power supplies again

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ed
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#1 power supplies again

Post by ed »

I'm looking for a +and- 9v supply so I modelled the positive side in psud and got way confused as usual....

the diagram shows the starting point. It shows a beautiful, ripple free 10+ volts, just right to regulate.
I was going to use the hammond 154e.

as soon as I put the 1666R series resistance into the choke psud throws a fit and gives me about 3ish volts with ripple aplenty.......

can anybody suggest where I should be reading to understand this, cos so far I havn't found any background..
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#2

Post by pre65 »

I too have had proplems with PSUD and low voltage circuits containing chokes.

If I remember correctly you need more volts in and much smaller chokes (in the mH range) to get things right.

I have got some spare 68mh chokes (about 2 ohms DCR) if you want to try one (or two). :) Try those values in PSUD and see what happens.

EDIT. I've now used all 4 of my 68mH chokes to try and cure a hum problem in GK-71.
Last edited by pre65 on Thu Nov 14, 2013 5:01 pm, edited 2 times in total.
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#3

Post by ed »

this one works a treat with hammond 155g.......there is ripple but it's in the uv range

just curious about the mechanism
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#4

Post by Mike H »

Are you giving it enough time to simulate? I think the default is 5 milliseconds or something equally daft (yes I've just checked), I have been caught out with this, wondering why there's massive 'ripple' and the DC Voltage is too low.

The 'ripple' was just the step response resonance while the thing starts up, actually.

But 5 ms doesn't give it enough time to get going properly.

HTH
 
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#5

Post by ed »

10 seconds.....start after 1 second
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#6

Post by Mike H »

Right so, I've tried the first circuit and it works fine.

BUT it won't allow me to insert a current tap at the end, says "this will be an illegal combination", so I had to use a 1k resistor instead.

It makes about 10.3VDC, and the ripple is so small that I can't measure it.

:?:
 
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#7

Post by Mike H »

Doh the default is not 5 ms, it's 5,000 ms Image (it's not a decimal point)
 
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#8

Post by ed »

I'm not sure what you're saying Mike.....did you put the series resistance into the choke spec?, i.e 1666R...see post #1

and if so, how on earth did you still get 10volts out
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#9

Post by Mike H »

Sorry I forgot. Just took the first diagram as shown...

OK.....


Yep it can't do it, choke resistance is too high. I get 4V out. No tantrums though, maybe cos still using 1k load resistor.
 
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#10

Post by ed »

Mike H wrote:Sorry I forgot. Just took the first diagram as shown...

OK.....


Yep it can't do it, choke resistance is too high. I get 4V out. No tantrums though, maybe cos still using 1k load resistor.
phew! it's not just me then.....

oh well, I'll plump for the 155G, 7H @ 40ma....it looks good in psud with 300R series.

thanks for looking anyways
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#11

Post by Mike H »

Yep 10 measly mA is too much :D

You might do it with a much bigger input Voltage, if you want to be bothered
 
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#12

Post by ed »

okey dokey

back again....I've ditched psud for the mo....I just can't bend it to my will.....

In time honoured fashion I stuck some bits together, roughly in the direction I'm heading....

funny poo going down at chez moi this afternoon. I built the attached power supply this afternoon, expecting + and - 9v. What I got was +9v and -9.11v.

Anybody got any experience with these regulators or why I might get such a discrepancy. I tried loading the output....450R to give 20ma and 220R to give 40ma and the voltage didn't move. I will be using this at about 15 to 20 ma.

It crossed my mind that the transformer wasn't adequate. I have a 2x18v in the box but I havn't tried it yet.

scratching my head....I know I'm in the right ball park but can't fathom the mismatch.....it's for a wien bridge so I imagine the voltages should match.
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#13

Post by IslandPink »

Sounds pretty close to me - straight off from stock parts !
Is there not some facility to adjust those regulators ?
Also, when it gets to the Wein bridge, is there not some set-up 'calibration ' you can use to get around this slight difference ?

I'd best let the brainy people chip-in though, not having direct experience of what you're making here . Andrew might be useful ...
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#14

Post by Andrew »

Probably close enough that the reg is within tolerance, the LM parts are OK for the money, I think you can expect about -50 to -60 db line rejection from them.

Scope the output you'd notice 50Hz and 100Hz mush breaking thru if it were dropping out, but 20mA is not exactly heavy going for these parts, many of them can handle several amps.

Nick might be able to chip in here, whats the application?

cheers,

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#15

Post by IslandPink »

For a Wien bridge apparently .
But maybe you could trim the -V side with a resistor to get 9.0V ?
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