Need circuit for 12 volt 2 Amp step down power supply from 18 volt 1.5 Amp Input

Question

I have a power supply which outputs 18v 1.5 amp. For the purpose of my project, I need a 12v 2 amp power supply. I was wondering, if I can make a simple buck converter to convert 18v 1.5amp DC to 12v 2amp DC. Any help is highly appreciated.

I searched Google and could only find 12-5v buck converter examples. I know my circuit will be similar but I am little worried about the values of the components specially the switching transistor (if used) and the capacitors. I am a beginner in DIY electronics. Please help.

In this regard, I must ask that, I had a 230v to 0-12v 2amp step-down transformer. I tried to utilize this transformer to make my 12v 2amp power supply. When I applied a full-wave bridge rectifier to the AC 12v output, my filter capacitor blown away. I tried with 2200uF 25v and 1000uF 50v capacitors. What is going wrong here - is the current too high for the capacitors? Also, if I remove the filter capacitor, the transformer shows 13v 3.5 amp in no-load condition - just attached to an multimeter. Is this expected?

Answer 1

12V AC reaches a peak voltage of about 17 volts, then via the rectifier it might produce about 15V DC across a suitable capacitor (rated at 25 volts). Maybe you had the capacitors wired back to front or maybe you misapplied the bridge rectifier. Maybe the bridge was broken in a previous experiment.

I'd still look for a buck regulator like this: -

Found here on ebay costing $2.86. It's a switching buck regulator that has an adjuster to set the output to be anywhere from 3V to 40V: -

Type / name:LM2596HVS DC-DC step-down module

Input Voltage:4.5V ~ 53V

Output Voltage:3V ~ 40V

Output Current:3A (max)

Conversion efficiency:92% (the highest)

Output Ripple:<30mV

Switching frequency:150KHz

Operating Temperature:-45 ℃ ~ +85 ℃

Size:43mm * 21mm * 14mm (L * W * H)