Transformer question

[tubesmuggler]

I have a quick noob question about a PT I have. It's secondaries are labeled like this:

250V/100mA - 0V - 250V/100mA

I'm not certain what this means the current rating is. I'm guessing another way to show this is 500VCT/200mA, correct?

Or is it 500VCT / 100mA ?


TIA!

 

[Tom Bavis]

500VCT @ 100 mA. DC output capacity will be about 100 mA as well. DC current could be more with choke input, but voltage would be too low for most applications.

 

[tubesmuggler]

Thank you sir!

 

[hemgjord]

On the same subject, I never got this really clear.
If I for example have a 500VCT @100mA TX what can I expect it to handle if used for bridge rectification instead of the (I suppose) expected full wave rectification.
Can I actually pull 100mA @ 500V?

/Olof

 

[Tom Bavis]

No, you can't get 100 mA since you have to supply capacitor ripple current as well as dc current - 60-70 mA would be more like it. With choke input you could get 90 mA or so. Duncan Amps PSU designer can give a good idea of the RMS transformer current for a given DC current.

 

[hemgjord]

No, you can't get 100 mA since you have to supply capacitor ripple current as well as dc current - 60-70 mA would be more like it. With choke input you could get 90 mA or so. Duncan Amps PSU designer can give a good idea of the RMS transformer current for a given DC current.

Hi there
Yes I am aware of this, it was late and I did not express myself very clear. I refered to actual AC current to be drawn from the secondary.
What I really wonder is; if a TX is spec'd at 500VCT@100mA, is this for use in a full wave circuit where you actually can draw approx 60-70 mA at 350VDC?
Or can it be used in a bridge circuit to supply 60-70mA @ 700VDC?

It is quite a difference.

/Olof

 

[Tom Bavis]

About 100 mA in a full-wave center-tap circuit, maybe 130 mA with choke input. About 60-70 mA at 700V in full-wave bridge. About 90 mA at 500V with FWB and choke input filter. Any of these result in about 100 mA RMS AC current in the transformer secondary.