CN205646962U - Alternating current -direct current conversion charging circuit - Google Patents

Abstract

The utility model discloses an AC-DC conversion charging circuit with a charging function, which comprises an AC-to-DC circuit, a charging circuit and a DC voltage conversion circuit. The AC-to-DC circuit is used to convert AC power into a first predetermined DC voltage output. The output terminal of the 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 the second predetermined DC voltage and the second predetermined DC voltage. Three preset DC voltages are output; the AC-to-DC circuit includes a transformer, a rectifier circuit and an overvoltage prevention circuit; the utility model improves the AC-DC conversion circuit, the DC voltage conversion circuit and the battery charging circuit respectively, and these three parts can realize Free switching, the power supply can provide 24V, 12V and 3.3V stable voltage in the case of AC 220V and battery.

Description

AC-DC conversion charging circuit

technical field

The utility model 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 actual use, the existing AC-DC conversion circuit is unstable in the continuity of the AC 220V on-off, and it is prone to work when it is impacted by the load current. abnormal. The utility model has the advantages of stable output when there is AC 220V voltage, and stable output by battery operation when there is no AC 220V voltage. In addition, the utility model also has the following advantages:

1. When connected to the AC 220V voltage, the stable output DC voltage is 24V, 12V and 3.3V, and the battery is charged according to the power condition. 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 increase accordingly, and 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 voltages to determine whether to charge and prevent the battery from overcharging or overdischarging. The reference voltage and comparison voltage in the circuit are obtained by dividing the voltage through 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 not to be mixed with the battery when connected to the AC 220V, and to prevent the battery current from flowing back. The isolated battery is designed to avoid direct charging of the battery by the power supply.

5. Convert DC 24V to DC 12V and DC 3.3V with a step-down regulator chip, which improves the working efficiency and stability of the power supply.

Utility model content

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

In order to realize the purpose of this utility model, adopt following technical scheme to realize:

An AC-DC conversion charging circuit, including 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 is 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 AC power of the first predetermined voltage after the transformer is transformed into a DC voltage of the first predetermined voltage;

The anti-overvoltage circuit is used to detect whether the converted DC voltage is higher than the first predetermined voltage. When the voltage is 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 to reduce the AC voltage on the low-voltage side.

The AC-DC conversion charging circuit is preferably:

The rectification circuit is composed of four diodes D3, D4, D5 and D6; the winding on the low-voltage side of the transformer includes three terminals, which are respectively connected to the relay and the rectification 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 switch contact of the relay 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 connected to the ground, and the cathode is connected to the anode of the diode D4; the cathode of the diode D3 and the diode D4 are connected as the output end of the rectification circuit.

The AC-DC conversion charging circuit is preferably:

The anti-overvoltage circuit includes: the first operational amplifier U1B, positive feedback resistor R7, transistor Q3, current limiting resistors R10, R11, voltage dividing resistors R15, R16, R19, R20, electrolytic capacitors CE1 and CE2 for filtering, resistor R11 and diodes 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 a 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 in series with R15 to the negative input end of U1B, one end of R20 is grounded, and the other end is connected in series with R16 to the negative input end of U1B;

The positive pole of CE2 is connected to the negative input terminal of U1B, and the negative pole is grounded; the positive pole of CE1 is connected to the base of Q3, and the negative pole is grounded; the output terminal of U1B is connected to R11, and the other end of R11 is connected to the base 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 terminal 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 is preferably:

The charging circuit includes a charging branch and a battery voltage detection circuit, the charging branch is used to charge the rechargeable battery, 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 , the battery voltage detection circuit controls the charging branch to charge the rechargeable battery.

The AC-DC conversion charging circuit is preferably:

The charging branch includes diodes D1, D2, D9, D10, D11, resistors R1, R6, triode 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 pole 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 pole 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-out 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, positive feedback resistor R5, resistors R8, R3, 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 terminal 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 terminal 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 pole of P1; between the output terminal of U1A and the voltage input terminal Connect to R5;

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

The AC-DC conversion charging circuit is 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; where:

The voltage input end is connected to the first predetermined DC voltage lead-out end VCC,

The leading end of VCC is connected to filter capacitor C6, the other end of C6 is grounded, one end of R21 is connected to the voltage input end, the other end is connected to the positive pole of diode D12, the negative pole of D12 is connected to filter capacitor C3, and the other end of C3 is grounded; the negative pole of D12 is connected to the voltage input end of U2, The voltage input terminal of U2 and the conduction time control terminal are connected to each other through R22, the voltage input terminal of U2 is connected to the positive pole of CE5, and the negative pole of CE5 is grounded; the negative pole of D12 is connected to R23, and the other end of R23 is connected to the input terminal of the undervoltage comparator of U2 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 output end of the internal circuit of U2 is connected to C7, the other end of C7 is grounded, the feedback end of U2 is also connected to R25, and the other end of R25 is grounded; the feedback end of U2 is also connected to C8, and the other end 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 is preferably:

The DC voltage conversion circuit also includes a DC voltage conversion chip U3, capacitors C4, C5, C9, and 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 pole of CE3 and C5, and the negative pole of CE3 and the other end of C5 are grounded.

