EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: sofakng on August 10, 2021, 02:40:24 am
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If I have a power supply that is rated for 15V at a maximum at 3A (ie. 45W) then can I use a buck converter to output a higher amperage at a lower voltage?
For example, can I convert 15V (3A max) to 5V but 9 amps? (excluding efficiency losses of course)
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Yes that's how it works, you'll lose 5-20% through efficiency though.
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For example, can I convert 15V (3A max) to 5V but 9 amps? (excluding efficiency losses of course)
Yes, but don't forget the converter will pull pulses of ~9A at the input side. That will overload your 3A supply unless you have a good size low ESR capacitor across the converter input.
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15 x 3 = 45w
5 x 9 = 45w
It's not gonna work, because you don't have 100% efficiency... at best you're gonna get up to maybe 95-97% efficiency, but closer to 90% efficiency is more realistic.
You'll probably want a regulator with a soft start mechanism or something like that so that the converter won't pull a huge amount of current when it starts and like others said, you'll need to have a good input capacitance to buffer the converter's demands.
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For example, can I convert 15V (3A max) to 5V but 9 amps? (excluding efficiency losses of course)
Yes, but don't forget the converter will pull pulses of ~9A at the input side. That will overload your 3A supply unless you have a good size low ESR capacitor across the converter input.
That is not necessarily the case. A current boosted buck regulator uses a tapped inductor to multiply the current and duty cycle reducing the peak input current. This is easy to demonstrate since the current requirements of the input switch are reduced proportional to the turns ratio of the inductor. The LT1074 datasheet (https://www.analog.com/media/en/technical-documentation/data-sheets/1074fds.pdf) shows an example of a 5 amp regulator producing a 10 amp output.
Just for edification, I calculated the input ripple current as 2 amps for a simple buck converter, and 0.27 amps if a bifilar wound tapped inductor is used, so quite a bit of difference. This would be a good application for polymer aluminum electrolytic capacitors to get a high enough ripple current rating without layout problems.
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Yes, but don't forget the converter will pull pulses of ~9A at the input side. That will overload your 3A supply unless you have a good size low ESR capacitor across the converter input.
IMHO, that proper capacitor should be assumed to be a part of what's called and sold as a "buck converter".
But it's a good remark because cheap Ebay crap may fail to provide proper capacitance, causing excessive ripple current seen by the upstream supply and its capacitors, destroying them as well. (Crappy supplies normally tend to destroy their own input caps anyway. In the buck converter, input capacitors are stressed the most.)