Switching power supply circuit composed of UC3842
The switching power supply circuit composed of UC3842, 220V output by C1, L1 filtrates electromagnetic interference, negative temperature coefficient of thermistor RT1 current limiting, and then rectified by Vc rectification, C2 filter, resistance R1, and potentiometer RP1 step-down after UC3842 The power supply terminal (7 foot) provides a start voltage for the UC3842. The rectifier filter voltage of the transformer after the circuit is activated, and the UC3842 provides normal operating voltage, and the other aspect is applied to the error amplifier. The phase input terminal 2 foot, provides a negative feedback voltage for UC3842, and the rule is that the smaller the duty ratio of the drive pulse, the smaller the output voltage is stabilized. 4 foot and 8 foot external R6, C8 determine the oscillation frequency, the maximum value of the oscillation frequency can reach 500 kHz. R5, C6 is used to improve gain and frequency characteristics. 6 The square wave signal output by the foot is driven by R7, R8, and the energy of the transformer is transferred to the respective windings of the transformer, and the DC voltage different from the digital value after the stream filter is used for load. The resistor R10 is used for current detection, and the 3 foot forming a current feedback ring is sent to the 3 foot of the UC3842 after filtration of R9 and C9. Therefore, the power source composed of UC3842 is a double closed loop control system. The voltage stability is very high. When the 3 foot voltage of UC3842 is higher than 1V, the oscillator is stopped, and the protective power tube is not overcurrent.
Switching power supplied by UC3842
Circuit debugging
此Circuit debugging需要注意：一是调节电位器RP1使电路起振，起振电流在1mA左右；二是起振后变压器③④绕组提供的直流电压应能使电路正常工作，此电压的范围大约为11～17V之间；三是根据输出电压的数值大小来改变R4，以确定其反馈量的大小；四是根据保护要求来确定检测电阻R10的大小，通常R10是2W、1Ω以下的电阻。
3842 charger circuit diagram (1)
The following figure is made of a single-ended fly-like pulse charger circuit composed of KA3842 + LM324 + HCF4060.
3842 charger circuit diagram (2)
Lithium ion battery charger circuit consists of a power input transform circuit, a constant current charging circuit, a constant voltage charging circuit, a working state indication circuit, and a battery voltage detection control circuit, as shown.
Photo takes the lithium ion battery charger circuit with LM358 operational amplifier
The power input conversion circuit consists of power transformer T, rectifier diode VD1 to VD4 and filter capacitance C1; constant current charging circuit consists of diode VD5, triple voltage regulator integrated circuit IC1 and resistor R1; constant voltage charging circuit consists of three end regulating Composition of circuit IC2 and resistor R2, R3; battery voltage detection control circuit consists of resistors R4 to R8, capacitance C2 to C4, potentiometer RP, regulator diode VS1, VS2, operational amplifier IC3, thyristor Vt, and relay K; operation status The circuit consists of resistance R9, R10, and light emitting diodes VL1, VL2.
After the AC 220V voltage is filtered through T-buck, VD1 to VD4 rectification and C1 filter, the constant transition of the battery GB is performed on the constant shut-off contacts of the constant current charging circuit and K. When the voltage of the battery rises to 4.2V, the IC3 outputs a high level, which causes VT to be triggered by VS2, and k is electrically actuated, its normally closed contact end is disconnected, normally open contacts, rectify filters The DC voltage is charged with the GB through the constant voltage charging circuit.
When the constant current is charged in the first stage, the VL2 is lit; when the constant voltage is charged at the second stage, the VL1 is lit.
After the circuit is installed, the R7 is disconnected, connect the power supply to adjust the resistance of RP, so that the center tap voltage is 4.2V. At the output of the IC2, the output of 47 Ω is connected to the ground, and the resistance of R2 is adjusted, so that the 2 foot voltage of the IC2 is 4.2V. Disconnect the power and false load, connect R7 and the battery GB to be charged, and then turn on the power to charge. Monitor both end voltages of GB to ensure that the voltage between the two ends of the GB reaches 4.2V, and the resistance of the RP should be fine-tuned.
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