CN108199462B - An AC-DC converter circuit - Google Patents

Abstract

The invention discloses an AC-DC conversion circuit, comprising an AC-to-DC circuit, a charging circuit and a DC-voltage conversion circuit, wherein: the AC-to-DC circuit is used to convert the AC power into a first predetermined DC voltage output, and the output terminal of the DC voltage It is connected to the input end of the charging circuit to charge the rechargeable battery; the output end is also connected to the input end of the DC voltage conversion circuit, which converts the first predetermined DC voltage into a second predetermined DC voltage and a third predetermined DC voltage output after voltage. The present invention has stable output when there is an AC 220V voltage, and when there is no AC 220V voltage, the stable output can be achieved by working with a battery.

Description

An AC-DC converter circuit

This application is a divisional application for an invention patent application with the application number "201610217109.X", the application date being April 8, 2016, and the invention name being "AC-DC conversion and charging circuit"

technical field

The invention relates to an AC-DC conversion circuit, in particular to an AC-DC conversion circuit with a charging function.

Background technique

The AC-DC conversion circuit provides input power for the DC motor drive circuit. In the actual use process of the existing AC-DC conversion circuit, the continuity of the AC 220V on-off is unstable, and it is easy to work when it is impacted by the load current. abnormal. The advantage of the present invention is that when there is an AC 220V voltage, the output is stable, and when there is no AC 220V voltage, the output is stable by battery operation. In addition, the present invention also has the following advantages:

1. When the AC 220V voltage is connected, the stable output DC voltage is 24V, 12V and 3.3V, and the battery is charged according to the power situation. When the AC 220V voltage is disconnected, the battery works and can also output DC 24V, 12V and 3.3V stably.

2. The AC 220V voltage is the mains power, which may be unstable. If the AC 220V mains power is too high, the output 24V will also increase accordingly, then the relay RLY1 will act to change the number of output turns, so that the voltage will drop. to ensure that the output DC voltage will not be too high.

3. The battery charging circuit uses a hysteresis comparator to compare the voltage to determine whether to charge or not to prevent the battery from being overcharged or overdischarged. The reference voltage and comparison voltage in the circuit are obtained by dividing the voltage by the voltage dividing resistor.

4. The battery is isolated by two cascaded diodes, and the battery is isolated from the DC 24V voltage, so as to avoid mixing with the battery when connecting the AC 220V, and prevent the battery current from flowing back. The design of the isolated battery is to avoid the direct charging of the battery.

5. The DC 24V is converted into DC 12V and DC 3.3V with a step-down voltage regulator chip, which improves the working efficiency and stability of the power supply.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a power supply suitable for driving a DC motor and other control units, and to improve the use stability of the power supply.

For realizing the purpose of the present invention, adopt following technical scheme to realize:

An AC-DC conversion charging circuit, comprising an AC-to-DC circuit, a charging circuit and a DC voltage conversion circuit, wherein:

The AC-to-DC circuit is used to convert the AC power into a first predetermined DC voltage output, and the output terminal of the DC voltage is connected to the input terminal of the charging circuit to charge the rechargeable battery;

The output terminal is also connected to the input terminal of the DC voltage conversion circuit, and the DC voltage conversion circuit converts the first predetermined DC voltage into a second predetermined DC voltage and a third predetermined DC voltage for output.

The AC-DC conversion charging circuit, preferably:

The AC-to-DC circuit includes a transformer, a rectifier circuit and an anti-overvoltage circuit;

The high-voltage side winding of the transformer is connected to a 220V AC power supply, and the low-voltage side winding is connected to a rectifier circuit, and the rectifier circuit is used to convert the first predetermined voltage AC power transformed by the transformer into a first predetermined voltage DC voltage;

The anti-overvoltage circuit is used to detect whether the converted DC voltage is higher than the first predetermined voltage. When higher than the first predetermined voltage, the anti-overvoltage circuit changes the number of turns of the winding on the low-voltage side of the transformer and reduces the AC voltage on the low-voltage side.

