Constant-voltage and constant-current switching power supply circuit

Abstract

The utility model particularly relates to a constant-voltage constant-current switching power supply circuit, which comprises a rectifier bridge DB1 and a transformer T1, the output end of the rectifier bridge DB1 is connected with the input end of the transformer T1, a switching chip IC is further connected between the rectifier bridge DB1 and the transformer T1, the sixth pin of the switching chip IC is connected with an overvoltage protection circuit, and the fifth pin of the switching chip IC is connected with an overvoltage protection circuit. The overvoltage protection circuit comprises a twenty-first resistor R21, a twenty-second resistor R22, a second triode Q2 and a voltage stabilizing diode ZD1. The beneficial effects of the utility model are that the pin 6 of the switch chip IC is connected with the overvoltage protection circuit, so that the VDD voltage can be prevented from being too high in a constant voltage mode, and the power supply is prevented from being reset.

Description

Technical Field

[0001] The utility model specifically relates to a constant voltage and constant current switching power supply circuit. Background Art

[0002] This product is used in fruit and vegetable cleaning machines. Generally, electrode sheets are used as loads. Based on the principle of water electrolysis, the electrode sheet current varies with the cleaning object, and the current varies greatly (for example, when cleaning fruits, the current is small, but when cleaning seafood, the current is very large due to the high salt content and high TDS value of seafood). Therefore, such products need to be designed with constant current. With the current solution, when the load current exceeds the constant current setting point, the output voltage will be pulled down a lot, and the VDD voltage of the power chip will also be easily pulled down to the shutdown limit, causing the power supply to reset. Summary of the invention

[0003] The utility model aims to solve at least one of the technical problems existing in the prior art. To this end, one purpose of the utility model is to provide a constant voltage and constant current switching power supply circuit that can prevent the VDD voltage from being too high and avoid power reset in a constant voltage mode.

[0004] According to the utility model, a constant voltage and constant current switching power supply circuit includes a rectifier bridge DB1 and a transformer T1, the output end of the rectifier bridge DB1 is connected to the input end of the transformer T1, a switch chip IC is also connected between the rectifier bridge DB1 and the transformer T1, and the 6th pin of the switch chip IC is connected to an overvoltage protection circuit. The overvoltage protection circuit includes a twenty-first resistor R21, a twenty-second resistor R22, a second triode Q2 and a voltage-stabilizing diode ZD1, the base of the second triode Q2 is connected to the twenty-second resistor R22, the common end between the base of the second triode Q2 and the twenty-second resistor R22 is respectively connected to the twenty-first resistor R21 and the voltage-stabilizing diode ZD1, the twenty-first resistor R21 is also connected to the collector of the second triode Q2, and the other end of the twenty-second resistor R22 is connected to the emitter of the second triode Q2.

[0005] Specifically, the pin 6 of the switch chip IC is further connected to a ninth resistor R9, the ninth resistor R9 is further connected to a tenth resistor R10, and one end of the tenth resistor R10 is connected to the output end of the rectifier bridge DB1.

[0006] To be more specific, the common end between the twenty-first resistor R21 and the collector of the second transistor Q2 is respectively connected to the third diode D3 and one end of the second electrolytic capacitor EC2, the second inductor L2 is connected between the other ends of the third diode D3 and the second electrolytic capacitor EC2, the other end of the Zener diode ZD1 is connected to the nineteenth resistor R19, one end of the nineteenth resistor R19 is connected to the twentieth resistor R20, and the common end between the nineteenth resistor R19 and the twentieth resistor R20 is connected to pin 4 of the switch chip IC.

[0007] Specifically, pin 1 of the switch chip IC is connected to a sampling resistor RCS, and the sampling resistor RCS is formed by a fifteenth resistor R15, a sixteenth resistor R16, a seventeenth resistor R17 and an eighteenth resistor R18 connected in parallel. Pin 3 of the switch chip IC is connected to a fourteenth resistor R14, and the fourteenth resistor R14 is connected to the sampling resistor RCS. Pin 2 of the switch chip IC is connected to a first transistor Q1 and pin 2 of the switch chip IC is connected to the base of the first transistor Q1. The collector of the first transistor Q1 is connected to the input end of the transformer T1. A second capacitor C2 and a nineteenth resistor R19 are connected in series between the collector and the emitter of the first transistor Q1, and the other end of the nineteenth resistor R19 is connected to the common end between the fourteenth resistor R14 and the sampling resistor RCS.

