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I have seen in many books and sites that we can build DC to AC converter circuits. My question is whether there is any limit for the range of DC voltage and AC voltage. Is it possible to get high AC voltage from very low DC voltage?

Let me give a small example to understand my question clearly. I have recently seen some posts:

12V DC to 220V AC Converter Circuit

Is it possible to convert just 12V DC voltage to that much 220V AC voltage? And also if I require 240V AC with 10V DC, what are the modifications to be done in this circuit?

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The DC-to-AC converter circuit is generally called an inverter. And yes, it's done all the time for various applications. –  Michael Kjörling Apr 28 at 13:11
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2 Answers 2

An electrical transformer is basically two coils of wire that are closely wound with each other but not electrically connected. These are used for converting AC power voltages to low voltage AC voltages such as in wall-warts. However, transformers can be reversed to convert a much smaller AC voltage into a much larger AC voltage. A good example is the ignition system on a petrol car. 12Vdc is the battery and voltages of around 10,000 volts can be produced.

In other words, the transformer is the key element in making a high voltage output from a small battery voltage. You can easily generate many thousands of volts from a 1.5V battery. You can add a rectifier and smoothing capacitor and you get a clean and relatively stable high voltage DC of (say) 10,000 volts from a 1.5 volt battery.

It is do-able but you also have to remember that power-out equals power-in minus losses. A switching circuit that can power a transformer from a 1.5V battery may be only ~70% efficient. This has to be borne in mind. Also, if you were generating 10,000 volts and the load on the output were 1mA i.e. a 10 M-ohm load, the power out would be 10W and the current taken from a 1.5V battery would be nearly 7A. Obviously, this is unsustainable for an AA-size battery and this becomes the biggest issue in generating high voltages from really small DC voltages.

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Yes it is possible to obtain even thousands of volts from 12 V (old CRT TVs did that to about 27 500 V, needed by tube's anode), because the maximum current divides by output/input voltage ratio. For example:

In theory, let's say you have a converter that you power from a 24 W supply. At 12 V this means maximum 2 A. If your converter outputs 220V it will have a maximum power of 70-80% of 24 W (based on design efficiency, sometimes even less). That means you'll get 18 W at 220 V. The maximum current will be 0.08 A.

All based on \$P = U \cdot I\$. In an ideal application \$P_{in} = P_{out}\$. In real situation \$P_{out} = P_{in} \cdot {Efficiency (per cent) \over 100}\$

To tweak the output voltage change the 12/220 V transformer with one of 10/240 V.

However be aware that this kind of converter won't perform very well under different loads (voltage will vary), because it doesn't have voltage feedback.

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Why adjusting the frequency should affect the output voltage? –  Vladimir Cravero Apr 28 at 9:15
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