Recently a friend of mine in their 50's, who runs a successful recording studio no less, asked me which power supply they needed to get to replace a broken one. WTF dude!?
If they were unsure which power supply to use, I realised there must be a lot of confusion around this issue, so it motivated me to throw together this blog post to perhaps reduce the overall angst in the universe a tiny fraction. As I go through I will parse only the relevant information starting at the potentially most lethal, moving through to the least.
lots of markings, numbers and pictures
input jack polarity
- CURRENT TYPE (DC or AC)
- CURRENT DRAW LIMIT
We have two options here: AC (alternating current) or DC (direct current). On the image of the power supply on the left we can see the manufacturer has clearly marked DC. However, on the right image we again have a symbol: A dash with three smaller dashes below it. This symbol represents DC. There is also a symbol for AC: a sine wave (see below).
Using an AC adaptor where a DC is expected will have a similar effect on your circuit to getting the polarity of the input jack wrong. DC where AC was expected probably won't have a detrimental effect although the device may appear to light up but not work.
This is the output voltage of the adaptor. Too low and your device won't operate properly. Too high and it could fry sensitive components.
CURRENT DRAW LIMIT
Our adaptor on the left is rated for 100mA and the right 200mA. This is how much current you can draw from the adaptor. If this value is too low, your device won't be able to draw enough current to work. It's fine to over estimate this value.
Our adaptor on the left is rated for American flavoured electricity (120V, 60Hz) and the one on the right UK flavoured (240V, 50Hz). Other regions around the world have their own voltages and frequencies and it is important that your adaptor is designed for your region so that it adapts the electricity into the form it says it will. This is particularly important if you trying to get DC power and want to prevent mains hum getting into your signal path.