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Increasing the DC 5V 250 mA adopter volt & amp.


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I want transformerless power supply with 24V 2 Amp and I think any existing cell phone battery adopter can do it for me. I have an DC adopter (5V 250 mA) and want some changes in the circuit to get my desired volt & amp. You can review the circuit of any of your adopter, as most peoples has such a adopters.
You may also suggest any other circuit that can provides me transformerless power supply with DC 24V 2 Amp.

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You can't boost both the current and the voltage, the 5V 250mA adaptor is rated for 5*0.25 = 1.25W, you want 2*24 = 48W.

Buy a higher powered power supply, there's no other way and it won't be transformerless, all mains power supplies have a transformer, even you little phone charger does but it might be a lightweight high frequency transformer inside a switched mode power supply.

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How about to use big resistor to drop the 220v AC to 24v AC then use bridge rectifier to convert it to DC?

That's a bad idea for two reasons: the DC side will not be isolated from the mains and the resistor will have to dissipate 392W.

A transformer would be a better idea but it's probably too large for what he needs.
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I think you can substitute a transformer and rectifier for capacitors and diodes if the power requirements are not high. But it would require many large capacitors and isn't worth the trouble. Generally you would require a transformer, rectifier, and voltage regulator.

His power requirements are too high. Transformerless power supplies are only any good for currents up to tens of mA, beyond that, the capacitor becomes as large and expensive as a transformer and they should only be used for fully enclosed circuits as the DC side is not isolated from the mains so needs to be treated with the same safety precautions.
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