[SSSSSmokey]

For anyone who has built the TEPS power supply, have you ever had this problem? I am totally finished except for one small problem: instead of outputing 24v like I planned, it outputs 50v. Adjusting the VSET (the trim pot) adjusts it from about 49.7 to 50.3. I have tried everything, changing the R4 (which is supposed to set the Vout along with the trim pot), but to no avail. With the trim pot and resistor removed, I got 100+ volts, but no matter how high value of a resistor I use I cannot get the output below 50v.

I am not a total n00b to electronics, but couldn't design a circuit myself or anything like that. I used basically everything from parts list on Tangent's website, not changing anything.

BTW if this helps here are the readings at the test points:
At 1 and 2: 37.3 vAC
At 5 and 3: 110.3! vAC, 50.3 vDC
At 4 and 5 (these equal output): 49.7 vDC

This is with a 470K ohms 1/2w KOA Speer (and the 500ohm trim pot removed).

I'll take more measurements with a NTE 2.2 ohm 2w resistor in place:
At 1 and 2: 37.7 vAC
At 5 and 3: 0.0 vAC? 50.7 vDC
At 4 and 5: 50.0 vDC exactly

I'm not skilled enough to read the schematic to find out what I did wrong. Another thing that is noteworthy: R5 is burning UP. It can't even touch it without burning myself, but that is when I had the 2.2 ohm res on there. It may have been trying to dissipate too much heat due to the low value of the other resistor though.

Thanks in advance for all your help!

 

[steinchen]

what transformer are you using ? seems to be too big

where did you put the 470K resistor in ? that value is way too high ... 2.2 ohms ? Not kilo-ohms ? 2.2 ohms is way too low.

did you only remove the pot or did you jumper across it ? just removing won`t work

since there is DC voltage after the rectifying bridge there is no point in measuring AC between points 5 and 3

 

[Jazper]

take some pictures of the top and the bottom of the board and post them.

I've been doing some thinking, check to see that your transformer is hooked up the right way around.

please tell me you're not feeding the teps with 110vAC (no transformer)

 

[en480c4]

I would highly suggest that you figure out what is wrong before putting power to the circuit again. Line voltage is nothing to fool with. And like others have said post up some pictures of the top and bottom of the board.

My thought is that you have incorrectly set the jumpers that determine if it's meant for 220 or 110 VAC. But that really is just a guess. A friend and I have built 4 of these and none have exhibited the symptoms your are describing.

HTH,

Ian

 

[en480c4]

Quote:

Originally Posted by Jazper please tell me you're not feeding the teps with 110vAC (no transformer)

I think you're confusing the STEPS and TREAD. Based on Smokey's desciption he's working on a STEPS which should have an on board transformer. If he fed AC to a TREAD we wouldn't be reading any of his posts and he'd be living up to his name.

Ian

 

[Jazper]

Quote:

Originally Posted by en480c4 I think you're confusing the STEPS and TREAD. Based on Smokey's desciption he's working on a STEPS which should have an on board transformer. If he fed AC to a TREAD we wouldn't be reading any of his posts and he'd be living up to his name. Ian

I genuinely laughed when I read that, thanks Ian

 

[mono]

Quote:

Originally Posted by en480c4 I think you're confusing the STEPS and TREAD. Based on Smokey's desciption he's working on a STEPS which should have an on board transformer. If he fed AC to a TREAD we wouldn't be reading any of his posts and he'd be living up to his name. Ian

Not necessarily, they're just boards- put what you want on one, you could use a Tread with proper parts for 80V out with 110V in, or a Steps without the limiting transformer onboard, for example if you wanted to exploit the LDOs for 3-5A at relatively HV, that transformer isn't going to fit on the PCB.

 

[mono]

SSSSSmokey, measure the voltage right before the regulator and compare it to your high post-regulator reading. I suspect you've installed one of the protection diodes backwards, the one that goes from output to input on the regulator (don't remember which part # it is on the schematic).

 

[dsavitsk]

fwiw, I had a similar problem with a Velleman which was caused by a blown regulator (it worked prior to a power surge/cap explosion.)

 

[n_maher]

Quote:

Originally Posted by mono Not necessarily, they're just boards

True, but he's claiming to have measured DC so either he's got a transformer on or off board or he's the first person in history (that I know) who's got DC voltage coming out of the wall. And if you'll take note of the test points that he mentions in his post he's working with a STEPS that is clearly not working correctly.

And you're also right that it doesn't really matter if it's a STEPS or a TREAD, the simple fact of the matter is that he's got something screwy going on with the circuit since A. the voltage is not adjustable and B. the output voltage is way high, but the AC voltage out of the transformer (between TP1 and TP2) is correct (assuming he's using the stock part).

Anyway, another request for pics please.

Nate

 

[SSSSSmokey]

I built this exactly from the directions on Tangent's site.

Heres some pics, with that headsink removed so you can see whats in there.

http://img88.imageshack.us/img88/6453/dsc011062bq.jpg
http://img88.imageshack.us/img88/6107/dsc011116aw.jpg

Any wires leading off are for the AC input. By regulator do you mean the IC? Or something else? I'm not very fluent in the jargon for all this stuff. I know transformer, pcb, capacitor, resistor, diode and thats about it. I'm always willing to learn though! If you say something complicated, just explain it and I'll learn it for next time.

For anyone who wants to help me but isn't too fresh on STEPS, here is the stuffing diagram off Tangent's site:
http://tangentsoft.net/elec/teps/misc/steps11-sg.pdf

Thanks a ton! I want to be listening to my Grado 225s tonight.

 

[dsavitsk]

check your diodes (not the rectifiers, but the little black cylinders near the regulator (the IC)). The little lines on one edge must be on the same edge as on the pcb. It is hard to see in your pics, but it looks like at least one, if not both of them are backwards.

-d

 

[MisterX]

Yup.... they do look like they are backwards.

 

[Jazper]

it looks like Q3 and Q2 are the wrong way around (still looking) (damn beaten to the punch)

(also check c7 is the correct way around)

 

[DaKi][er]

both the diodes are around the wrong way

also you have to have r3, r4 and Vset installed as well as they set the voltage out, make sure they are calculated to what voltage you want as well with V=1.25(1+R4/R3)