[0008] Specifically, the collector of the first transistor Q1 is also connected to a first diode D1, and the first diode D1 is respectively connected to a resistor-capacitor circuit, which includes a fifth resistor R5, a sixth resistor R6, a first capacitor C1, a seventh resistor R7 and an eighth resistor R8. The fifth resistor R5, the sixth resistor R6 and the first capacitor C1 are connected in parallel, and a common end of one side of the fifth resistor R5, the sixth resistor R6 and the first capacitor C1 is connected to one end of the seventh resistor R7 and the eighth resistor R8, and the other common end of the seventh resistor R7 and the eighth resistor R8 is connected to the first diode D1.

[0009] Specifically, the output end of the rectifier bridge DB1 is provided with a first electrolytic capacitor EC1, the input end of the rectifier bridge DB1 is connected to a power inductor LF1, and the power inductor LF1 is connected to a connector J1.

[0010] The beneficial effect of the utility model is that the circuit is connected to an overvoltage protection circuit through the 6th pin of the switch chip IC, which can prevent the VDD voltage from being too high in the constant voltage mode and avoid power reset. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings.

[0012] Figure 1 It is a circuit diagram of the utility model. DETAILED DESCRIPTION

[0013] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0014] Reference below Figure 1 A constant voltage and constant current switching power supply circuit according to an embodiment of the utility model is described, including a rectifier bridge DB1 and a transformer T1, the output end of the rectifier bridge DB1 is connected to the input end of the transformer T1, a switch chip IC is also connected between the rectifier bridge DB1 and the transformer T1, and the 6th pin of the switch chip IC is connected to an overvoltage protection circuit, the overvoltage protection circuit includes a twenty-first resistor R21, a twenty-second resistor R22, a second triode Q2 and a voltage stabilizing diode ZD1, the base of the second triode Q2 is connected to the twenty-second resistor R22, the common end between the base of the second triode Q2 and the twenty-second resistor R22 is respectively connected to the twenty-first resistor R21 and the voltage stabilizing diode ZD1, the twenty-first resistor R21 is also connected to the collector of the second triode Q2, and the other end of the twenty-second resistor R22 is connected to the emitter of the second triode Q2. This circuit is connected to the overvoltage protection circuit through the 6th pin of the switch chip IC, which can prevent the VDD voltage from being too high and avoid power reset in the constant voltage mode.

[0015] The 6th pin of the switch chip IC is also connected to the 9th resistor R9, which is also connected to the 10th resistor R10, and one end of the 10th resistor R10 is connected to the output end of the rectifier bridge DB1. The common end between the 21st resistor R21 and the collector of the second transistor Q2 is respectively connected to the third diode D3 and one end of the second electrolytic capacitor EC2, and the second inductor L2 is connected between the other ends of the third diode D3 and the second electrolytic capacitor EC2. The other end of the voltage zener diode ZD1 is connected to the 19th resistor R19, and one end of the 19th resistor R19 is connected to the 20th resistor R20. The common end between the 19th resistor R19 and the 20th resistor R20 is connected to the 4th pin of the switch chip IC. The 1st pin of the switch chip IC is connected to the sampling resistor RCS, and the sampling resistor RCS is composed of the 15th resistor R15, the 10th resistor R20 and the 20th resistor R20. The sixth resistor R16, the seventeenth resistor R17 and the eighteenth resistor R18 are connected in parallel, the 3rd pin of the switch chip IC is connected to the fourteenth resistor R14, the fourteenth resistor R14 is connected to the sampling resistor RCS, the 2nd pin of the switch chip IC is connected to the first transistor Q1 and the 2nd pin of the switch chip IC is connected to the base of the first transistor Q1, the collector of the first transistor Q1 is connected to the input end of the transformer T1, the second capacitor C2 and the nineteenth resistor R19 are connected in series between the collector and the emitter of the first transistor Q1, and the other end of the nineteenth resistor R19 is connected to the common end between the fourteenth resistor R14 and the sampling resistor RCS.