The AC-DC conversion charging circuit, preferably:

The rectifier circuit is composed of four diodes D3, D4, D5 and D6; the low-voltage side winding of the transformer includes three terminals, which are respectively connected to the relay and the rectifier circuit;

The first terminal is connected to the normally closed contact of the relay; the middle terminal is connected to the normally open contact of the relay; the second terminal is connected to the anode of the diode D3 in the rectifier circuit; the relay switch contact is connected to the anode of the diode D4; the anode of the diode D5 is grounded , the cathode is connected to the anode of the diode D3; the anode of the diode D6 is grounded, and the cathode is connected to the anode of the diode D4; the cathode of the diode D3 and the cathode of the diode D4 are connected as the output end of the rectifier circuit.

The AC-DC conversion charging circuit, preferably:

The anti-overvoltage circuit includes: the first operational amplifier U1B, the positive feedback resistor R7, the transistor Q3, the current limiting resistors R10, R11, the voltage dividing resistors R15, R16, R19, R20, the electrolytic capacitors CE1 and CE2 for filtering, the resistor R11 and the diode D7; where:

The positive feedback resistor R7 is connected between the positive input terminal and the output terminal of U1B; the output terminal is connected to the base of Q3;

One end of R10 is connected to the DC voltage output whose voltage value is half of the second predetermined DC voltage, and the other end is connected to the positive input terminal of U1B;

One end of R19 is connected to the output end of the rectifier circuit, the other end is connected to the negative input end of U1B in series with R15, one end of R20 is grounded, and the other end is connected to the negative input end of U1B in series with R16;

The positive pole of CE2 is connected to the negative input terminal of U1B, and the negative pole is connected to ground; the positive pole of CE1 is connected to the base of Q3, and the negative pole is connected to the ground; the output terminal of U1B is connected to R11, and the other terminal of R11 is connected to the base level of Q3;

The collector of Q3 is connected to the negative pole of the electromagnetic coil of the relay, the emitter of Q3 is grounded, the positive pole of the electromagnetic coil of the relay is connected to the output end of the rectifier circuit; the positive pole of D7 is connected to the negative pole of the electromagnetic coil of the relay, and the negative pole is connected to the positive pole of the electromagnetic coil.

The AC-DC conversion charging circuit, preferably:

The charging circuit includes a charging branch and a battery voltage detection circuit, the charging branch is used to charge the rechargeable battery, and the battery voltage detection circuit is used to detect the voltage of the rechargeable battery, when the voltage of the rechargeable battery is lower than a predetermined voltage threshold When the battery voltage detection circuit controls the charging branch to charge the rechargeable battery.

The AC-DC conversion charging circuit, preferably:

The charging branch includes diodes D1, D2, D9, D10, D11, resistors R1, R6, transistor Q1, and rechargeable battery P1;

The output terminal of the rectifier circuit is connected to the positive pole of D1, the negative pole of D1 is connected to the positive pole of D2, and the negative pole of D2 is connected to the base pole of Q1;

The negative electrode of D2 is connected to R3, the other end of R3 is connected to the collector of Q2, one end of R1 is connected to the output end of the rectifier circuit, the other end is connected to the collector of Q1, the emitter of Q1 is connected to R6, the other end of R6 is connected to the positive electrode of D10, D10 The negative pole of the battery is connected to the positive pole of the rechargeable battery P1, the output terminal of the rectifier circuit is connected to the positive pole of D9, the negative pole of D9 is the first predetermined DC voltage lead terminal VCC, the negative pole of D9 is connected to the negative pole of D11, the positive pole of D11 is connected to the positive pole of P1, The negative pole of P1 is grounded;

The battery voltage detection circuit includes: a second operational amplifier U1A, a filter capacitor C1, voltage dividing resistors R2, R4, R9, R14, R12, R13, R17, R18, a positive feedback resistor R5, resistors R8, R3, a diode D8, Transistor Q2; where:

