# AC voltage doubler



## Mr. Sharkey (Jul 26, 2007)

The circuit you describe was used in low-end tube-type televisions where the manufacturer needed a higher B+ but didn't want to go to the expense of installing a step-up transformer.

In fact, the same principle is used in computer switching power supplies that can run at dual voltages (120/240).

If the output voltage is doubled, then the input current must be doubled also. While the circuit is supplying current to the load, the input is not only supporting that, but charging the capacitor for the next half-cycles step-up, basically, two loads instead of one. Output wattage is approximately the same as input wattage, meaning the input current is twice the output current (less losses).


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## Twilly (Jan 22, 2008)

If the voltage is doubled, then the current should be halved... Ohms law I=V X R


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## piotrsko (Dec 9, 2007)

UH, no you are dealing with capacitor discharge and the related LC time constants. accross the appropriate impedance, in theory, a capacitor ought to be able to deliver an infinite current until the joules stored are moved into the circuit.

this is why the boom box people use 1 farad caps. This is also an old dinosaur tube trick to build a cheap phigh current power supply.


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## dataman19 (Oct 7, 2009)

You do remember that diode based voltage doublers only work with an ac input - right?
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They don't double the available voltage - they double the supplied voltage...
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They double the output voltage by providing a path for the positive portion of the sine wave, and then the negative portion. What you say - negative added to positive is zero!!! Not quite so fast with the judgment...
When the AC Goes Positive the positive biased diode conducts and provides a rising and dropping DC voltage (most of us call this a pulsing DC). So when the AC Voltage croses the zero mark and starts going negative the positive diode is reversed biased (cuts off) - but the negative diode is biased to turn on (because it is negative biased) and provides a rising, then decreasing voltage at the output. 
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Since the Two Diodes are connected Cathode to Anode you effectively have two pulses of DC at the output (similar to a full wave rectifier) but with the advantage that the available voltage is effectively doubled. A full wave rectifier only provides a combined DC Pulse - the doubler Provides a double DC Pulse (Hence the term voltage doubler).
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The down side is that the voltage is doubled (yes) but the available current is not. This is a fact that is understood by those group membres who are constantly reminding others that 1 Amp DC draw on the 160V Battery pack supplied to a DC/DC Converter will thoretically supply 11.5 Amps at 13.8VDC. (1 Amp at 160V = 160Watts - 11.66 Amps at 13.8VDC = 158.7 Watts). 
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When comparing power to power in any DC system you must compare watts to watts. This is the power and 160 Watts is 160 Watts at 13.8V, 144V, or 160VDC. The values for DC Volts and DC amps change - but they should all equal the same wattage. Hence the term "True Power".
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Yes I think that power factor and efficiency change the practical application and the real worl rules - but watts be watts, while all amps and volties are not equal.
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dataman19


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