[0016] The collector of the first transistor Q1 is also connected to a first diode D1, and the first diode D1 is respectively connected to a resistance-capacitance circuit, which includes a fifth resistor R5, a sixth resistor R6, a first capacitor C1, a seventh resistor R7 and an eighth resistor R8. The fifth resistor R5, the sixth resistor R6 and the first capacitor C1 are connected in parallel, and a common end of one side of the fifth resistor R5, the sixth resistor R6 and the first capacitor C1 is connected to one end of the seventh resistor R7 and the eighth resistor R8, and the other common end of the seventh resistor R7 and the eighth resistor R8 is connected to the first diode D1. The resistance-capacitance circuit is used to prevent the current from changing sharply when an instantaneous or sudden current occurs, thereby protecting other components in the circuit.

[0017] The output end of the rectifier bridge DB1 is provided with a first electrolytic capacitor EC1, the input end of the rectifier bridge DB1 is connected to a power inductor LF1, and the power inductor LF1 is connected to a connector J1. The connector J1 inputs 220VAC.

[0018] This circuit is used in fruit and vegetable cleaning machine. The output end of transformer T1 is connected to a load, which is an electrode sheet (15V / 3A). The switch chip IC1 of Biyiwei KP212LGA is used. Since there are many objects to be cleaned, such as vegetables, fruits, meat and seafood, the TDS of different ingredients vary greatly, and the current also varies greatly. Therefore, the switching power supply needs to be designed according to the constant voltage / constant current mode; that is, before the load current reaches the constant current point, it works in the constant voltage mode, and the output voltage is about 15V. When the load current exceeds the constant current setting point by about 3A, the chip VFB voltage drops below 2V and enters the constant current mode. At this time, the output voltage will be greatly reduced, and the minimum will be reduced from the normal 15V to 5V; at the same time, the VDD voltage will also drop. In order to ensure that the VDD voltage will not drop to the chip shutdown voltage (8V or below), it is necessary to improve the design of the auxiliary winding and output winding of transformer T1, and add a VDD overvoltage protection circuit. According to the parameters of the schematic diagram, the specific calculation is as follows.

[0019] The voltage VA of the second inductor L2 is calculated. The typical value of the chip VFB reference voltage is 2.0V, the twentieth feedback resistor R20=30K, and the nineteenth resistor R19=2.6K.

[0020] Since VFB / R19 = the second inductor L2 / the twentieth resistor R20 + the nineteenth resistor R19 , the voltage VA of the second inductor L2 is calculated to be = the twentieth resistor R20 + the nineteenth resistor R19 / the nineteenth resistor R19 * VFB = 25.1V.

[0021] Calculate the volts per turn of the second inductor L2 = 25.1V / 13 turns = 1.93V.

[0022] Calculate the output voltage VO = 8 turns * 1.93 = 15.44V.

[0023] Calculate the constant current setting point: ICC=1 / 4*NP / NS*0.5V / RCS=1 / 4*5.5*0.5 / 0.205=3.35A (5.5 is the primary turns ratio of transformer T1).

[0024] When the load current reaches the 3.35A constant current point, the output voltage of transformer T1 will drop a lot. According to the actual test of customer requirements (maximum TDS=3000), the output voltage will drop to about 5V. In order to ensure that the VDD voltage will not drop below 8V, it is necessary to consider increasing the number of turns of the auxiliary winding of transformer T1. After actual test and adjustment, it is designed according to 8 turns of output winding and 13 turns of auxiliary winding. Since the volts per turn of the output winding and the auxiliary winding are in a 1:1 relationship, when the output voltage is 5V, the volts per turn of the output winding is: 5V / 8 turns=0.625V, then the output voltage of the auxiliary winding VA=0.625*13=8.125V, which meets the minimum requirement of the switch chip shutdown voltage.

[0025] On the other hand, when the load is between a small current (light load) and 3.35A (constant current point), the switching power supply works in constant voltage mode. As the output power increases, VFB decreases, the PWM duty cycle increases, and the VDD voltage increases. Therefore, it is necessary to limit the voltage on the VDD pin of the switching chip so as not to exceed the chip OVP protection voltage (30V). The protection circuit can limit the VDD voltage to less than 24V; thereby avoiding power reset problems; (Note: Normal operating voltage range: 16.3V~28V).