The ground terminal of U1A is grounded, and the voltage input terminal is connected to the second predetermined DC voltage input terminal;

One end of C1 is connected to the working voltage input end, and the other end is grounded;

One end of R2 is connected to the second predetermined DC voltage input end, the other end is connected to R4, and the other end of R4 is connected to the positive input end of U1A;

One end of R9 is connected to the positive input end of U1A, the other end is connected to R14, the other end of R14 is grounded, the voltage between R9 and R4 is half of the second predetermined DC voltage, and the voltage is output from the connection point of R9 and R4;

The negative input end of U1A is connected to R17, the other end of R17 is connected to R18, and the other end of R18 is grounded; the negative input end of U1A is also connected to R12, the other end of R12 is connected to R13, and the other end of R13 is connected to the positive electrode of P1; between the output end of U1A and the voltage input end connect R5;

The output end of U1A is connected to R8, the other end of R8 is connected to the positive electrode of D8, the negative electrode of D8 is connected to the base electrode of Q2; the emitter electrode of Q2 is connected to the ground, the collector electrode of Q2 is connected to R3, and the other end of R3 is connected to the negative electrode of D2 and the base electrode of Q1.

The AC-DC conversion charging circuit, preferably:

The DC voltage conversion circuit includes voltage input terminals, filter capacitors C3, C6, resistors R21-R26, diode D12, step-down conversion chip U2, electrolytic capacitors CE4, CE5, capacitors C2, C7, C8, and inductor L1; among them:

The voltage input terminal is connected to the first predetermined DC voltage lead terminal VCC,

The VCC terminal is connected to the filter capacitor C6, the other end of C6 is grounded, one end of R21 is connected to the voltage input terminal, the other end is connected to the anode of diode D12, the cathode of D12 is connected to the filter capacitor C3, and the other end of C3 is grounded; the cathode of D12 is connected to the voltage input terminal of U2, The voltage input terminal of U2 and the on-time control terminal are connected to each other through R22, the voltage input terminal of U2 is connected to the positive terminal of CE5, and the negative terminal of CE5 is connected to ground; the negative terminal of D12 is connected to R23, and the other terminal of R23 is connected to the input terminal of U2 undervoltage comparator and R26. The other end of R26 is grounded, the ground end of U2 is grounded, the bootstrap capacitor pin of U2 is connected to the SW conversion node through C2, the SW conversion node of U2 is connected to L1, the other end of L1 is connected to R24, and the other end of R24 is fed back to U2 The regulated output terminal of U2 is connected to C7, the other terminal of C7 is connected to ground, the feedback terminal of U2 is also connected to R25, and the other terminal of R25 is connected to ground; the feedback terminal of U2 is also connected to C8, and the other terminal of C8 is connected to The connection point of L1 and R24 is connected, the connection point is connected to the positive pole of CE4, and the negative pole of CE4 is grounded.

The AC-DC conversion charging circuit, preferably:

The DC voltage conversion circuit also includes a DC voltage conversion chip U3, capacitors C4, C5, C9, and an electrolytic capacitor CE3;

The voltage input terminal of U3 is directly connected to the chip select terminal and connected to the connection point of L1 and R24. The voltage input terminal is connected to C9, the other end of C9 is grounded, the ground terminal of U3 is grounded, the bypass terminal of U3 is connected to C4, and the other end of C4 is grounded , the voltage output terminal is connected to the positive terminal of CE3 and C5, and the negative terminal of CE3 and the other terminal of C5 are grounded.

The AC-DC conversion charging circuit, preferably:

The connection point of L1 and R24 is the second predetermined DC voltage output terminal.

The AC-DC conversion charging circuit, preferably:

The voltage output terminal of U3 is a third predetermined DC voltage output terminal.

