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Electronics => Beginners => Topic started by: bborisov567 on October 18, 2022, 05:20:06 pm

Title: Noisy power supply adapter
Post by: bborisov567 on October 18, 2022, 05:20:06 pm

Recently i built a clock with arduino and max7221 for 7 segment display. I use old Nokia charger adapter as a power supply. It is connected to the Vin of the arduino and the max7221 is connected to the 5v rail. Everything is fine until i set the display at low brightness, then the adapter starts hissing. I have 220uf cap on the Vin rail and 10uf+100nf on 5v rail. My question is - can i do something or i should get good old transformer?

Title: Re: Noisy power supply adapter
Post by: fourtytwo42 on October 18, 2022, 05:50:17 pm

Could well be it likes a minimum load, I assume as the brightness is reduced so is the load current. So maybe add a suitable resistor from 5v to 0v.
If you happen to be on a long ADSL line these "Asian" power supplies can also wreck your broadband connection!

Title: Re: Noisy power supply adapter
Post by: bborisov567 on October 18, 2022, 07:09:43 pm

Yes, that seems to be the case! After adding 180 ohm resistor the hissing becomes barely audibly. Thank you!