure 6 shown.

[0038] The advantages of the utility model include:

[0039] First, the use of high-speed switching optocouplers to achieve isolation control between the MCU control circuit and the switching power supply output voltage has strong circuit safety and high reliability. At the same time, it can achieve the requirement that one MCU control circuit can simultaneously control the output voltages of multiple switching power supplies. Through feedback control, it is ensured that each voltage can achieve high accuracy.

[0040] Second, the PWM wave with adjustable duty cycle is used to adjust the output voltage of the switching power supply. The MCU control circuit is simple and easy to implement. At the same time, digital signals are used instead of analog signals to minimize the impact of noise.

[0041] Third, the high-precision PWM conversion chip GP8101S is used to convert the PWM signal duty cycle into a DC signal, making the circuit adjustment linear and wide in adjustment range.

[0042] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the utility model, rather than to limit it. Although the utility model has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. These modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the utility model, and they should all be included in the scope of the claims and specification of the utility model.

Claims

1. An isolated power supply output voltage regulation circuit, comprising an MCU control circuit and a switching power supply output circuit; characterized in that The isolated power supply output voltage regulation circuit also includes an optocoupler isolation circuit, a signal processing circuit and a PWM conversion circuit. The MCU control circuit is connected to the input end of the optocoupler isolation circuit and shares a common signal ground. The output end of the optocoupler isolation circuit is connected to the input end of the signal processing circuit. The output end of the signal processing circuit is connected to the input end of the PWM conversion circuit. The output end of the PWM conversion circuit is connected to the switching power supply output circuit. The output end of the switching power supply output circuit is also connected to the MCU control circuit for feeding back the output voltage signal to the MCU control circuit.

2. The isolated power supply output voltage regulation circuit according to claim 1, characterized in that The optical coupler isolation circuit includes an optical coupler, and the optical coupler adopts a high-speed switching type optical coupler.

3. The isolated power supply output voltage regulation circuit according to claim 2, characterized in that The signal processing circuit is a signal inversion circuit. The signal output by the optocoupler is inverted by the signal inversion circuit and then transmitted to the PWM conversion circuit at the subsequent stage.

4. The isolated power supply output voltage regulation circuit according to claim 2, characterized in that The signal processing circuit includes a current limiting resistor, and the signal output by the optocoupler is directly transmitted to the PWM conversion circuit of the subsequent stage through the current limiting resistor.

5. The isolated power supply output voltage regulation circuit according to claim 1, characterized in that , the PWM conversion circuit includes a capacitor C2, a capacitor C3, a TVS tube Z1 and a chip N2; The VCC terminal of the chip N2 is grounded through the capacitor C2, the output terminal of the chip N2 is grounded through the capacitor C3, and the TVS tube Z1 is connected in parallel with the capacitor C3.

6. The isolated power supply output voltage regulation circuit according to claim 5, characterized in that ,The chip N2 adopts GP8101S, and the PWM end of the chip N2 serves as the input end of the PWM conversion circuit.

7. The isolated power supply output voltage regulation circuit according to claim 5, characterized in that , the anode of the TVS tube Z1 is grounded, and the cathode of the TVS tube Z1 is connected to the output end of the chip N2.

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