Description of drawings

FIG. 1 is a schematic structural diagram of an AC-DC conversion circuit with a charging function;

Figure 2 is a schematic diagram of an AC-to-DC circuit;

Figure 3 is a schematic diagram of the battery charging circuit;

Figure 4 is a schematic diagram of a DC voltage conversion circuit.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. The components of the embodiments of the invention generally described and illustrated in the drawings herein may be arranged and designed in a variety of different configurations. Thus, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but is merely representative of selected embodiments of the invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present invention.

As shown in Figure 1, the AC-DC conversion circuit with charging function of the present invention includes an AC-to-DC circuit, a battery charging circuit and a DC voltage conversion circuit. The above three circuits are described below with reference to Figures 2-4 respectively.

As shown in Figure 2, the circuit structure of the AC-to-DC circuit is as follows: the two terminals of the high-voltage end of the power frequency transformer are connected to the AC 220V mains power supply (the transformer can choose the transformer of the model TTO-1-632-00), the transformer is low The three terminals of the voltage end are respectively connected to a relay (its model can be AZ943S) and a rectifier circuit composed of four diodes. The first terminal AC0 on the low-voltage side of the transformer is connected to the normally closed contact-pin 3 of the relay AZ943S; the middle terminal AC1 on the low-voltage side of the transformer is connected to the normally-open contact-pin 2 of the relay AZ943S; the second terminal AC2 on the low-voltage side of the transformer is connected To the anode of diode D3 in the rectifier circuit; the switch contact of relay AZ943S, that is, the first pin is connected to the anode of diode D4; the anode of diode D5 is connected to the anode of diode D3; the anode of diode D6 is connected to the anode of diode D4; the anode of diode D6 is connected to the anode of diode D4 ; The diode D3 is connected to the negative pole of the diode D4 as the output terminal of the rectifier circuit, and the output is a DC 24V voltage.

The LM358 chip is a hysteresis comparator, including 2 groups of operational amplifiers. In the circuit diagram, U1A and U1B are used to indicate that the operational amplifier U1B works through pins 5, 6, and 7 of the LM358 chip. The 50KΩ resistor R7 connected to U1B is a positive feedback resistor. The terminal is connected to pin 5 (positive input end) and pin 7 (output end) of U1B to ensure that pin 7 outputs enough voltage to trigger Q3, which is a transistor 9013. R10 is a 50KΩ resistor, one end is connected to 6V voltage, the 6V voltage is obtained after the 12V voltage in the battery charging circuit is divided by the resistor, the other end of R10 is connected to the 5th pin of U1B, which is used to protect the 5th pin of LM358, which is to limit the current Function, limit the size of the current flowing into pin 5 to avoid burning U1B. R15, R16, R19, R20 are voltage divider resistors with resistance values of 50KΩ, 15KΩ, 50KΩ and 20KΩ respectively. One end of R19 is connected to the 24V DC voltage at the output end of the rectifier circuit, and the other end is connected in series with R15 and then connected to the 6th pin of LM358 (negative input). end), one end of R20 is grounded, the other end is connected in series with R16 and then connected to pin 6 of LM358. R15, R16, R19, and R20 are used to divide the rectified 24V voltage and input it to pin 6 of LM358. CE1 and CE2 are 100μF/20V electrolytic capacitors, which are used for filtering. The positive pole of CE1 is connected to pin 6 of U1B, and the negative pole is grounded; the positive pole of CE2 is connected to the base level of Q3, and the negative pole is grounded. Pin 7 of U1B is the output end, connected to the 4.7KΩ resistor R11, and the other end of R11 is connected to the base of Q3. The collector of Q3 is connected to the negative pin 5 of the electromagnetic coil of the relay, and the emitter of Q3 is grounded. The positive pin 4 of the electromagnetic coil of the relay is connected to the rectified output DC voltage of 24V; the diode D7 is connected to the positive and negative pins 4 and 5 of the electromagnetic coil of the relay. D7 is an optional model of 1N4148. Pin 4 of relay RLY1, D7 is a protection diode. Under normal power-on conditions, the DC voltage 24V is applied to the negative electrode of D7, and D7 is in the cut-off state, so the diode does not play any role in the circuit, nor does it affect the work of other circuits. At the moment when the circuit is powered off, both ends of the relay generate a reverse electromotive force that is positive and negative, and has a large amplitude. The current generated to the electromotive force forms a loop through the diode D7 with a small internal resistance. After the diode is turned on, the voltage drop of the tube is very small, so that the amplitude of the reverse electromotive force at both ends of the relay is greatly reduced, and the purpose of protection and driving is achieved.

