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Choosing power supply, how to get the voltage and current ratings?

My DC adapter for a cordless mike has broken It' ratings are:

Input 230-240V ~ 50Hz 30mA Output 20V 250mA

Living in a country where it is not always possible to get the things we want, we often have to improvise.

I have an old laptop adapter - input 100-240V 50-60Hz Output 19V 1.58A (not mA!)

Can I use this to supply the power to the control box for my mike?

Thanks very much



marked as duplicate by stevenvh, AndrejaKo, W5VO Sep 10 '12 at 13:08

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.


First, Current draw: Your laptop adapter output is rated for 1580 mA output draw. Since your mic adapter ouputs less than that (and the microphone must require less than that), the current draw aspect is fine.

Next, Voltage: Voltage at your mic adapter output was 20V, so presumably the mic requires around 20V. The voltage at your laptop adapter output is 19V. This MIGHT be an issue - Check the operating voltage specification of your mic itself (not the adapter). If you have access to the mic's datasheet, check to see if it can function at a supply of 1V less than the the 20V.

Actually, even if you don't have the datasheet, you could just practically connect and test it out. You won't have any problems because you're on the safe side for both the voltage and the current requirements.


Provided that both output are DC, 19V should be enough (20V-5%) to power your mike. You'll have to adapt the connector, and be careful about the polarity.


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