Half bridge smps voltage drop problem - Page 2 - 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 25th March 2006, 11:30 AM   #11
diyAudio Member
 
Join Date: May 2005
Location: Avesnes/Helpe
Mzzj,

50 turns with 35kHz gives Bmax=230mT (2300Gauss)

Bmax previous value was 200mT (62.5kHz 32turns)
so what's the difference ?

So you think it's not the reason for the secondary voltage drop ?

My problem may come from primary voltage ripple:
660uF*2 maybe isn't enough for 2A (primary current)
I'd like to get 300W.

Thanks
  Reply With Quote
Old 25th March 2006, 11:39 AM   #12
mzzj is offline mzzj  Finland
diyAudio Member
 
Join Date: Jul 2005
Location: 65N 25E
Quote:
Originally posted by alexclaire
Mzzj,

50 turns with 35kHz gives Bmax=230mT (2300Gauss)

Bmax previous value was 200mT (62.5kHz 32turns)
so what's the difference ?

So you think it's not the reason for the secondary voltage drop ?

My problem may come from primary voltage ripple:
660uF*2 maybe isn't enough for 2A (primary current)
I'd like to get 300W.

Thanks
Saturation limit is something like 300-400mT

Limiting factor is core loss, ie how much core is going to heat.

Yeah, reason for secondary voltage drop is definetely somewhere else.

How much ripple you have on primary caps? Dont tell us that you dont have a scope and safety isolation transformer?
  Reply With Quote
Old 25th March 2006, 01:27 PM   #13
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
You can calculate expected voltage ripple quite easily:

For any capacitor, dV = (average)current * time / capacitance.

Take time=7ms (approx. dead time of a rectified mains sinewave), current=half the primary current (it's only drawn from each capacitor bank during half of the time, so average value is halved), and capacitance=the value for a single bank.

For 660uF, 32:8 turns and 32V output into 4.7 ohms that gives approx 9V p-p (in each capacitor bank). Measured value should be quite close.
  Reply With Quote
Old 25th March 2006, 05:46 PM   #14
diyAudio Member
 
Join Date: May 2005
Location: Avesnes/Helpe
Back again,

I have an oscilloscope but my digital camera is out of order so i have to find one to share screenshots.

I was thinking about one thing:

my power supply (12V) onboard has a current capability of 200mA, maybe it's not enough to feed both SG3525 and IR2213 driving 2*IRF740.

What do you think about this ?

It could explain the voltage drop when the transformer is loaded.

I can't make any measure right now,I've blown the power stage (IR2113 and IRF740)...
  Reply With Quote
Old 25th March 2006, 05:57 PM   #15
mzzj is offline mzzj  Finland
diyAudio Member
 
Join Date: Jul 2005
Location: 65N 25E
Quote:
Originally posted by alexclaire
Back again,

I have an oscilloscope but my digital camera is out of order so i have to find one to share screenshots.

I was thinking about one thing:

my power supply (12V) onboard has a current capability of 200mA, maybe it's not enough to feed both SG3525 and IR2213 driving 2*IRF740.

What do you think about this ?
(IR2113 and IRF740)...
200mA should be enough if guess IRF740 specs right. For big mosfets like IRF450 200mA would be possible if switching way over 100khz.
Or calculate it from gate capacitance and freq. P=f*C*U^2
  Reply With Quote
Old 25th March 2006, 08:50 PM   #16
diyAudio Member
 
N-Channel's Avatar
 
Join Date: Mar 2003
Location: Sol System
Send a message via AIM to N-Channel
Default Back Again

Hi Alex et al.

First off, mzzj: I don't t hink I swapped my #s, but I may have worded my question to Alex a little poorly. Nothing gets past this crowd! I referred to F(osc) and F(sw) because, as we all know, for dual-channel PWM chips, F(osc) =2F(sw). That's where the confusion may have come in.