The working principle of the AC to DC circuit is as follows:

Use the TTO-1-632-00 type power frequency transformer to convert the AC 220V voltage into the 24V voltage that the device can use. The four diodes D3, D4, D5 and D6 play a rectifying role to convert the AC 220V voltage into DC 24V Voltage.

The hysteresis comparator LM358 is used to compare whether the converted 24V DC voltage is too high. The specific comparison process is: U1B works through pins 5, 6, and 7 of LM358, and the input voltages of pins 5 and 6 are compared. If the 24V voltage is too high, pin 7 outputs a high level, triggering the 9013 diode Q3, making the relay normally The open contact is closed, thereby changing the number of turns of the secondary winding on the low-voltage side of the transformer (reducing the number of turns of the secondary winding), reducing the output voltage.

Because the AC 220V voltage is the mains, it may be unstable. If the AC 220V mains is too high, the output 24V will also increase accordingly, then the relay will act to change (reduce) the number of output turns, so that the output voltage will increase. down to ensure that the output DC voltage will not be too high.

As shown in Figure 3, it is a battery charging circuit. The 12V voltage input terminal in the figure is connected to the DC 12V voltage obtained by converting the DC 24V voltage through the DC voltage conversion circuit. U1A works through pins 1, 2, 3, 4, and 8 of the LM358 chip, of which pin 8 is the power supply terminal and pin 4 is grounded. Pin 8 is connected to the 12V voltage input terminal for power supply. The capacitor C1 is a 0.1μF capacitor, which is used for filtering. One end is connected to the 12V voltage input terminal, and the other end is grounded. R2 and R4 are voltage divider resistors with resistance values of 47KΩ and 4.7KΩ respectively. One end of R2 is connected to the 12V voltage input terminal, the other end is connected to R4, the other end of R4 is connected to pin 3 of U1A (positive input terminal), and R9 and R14 are voltage dividers. The resistances are all 47KΩ. One end of R9 is connected to pin 3 of U1A, the other end is connected to R14, and the other end of R14 is grounded. According to the principle of voltage division, calculated from the resistance values of R2, R4, R9 and R14, the voltage value of pin 3 of U1A is 6V. Pin 2 of U1A (negative input end) is connected to 25KΩ resistor R17, the other end of R17 is connected to 4.7KΩ resistor R18, and the other end of R18 is grounded; U1A pin 2 is also connected to 50KΩ resistor R12, the other end of R12 is connected to 50KΩ resistor R13, and the other end of R13 Connect to the positive pole of the rechargeable battery P1. Pin 1 of U1A is the output end, and a positive feedback pull-up resistor R5 is connected between pins 1 and 8 of U1A, and the resistance value of R15 is 100KΩ. Pin 1 of U1A is connected to 100KΩ resistor R8, the other end of R8 is connected to the positive electrode of 1N4148 diode D8, and the negative electrode of D8 is connected to the base level of 9013 transistor Q2; the emitter of Q2 is grounded. The DC voltage 24V is connected to the base of TIP42 transistor Q1 through two cascaded 1N4007 diodes D1 and D2, 24V is connected to the positive electrode of D1, the negative electrode of D1 is connected to the positive electrode of D2, and the negative electrode of D2 is connected to the base electrode of Q1. The negative electrode of D2 is connected to the 10Ω resistor R3, and the other end of R3 is connected to the collector of Q2. R1 is a cement resistance of 5Ω/2W, one end of R1 is connected to the DC voltage 24V input end, and the other end is connected to the collector of Q1. The emitter of Q1 is connected to the 10Ω/2W cement resistor R6, the other end of R6 is connected to the positive electrode of the 1N5819 diode D10, and the negative electrode of D10 is connected to the positive electrode of the rechargeable battery P1.

