# What's the max current of a power adapter that's rated at 24V Max 7W if I regulate it down to 3.3v?

Does it matter if I regulate it down to 3.3v (probably linear) or will the max current still be 290mAh?

• linear regulators don't affect current, it's the same at all voltages in the series. A criterion for SMPS is current amplification, where there's more current at lower voltages. Mar 26, 2018 at 21:44

Does it matter if I regulate it down to 3.3v (probably linear) ...

Linear will have the same current limit as the supply.

... or will the max current still be 290mAh?

'mAh' is a measure of current by time and usually used for battery energy specifications or use.

$I = \frac {P}{V} = \frac {7}{24} = 0.29 \ \text A$. 290 mA is the correct answer.

You might want to consider using a buck converter, which will trade the lower voltage for a higher current. This will also have the advantage that it will create less heat to dump overboard, and will use less power from the 24V supply.

A linear method, max amps is 7/24 or .290 amp max , x3.3V yields 0.957 watts max and wasting 6.043 watts max.

A buck converter, assuming poor efficiency due to small size, may yield (armwaving) 1.0 amp, or 3.3 watts and wasting 3.7 watts.

• So are you saying if I use a linear regulator to get down to 3.3V I can only safely pull ~1W from this adapter and if I use a buck I can use ~3W (both are still too low for my needs however) Mar 27, 2018 at 19:54
• @RyanDetzel that is correct, unless you get a much higher efficiency buck converter than I am willing to handwave. Perhaps you should elucidate in your question the reason for using a power supply which is such a wild mismatch to your needs? Mar 27, 2018 at 21:48