Diode Voltage multipliers

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Mike
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Diode Voltage multipliers

Post by Mike » Thu Aug 21, 2003 5:19 am

I need to power a 120VAC device from a 12VDC supply. I know that this can be accomplished using step-up transformers, but they lose too much current. I was then looking through a book of mine, and came across Diode Voltage Doublers, Triplers, and Quadruplers. There was also a suggested circuit for a cascade multiplier, which lets you get as much power as needed, in my case, 10X. Do these circuits lose current like transformers when they are increasing voltage? My 120V device runs off of AC, and these circuits produce DC, so could I use a bridge rectifier backwards (DC in AC out)? Also, what would be a good diode to use?<p>-Mike

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Re: Diode Voltage multipliers

Post by k7elp60 » Thu Aug 21, 2003 6:14 am

Mike,
The most efficient way is with an inverter. They first convert the DC to AC then step it up thru a transformer. The output is generally a modified sine wave and most 120VAC devices work fine on it. They are pretty efficient. As I recall over 90%. The thing to remember is power.
If you need 120 volts at 300 watts, it will still take over 300 watts at 12 volts DC. In this case over 25 amps, to change the voltage from 12VDC to 120 VAC.
Ned

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Chris Smith
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Re: Diode Voltage multipliers

Post by Chris Smith » Thu Aug 21, 2003 11:16 am

Remove from your transformer circuit the Bridge rectifier that makes it in to DC, then run your Cap/Diode multiplier to get your step up AC out put. These work well for low current apps, and high voltage apps like lasers, but are not the most efficient way to convert. Your power rating make that choice. In MY high volts apps like Lasers and Infra red scopes, they draw milli or micro or pico amps from batteries [9 volts to several kv in the scope Or 12volts to 14k starting volts in the laser] so the conversion is well suited. However if your in the milli amps and up, the caps and diodes also have to be rated heavy for that amperage, times the voltage.

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haklesup
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Re: Diode Voltage multipliers

Post by haklesup » Thu Aug 21, 2003 1:34 pm

Simply put, there is no getting around the law of conservation of energy and Ohms law.<p>Pin=Pout
P=IV (ok, not preciisly ohms law V=IR but derived from it and the power law P=I^2R) <p>So, I*V in = I*V out regardless of the technology you use in between. <p>The only area you have flexibility is efficiency because P out is actually the power you get to use (V*I) plus the power you loose to heat in your circuit (I^2R).<p>For conversion of AC power, nothing really beats a transformer for changing voltages so long as good quality low resistance copper is used in the windings and the core is saturated at the frequency you are using.<p>You want to simultaniously increse voltage and change to AC. As Ned pointed out, an Inverter is the technology of choice for doing this. There are many inverters for use in cars for sale at camping, automotive and department stores. I have seen retail units exceeding 6000W. A typical 450W inverter sells for about $50.<p>If the quality of the AC power at the output is critical (i.e. need a good clean sine wave) then a more expensive inverter with better filtering is in order.<p>Doide doublers and triplers are more often used to generate voltages much higher than 120V. A negative ion generator outputs 8kV or more but at pA or less of current for example.

ljbeng
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Re: Diode Voltage multipliers

Post by ljbeng » Thu Aug 21, 2003 2:45 pm

Let me ask:<p>What is the 120vac device? Is it something that is creating dc itself? If so, can the battery directly power the circuitry?

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MrAl
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Re: Diode Voltage multipliers

Post by MrAl » Thu Aug 21, 2003 4:16 pm

Hello there,<p>The best way to go for this is to buy an
inverter like someone else suggested.
You have to have somewhat regulated voltage
and that requires a control circuit as well.
You can not use a voltage step up using diodes
and capacitors because you need ac, and you
can not use a bridge rectifier backwards to
get ac from dc because this device isnt made
for that, and getting ac from dc is much more
complex then that.
Because of the extra complexities of converting
dc to ac my recommendation is to simply buy a
commercially available inverter. At least this
way you know it is going to work and shouldnt
blow out whatever it is you are powering.<p>Sometimes you can examine the input section of
the device to see if it uses a rectifier circuit
to convert the ac into dc. If this is the case,
and it doesnt also require the ac itself for any
timing or other circuits then you might be able
to mod the input circuit so you can power it with
dc instead of ac. I dont suggest doing this
though unless you have experience with these kinds
of circuits and know what to look for, as well as
the possibly dangers that could arise from a
misjudgement about the circuit, which includes
a possible shock hazard.<p>
Take care for now,
Al
LEDs vs Bulbs, LEDs are winning.

Mike
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Re: Diode Voltage multipliers

Post by Mike » Fri Aug 22, 2003 5:54 am

First, I do not have a transformer circuit. That is what I would have used, but I found that all of my 120-->12 transformers wouldn't work backwards (12-->120). So, I found the diode circuits. Now I know that diodes are not the way to go. I guess I should have said that I need an inverter. It will be used in a car to power a TV, DVD player, and charge a laptop at the same time. I was thinking somewhere in the range of 500W, to be safe. Does anybody know of a good site to find transformer inverter circuits?<p>-Mike

Rodney
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Re: Diode Voltage multipliers

Post by Rodney » Fri Aug 22, 2003 8:42 am

I hope you realize that to power a 500 watt load, you will be drawing about 50 amperes from your 12 volt source. Do you realize the size of the wire and connectors you will need for this if you have any line length.

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Re: Diode Voltage multipliers

Post by rosborne » Fri Aug 22, 2003 1:09 pm

Transformers should work backwards.
-Rick

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dacflyer
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Re: Diode Voltage multipliers

Post by dacflyer » Fri Aug 22, 2003 3:07 pm

comment from beginning.......so could I use a bridge rectifier backwards (DC in AC out)? Also, what would be a good diode to use?<p>
just had to say.... never heard of such a thing...whould be cool to have tho....
only thing close to that is just a inverter itself...ok, i used my 2 cents worth... bye

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Joseph
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Re: Diode Voltage multipliers

Post by Joseph » Fri Aug 22, 2003 7:46 pm

The way inverters used to be made was simpler. It did basically use a 120-12Vac transformer connected backwards and driven with a 60 hz square wave.

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