The DC 24V voltage is connected to the positive pole of the 10A02 diode D9, and the negative pole of D9 is the VCC terminal, which provides power for the DC voltage conversion circuit. The negative pole of D9 is connected to the negative pole of the 10A02 diode D11, the positive pole of D11 is connected to the positive pole of the rechargeable battery P1, and the negative pole of the rechargeable battery is grounded.

The working principle of the battery charging circuit is as follows:

The 24V DC voltage output terminals are connected to D1 and D2 to reduce the voltage and protect the base stage of Q1. Since one diode has insufficient step-down capability, this circuit requires two diodes in series, and the step-down value of each diode is 0.7. V.

R5 is a positive feedback pull-up resistor to prevent the drive capability of pin 1 output of LM358 from being insufficient to increase the output voltage of pin 1 of LM358. The R1 and R6 resistors have larger powers to limit the current when charging the battery. The resistors R2, R4, R12, R14 and the resistors R12, R13, R17, and R18 are used to divide the voltage. The resistors R12 and R14 are connected in series to facilitate the adjustment of the resistance value.

The battery P1 is isolated from the 24V DC voltage output terminal through the isolation of diodes D9 and D11. Through this circuit setting, when the AC 220V power supply is directly used, the 24V DC output voltage will be slightly higher than the output voltage of the positive electrode of the battery, so only 24V The DC voltage output terminal outputs current, and the battery output is blocked by D11, which can avoid mixing with the battery and prevent the battery current from flowing back. This isolated battery design can also avoid the 24V DC voltage output directly charging the battery. When not using the 220V AC power supply, the battery is used as the power supply.

The role of U1A and its peripheral circuits is to wait until the battery voltage is less than 6V before charging the battery, otherwise it will not charge. R2, R4, R9, and R14 are voltage divider resistors. According to the voltage divider principle, the DC voltage of 6V is obtained, which provides a reference voltage for pin 3 of U1A; R12, R13, R17, and R18 are also voltage divider resistors. According to the voltage division principle, the DC voltage of 5.5 V (actually, since the accuracy of the resistance value and the actual voltage are higher than 24V, the actual calculated value can be approximately considered to be 6V), which provides a comparison voltage to pin 2 of U1A.

When the battery voltage is less than 24V, the 1 pin of the hysteresis comparator LM358 outputs a high level, and after the R5 enhances the voltage and the protection function of R8 (current limiting) and the isolation of D8, Q2 is turned on. D8 plays the role of preventing reverse voltage from pouring back into the operational amplifier. After Q2 is turned on, the base of Q1 is lowered to the level, so that Q1 is turned on. After Q1 is turned on, the DC 24V power supply passes through the current limiting resistors R1 and R6, and is directly added to the positive electrode of the battery after being isolated by the protection of D10, so that the battery can be charged. D10 is to prevent the battery voltage from flowing back into the power supply. The battery voltage added to the collector of Q1 may cause damage to the triode.

