The UC3842 has built-in zener diode that limits voltage, providedĮE25 core was used for the transformer. 50k resistor is used for startup from the high voltage DC bus. High voltage MOSFET (IRF840) directly as it has a built-in MOSFETĭriver. Primary side PWM is controlled by UC3842 chip. I have designed the PCB myself and have wound the transformer myself, at home.ġA offline flyback power supply with UC3842 A fuse has been usedĪ 200-ohm resistance is used at the output as "dummy load". Of the LARGE BULK capacitors at the primary side. Has been used at the input side to limit inrush current due to charging The output inductor is the large toroidal inductor beside Zener-optocoupler based voltage feedback loop. The output voltage is kept regulated using a Rectified with schottky rectifier STPS3045 and an LC filter is used toįilter to pure DC. The output of the ETD39-based transformer is Power dissipated by the 7812 is not too high and no heat sink is Voltage difference between 7812 input and output is not too great, the Rectified, filtered and regulated to 12V with a 7812 to power the (18V 100mA) is used to provide auxiliary low voltage output, which is
2 bulk capacitors (470uF, 200V each) are used for the The output signals of the SG3525 are fed intoĪ IR2110 high-low side driver which drives the 2 MOSFETs (IRF840)Ĭonfigured for half-bridge topology. Primary side PWM is controlled by SG3525 PWM chip. To be incorporated in SMPS inverter with charger.
A range of zero to 50% is obtained by the UC1844 and UC1845 by the addition of an internal toggle flip flop which blanks the output off every other Clock cycle.Final test circuit (on PCB) for battery charging. The UC1842 and UC1843 CAN operate to duty cycles approaching 100%. The corresponding thresholds for the UC1843 and UC1845 are 8.4 V and 7.6 V. The UC1842 and UC1844 have UVLO thresholds of 16 VON and 10 VOFF, ideally suited to off-line applications. The output stage, suitable for driving N-Channel MOSFETs is low in the off state.ĭifferences between members of this family are the under-voltage lockout thresholds and maximum duty cycle ranges. Internally implemented circuits include under-voltage lockout featuring start up current less than 1 mA, a precision reference trimmed for accuracy at the error amp input, Logic to insure latched operation, a PWM Comparator which also provides current limit control, and a totem pole output stage designed to source or sink high peak current. The UC3842 3/4/5 family of control devices provides the necessary features to implement off-line or dc-to-dc fixed frequency current mode control schemes with a minimal external parts count.
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