Question about voltage multipliers - diyAudio
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 11th November 2008, 10:04 AM #1 diyAudio Member   Join Date: Sep 2003 Location: Liège Question about voltage multipliers I know how to use basic voltage doublers, triplers and the like. But is there a way to multiply an ac voltage by 1.5 ? I need about 24-25VDC regulated out of a 18VAC xformer for a small load (about 50ma). Thanks in advance. __________________ Ben.
 11th November 2008, 10:29 AM #2 diyAudio Moderator     Join Date: Sep 2007 Best bet is a doubler and regulator for so small a current. 78L12 + 12 volt zener for example.
 11th November 2008, 10:35 AM #3 diyAudio Member     Join Date: Sep 2003 Location: Midland, Michigan Under such a light load, the transformer may put out somewhat more than 25 volts. If you're lucky, you may need nothing more than a bridge rectifier and a 7824 regulator. Measure the transformer secondary voltage with no load. Otherwise, I agree with Mooly. Voltage doubler and a regulator. __________________ Frank
 11th November 2008, 10:51 AM #4 diyAudio Member   Join Date: Sep 2003 Location: Liège Thanks. It seems like I have no choice... - actually the transformer is also used for other stuff at 200ma/17VDC, so I don't expect it to put it a lot more voltage than what it's rated for. A quick check shows me about 25VDC after rectification and filtering. - with a doubler, I can expect about 44VDC. That means about 20*0.05= 1W of dissipation for the regulator. That's why I asked about this. __________________ Ben.
 11th November 2008, 11:05 AM #5 diyAudio Moderator     Join Date: Sep 2007 Could you perhaps play around with the value of the caps in the doubler --- using the reactance as a wattless dropper and so on --- and still have reasonable DC voltage for the regulator to work off without the ripple component being too high. Would have to think about that.
 11th November 2008, 03:41 PM #6 diyAudio Member     Join Date: Sep 2006 Hi, Fractional voltage multiplier do exist, but they're probably too complicated for your application. I would use a regular voltage doubler, but with a small input capacitor serving also as ballast, and a shunt regulator at the output. A capacitive supply in fact. The power that will be wasted is tolerable, and the complexity is minimal. LV
 11th November 2008, 03:58 PM #7 diyAudio Member     Join Date: Dec 2005 Location: the north One small 2x12 VAC, <= 5 VA transformer is not a big cost. __________________ lineup
diyAudio Member

Join Date: Sep 2003
Location: Liège
Quote:
 Originally posted by lineup One small 2x12 VAC, <= 5 VA transformer is not a big cost.
No, but space is an issue. The aim of this is to provide a higher regulated voltage for an (headphones) amplifier front end, using the existing power rails.

I think I will go for a voltage doubler but I'll stick a pair of 33R/2W resistor in serie before the voltage doubler.
__________________
Ben.

 12th November 2008, 09:04 AM #9 diyAudio Member     Join Date: Dec 2005 Location: the north i see. can you please post your circuit used later and tell us how well it works thanks __________________ lineup

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