Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

Offline 20W Flyback SMPS failing QP radiated emissions at peaks 57MHz to 184MHz

Status
Not open for further replies.
T

treez

Guest
Newbie level 1
Hi,
Its an offline 20w flyback SMPS in an earthed metal enclosure with its output coming out of the enclosure on a 2 metre cable...(going to a DCDC buck onverter)
What is the likely culprit of these frequencies?
--- Updated ---

Please also confirm that cable ferrites are no use for these frequencies?
 

no snubber on the o/p diode the most likely cause ...
 
  • Like
Reactions: treez

    T

    Points: 2
    Helpful Answer Positive Rating
Thankyou. I placed RC snubbers on Aux and Sec of 220pF,47R (all i had in the lab) and it didnt improve the "el cheapo" radiated emissions scan that i did after fitting these RC snubbers.
(This el cheapo scan simply involved torroid wrapping the cable from the flyback through a near field probe loop (18 turns), and then looking at the probe output with a spctrum analyser (SA1002A)
 

try to look at output diode and power MOSFET source-drain and measure the freq of oscillations at this points, is any correlations with peaks
 
  • Like
Reactions: treez

    T

    Points: 2
    Helpful Answer Positive Rating
try to look at output diode and power MOSFET source-drain and measure the freq of oscillations at this points, is any correlations with peaks
Click to expand...
Thankyou yes i was doing this, but the frequency of the oscillations there was nowhere near like the failure frequencies....mind you, i only had a 100MHz scope to look there. But then again, maybe the scope capacitance was making it seem lower in frequency than it really is.
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top