CN221688507U - A step-down circuit and a switching power supply - Google Patents

Abstract

The utility model discloses a step-down circuit and a switching power supply, wherein the step-down circuit comprises a feedback module and a control module, wherein the feedback module is connected to the control module; the feedback module comprises a three-terminal adjustable shunt reference voltage source, a first resistor, a second resistor and a third resistor, wherein the reference end of the three-terminal adjustable shunt reference voltage source is connected to the voltage output end through the first resistor, the reference end of the three-terminal adjustable shunt reference voltage source is also connected to the power supply ground through the second resistor, the anode of the three-terminal adjustable shunt reference voltage source is connected to the power supply ground through the third resistor, and the anode of the three-terminal adjustable shunt reference voltage source is connected to the signal ground. The utility model introduces a third resistor in the feedback module and is connected between the three-terminal adjustable shunt reference voltage source and the power supply ground, thereby reducing the output voltage, avoiding the problem of over-power use of the power supply due to the output requiring a larger current, and effectively playing the role of active output voltage reduction.

Description

A step-down circuit and a switching power supply

Technical Field

The utility model belongs to the field of switching power supplies, and in particular relates to a step-down circuit and a switching power supply.

Background Art

Switching power supplies are currently showing a development trend of high efficiency, high power density, and multiple applications. There are more and more places where large current is required for output. In some special application places, especially where there is a greater demand for output current and the output voltage requirement is not particularly high, when the output current exceeds the rated current, it is easy to cause reliability risks due to excessive power and affect the service life of the power supply.

Summary of the invention

In view of this, an object of the present invention is to provide a step-down circuit and a switching power supply, which can actively reduce the output voltage and thus reduce the power.

In order to achieve the above purpose, the utility model adopts the following technical solutions:

In a first aspect, the utility model provides a step-down circuit, the step-down circuit comprising a feedback module and a control module, the feedback module being connected to the control module;

The feedback module includes a three-terminal adjustable shunt reference voltage source, a first resistor, a second resistor and a third resistor, the cathode of the three-terminal adjustable shunt reference voltage source is connected to the voltage input terminal, the cathode of the three-terminal adjustable shunt reference voltage source is connected to the reference terminal of the three-terminal adjustable shunt reference voltage source through the control module, the reference terminal of the three-terminal adjustable shunt reference voltage source is connected to the voltage output terminal through the first resistor, the reference terminal of the three-terminal adjustable shunt reference voltage source is also connected to the power supply ground through the second resistor, the anode of the three-terminal adjustable shunt reference voltage source is connected to the power supply ground through the third resistor, and the anode of the three-terminal adjustable shunt reference voltage source is connected to the signal ground.

Furthermore, the control module includes a fourth resistor, a first capacitor and a second capacitor, the first end of the fourth resistor is connected to the cathode of the three-terminal adjustable shunt reference voltage source, the second end of the fourth resistor is connected to the reference end of the three-terminal adjustable shunt reference voltage source through the second capacitor, and the cathode of the three-terminal adjustable shunt reference voltage source is connected to the reference end of the three-terminal adjustable shunt reference voltage source through the first capacitor.

Furthermore, the step-down circuit also includes an optocoupler circuit module connected between the cathode of the three-terminal adjustable shunt reference voltage source and the voltage input terminal, the first input terminal of the optocoupler circuit module is connected to the voltage input terminal, and the second input terminal of the optocoupler circuit module is connected to the cathode of the three-terminal adjustable shunt reference voltage source.

Furthermore, the optocoupler circuit module includes a fifth resistor, a sixth resistor, a seventh resistor and an optocoupler, the anode of the optocoupler diode of the optocoupler is connected to the voltage input terminal through the sixth resistor, the anode of the optocoupler diode of the optocoupler is connected to the cathode of the optocoupler diode of the optocoupler through the seventh resistor, the cathode of the optocoupler diode of the optocoupler is connected to the cathode of the three-terminal adjustable shunt reference voltage source, the collector of the optocoupler transistor of the optocoupler is connected to the feedback terminal through the fifth resistor, and the emitter of the optocoupler transistor of the optocoupler is connected to the analog ground.

In a second aspect, the utility model provides a switching power supply, comprising the step-down circuit as described in the first aspect.

