The Shop > Electronics & IC Programing
Digital oscilloscope project/kit
RobWilson:
:lol: :lol: :lol: :lol: I was full of the party spirits when I redrew it last night Dave ,,,,,,,,,,,,,you try reading with a pint and a half of vodka and coke in you :lol: :lol: :beer:
Cheers Rob , could do with some bait myself .
RobWilson:
--- Quote from: Bluechip on December 31, 2015, 09:38:45 AM ---
BTW
I think your 0V centre-tap should be grounded ??
And that is the symbol for a safety earth, ground is an inverted triangle. :thumbup:
What current are you drawing from these regulators anyway? The 12V ic's. will have some 25V i/p, this gives about 13V dropped across them. If I assume the max. of 1A they will dissipate some 13W which is a lot for a TO220 package without a fairly large heat-sink and/or a fan. A 15 - 0 - 15 transformer would be a bit better ...
Dave
--- End quote ---
oops I thought there was something else missing ,its grounded :zap: ,, about 200 milli amps Dave
Have a butchers at the new new version PDF :lol:
Rob
John Rudd:
Well, my thoughts are:
The fuse is in the wrong position ......transformer primary would be better......
Not sure if there's sufficient headroom for the 9.0 v reg to work properly.....3.0v differential between in and out....close to the drop out voltage.....
If I were designing it, I'd be looking for around 16.0v in to the 12.0v reg, then connect the 9.0v to the 16.0 v supply....
A 15-0-15 transformer would be better as Dave says....I'd even try going as low as 12-0-12 to reduce the dissipation even further.....
Item 311 512 from https://www.esr.co.uk/electronics/products/frame_transformers.htm
RobWilson:
--- Quote from: John Rudd on December 31, 2015, 10:29:11 AM ---Well, my thoughts are:
The fuse is in the wrong position ......transformer primary would be better......
Not sure if there's sufficient headroom for the 9.0 v reg to work properly.....3.0v differential between in and out....close to the drop out voltage.....
If I were designing it, I'd be looking for around 16.0v in to the 12.0v reg, then connect the 9.0v to the 16.0 v supply....
A 15-0-15 transformer would be better as Dave says....I'd even try going as low as 12-0-12 to reduce the dissipation even further.....
Item 311 512 from https://www.esr.co.uk/electronics/products/frame_transformers.htm
--- End quote ---
Cheers John
I will move the fuse , I should have had a question mark next to it .
I have at hand a 12-0-12 and a 18-0 -18 transformer , the simulation did not like the 12-0-12 transformed ,no head room , and the simulator says I should get 9.74v :scratch:
See new new new attachment lol
Cheers for the input lads :thumbup:
Rob
Bluechip:
John is right, it will work with a 12 0 12 transformer .... depends somewhat on the VA rating ... :thumbup: so what is the rating on the one you have ??
Why ??
OK. So, lets imagine we have a tranny 12 0 12 out at 24VA [for no other reason that it's easy to work out] :thumbup:
24vac out 24VA gives 1 amp load current.
BUT ... trannies here assume the EU nominal volts in to be 230vac ... we're often nearer 245vac.
The output voltage is at the full rated load ! ie. 1 amp.
Now we come to LOAD REGULATION
On a relatively small tranny it won't be very good, at 24 VA it's probably about 12%.
Which means at no load the output volts will be 12% higher than the full load 24 vac ie. some 26 vac.
To compound the felony we are shoving more volts into it than the 230vac nominal.
The upshot of this tripe means we will get considerably more DC volts, AT SMALL LOADS, than we think.
Hence a 12 0 12 12VA tranny will be quite OK in practice even if your wretched simulator doesn't think so.
If you get one of these really titchy 3VA trannies and measure the no-load volts out you will be surprised [ at first anyway] they are often way above the advertised value :zap: but shove a 50mA load on them and they calm down.
Dave
Somewhere I have the schematic for one I built, see if I can find it ... might be on the laptop ... :scratch:
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