PAGE 126 OF 150 · POWER SUPPLIES & BATTERIES
Using a Wall Adapter
Check voltage, current and polarity first.
LED SYMBOLTriangle points from anode to cathode; the arrows show light leaving the part.
Reading the label
A wall adapter's label gives its output voltage, maximum current and plug polarity. Choose one whose voltage matches your circuit and whose current rating is at least as high as the load.
- A 12 V 1 A adapter can supply up to 1 A at 12 V.
- Unregulated adapters can give a higher voltage than the label when lightly loaded.
- Check the barrel plug polarity symbol, since centre-positive is common but not universal.
Safety
Use certified adapters, keep them dry and never open the case. Switching types are lighter and more efficient than old transformer types.
REMEMBER
Voltage must match; current rating only needs to be high enough.Try it yourself
Sketch the circuit on paper first, calculate the values, then build it on a solderless breadboard using a low-voltage supply. Measure with a multimeter before you make anything permanent.
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