Compared with the prior art, the utility model has the following beneficial effects:

The utility model introduces a third resistor in the feedback module and connects it between the three-terminal adjustable shunt reference voltage source and the power ground, thereby reducing the output voltage, avoiding the problem of over-power usage of the power supply due to the output requiring a larger current, and effectively plays the role of active output voltage reduction. In addition, the utility model has a simple circuit structure, is easy to implement, and can effectively reduce production costs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a circuit schematic diagram of a step-down circuit of the utility model;

FIG. 2 is a schematic diagram of an application circuit of a step-down circuit embodiment of the utility model.

DETAILED DESCRIPTION

In order to make the purpose, technical solution and advantages of the utility model more clear, the utility model is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the utility model and are not used to limit the utility model.

Referring to FIG1 , an embodiment of the utility model provides a step-down circuit, the step-down circuit includes a feedback module 100 and a control module 200 , the feedback module 100 is connected to the control module 200 ;

The feedback module 100 includes a three-terminal adjustable shunt reference voltage source U1, a first resistor R1, a second resistor R2 and a third resistor. The cathode of the three-terminal adjustable shunt reference voltage source U1 is connected to the voltage input terminal, the cathode of the three-terminal adjustable shunt reference voltage source U1 is connected to the reference terminal of the three-terminal adjustable shunt reference voltage source U1 through the control module 200, the reference terminal of the three-terminal adjustable shunt reference voltage source U1 is connected to the voltage output terminal through the first resistor R1, the reference terminal of the three-terminal adjustable shunt reference voltage source U1 is also connected to the power ground GND through the second resistor R2, the anode of the three-terminal adjustable shunt reference voltage source U1 is connected to the power ground GND through the third resistor, and the anode of the three-terminal adjustable shunt reference voltage source U1 is connected to the signal ground SGND.

In this embodiment, Vo is set as the output voltage; the first resistor R1 and the second resistor R2 are respectively the feedback pull-up resistor and the pull-down resistor, and Vref is the reference voltage of the three-terminal adjustable shunt reference voltage source U1; when the third resistor is not set, R3 is set as a 0Ω resistor;

Then: Vo = Vref*(R1+R2)/R2——(1)

Assume Vo is the output voltage; Io is the output current; the first resistor R1 and the second resistor R2 are the feedback pull-up and pull-down resistors respectively; _VR2 is the voltage across the second resistor R2; after the third resistor is set, Vx is the voltage across the third resistor R3. Since the two ends of the third resistor R3 are connected to GND and SGND respectively, the actual current flows from GND to SGND. At this time, the current on the third resistor R3 is -Io; Vref is the reference voltage of the control IC; then:

(1) R3*(-Io) = -Vx;

(1) _VR2 +Vx = Vref;

(2) _VR2 = Vref - Vx;

(3)Vo=R1*(Vref-Vx)/R2+Vref;

(4)Vo=Vref*(R1+R2)/R2-Vx*R1/R2;

Finally, we get: Vo = Vref*(R1+R2)/R2-R3*Io*R1/R2——(2);

Through the above calculation, it can be concluded that after the two ends of the third resistor R3 introduced by connecting the output negative terminal GND and the output feedback pull-down resistor to the A pole of the three-terminal adjustable shunt reference voltage source U1, by comparing the above output voltage Vo calculation formula (1) and formula (2), it can be concluded that the output voltage Vo is reduced by R3*Io*R1/R2 voltage. In this embodiment, when the output load current increases, the line loss increases, and the output voltage can be reduced accordingly, thereby eliminating the problem of over-power use of the power supply due to the need for a larger output current, and effectively plays the role of active output voltage reduction. In this embodiment, the first resistor R1 and the second resistor R2 can adjust the resistance value according to different output voltages, and the third resistor R3 can adjust the resistance value according to different line impedances and the output current required, so as to adjust the output voltage.

In one embodiment, the control module 200 includes a fourth resistor R4, a first capacitor C1 and a second capacitor C2, the first end of the fourth resistor R4 is connected to the cathode of the three-terminal adjustable shunt reference voltage source U1, the second end of the fourth resistor R4 is connected to the reference end of the three-terminal adjustable shunt reference voltage source U1 through the second capacitor C2, and the cathode of the three-terminal adjustable shunt reference voltage source U1 is connected to the reference end of the three-terminal adjustable shunt reference voltage source U1 through the first capacitor C1.

In this embodiment, the control module 200 is composed of a first capacitor C1, a second capacitor C2 and a fourth resistor R4. The stability, accuracy and speed of the output can be adjusted by adjusting the first capacitor C1 and the second capacitor C2 of the loop.

