Hello I'm trying to build regulated power supply using LM317 and 337.
I'm using pcb rework from komitart schematic and pcb provided below. Only the leds and their resistors, and fuses are not used in my pcb.
Transformer output is 2x22 volts AC, the positive part of power supply with 317 works perfectly, but I can't figure out what's wrong with the negative part.
The output voltage cannot be regulated, stays 28.5 volts all the time and when I try to adjust the trim pot, 220 ohm resistor start smoking and then burns completely, while the LM377 stays cold all the time.
Another LM337 replaced with brand new purchased from trusted store, recheck everything many times, no short circuit between the copper traces, tried three different brands of LM337, OnSemi, ST Microelectronics and Farnell, and still no luck.
Just to mention that there is no error in placing the regulators, is the same as in komitart pcb, facing each other while the heatsinks are from outer sides.
I'm using pcb rework from komitart schematic and pcb provided below. Only the leds and their resistors, and fuses are not used in my pcb.
Transformer output is 2x22 volts AC, the positive part of power supply with 317 works perfectly, but I can't figure out what's wrong with the negative part.
The output voltage cannot be regulated, stays 28.5 volts all the time and when I try to adjust the trim pot, 220 ohm resistor start smoking and then burns completely, while the LM377 stays cold all the time.
Another LM337 replaced with brand new purchased from trusted store, recheck everything many times, no short circuit between the copper traces, tried three different brands of LM337, OnSemi, ST Microelectronics and Farnell, and still no luck.
Just to mention that there is no error in placing the regulators, is the same as in komitart pcb, facing each other while the heatsinks are from outer sides.
I don't know if it has anything to do with it, but with the output open, the load current of the regulators is below the 10 mA recommended minimum (just the approximately 5.6 mA through the feedback resistors).
More importantly, the polarity of the diode in the bottom right corner is wrong.
More importantly, the polarity of the diode in the bottom right corner is wrong.
Oscillations? Check with scope.
I use 240ohm resistors for lm337sp and lm237kc without issues. Lm237kc spec requires less minimum current than the regular lm337. To bad TI has recently made Lm237 eol however
Not the best layout, the 104 caps should be right at input pins of the regulators.
I use 240ohm resistors for lm337sp and lm237kc without issues. Lm237kc spec requires less minimum current than the regular lm337. To bad TI has recently made Lm237 eol however
Not the best layout, the 104 caps should be right at input pins of the regulators.
You're right 👍More importantly, the polarity of the diode in the bottom right corner is wrong.
This is my first time to build something straight from pcb without checking the schematic.
The pcb placement of that diode is wrong. I replace it and now working like charm even without heatsinks.
Thank you very much, have a blessed day and nice weekend.
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