Quick question: Power supply clicking  - Page 1
Forum section: electronics / repair

author: a111087
author_rank: Contributor
timestamp: April 12, 2016, 11:56:51 pm
content: Hi,I have a power supply for electric screwdriver and while i don't have any screwdrivers to plug in and test, I did notice that power supply makes clicking noise (fairly loud, about every half of a second).There are two settings on power supply 20volt and 30volt. There is never any noise on 30v.If I turn on power supply while its set to 20v, there will be no noise.Noise comes on ONLY when PSU is switched from 30v to 20v while power is on.Power supply looks like this:http://g01.a.alicdn.com/kf/HTB1ZxdcIpXXXXXbaXXXq6xXFXXXL/205568708/HTB1ZxdcIpXXXXXbaXXXq6xXFXXXL.jpgI have two of these and they do the same clicking sound. I took both apart, looked at the boards, didn't see anything out of place visually. just sprayed both with contact cleaners, measured output voltages (they were 20v and 30v, as they should be).I had same model power supplies before and they didn't make clicking noise... So, idk what to think. Are they ok or should i be worried?Thanks!

author: Miyuki
author_rank: Frequent Contributor
timestamp: April 13, 2016, 10:50:42 am
content: So just not switch while power is onIt is quite common design fault that smps make clicking noise. It is safe to use, just annoying.

author: Delta
author_rank: Super Contributor
timestamp: April 13, 2016, 10:53:40 am
content: I'm certainly no expert on SMPSs, but Ithinkthis clicking sound is due the the SMPS not being able to regulated the output voltage down low enough when there's little or no load; so it essentially shuts itself down and restarts regularly. (Is that called "burp mode" or something).You shouldn't hear it when they've got a proper load on them...

author: Richard Head
author_rank: Frequent Contributor
timestamp: April 13, 2016, 11:28:37 am
content: This is a common symptom with SMPS's. There is a series resistor from the HV supply to the control IC. It gradually charges a small electrolytic cap across the Vcc pin of the control IC. When the voltage reaches the turn-on threshold of the IC it starts supplying gate drive pulses the the gate of the MOSFET and in the process discharges the electrolytic capacitor. When the capacitor voltage drops below the turn-off threshold of the IC it switches off again and the cap gradually recharges. Normally the PSU comes to life after the first cycle and provides feedback to the Vcc pin before the turn-off threshold is reached so you never hear the clicking sound.Presumably the PSU is not generating the feedback voltage to allow the control IC to continue oscillating and that's why it's locked in a continuous click-click cycle.There is probably an output diode (or maybe capacitor) shorting that isn't allowing the output voltage to rise. It sounds like a flaw (what's new!) in the thermal design. If you manage to repair it you should try to address the cause so it doesn't happen again.Dick

author: a111087
author_rank: Contributor
timestamp: April 13, 2016, 02:52:09 pm
content: Thanks to everyone!

author: Zbig
author_rank: Frequent Contributor
timestamp: April 13, 2016, 03:39:12 pm
content: I don't know about the noise but that's one weird model symbol to place above a circular socket, complete with an "arrow marks the spot"... Okay okay, I'll grab my coat.