woody

Hi Audioguru Been putting this through its paces. When I use the pot to reduce voltage under load (250 mA) from max, it cuts to 14 volts and 130 mA very soon after turning the pot. When I turn the pot fully up it stays at 14 v. The only way I can get it back up is to switch the whole thing off and back on again. Is there anyway I can unlatch this hangup, please? >:( L200 is running cool. I presume its the TL071 that is dictating? Woody

Hi Audioguru I replaced the L200. It is bolted and electrically insulated on a large heatsink. R3 is a 0.1 Ohm 10 Watt resistor. The main filter cap is 6800 uF and is doing its job. Still no joy. L200 pin readings are : (1) 33v (2) 1.23 - 1.38v (3) 0v (4) 0 - 1.23v (5) 0.9v TL071 readings are: (2) 0.9 - 1.23v (3) 0.8v (4) 0v (6) as 2 above (7) 33v Readings taken with a 66 Ohm load and swinging the pots fully. I must have done something stupid! I have checked the tracks again !!!!! while writing this have discovered micro break in track connecting pin 3 of L200 to the rest of ground. Now all is fine and lesson learned. Thank you for staying with me on this Woody

Ho Audioguru I swapped the 741 for a TL071. I get 30.6 Volts out regardless of volts pot setting. When I put a load on the output (66 Ohm) the volts drop to 0.9 and current is 13 mA. (At least it looks like Ohms Law is working!) Any idea what's wrong please Woody

Audioguru Many thanks - I will try the Op Amps you suggest and let you know the result Woody

Hi y'all Can someone help please: Made a current limiting PSU from circuit in the L200 spec sheet as below. Can't get the current limiter to work and am thinking I'm frying the OpAmp. :'( It gets 30 volts but its own spec sheet says 22 volts max. Is there a solution or am I barking up the wrong tree? Thanks Woody

Hi Audioguru Thanks for the response. Problem is I bought them from a seller on eBay located in California who seems to have got them from a Chinese? source. - and I'm in the UK! >:( That having been said they seem good quality. You are right there is RF flying around as I get a fluctuating display on the current meter with only one input lead connected. Re your earlier post what value caps do you advise - 100pF or similar? Thank you for all the help Woody

Hi MP Thanks for the reply. The meters need a 5v supply to function. The other psu is purely serving as a source of an imput to be measured. What about putting a link between the -ve 5v supply and the -ve input? as per attached? Sorry to be a pain but I need these working for my new 0-30v psu now under construction. Woody

Sorry - trying again woody

Hi MP/Audioguru Not exactly a scematic but hope it serves the purpose Woody

Hi Audioguru I'm measuring voltage of a separate (different) PSU output at its panel terminals and current being drawn from the same source to run the fan - just to give me a measurable load. Meters are powered by the little PSU at 5v. So I'm not trying to get the meters to measure their own circuit. Woody PS You are also right - this little tx gets quite warm with no load! (I do have a LED at the output to remind me its on - but thats only drawing 8mA).

Hi Audioguru Thank you for the reply. The LED meters each draw approx 41mA (measured) when lit (3 1/2 digit) and functioning. I'm using a 4,700uF cap for smoothing. Fan is drawing 110mA making a total of 190mA. Total is well within tx spec. Any advice on the 'mutual interference' of the two meters? ??? Thanks Woody

Hello - this thread has gone very quiet - everybody soldering?? Some help ,please: While waiting for my main PSU pcb to arrive I've been putting together an auxillary psu for my two LED voltage and current meters and a 12v supply for a fan I want to put in the PSU box. I've used two 7805s off the same tx which gives me 5v fixed and a 7805 with a divider which gave me 5- 14 volts which I've fixed at 12v by a preset. The two meters work fine on test except when I run them together. Voltmeter display drops to 0.3v (actual volts remain at 12) and current display fluctuates reading 3-4 amps (which is not right for a 250mA tx! Can someone tell me what will fix it. Othe Q is that the little tx runs Very hot. Meters draw 40 mA each and fan draws 110 mA - so less than 200 all up. Do these little transformers run hot anyway or am I heading for a small bonfire. Thanks Woody

Audioguru Many thanks for the advice Woody

Hello I'm an 'old' newbie recently retired. Am returning to my electronics hobby after 30 years! I made a 1A current adjustable psu many years ago but it got the boot in the many moves around the world. I've followed this thread for some time and was close to buying a kit of parts for the project from my UK source when I read of all the mods. Will there be a chance to purchase a pcb which incorporates all the changes? - 3A is fine for me, I don't need 5A. (I don't need the full kit then) I have sourced all the components here except the Op Amps. I cannot find MC34071AP or TLE2141CP or certified equivelents. Any advice please. Best wishes to a great forum and the very knowledgeable contributors Woody