The AC-DC conversion charging circuit is preferably:

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

The AC-DC conversion charging circuit is preferably:

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

Description of drawings

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

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

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

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

detailed description

The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Apparently, the described embodiments are only some of the embodiments of the present invention, not all of them. The components of the embodiments of the invention generally described and illustrated in the figures herein may be arranged and designed in a variety of different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments of the present utility model, all other embodiments obtained by those skilled in the art without making creative efforts belong to the scope of protection of the present utility model.

As shown in Fig. 1, the AC-DC conversion circuit with charging function of the utility model includes an AC-to-DC circuit, a battery charging circuit and a DC voltage conversion circuit. The above-mentioned three-part circuits will be described below in conjunction with FIGS. 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 industrial frequency transformer are connected to the AC 220V mains power supply (the transformer can be a transformer of the type TT0-1-632-00), and the low voltage of the transformer is The three terminals of the voltage end are respectively connected to a relay (its model may 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 of the relay AZ943S - pin 3; the intermediate terminal AC1 on the low voltage side of the transformer is connected to the normally open contact of the relay AZ943S - pin 2; the second terminal AC2 on the low voltage side of the transformer is connected to To the positive pole of diode D3 in the rectifier circuit; the switch contact of relay AZ943S, that is, the first pin is connected to the positive pole of diode D4; the positive pole of diode D5 is grounded, and the negative pole is connected to the positive pole of diode D3; the positive pole of diode D6 is grounded, and the negative pole is connected to the positive pole of diode D4 ; The diode D3 is connected to the cathode 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 sets 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 terminal) and pin 7 (output terminal) of U1B to ensure that pin 7 outputs enough voltage to trigger Q3, which is a triode 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 resistors, and the other end of R10 is connected to pin 5 of U1B, which is used to protect pin 5 of LM358, that is, to limit the current The role is to limit the current flowing into pin 5 to avoid burning out U1B. R15, R16, R19, and R20 are voltage divider resistors, whose resistance values are 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 to the 6th pin of LM358 (negative input terminal), one end of R20 is grounded, and the other end is connected in series with R16 to the 6th pin of LM358. R15, R16, R19, and R20 are used to divide the rectified 24V voltage and input it to 6th pin 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 of Q3, and the negative pole is grounded. Pin 7 of U1B is the output terminal, connected to 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 pole 5 of the electromagnetic coil of the relay, and the emitter of Q3 is grounded. The positive pole 4 of the electromagnetic coil of the relay is connected to the DC voltage 24V output by the rectifier; the diode D7 is connected to the positive and negative poles 4 and 5 of the electromagnetic coil of the relay. Pin 4 of relay RLY1, D7 is a protection diode. Under normal power-on conditions, the DC voltage 24V is applied to the negative pole of D7, and D7 is in a cut-off state, so the diode does not play any role in the circuit and does not affect the work of other circuits. At the moment when the circuit is powered off, the two ends of the relay generate a reverse electromotive force, which is positive and negative, with 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 tube voltage drop is very small, so that the magnitude of the reverse electromotive force at both ends of the relay is greatly reduced, and the purpose of protecting the drive is achieved.

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

Use the TT0-1-632-00 power frequency transformer to convert the AC 220V voltage into a 24V voltage that can be used by the equipment. The four diodes D3, D4, D5 and D6 play a rectification role and 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 the LM358, and compares the input voltages of pins 5 and 6. If the 24V voltage is too high, pin 7 outputs a high level, triggering the 9013 diode Q3, so that the relay normally The open contact is closed, thereby changing the number of turns of the secondary coil on the low-voltage side of the transformer (reducing the number of turns of the secondary coil), and reducing the output voltage.

