Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronic 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

LOPT/FBT Tester for SMPS transformers

Status
Not open for further replies.

mero_shearar

Junior Member level 1
Joined
Apr 4, 2005
Messages
19
Helped
1
Reputation
2
Reaction score
1
Trophy points
1,283
Activity points
1,469

mero_shearar

Junior Member level 1
Joined
Apr 4, 2005
Messages
19
Helped
1
Reputation
2
Reaction score
1
Trophy points
1,283
Activity points
1,469
www.lopt/fbt.com

Hi
Can i use this tester to test SMPS transformers ?
Regards
 

E-design

Advanced Member level 5
Joined
Jun 1, 2002
Messages
2,014
Helped
507
Reputation
1,016
Reaction score
407
Trophy points
1,363
Activity points
14,195
lopt/fbt

It should work if your SMPS transformer's operating frequency is around 16-17kHz. For higher frequencies the width of the pulse applied to excite the transformer should be short compared to the natural oscillation period of the transformer under test.

Note that you can do the same test with a function/pulse generator and a scope. I have been using this technique for many years. You should know something about the transformer, like the operating frequency. Then apply a short pulse ≈5-10Vp-p through a low value resistor ≈100Ω to the primary winding while looking at the ringing on the scope (connected on winding side of resistor). If you see just a short spike with very little ringing, you may have shorted windings somewhere. If you see healthy ringing with a nice exponential decay over a couple of cycles, chances are you are OK.

Another test I do sometimes with the suspect transformer out of circuit: Apply a sine wave of fixed amplitude through a resistor from the function gen. Start well below the operating frequency (at least one decade lower), and slowly turn/sweep the frequency up while looking at the scope connected on coil side. A healthy transformer will tend to peak near the correct frequency. A faulty transformer with shorted turns will attenuate the signal over the sweep range.
 

mero_shearar

Junior Member level 1
Joined
Apr 4, 2005
Messages
19
Helped
1
Reputation
2
Reaction score
1
Trophy points
1,283
Activity points
1,469
lopt/fbt tester

Hi E-design
Thanks for your fast reply, it is very useful but i don't have an oscilloscope so i can't do the tests you metioned befor
i know that this tester is for testing FBT witch operates at 15625Hz
but are not there any modifications to make it test SMPS that operates up to 100KHz ?

Ragards
 

E-design

Advanced Member level 5
Joined
Jun 1, 2002
Messages
2,014
Helped
507
Reputation
1,016
Reaction score
407
Trophy points
1,363
Activity points
14,195
fbt testr schematic diagram

If you make R5 variable (smaller ) you will be able to get shorter pulses. R4 should be OK as is. They already use a differentiator to provide a short spike, so I don't think the setting will be critical as the period is long at around 100ms. You may need to switch in lower values of C3 to achieve resonance at higher frequencies.
 

Status
Not open for further replies.
Toggle Sidebar

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top