Step down transformer in reverse - safety and performance

[johnnyx]

I used a transformer with two 18vac secondaries to provide 100vdc, used to activate 100vdc solenoids, using a voltage doubler circuit.

 

[mr_zener]

A little update 🙂 I ended up getting 249Vdc with the transformer configuration!

Using a 0.33Ohm resistor for current sensing, I got 1.1V peak so 1.1x3 = 3.3A peaks:

I have had this circuit running for about half an hour and the first transformer is only slightly warm to the touch (around 37C)
Do you think that load will be okay for extended listening periods on the 3A 36VA rated transformer?

 

[Tom Bavis]

The RMS value is half that - about 1.6A. That's the value that matters. Transformers don't care about peak current.

 

[Merlinb]

I have had this circuit running for about half an hour and the first transformer is only slightly warm to the touch (around 37C)
Do you think that load will be okay for extended listening periods on the 3A 36VA rated transformer?

That looks very comfortable, yes

 

[mr_zener]

Ahhh yes, my oscilloscope even tells me Vrms. This is good news 🙂 so am I ok as long as I have a max Vrms current of < 2.5?

 

[mr_zener]

Power supply PCB design almost complete.

Back of the board:

DRC checks run without error.

There will be aluminum L used for heat sinks at the top and bottom of the board.
Top and bottom fill zone layer are GND connected and have a 1.5mm clearance, is this all good?
I'm thinking LAR2G121MELZ30 Nichicon LAR 400V 120uF for the main high voltage filter caps?

 

[mr_zener]

Also looking for a suitable bridge rectifier package that is small with minimal voltage drop. There doesn't seem to be any schottky options in a similar package.
Looks like making the PCB bigger to accommodate 4x schottky diodes or live with the voltage drop 🙄

 

[Tom Bavis]

Will cost about $4.50, but DigiKey stocks dual Schottky diodes (60V, 15A) in TO-220, a common cathode plus a common anode to make full bridge. Isolated tab, so they could attach to the same heatsink if required (probably not). The series style, which could use two identical parts, seems to be extinct.

DSTF3060C
DIODE ARR SCHOT 60V 15A ITO220AB
Littelfuse Inc.

DSTF3060CR
DIODE ARR SCHOT 60V 15A ITO220AB
Littelfuse Inc.

 

[mr_zener]

Thanks! I did see TO-220 schottky's, but only saw them in common cathode and dismissed the idea.
I don't know why they don't just make them in one convenient package?