Because the AC 220V voltage is the commercial power, it may be unstable. If the AC 220V commercial power is too high, the output 24V will increase accordingly, and the relay will act to change (decrease) the output turns, so that the output voltage will be reduced. 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 after the DC 24V voltage is converted by 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. Capacitor C1 is a 0.1μF capacitor for filtering. One end is connected to the 12V voltage input end and the other end is grounded. R2 and R4 are voltage divider resistors, the resistance values are 47KΩ and 4.7KΩ respectively, one end of R2 is connected to the 12V voltage input terminal, the other end is connected to R4, and the other end of R4 is connected to U1A’s 3 pin (positive input terminal), R9 and R14 are voltage dividers Resistor, the resistance value is 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 terminal) 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; pin 2 of U1A is also connected to 50KΩ resistor R12, and 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 an output terminal, and a positive feedback pull-up resistor R5 is connected between pin 1 and pin 8 of U1A, and the resistance of R15 is 100KΩ. Pin 1 of U1A is connected to 100KΩ resistor R8, the other end of R8 is connected to the positive pole of 1N4148 diode D8, the negative pole of D8 is connected to the base stage 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 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 of Q1. The negative pole 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 5Ω/2W cement resistor. 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 10Ω/2W cement resistor R6, the other end of R6 is connected to the positive pole of 1N5819 diode D10, and the negative pole of D10 is connected to the positive pole of 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 to provide power for the DC voltage conversion circuit. The negative pole of D9 is connected with the negative pole of 10A02 diode D11, the positive pole of D11 is connected with 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 of Q1. Since one diode is not capable of reducing the voltage, this circuit needs two diodes in series. The voltage reduction value of each diode is 0.7 V.

R5 is a positive feedback pull-up resistor to prevent insufficient drive capability of the LM358's 1-pin output and to increase the LM358's 1-pin output voltage. The resistors R1 and R6 have large power to limit the current when charging the battery. Resistors R2, R4, R12, R14 and resistors R12, R13, R17, R18 act as voltage dividers, and resistors R12 and R14 are connected in series for the convenience of adjusting the resistance value.

The battery P1 is isolated from the 24V DC voltage output terminal by means of diodes D9 and D11. With this circuit setting, when directly connected to an AC 220V power supply, the 24V DC output voltage will be slightly higher than the output voltage of the positive pole 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 24V DC voltage output from direct charging batteries. When the 220V AC power supply is not used, the battery is used as the power supply.

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

When the battery voltage is less than 24V, pin 1 of the hysteresis comparator LM358 outputs a high level, and after the voltage enhancement of R5, the protection function of R8 (current limiting) and the isolation of D8, Q2 is turned on. D8 plays the role of preventing the reverse voltage from pouring into the operational amplifier. After Q2 is turned on, the base of Q1 is lowered to turn on Q1. After Q1 is turned on, the DC 24V power supply passes through the current limiting resistors R1 and R6, and after being protected and isolated by D10, it is directly added to the positive pole of the battery, so that the battery can be charged. D10 is to prevent the battery voltage from being poured into the power supply. The battery voltage applied 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 pole of the S1D diode D12, the negative pole 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 (voltage input terminal) of U2, and U2 is an LM25017 step-down conversion chip. Pin 2 and pin 4 (on-time control end) of U2 are connected to each other through a 360KΩ resistor. Pin 2 of U2 is connected to the positive pole of 100μF/50V electrolytic capacitor CE5, and the negative pole of CE5 is grounded. The negative pole of D12 is connected to 360KΩ resistor R23, the other end of R23 is connected to U2’s 3-pin (input terminal of the undervoltage comparator) and 91KΩ resistor R26, the other end of R26 is grounded, U2’s 1-pin (ground terminal) is grounded, and U2’s 7-pin ( Bootstrap capacitor pin) and pin 8 (SW conversion node) are connected through 10nF capacitor C2, pin 8 of U2 is connected to 100μH inductor L1, the other end of L1 is connected to 12KΩ resistor R24, and the other end of R24 is connected to pin 5 of U2 (feedback terminal) connected. Pin 6 of U2 (internal circuit regulator output terminal) is connected to 1μF capacitor C7, and the other end of C7 is grounded. Pin 5 of U2 is also connected to 1.4KΩ resistor R25, and the other end of R25 is grounded. Pin 5 of U2 is also connected to 1nF capacitor C8, and the other end of C8 is connected to the connection point of L1 and R24. The voltage value of this connection point is 12V, which is the calculated output voltage of the chip. 12V is connected to the positive electrode of 100μF/25V electrolytic capacitor CE4. The negative pole of CE4 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 terminal) and pin 3 (chip select terminal) of U3 are directly 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 terminal) of U3 is grounded, pin 4 (bypass terminal) of U3 is connected to 100nF bypass capacitor C4, the other end of C4 is grounded, and the 3.3V output from pin 5 (voltage output terminal) is connected to a 100μF/25V electrolytic The positive pole of capacitor CE3 and the 100nF capacitor C5, the negative pole 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 filtering, the function of R21 is current limiting, and the function of diode D12 is to prevent reverse connection and protect U2.

