The schematic of the charger is shown in Figure 13. The single-excitation charger startup circuit is different from the half-bridge type. It is generally taken directly from the smooth DC power after the mains rectification and filtering. The integrated circuit is also mainly UC3842, UC3845 and UC3844N. There is also a three-terminal switch type TOP226 integrated with a more compact circuit. Block, UC38xx is a current-controlled PWM single-output dedicated chip. Widely used in power supply products such as computer monitor power supplies and electric vehicle chargers. Similar to the TL494, the UC38xx contains an internal circuit necessary for the PWM dedicated chip such as an oscillator (OSC), error amplifier, pulse width modulation (PWM), and reference voltage generation. It also has three features, totem pole output circuit, output current up to 1A, can directly drive the power switch VDMOS tube: with an internal adjustable reference power supply. Undervoltage lockout can be performed; this locked PWM can be pulse-by-pulse current limit, also called weekly (period) limit. KNL1-100 Residual Current Circuit Breaker
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In Fig. 13, R18, D5, N5, etc. constitute a start-up and power supply circuit. Power on instantly. The smoothed DC power after the mains rectification and filtering is applied to the UC38457 pin through R18 to start the power supply. At this time, D5 is reverse biased. After the UC3845 works, the windings of the switching transformer have induced voltage. The secondary winding voltage is regulated by D4 for N5 to regulate, and D5 is turned on to provide a stable working voltage for the UC3845 to complete startup and power supply. In the figure, LM393 is a deformed Schmitt voltage comparator used as mains overvoltage protection. When the mains is overvoltage, the comparator flips, pin 1 is low, and D3 turns on to turn off UC3845. The output-regulated negative feedback system consists of a photocoupler, a reference power supply N6, RV1, R27, R26, R23, and the like. Voltage regulation process: When the output voltage rises for some reason, the current flowing through the photocoupler LED increases, the light intensity increases, and the photocoupler phototransistor intensifies conduction. The internal resistance is reduced, so that the voltage of pin 2 of UC3845 rises, the PWM duty cycle is reduced, and the output voltage is pulled down. Conversely, increasing the PWM duty cycle and pulling the output voltage high will automatically stabilize the output voltage.
1) Overcurrent (overload) protection switch tube overcurrent signal is taken from resistors R3, R4. Once the switch tube is overcurrent, the voltage of pin 3 of UC3845 exceeds 1V, and the internal circuit will turn off the output to realize overcurrent (also called overload) protection. Increasing the sampling resistance is to reduce the operating point of the starting current, and the power output power is also reduced accordingly.
2) Overvoltage protection power supply output LM339 four voltage comparators A, B, C, D inverting terminal potential are fixed at +5V. A and B detect the output voltage. When the output voltage is low, the initial stage of charging, A's 2 pin is low level, low voltage light LOW is bright, B's 1 foot is also low level, high voltage light HI is also bright; When the charging voltage rises. A flips, the low voltage lamp LOW goes out, the high voltage lamp HI continues to light, when the battery will be full, the battery voltage rises, B flips, 1 pin is high level, and the high pressure lamp HI goes out. At the same time, the (13) pin of C is high level, the (14) pin of D is also high level, N7 is turned on, J1 is connected, J1-1 (normally closed) is disconnected, and the sampling resistor R4 is connected. The current sampling resistor is turned on, and the starting current is controlled to lower the output current, and the floating charging phase is entered. N4, W1, R8, and R7 form a 12V regulated power supply, providing power for a 12V relay.
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