dual-output transformer

[bahstrike]

I have a 12VA CT transformer,  from which I would like to get both  24vdc and 12vdc.
As shown, I use Top-Center to get 12v,  and  Top-Bottom  to get 24v.
The transformer is rated for  500 mA @ 24v series output,  and  1 A  @ 12v  parallel output.
I expect to simultaneously draw maximum  35mA  @ 24vdc,    and maximum  200mA @ 12vdc.

This is my first circuit utilizing mains AC.
Do you think this configuration with these loads could cause unexpected behavior?
I am concerned that the load on first half of the secondary might affect the 24v series output. (?)

[Hero999]

That should be fine but you only need one bridge rectifier not two.

Here's an example:
http://www.electronics-lab.com/blog/?p=109

[Kevin Weddle]

The circuit looks okay. But use normal power supply diodes because the average current could be too high for some diodes. You can estimate the amount of average current, but any power supply diode will be good enough that circuit.

[bahstrike]

KevinIV:
its alright, the diodes are actually the DB104 chip  (bridge rectifier  1A 400V).

the current consumption predictions I made were only to show that the Top-Center  output (~2.4 watts)  is a lot higher than  Top-Bottom  (~0.84 watts)
..which leaves the bottom half of the coil used at a lighter load, and used in conjunction with the already loaded top half..
I didn't know if that might cause problematic funkiness with reactances/inductances/what-have-you..



Hero999:
that's an interesting circuit..    i started to type  "doesn't the GND need some sort of rectification, especially with additional smoothing and regulation"...  until i saw the 1n4004's..  :)

i will give the alternative design some thought for a future use, but i am comfortable with using two rectifiers and my particular circuit does not require common GND  between the supplies.



since my 24v usage is so limited  (only needed to switch on an optoisolator in a remote device),  i have given thought about just using a voltage boost IC.  I am only building a prototype;  I may look again for one in the end-user design of this device.  If you know of a good boost IC  feel free to recommend  :D

[Kevin Weddle]

It shouldn't have any effect on the circuit. But I'll guess some loads can afffect the voltage. And also it mostly assumed the load changes the impedance not affecting the voltage source.

[Hero999]

Hero999:
that's an interesting circuit..     i started to type  "doesn't the GND need some sort of rectification, especially with additional smoothing and regulation"...   until i saw the 1n4004's..  :)

The circuit will work without the 1N4001s which are only there to ensure the regulator doesn't get exposed to a negative voltage during short circuit conditions.

i will give the alternative design some thought for a future use, but i am comfortable with using two rectifiers and my particular circuit does not require common GND  between the supplies.

The definition of GND is irrelevant as far as the operation of the circuit is concerned. GND or 0V is just the reference from where all voltages and currents are measured, you can call the -12V rail 0V and you'll have 0V, +12V and +24V. If it doesn't need to be regulated you could remove the voltage regulators.

i will give the alternative design some thought for a future use, but i am comfortable with using two rectifiers and my particular circuit does not require common GND  between the supplies.

Using two bridge rectifiers has no benefit, if anything it's worse: more cost and more to go wrong.

[bahstrike]

thanks for the assertion guys