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Oct 21, 2023 at 17:08 answer added Pat timeline score: 1
Jan 6, 2023 at 19:21 comment added StainlessSteelRat Why R3? R3 should be a fixed resistor of 120Ω or 240Ω. From datasheet, pg 1 An output capacitor can be added to improve transient response, while bypassing the adjustment (LM350A) pin will increase the regulator's ripple rejection. Try a decoupling capacitor on the adjustment terminal.
Jan 6, 2023 at 16:48 comment added Jay M @Pat. Yes, a DCDC is another (broad) name for a sub-type of switching regulator. The others being AC/DC (aka off-line) and 'inverter'. In your case Google DC/DC module. The issue with your ADJ may be the length of the wires and/or how they are routed rather than the pots. Keep everything tight and twist wires to remove magnetic coupling.
Jan 6, 2023 at 16:37 comment added Pat @Andy aka - Ah, I see Andy aka, your comment is along the lines of Jay M. The ADJ pin. OK, I'll study up in that direction. Thanks!
Jan 6, 2023 at 16:32 comment added Pat @Jay M - I see. Your suggestion is along the lines of Andy aka in that the problem may be in what is attached to the ADJ pin. Thanks for giving me a direction to study on. Are the 5K and 1k potentiometers big enough? By DCDC converters, do you mean the switching regulators?
Jan 6, 2023 at 16:18 comment added Pat @Jay M - Thanks for the info. Well I DO have the 5K and 1K potentiometers that I use to adjust the output and that attach directly to the ADJ pin.
Jan 6, 2023 at 16:04 comment added Pat @JRE - I am using an electrolytic capacitor on C5. I could check out tantalum capacitors. Yes, the author of the datasheet really seems to like tantalum tantalum capacitors because, according to them, they have low impedance even at high frequencies. I'll look into getting tantalum capacitors. Thanks for the info.
Jan 6, 2023 at 14:55 comment added Jay M I would avoid high current linear regulators these days as decent off the shelf DCDC converters are better and far more efficient (get far less hot!!). But, sticking with linear, I'd question your inputs to the feedback ADJ pin. If you have any capacitance or inductance here (read long wires or big variable resistors) then you will introduce a delay which will cause the oscillation you see.
Jan 6, 2023 at 14:32 comment added JRE @pat: What kind of capacitor did you use for C5 (the output capacitor of the LM35T?) That part was made back in days when ceramica capacitors with high capacities weren't available - the datasheet mentions using a tantalum capacitor. A ceramic capacitor might cause the problem, and the datasheet won't warn against it because that wasn't a possibility back when the LM350 was developed.
Jan 6, 2023 at 14:24 history edited JRE CC BY-SA 4.0
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Jan 6, 2023 at 12:58 comment added Pat I do not have any right now but thought about a 0.1uF for input and have experimented with a 220uF for the output (which did help reduce the 7905 Vpp output noise). Do you adding them might help reduce the LM350T oscillation issue?
Jan 6, 2023 at 12:49 comment added Andy aka Where are your input and output capacitor decouplers on the 7905?
Jan 6, 2023 at 12:39 history asked Pat CC BY-SA 4.0