[0026] This circuit is designed according to the above parameters and has passed the actual test by the customer, thus meeting the requirements.

[0027] Although the embodiments of the present invention have been shown and described, those skilled in the art will appreciate that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A constant voltage and constant current switching power supply circuit, comprising a rectifier bridge DB1 and a transformer T1, wherein the output end of the rectifier bridge DB1 is connected to the input end of the transformer T1, characterized in that: A switch chip IC is also connected between the rectifier bridge DB1 and the transformer T1. Pin 6 of the switch chip IC is connected to an overvoltage protection circuit. The overvoltage protection circuit includes a twenty-first resistor R21, a twenty-second resistor R22, a second transistor Q2 and a Zener diode ZD1. The base of the second transistor Q2 is connected to the twenty-second resistor R22. The common end between the base of the second transistor Q2 and the twenty-second resistor R22 is respectively connected to the twenty-first resistor R21 and the Zener diode ZD1. The twenty-first resistor R21 is also connected to the collector of the second transistor Q2. The other end of the twenty-second resistor R22 is connected to the emitter of the second transistor Q2.

2. A constant voltage and constant current switching power supply circuit according to claim 1, characterized in that: Pin 6 of the switch chip IC is also connected to a ninth resistor R9, the ninth resistor R9 is also connected to a tenth resistor R10, and one end of the tenth resistor R10 is connected to the output end of the rectifier bridge DB1.

3. A constant voltage and constant current switching power supply circuit according to claim 1, characterized in that: The common end between the twenty-first resistor R21 and the collector of the second transistor Q2 is respectively connected to the third diode D3 and one end of the second electrolytic capacitor EC2, the second inductor L2 is connected between the other ends of the third diode D3 and the second electrolytic capacitor EC2, the other end of the Zener diode ZD1 is connected to the nineteenth resistor R19, one end of the nineteenth resistor R19 is connected to the twentieth resistor R20, and the common end between the nineteenth resistor R19 and the twentieth resistor R20 is connected to pin 4 of the switch chip IC.

4. The constant voltage and constant current switching power supply circuit according to claim 1, characterized in that: Pin 1 of the switch chip IC is connected to a sampling resistor RCS, and the sampling resistor RCS is formed by a fifteenth resistor R15, a sixteenth resistor R16, a seventeenth resistor R17 and an eighteenth resistor R18 connected in parallel. Pin 3 of the switch chip IC is connected to a fourteenth resistor R14, and the fourteenth resistor R14 is connected to the sampling resistor RCS. Pin 2 of the switch chip IC is connected to a first transistor Q1 and pin 2 of the switch chip IC is connected to the base of the first transistor Q1. The collector of the first transistor Q1 is connected to the input end of the transformer T1. A second capacitor C2 and a nineteenth resistor R19 are connected in series between the collector and the emitter of the first transistor Q1, and the other end of the nineteenth resistor R19 is connected to the common end between the fourteenth resistor R14 and the sampling resistor RCS.

5. A constant voltage and constant current switching power supply circuit according to claim 4, characterized in that: The collector of the first transistor Q1 is also connected to the first diode D1, and the first diode D1 is respectively connected to the resistance-capacitance circuit, which includes a fifth resistor R5, a sixth resistor R6, a first capacitor C1, a seventh resistor R7 and an eighth resistor R8. The fifth resistor R5, the sixth resistor R6 and the first capacitor C1 are connected in parallel, and a common end of one side of the fifth resistor R5, the sixth resistor R6 and the first capacitor C1 is connected to one end of the seventh resistor R7 and the eighth resistor R8, and the other common end of the seventh resistor R7 and the eighth resistor R8 is connected to the first diode D1.

6. The constant voltage and constant current switching power supply circuit according to claim 1, characterized in that: The output end of the rectifier bridge DB1 is provided with a first electrolytic capacitor EC1, the input end of the rectifier bridge DB1 is connected to a power inductor LF1, and the power inductor LF1 is connected to a connector J1.

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