# Electronic Circuits and Projects Forum

1. ## Help with duel transformer

sup guys,
lets say i have this kind of transformer:
http://imageshack.us/f/820/mje13009.png/
(dont look at the total circuit, just on the transformer)

now, i bought a power supply and i decided to look inside it.
i found that there is a transformer with 1 primary and 2 secondery coils just like the circuit above
also, one of them gives 8v and the other 24v.

but i also noticed that there is only ONE diode bridge for two coils?
hows that possible? or there is a way to convert 2 AC connections via one diode bridge?

thanks.

2. i found that there is a transformer with 1 primary and 2 secondery coils just like the circuit above also, one of them gives 8v and the other 24v.
Yes, transformers do that sort of thing.

but i also noticed that there is only ONE diode bridge for two coils?
hows that possible? or there is a way to convert 2 AC connections via one diode bridge?
You cannot use a bridge rectifier for two different supplies at the same time.
I think that you completely misunderstand how that PSU works.

If you want a better explanation, I think that you need to show a schematic of the PSU.

JimB

3. You cannot use a bridge rectifier for two different supplies at the same time.
thats why i couldnt solve the problem my self, and come to this forum.
but still, my power supply uses 2 different secondery coils, and i searched the whole board, there is only 4 diodes on it (the board is about 3x3 cm - nothing rly to search)
but still. they used convertation from AC to DC somehow using only those 4 diodes and 2 different supplices..

4. For a center tapped secondary you can use one bridge rectifier to cover two DC output voltages. Connect bridge across total transformer secondary. Take the second DC voltage from the transformer center tap to ground which will provide half the DC voltage. (assuming diode drops are insignificant compared to transformer secondary voltage).

The current for the two bridge diodes going to full voltage DC+ will take just the full voltage load current. The two diodes in the bridge going to ground will take the current of the full voltage load plus the transformer center tap DC load.

5. For a center tapped secondary you can use one bridge rectifier to cover two DC output voltages. Connect bridge across total transformer secondary. Take the second DC voltage from the transformer center tap to ground which will provide half the DC voltage. (assuming diode drops are insignificant compared to transformer secondary voltage).

The current for the two bridge diodes going to full voltage DC+ will take just the full voltage load current. The two diodes in the bridge going to ground will take the current of the full voltage load plus the transformer center tap DC load.
ahh good one. thanks!

thats the answer i was looking for..

thanks again!

6. For a center tapped secondary you can use one bridge rectifier to cover two DC output voltages. Connect bridge across total transformer secondary. Take the second DC voltage from the transformer center tap to ground which will provide half the DC voltage. (assuming diode drops are insignificant compared to transformer secondary voltage).
Agreed.
But that is for a CENTRE TAPPED transformer, where we would expect one supply to be twice the other.

In this case:
one of them gives 8v and the other 24v.
So the transformer would not be centre tapped.
There could of course be voltage regulators, but that was not stated in the original question.

JimB

7. Give this link a read. Note how transformer secondaries in the case of dual secondaries can be placed in series and parallel configurations, consider it would be unwise to parallel secondaries of different voltages as you mention as to voltages but in the case of dual secondaries it would not be unusual to place the secondaries in series to make a dual +/- supply using a single bridge. Doing so amounts to a single center tapped secondary. Additionally the 24 volt and 8 volt could be placed in series to make a -8 volt / +24 volt power supply using a single bridge or a +8 and -24 volt supply. Anyway the link may be helpful reading.

Ron

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