Series resonant SMPS question - diyAudio
Go Back   Home > Forums > Amplifiers > Power Supplies

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 16th July 2005, 03:42 PM   #1
Andy F is offline Andy F  Spain
diyAudio Member
 
Join Date: Jul 2003
Location: Northwest Spain
Question Series resonant SMPS question

Hi:

I am working on a Half bridge SMPS as a power supply for 2 B&O Icepower 500a audio amplifier modules, but it could be useful for another similar amps. So I use a pair of IRFP450B MOSFETS driven by an IR2156 ballast control & driver IC. Fixed oscillating frec at 126kHz with an 80% of duty cycle(20% dead time) no PWM.
The output transformer is build using an E42 Epcos core and it is connected from the common point of the two mosfets to a common point between + and - legs through a pair of capacitors calculated to obtain a resonant frec. (1/2*PI*(Leakage L*C)^0.5)
I tested the design and the prototype works fine(2 amps plugged simultaneusly) and it looks very stable.The transformer waveforms are clean and I do not have thermal problems by now. My question is the way to check if the real resonant frecuency is close to my calculations.(I measured the transformer primary Leakage L needed for my formula conecting a LC Meter on the primary with the secondaries shorted).
I,m thinking about to put a sense resistor with a very small value (maybe 0.1 or 0.2 ohms-10 watts) in series with the transformer primary to "see"" the primary current on my scope comparing to the drain-source voltage on the other probe of the scope to check if it is in phase and to check how it looks.

Someone has another method to check this?
  Reply With Quote
Old 18th July 2005, 08:52 PM   #2
cerrem is offline cerrem  United States
diyAudio Member
 
Join Date: Jun 2005
Location: San Diego, CA
I can calculate the winding leakage pretty accurately if I see the winding sheet.....Also, when using the short circuit method of measuring leakage, you should limit the primary test current to the same as it would be durring normal operation....

Also..If you post the schematic I can better have idea of how to help you measure...I am familiar with the IR parts you mention, since I have used them before....especially the ballast controller...Have you considered the IR 1856 for a driver????

Chris
  Reply With Quote
Old 18th July 2005, 09:17 PM   #3
diyAudio Member
 
Join Date: Dec 2002
Location: Slovenia
Hi,

safer method of current measurement would be current transformer. Just wind around 100 turns on 10mm OD or larger ferrite toroid. Preferably use single layer winding, so that is usually 0.15 or 0.2 mm magnet wire. Terminate the winding with low ohm (several Ohms) noninductive resistor. Your current probe is ready. You just stick toroid on wire where you want to measure current (high frequency AC only of course).

Best regards,

Jaka Racman
  Reply With Quote
Old 19th July 2005, 10:32 AM   #4
Andy F is offline Andy F  Spain
diyAudio Member
 
Join Date: Jul 2003
Location: Northwest Spain
Hi:

I have some current sense samples from Coilcraft so I can put one of these in series with the output trafo for current measurement. Anyway, I would like to know a better way to measure or calculate the Leakage inductance needed.
I attach the basic schematic and winding sheet.

Regards.
Attached Files
File Type: zip smps1.zip (56.2 KB, 302 views)
  Reply With Quote
Old 20th July 2005, 03:48 PM   #5
Eva is offline Eva  Spain
diyAudio Member
 
Eva's Avatar
 
Join Date: Oct 2003
Location: Near the sea
Send a message via MSN to Eva
I think that you have made several mistakes.

You should connect one end of the primary, through a several-microfarads DC filtering capacitor, to a low-impedance node centered half way between Vcc and ground, for example the junction between R2 and R3.

The other end, the one that is being switched, is the one that may be allowed to resonate by placing suitable capacitors. But it's hardly required because the voltage will always inmediately spring towards the opposite rail after turn-off. So you will get zero-voltage zero-current turn-on by just operating the converter near 100% duty cycle.

Also, your output diodes are improperly connected. A2 of D8 should be connected to S2- of TR3, and K2 of D3 should be connected to S1+ of TR3. This is requied in order to guarantee symmetric operation, otherwise the capacitively coupled end of the transformer may slew towards one of the rails and +-50V outputs would also lose balance.

Concerning current measurement, the most practical way to do it on floating nodes is by means of current transformers, otherwise you would need very expensive differential oscilloscope probes. However, current transformers have its limitations, they must be either excited in a fully symmetric fashon or allowed to reset its flux, otherwise they will saturate and stop providing a precise measurement.
  Reply With Quote
Old 22nd July 2005, 02:03 PM   #6
diyAudio Member
 
Join Date: Jan 2005
Location: Haarlem
Send a message via AIM to Joep Zonnebloem Send a message via MSN to Joep Zonnebloem Send a message via Yahoo to Joep Zonnebloem
Quote:
Originally posted by Eva

Concerning current measurement, the most practical way to do it on floating nodes is by means of current transformers, otherwise you would need very expensive differential oscilloscope probes. However, current transformers have its limitations, they must be either excited in a fully symmetric fashon or allowed to reset its flux, otherwise they will saturate and stop providing a precise measurement.
Would a Hall effect based current sensor be suitable? E.g. http://www.allegromicro.com/sf/0704/

Regards, JZ
__________________
-
  Reply With Quote
Old 22nd July 2005, 06:26 PM   #7
mzzj is offline mzzj  Finland
diyAudio Member
 
Join Date: Jul 2005
Location: 65N 25E
Quote:
Originally posted by Eva

The other end, the one that is being switched, is the one that may be allowed to resonate by placing suitable capacitors. But it's hardly required because the voltage will always inmediately spring towards the opposite rail after turn-off. So you will get zero-voltage zero-current turn-on by just operating the converter near 100% duty cycle.

I think in many cases some extra capasitance is beneficial, without extra caps you rely entirely on mosfet internal output capacitance, it might be too much variable or not enough for high leakage/series inductance. (even more since this is relatively low freq case)
Running very close to 50% pulse width with high dV/dt requires beefy gate drivers if mosfet dissipation is to be kept reasonable and is not so good from emc-point. So you lose all the benefits of ZVS/ZCS. I guess something like 40-45% duty cycle migh be good compromise(depends on freq), peak currents are still reasonable and resonant switching has plenty of time to happen.
  Reply With Quote
Old 3rd May 2010, 02:36 PM   #8
Account Disabled
 
Join Date: Oct 2008
Can you share your design?

Show us something, since this is a DIY. I like to learn from here , as usual


Thank you MR: ANdyF
  Reply With Quote
Old 3rd May 2010, 03:43 PM   #9
AP2 is offline AP2  Italy
Banned
 
Join Date: Dec 2009
Location: Italy
You can see the behavior of signals on the primary probe on the secondary connecting the AC-GND on one side. with no load at output.
DT and some defects are clearly visible.
schema to make some changes. (my opinion)
C20 10uF add electr.
C22 10uF add electr.
eliminated C25-26 and put in series at P1 + 330nF.
p2-connect at center snap-in (R2-R5)
if you can turn on primary side winding 1.5 + one diode, it solve +14 V at TP3.
try to see these changes (differences) in SEC-AC probe when the output load.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
SMPS question funky2x Power Supplies 5 23rd June 2008 11:34 PM
Resonant SMPS Serge66 Power Supplies 3 6th December 2007 08:26 PM
Resonant SMPS DFI Parts 1 5th December 2007 08:24 PM
wiring smps in series morpheus82 Power Supplies 34 13th November 2006 06:50 PM


New To Site? Need Help?

All times are GMT. The time now is 05:27 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2