As shown in Figure 4, it is a DC voltage conversion circuit, the VCC terminal is connected to a 1μF filter capacitor C6, and the other end of C6 is grounded. R21 is a 1Ω resistor, one end of R21 is connected to the VCC end, the other end is connected to the positive electrode of the S1D diode D12, the negative electrode of D12 is connected to a 100nF filter capacitor C3, and the other end of C3 is grounded. The negative pole of D12 is connected to pin 2 of U2 (voltage input terminal), and U2 is the LM25017 step-down conversion chip. Pins 2 and 4 of U2 (on-time control terminal) are connected to each other through a 360KΩ resistor. Pin 2 of U2 is connected to the positive pole of the 100μF/50V electrolytic capacitor CE5, and the negative pole of CE5 is grounded. The negative pole of D12 is connected to the 360KΩ resistor R23, the other end of R23 is connected to the 3-pin of U2 (the input end of the undervoltage comparator) and the 91KΩ resistor R26, the other end of R26 is grounded, the 1-pin of U2 (ground terminal) is grounded, and the 7-pin of U2 ( Bootstrap capacitor pin) and pin 8 (SW conversion node) are connected through 10nF capacitor C2, pin 8 of U2 is connected with 100μH inductor L1, the other end of L1 is connected with 12KΩ resistor R24, and the other end of R24 is connected with pin 5 of U2 (feedback end) connected. Pin 6 of U2 (internal circuit voltage regulator output end) is connected to 1μF capacitor C7, and the other end of C7 is grounded. Pin 5 of U2 is also connected to the 1.4KΩ resistor R25, and the other end of R25 is grounded. Pin 5 of U2 is also connected to the 1nF capacitor C8, and the other end of C8 is connected to the connection point of L1 and R24. The voltage of this connection point is the calculated output voltage of the chip 12V, and 12V is connected to the positive electrode of the electrolytic capacitor CE4 of 100μF/25V. CE4 negative is grounded. U3 is LP2992AIM5-3.3 chip, which is used to convert DC 12V voltage into DC 3.3V voltage. Pin 1 (voltage input end) and pin 3 (chip selection end) of U3 are directly connected and connected to the connection point of L1 and R24. Pin 1 is connected to 100nF capacitor C9, and the other end of C9 is grounded. Pin 2 (ground) of U3 is grounded, pin 4 (bypass) of U3 is connected to a 100nF bypass capacitor C4, the other end of C4 is grounded, and the 3.3V output from pin 5 (voltage output) is connected to a 100μF/25V electrolytic The positive electrode of capacitor CE3 and the 100nF capacitor C5, the negative electrode of CE3 and the other end of C5 are grounded.

The working principle of the DC voltage conversion circuit is as follows:

The function of C6 is to filter, the function of R21 is to limit the current, and the function of diode D12 is to prevent reverse connection and protect U2.

Calculation of output voltage of U2:

The 3-pin UVLO of U2 is the input end of the undervoltage comparator. When VBUS<V _UVLO , the U2 chip does not start and is in the shutdown mode.

That is, when the input voltage of pin 3 of U2 is less than 6.07V, the chip U2 does not work.

The present invention converts DC 24V into DC 12V and DC 3.3V with a step-down voltage regulator chip, thereby improving the working efficiency and stability of the power supply.

The AC/DC conversion circuit of the present invention has the advantages that the present invention has the advantages of stable output when there is an AC 220V voltage, and stable output by battery operation when there is no AC 220V voltage.

The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited to this. Any person skilled in the art who is familiar with the technical scope disclosed by the present invention can easily think of changes or replacements, which should cover within the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims (2)

1. The utility model provides an alternating current-direct current converting circuit, is including exchanging converting circuit, charging circuit and direct current voltage converting circuit, its characterized in that:

the alternating current-to-direct current conversion circuit is used for converting alternating current into first preset direct current voltage and outputting the first preset direct current voltage, and the output end of the direct current voltage is connected with the input end of the charging circuit to charge the rechargeable battery;

the output end is also connected with the input end of a direct current voltage conversion circuit, and the direct current voltage conversion circuit converts the first preset direct current voltage into a second preset direct current voltage and a third preset direct current voltage and then outputs the second preset direct current voltage and the third preset direct current voltage;

the alternating current-to-direct current circuit comprises a transformer, a rectifying circuit and an overvoltage preventing circuit;

