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vinay 19th March 2002 04:28 AM

DIY - Adjustable Power Supply Design
Hello All,

I want to build an adjustable +/- 100V power supply. Nothing particularly fancy, but would like to use my toroid with dual 120v secondaries.

Any designs (that are not terribly involved) out there within the reach of a DIYer?



leroy 19th March 2002 07:50 AM

I suggest the use of an autotransformer (Variac) and an ordinary bridge+capacitor approach.

ralf 19th March 2002 12:05 PM

further question

when i use a variac as transformer, with a bridge- from where do i get the ground, which will be connected to the mid of the capacitors?

When i use a "normal" transformer, it`s symmetrical, that means the ground i need is the connection of two cables, coming out of the transformer, plus the two ac - cables, which are connected to the bridge.

But on a variac i have only two cables -ac !


leroy 19th March 2002 12:22 PM

Always use a Variac in combination with a 'normal' transformer since the Variac output is NOT ISOLATED from the mains.
Then you already solve the problem mentioned above.

UrSv 19th March 2002 12:38 PM

2 Attachment(s)
You say you have a toroid with dual 120 V secondaries. Use the Variac to feed the primary of your toroid and take the dual secondaries as the "normal" supply with bridges and caps.

Something like this:


grataku 19th March 2002 04:40 PM

what do you want to do exactly? 2X120VAC to +/-100VDC? If so that is going to involve a lot of power dissipation. How much current do you plan to draw?
If it's more than 200mA you better buy a new transformer. The variac alternative will work but it's awfully clunky. Plus you would be limited in the A of your VA rating.
To get +/- 100DC unregulated you will need a trafo more in the order of 2x60VAC.

vinay 19th March 2002 05:15 PM

More details
The transformer is about 300VA.

I would like to get about 300 to 500 ma.

I have to check, but i think I can set up for +/-60V (+/- 84V rectified).

I want a general purpose (with at least some regulation) power supply, although I would like to use for the Balanced Zen Line Stage, when not using for other activities.



grataku 20th March 2002 05:46 PM

Look in Geoff site he's got one adjustable regulator circuit that kind of works.
Actually you just need to adjust the voltage prior to loading and it's fine.
You could change a few components to make it siutable for your application.
If you really want to drop from ~170 rect. to 100 regulated and get 500mA out of it you are going to need some big mama transistors. 500mA at 70 V is probably dangerously close to the SOAR limit of the 2N3055. You should be able to do it with more transistors in parallel followed by a 0.33 ohm emitter resistor or with a MJ150XX-type transistors. In any case, the transistor on each side of the PS should be equipped with a heatsink able to dissipate ~50W continuously.

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