2020年12月11日 · Hi, everyone. I'm building a 110VAC-12VDC 120W Flyback converter using UC3842, and have some problems with the start-up circuit and output PWM signal. In the beginning, the design spec at first: Input: 110VAC Output:12VDC 10A Switching frequency: 107kHz Transformer core: PQ35/35 (unknown...

2020年10月20日 · It is part of the current mode feedback control circuit of the UC3842. Make sure in normal, the I sense voltage is less than 1V to avoid current limiting kicks in. To design for a constant current source the feedback voltage is not sensing from the output.

2024年9月26日 · I'm repairing a monitor with a SMPS utilizing a UC3842 IC. I've tested the monitor in my shop and worked fine. When I get to the customer's site, it wouldn't startup. The difference is the input AC (My shop = 120 to 130 VAC. He's shop is 118VAC). At his site, I tested the Vcc voltage to pin 7 of the UC3842.

2020年10月20日 · I have an electronic 48V 30A battery charger. This charger had problem with UC3842 2 times and we repaced it each time and got the charger working again. This time we replaced it and can't find any other bad component, but the charger is not working. The supply voltage on the IC (between pin 7 and 5) is varying from approx 11.5VDC to 13VDC.

2020年12月11日 · Flyback converter question using UC3842. Thread starter johnson35762; Start date Dec 11, 2020; Tags

2024年12月17日 · UC3842 is good enough for a IRF840 @ 100kHz. Probably not at higher frequencies or with a bigger MOSFET. It is OLD as @ronsimpson says, and so is the IRF840, but they both still work. You'll get performance like an OLD flyback design! THere are lots of designs like that out there, still working and still being made.

2017年1月20日 · phenomenon: to realize an adjustable module PWM: UC3842 using switching power IC，open loop system; Vf pin was connected with Potentiometer adjustment feedback voltage, compensation pin was not connected. the result was not as i expected. i can indeed change the duty cycle via potentiometer outside, but in a very small arrange and not accurate ...

2020年1月10日 · Hi, I want to design a Flyback, no problem with the transformer, Clamp .. etc. Now I want to design the feedback circuit using a TL431 and an Optocoupler. 1) How to calculate the Feedback component values for the UC3842/3? 2) How to regulate several outputs?

2020年11月25日 · It is very hard to get a UC3842 to work (making it from nothing). Here I used a LT1242 which is a UC3842. Because this circuit takes a long time to start up I added V2 and D7 to jump start it. ".IC" command should work but not today LOL. You will need to hit "ESC" key a couple of times with the mouse over the schematic to get it to simulate faster.

2012年1月11日 · if I were to change my input value from vac 160-270 and output should be 55v 4a(this is separately based on transformer design),what are the values of R and C that should be changed surrounding the 8 pins of UC3842?