Re: 9VAC from 5VDC?

From: Jim Brain <>
Date: Fri, 13 Sep 2013 22:54:41 -0500
Message-ID: <>
On 9/13/2013 9:57 PM, Bil Herd wrote:
> Do you want to create AC from DC or from AC? (thought is was 5 VDC as
> input)
AC from DC.

A uC will run a 50Hz/60Hz DSS routine, either outputting to a PWM 
channel or R2R DAC.
The output will drive a power transistor to the first pin of the Xformer 
primary winding.
The second pin will be at ground.

The secondary winding will then have an isolated AC voltage.

Since my AC is rusty, I realize now that 9VAC is 9VAC RMS, which is, as 
john notes, 12.73Vpeak, or ~25Peak to peak.  So, the secondary winding 
needs to give ~25V.  Since the primary will probably have 4.7V PtP, 
that's 1:5 (gives 23.5V, assuming no loss, which is not realistic, so 
say 22VPtP, which is 11V peak, or 7.7VAC RMS).  Maybe 1:6 would be better.

If such a transformer cannot be found, I could build a voltage 
quintupler (5 power diodes and 5 power caps, I assume heavy caps), but 
I'd rather let the transformer bump up the voltage.  Either way, the 
transistor need to support 5A of power.

If 1:3 can be found, I could create two half wave PWMs/R2R channels.  
With 4 transistors, I could drive the 5V through one way for half a 
cycle, then the other way for half a cycle, but that means I'm only 
drive 4.3V (2 PN junction drops).

If I use the PWM into some FETS and do the filtering on the output of 
the FETs, I might be able to do 5V swing, but I am much less familiar 
with FET operation, so I would have to breadboard it.  It also would 
then require larger capacitors and higher wattage resistors.


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Received on 2013-09-14 04:01:29

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