Alex,

My primary was 38T of #22 (tri-filar), V(pri) was 160V (Voltage doubler for 120VAC on our side of the Pond). The primary turns equation I used came from Chryssis' book, chapter 4 "The High Frequency Power Transformer". I will have to dig out the equation, but after a fashion, I had reduced the transformer design process down to 8-12 very concrete cut-n-dried steps. The variation in the number of steps was determined by the complexity of the transformer (# of secondaries, etc.). When i find the equation, I will also type out my design process. For the timing and compensation components:
R(t) = 2.21KW
C(t) = 10nF
R(d) = 0W,

yielding an oscillator frequency of = 64.6kHz, and a switching frequency of 32.32kHz.

Compensation at pin 9 is 49.9kW paralleled with 1000pF, going to ground. Opto current was set a 1mA over 60V (so 60kW. No Zener, but in a previous version, I did use a TL431 for a reference, compensated at the TL431. Have to go for now (child is stirring from nap), but I will be back soon.

Steve
  Reply With Quote
Old 25th March 2006, 10:05 PM   #17
diyAudio Member
 
N-Channel's Avatar
 
Join Date: Mar 2003
Location: Sol System
Send a message via AIM to N-Channel
Default Start-up

Alex,

How do you derive the 12V for the PWM & Driver chips? I gather it is an auxiliary winding on the main core. Do you use a Zener-pass regulator for the start-up ckt?

This is how I did mine. TIP50 (400Vce) with a 16kW power resistor in series from the high-voltage bus (~320-330VDC) to the collector of the TIP. 1N5242 (12V 500mW) and 440kW provide the reference for the transistor. My auxiliary winding put out ~16V, so when it started producing voltage, this automatically shut down the start-up ckt. The SG3525 needs a start-up ckt capable of providing atleast 50mA, beacuse it's start-up current is the same as it's operating current, ~20mA. As mzzj stated, 200mA should be enough to power the '3525 and the '2113.

I have decided to rebuild this power supply, as I still have most of the parts lying around. I think I will replace the IRF740s (400Vdss) with IRF840s (500Vdss), because I might want to PFC the front end. Everything else, except the transformer's primary turns, I think I will keep the same.

Oh yeah, one other thing- I found that stacking two toroid cores helped me in the power capacity department. I've done this using the same FT-140-77 cores for some 12V push-pull converters I did in the past. Haven't tried it for off-line yet. This might be worth looking into. Sure, it will change some of your numbers around, but you will have more headroom and avoid core saturation.

still looking for those equations.....

Ciao for now,

Steve
  Reply With Quote
Old 25th March 2006, 10:16 PM   #18
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
alexclaire:

How did you manage to blow the power stage?
  Reply With Quote
Old 25th March 2006, 11:46 PM   #19
diyAudio Member
 
N-Channel's Avatar
 
Join Date: Mar 2003
Location: Sol System
Send a message via AIM to N-Channel
Unhappy Magic Smoke

Eva,

If it's because of what I suspect, probably his '2113 caused one or both of the '740s to blow. Perhaps the floating drive for the upper MOSFET crapped out. This happened to me. After I took apart my 3525-2113 based PSU, I tried to re-do it on a pc board. Powered it up, and the 2113 and one of the IRFP350s (TO-247 version of the '740) promptly let the Magic Smoke out. This led to the failure of the lower MOSFET about a second and a half later. I did not have a can of magic smoke to put back in.....

I believe in one of the other threads, eva, you stated your reluctance to use these floating gate-driver ICs because they tend to fail more often than not. I bleieve you said that driver transformers were still better from a reliability standpoint. Please correct me if I'm wrong.
  Reply With Quote
Old 26th March 2006, 02:53 AM   #20
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 have a few IR2112 in an antistatic bag somewhere, they look fancy but I have never used them. I feel more attracted towards transformers as they allow to provide both power and signal to your own custom gate drive circuit, that may be as simple as a PNP transistor to speed up turn-off and a couple of resistors and diodes, while keeping galvanic isolation and allowing for secondary-side control. Also, transformers doesn't blow everytime a power device dies, and they protect the control circuit.
  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
half bridge SMPS secondary voltage drop problem ? alexclaire Power Supplies 6 10th November 2006 03:19 PM


New To Site? Need Help?

All times are GMT. The time now is 06:53 PM.


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