# Power Supply

Discussion in 'The Projects Forum' started by jegonz, Jan 25, 2008.

1. ### jegonz Thread Starter Member

Jan 25, 2008
19
0
Hello, I'm new at this forum things, so not that sure how this works, but here is my question>
I want to do a variable 9V 1A (or 2A) output source that willl be feed a motor driver that is conected to a 3W step up tranformer (1:24). The control signals of the H-bridge will be a square 4KHz wave, and the output in the transformer I want to be the nearest as possible the control signals (4KHz square wave) but higher voltage (and at least need 3W for a 1Khz load).
Right now I have a circuit made, that works with a 9V battery, plug directly to the motor driver, and I get aftert the transformer a almost squarish wave with the desire output. So the things I need some opinion and help is in making the digitally variable 9V source, and how to make the output wave form as square as possible if the load is and serial RC circuit.
Suggestions and ideas will be appreciate!

2. ### beenthere Retired Moderator

Apr 20, 2004
15,815
282
Your transformer is going to round up the output no matter how hard you drive it. And, by the way, 3 watts with a 9 volt supply comes to 333 ma current (P = EI).

If the stepped up voltage is the source for the H-bridge, it should be DC in nature. The H-bridge PWM drive will chop it through the load. So rectify and filter the transformer output to make that voltage DC before sourcing the H-bridge.

3. ### jegonz Thread Starter Member

Jan 25, 2008
19
0
Yeah I know that 3W with 9V is around 333ma, but maybe I didn't explain myself well... the thing is that the source is to feed the transformer, so the H-bridge is before the transformer, after the step-up is only the load, there is where I need the 3W output, for the load... to get at least 50mA, that means I want to step up to 60 or more volts. So I need at least 6 times the current in the primary of the transformer, in this case will be like 24 times the output current I want in the secondary (step-up). That is why I want the source to drive 2 Ampers and that the voltage can be digitally controled.

4. ### thingmaker3 Retired Moderator

May 16, 2005
5,072
6
Total power out of a transformer is only slightly less than total power in.

Six times 0.05A is approximately 0.3A.

Why do you need 24x current available? Will you be using a different load drawing 0.2A? If so, you'll need a 12 Watt transformer.

5. ### jegonz Thread Starter Member

Jan 25, 2008
19
0
mmm... well the transformer is the one I have now(1:24), and the thing is I need at least 60V (9V at the input) with at least 50mA in the output (that is why I think the 3W is ok, but now not that sure...jeje). The load is an R-C series circuit with a total impedance around 500 to 1500 ohms.
Thanks!

6. ### thingmaker3 Retired Moderator

May 16, 2005
5,072
6
I don't think 60/24 = 9. I think it might be closer to 2.5

Your input needs to be 2.5V at 1.2A. If you put 9V into a 1:24 xfo, the o/p will be 216V.

7. ### jegonz Thread Starter Member

Jan 25, 2008
19
0
ahh yes the voltage is 216V, but because is only 3W, then the voltage will drop around 50V, with a 1000 ohm impedance, and then the current will be what Im looking for.
But then again that is not the problem I have. What I need an idea or guidance to do a digital controlled source, that can give me around 9V, 2A in the output; that will feed the transformer input.

Anyways, Thanks for the comments, they make me re-think of what I have done.!