In one embodiment, the step-down circuit also includes an optocoupler circuit module 300 connected between the cathode of the three-terminal adjustable shunt reference voltage source U1 and the voltage input terminal, the first input terminal of the optocoupler circuit module 300 is connected to the voltage input terminal, and the second input terminal of the optocoupler circuit module 300 is connected to the cathode of the three-terminal adjustable shunt reference voltage source U1.

In this embodiment, the optocoupler circuit module 300 includes a fifth resistor R5, a sixth resistor R6, a seventh resistor R7 and an optocoupler OP1, the anode of the optocoupler diode of the optocoupler OP1 is connected to the voltage input terminal through the sixth resistor R6, the anode of the optocoupler diode of the optocoupler OP1 is connected to the cathode of the optocoupler diode of the optocoupler OP1 through the seventh resistor R7, the cathode of the optocoupler diode of the optocoupler OP1 is connected to the cathode of the three-terminal adjustable shunt reference voltage source U1, the collector of the optocoupler transistor of the optocoupler OP1 is connected to the feedback terminal through the fifth resistor R5, and the emitter of the optocoupler transistor of the optocoupler OP1 is connected to the analog ground AGND.

In this embodiment, the feedback terminal FB is a feedback signal pin of the control IC. By feeding back different feedback signals, different control signals are sent out through the IC control, thereby controlling the transformer T1, as shown in FIG. 2, affecting the voltage input terminal Vo1, and obtaining different input voltages.

In addition, an embodiment of the utility model further provides a switching power supply, comprising the step-down circuit as described in the above embodiment.

The above description is not a limitation of the present invention. Any changes, modifications, additions or substitutions made by ordinary technicians in this technical field within the essential scope of the present invention should also fall within the protection scope of the present invention.

Claims (5)

1. A step-down circuit, characterized in that: the step-down circuit comprises a feedback module and a control module, and the feedback module is connected to the control module; The feedback module includes a three-terminal adjustable shunt reference voltage source, a first resistor, a second resistor and a third resistor, the cathode of the three-terminal adjustable shunt reference voltage source is connected to the voltage input terminal, the cathode of the three-terminal adjustable shunt reference voltage source is connected to the reference terminal of the three-terminal adjustable shunt reference voltage source through the control module, the reference terminal of the three-terminal adjustable shunt reference voltage source is connected to the voltage output terminal through the first resistor, the reference terminal of the three-terminal adjustable shunt reference voltage source is also connected to the power supply ground through the second resistor, the anode of the three-terminal adjustable shunt reference voltage source is connected to the power supply ground through the third resistor, and the anode of the three-terminal adjustable shunt reference voltage source is connected to the signal ground. 2. The step-down circuit according to claim 1 is characterized in that the control module includes a fourth resistor, a first capacitor and a second capacitor, the first end of the fourth resistor is connected to the cathode of the three-terminal adjustable shunt reference voltage source, the second end of the fourth resistor is connected to the reference end of the three-terminal adjustable shunt reference voltage source through the second capacitor, and the cathode of the three-terminal adjustable shunt reference voltage source is connected to the reference end of the three-terminal adjustable shunt reference voltage source through the first capacitor. 3. The step-down circuit according to claim 1 is characterized in that the step-down circuit also includes an optocoupler circuit module connected between the cathode of the three-terminal adjustable shunt reference voltage source and the voltage input terminal, the first input terminal of the optocoupler circuit module is connected to the voltage input terminal, and the second input terminal of the optocoupler circuit module is connected to the cathode of the three-terminal adjustable shunt reference voltage source. 4. The step-down circuit according to claim 3 is characterized in that the optocoupler circuit module comprises a fifth resistor, a sixth resistor, a seventh resistor and an optocoupler, the anode of the optocoupler diode of the optocoupler is connected to the voltage input terminal through the sixth resistor, the anode of the optocoupler diode of the optocoupler is connected to the cathode of the optocoupler diode of the optocoupler through the seventh resistor, the cathode of the optocoupler diode of the optocoupler is connected to the cathode of the three-terminal adjustable shunt reference voltage source, the collector of the optocoupler transistor of the optocoupler is connected to the feedback terminal through the fifth resistor, and the emitter of the optocoupler transistor of the optocoupler is connected to the analog ground. 5. A switching power supply, characterized by comprising the step-down circuit according to any one of claims 1 to 4.