The output voltage calculation of U2:

(approximately equal to 12V).

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

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; UVLO</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1.225</span>}\mathrm{<span\; class="notranslate">\; V</span>}<span\; class="notranslate">\; \&times;</span>\frac{\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; twenty\; three</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 26</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 26</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1.225</span>}\mathrm{<span\; class="notranslate">\; V</span>}<span\; class="notranslate">\; \&times;</span>\frac{\mathrm{<span\; class="notranslate">\; 360</span>}\mathrm{<span\; class="notranslate">\; K</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 91</span>}\mathrm{<span\; class="notranslate">\; K</span>}}{\mathrm{<span\; class="notranslate">\; 91</span>}\mathrm{<span\; class="notranslate">\; K</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 6.07</span>}\mathrm{<span\; class="notranslate">\; V</span>}$

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

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

The AC-DC conversion circuit of the present utility model has the advantage that the utility model has the advantages of stable output when there is AC 220V voltage, and stable output by battery work when there is no AC 220V voltage.

The above are only specific embodiments of the present utility model, but the scope of protection of the present utility model is not limited thereto. Anyone familiar with the technical field can easily think of changes or replacements within the technical scope disclosed in the present utility model. All should be covered within the protection scope of the present utility model. Therefore, the protection scope of the present utility model should be based on the protection scope of the claims.

Claims (4)

1. An AC-to-DC conversion charging circuit, comprising an AC to DC circuit, a charging circuit and a DC voltage conversion circuit, is characterized in that: 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-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 AC power of the first predetermined voltage after the transformer is transformed into a DC voltage of the first predetermined voltage; The anti-overvoltage circuit is used to detect whether the converted DC voltage is higher than the first predetermined voltage. When the voltage is 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 to reduce the AC voltage on the low-voltage side. 2. The AC-DC conversion charging circuit according to claim 1, characterized in that: The rectification circuit is composed of four diodes D3, D4, D5 and D6; the winding on the low-voltage side of the transformer includes three terminals, which are respectively connected to the relay and the rectification 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 switch contact of the relay 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 connected to the ground, and the cathode is connected to the anode of the diode D4; the cathode of the diode D3 and the diode D4 are connected as the output end of the rectification circuit. 3. The AC-DC conversion charging circuit according to claim 1, characterized in that: The charging circuit includes a charging branch and a battery voltage detection circuit, the charging branch is used to charge the rechargeable battery, 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 , the battery voltage detection circuit controls the charging branch to charge the rechargeable battery. 4. The AC-DC conversion charging circuit according to claim 1, characterized in that: 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; where: The voltage input end is connected to the first predetermined DC voltage lead-out end VCC, The first predetermined DC voltage lead-out terminal VCC is connected to the filter capacitor C6, the other end of the filter capacitor C6 is grounded, one end of the resistor R21 is connected to the voltage input end, the other end is connected to the positive pole of the diode D12, the negative pole of the diode D12 is connected to the filter capacitor C3, and the other end of the filter capacitor C3 Grounding; the cathode of the diode D12 is connected to the voltage input terminal of the step-down conversion chip U2, the voltage input terminal of the step-down conversion chip U2 and the on-time control terminal are connected to each other through the resistor R22, and the voltage input terminal of the step-down conversion chip U2 is connected to the electrolytic capacitor CE5 The positive pole of the electrolytic capacitor CE5 is grounded; the negative pole of the diode D12 is connected to the resistor R23, the other end of the resistor R23 is connected to the input terminal of the undervoltage comparator of the step-down conversion chip U2 and the resistor R26, the other end of the resistor R26 is grounded, and the other end of the step-down conversion chip U2 The ground terminal is grounded, the bootstrap capacitor pin of the step-down conversion chip U2 is connected to the SW conversion node through the capacitor C2, the SW conversion node of the step-down conversion chip U2 is connected to the inductor L1, the other end of the inductor L1 is connected to the resistor R24, and the resistor R24 The other end is connected to the feedback terminal of the step-down conversion chip U2, the internal circuit voltage stabilization output terminal of the step-down conversion chip U2 is connected to the capacitor C7, the other end of the capacitor C7 is grounded, and the feedback terminal of the step-down conversion chip U2 is also connected to the resistor R25. The other end of the resistor R25 is grounded; the feedback end of the step-down conversion chip U2 is also connected to the capacitor C8, and the other end of the capacitor C8 is connected to the connection point of the inductor L1 and the resistor R24, which is connected to the positive pole of the electrolytic capacitor CE4, and the electrolytic capacitor CE4 Negative ground.