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Hello guys, first i wish all of you happy holiday. I have a problem, i need to make floating power supply for a voltmeter for power suplly. Voltmeter cant be supplied directly from what i will be measuring, because it will not work, so i need little floating psu which i can build into.
My first thought was to use a little coil (from GDT) with 30:15 turns and hook it from the output of trafo, but it went wrong and coil is overheating. I tried current limit it, but with no success ( i think it is the thing where coil cant get any more power into itself, saturation maybe, i'm not sure)
Is there any little circuit, chip, or something which can help me?
Only circuit i can think is to use some little halfbridge with resonant circuit, and use it to power my trafo.
Registered Member #2901
Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837
A 30 turn primary won't have enough magnetizing induction at 50 Hz.
Why not simply take an old mains transformer based power supply from an old charger or something? Dunno about you, but I have a drawer full. Some high frequency SMPS will be smaller, but is it worth the effort?
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546
If this voltmeter is one of those LCD panel types that needs little current, what you could try is an inductive pickup coil placed somewhere on the mains transformer, or even slip a winding around the main coil, once you know how many volts-per-turn the core operates at.
Registered Member #4230
Joined: Sat Nov 26 2011, 05:50AM
Location: Socketville
Posts: 53
At mains frequency, you need an iron core and enough turns on the primary to keep it from saturating. Use lots of insulation between the primary and secondary by winding them on different parts of the core, or wrapping the primary with PTFE tape before putting the secondary on. Polypropylene or Polyethylene tape works better. Polyimide works the best but costs more. You can also put a grounded piece of foil or foil tape between them to reduce capacitative leakage. Don't forget to insulate the foil from itself or else you'll have a dead short!
Core - PTFE or nice thick coil form - Primary - PTFE - foil with ground tap - PTFE - secondary - more PTFE.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
In order of cost/complexity - a battery would run for 100's hours - a small (e.g. 3 VA) isolating transformer, bridge rectifier, capacitors and 78xx regulator - a small Royer/zvs/cfpr inverter - a small (e.g. TOP223) mains powered smpsu - a DC/DC converter module
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floating power supply in another psu
