Re: How do I convert 0-10V to -5V +5V differential?


John Fields wrote:
> On 31 Aug 2005 13:13:19 -0700, kasterborus@xxxxxxxxx wrote:
>
> >Thanks for you all your help - I have all the parts to build the op-amp
> >solution at home - the only thing that puzzles me a bit is the
> >+15V/-15V power to the 741 - how do I create +15 and -15V from a
> >standard transformer.
>
> ---
> Since the 741 can take an input supply of plus and minus 22 volts,
> max, you can easily get less than that that from a simple,
> unregulated, half wave supply using a 12V transformer, like this:
>
>
>
> +--[IN4001>]----------+---->+17V
> | |
> | |
> MAINS>--+ || +--[<1N4001]--+-------|---->-17V
> | || | | |
> P || S | |+
> R || E [C1] [C2]
> I || C |+ |
> | || | | |
> MAINS>--+ || +-------------+-------+---->GND
>
>
>
> Since your output is only going to swing between +5 and -5V, and the
> 741 needs about 3V above and below that to let that happen, you've
> got about 9V of headroom to either rail so C1 and C2 can be fairly
> modest, depending on what else you're going to use the supply for.
>
> What can you tell us about the load?
>
> --
> John Fields
> Professional Circuit Designer

Mr. Fields has given the best solution. The OP might want to add a
couple of protection diodes to keep the inputs in the range of the
supplies and the caps from being reverse-biased at turn-on, like this
(view in fixed font or M$ Notepad):

` D
` o------o-------->|----o-----o------o+14VDC
` | +| |
` | C --- - D
` o------|---. --- ^
` | | | |
` 10.2VAC | '----------o-----o------o
` from | +| |
` Wall Wart | C --- - D
` | --- ^
` | D | |
` '--------|<----o-----o------o-14VDC
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

Radio Shack P/N:
Wall wart:
9-13VAC/800mA AC-to-AC Adapter $16.99 Model: 273-1631 (set for 10.2VAC)

C:
470µF 35V 20% Axial-Lead Electrolytic Capacitor $1.39 Catalog #:
272-1018

D:
25 Rectifier Diodes (1N400X) $2.59 Catalog #: 276-1653

Any 9VAC to 12VAC wall wart rated for over 50mA and up to 1 amp will do
fine, as well as any 1N400X diode and any cap over 470uF, rated at
25VDC or above. The OP should be able to scrounge the components he
needs from his junkbox.

However, the OP really should look at the docs on his galvo amp again.
Nearly all of the ones I'm familiar with have the dual supplies
accessible from a terminal block or connector somewhere on the chassis.

Good luck
Chris

.

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