the high-voltage side winding of the transformer is connected with a 220V alternating-current power supply, the low-voltage side winding of the transformer is connected with a rectifying circuit, and the rectifying circuit is used for converting alternating current with first preset voltage after the transformer transforms into direct-current voltage with the first preset voltage;

the overvoltage preventing circuit is used for detecting whether the converted direct-current voltage is higher than a first preset voltage or not, and when the converted direct-current voltage is higher than the first preset voltage, the overvoltage preventing circuit changes the number of turns of a winding on the low-voltage side of the transformer and reduces the alternating-current voltage on the low-voltage side;

the overvoltage protection circuit includes: the circuit comprises a first operational amplifier U1B, a positive feedback resistor R7, a triode Q3, current limiting resistors R10 and R11, voltage dividing resistors R15, R16, R19 and R20, electrolytic capacitors CE1 and CE2 for filtering and a diode D7, wherein: a positive feedback resistor R7 is connected between the positive input end and the output end of the U1B; the output end is connected with the base of the Q3; one end of the R10 is connected with a direct current voltage output with the voltage value being half of the second preset direct current voltage, and the other end is connected with the positive input end of the U1B; one end of R19 is connected with the output end of the rectification circuit, the other end is connected with R15 in series and then connected with the negative input end of U1B, one end of R20 is grounded, and the other end is connected with R16 in series and then connected with the negative input end of U1B; the anode of CE2 is connected with the cathode input end of U1B, and the cathode is grounded; the anode of CE1 is connected with the base of Q3, and the cathode is grounded; the output end of U1B is connected with R11, and the other end of R11 is connected with the base stage of Q3;

the collector of the Q3 is connected with the negative electrode of the electromagnetic coil of the relay, the emitter of the Q3 is grounded, and the positive electrode of the electromagnetic coil of the relay is connected with the output end of the rectifying circuit; the anode of D7 is connected with the cathode of the relay electromagnetic coil, and the cathode is connected with the anode of the electromagnetic coil;

the direct-current voltage conversion circuit comprises a voltage input end, filter capacitors C3 and C6, resistors R21-R26, a diode D12, a voltage reduction conversion chip U2, electrolytic capacitors CE4 and CE5, capacitors C2, C7 and C8 and an inductor L1; the voltage input end is connected with a first preset direct-current voltage leading-out end VCC, the VCC leading-out end is connected with a filter capacitor C6, the other end of the C6 is grounded, one end of R21 is connected with the voltage input end, the other end of the R21 is connected with the anode of a diode D12, the cathode of the D12 is connected with a filter capacitor C3, and the other end of the C3 is grounded; the negative electrode of the D12 is connected with the voltage input end of the U2, the voltage input end of the U2 and the conduction time control end are connected with each other through the R22, the voltage input end of the U2 is connected with the positive electrode of the CE5, and the negative electrode of the CE5 is grounded; the negative electrode of D12 is connected with R23, the other end of R23 is connected with the input end of the U2 undervoltage comparator and R26, the other end of R26 is grounded, the ground end of U2 is grounded, the bootstrap capacitor pin of U2 is connected with the SW conversion node through C2, the SW conversion node of U2 is connected with L1, the other end of L1 is connected with R24, the other end of R24 is connected with the feedback end of U2, the voltage stabilizing output end of the internal circuit of U2 is connected with C7, the other end of C7 is grounded, the feedback end of U2 is also connected with R25, and the other end of R25 is grounded; the feedback terminal of U2 is also connected to C8, the other end of C8 is connected to the connection point of L1 and R24, which is connected to the positive pole of CE4, and the negative pole of CE4 is connected to ground.

2. The ac-dc conversion circuit of claim 1, wherein:

the charging circuit comprises a charging branch and a battery voltage detection circuit, the charging branch is used for charging the rechargeable battery, the battery voltage detection circuit is used for detecting the voltage of the rechargeable battery, and when the voltage of the rechargeable battery is lower than a preset voltage threshold, the battery voltage detection circuit controls the charging branch to charge the rechargeable battery.

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