0-15V 0-120A adjustable PSU attempt with average current control. - Page 5 - 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 29th September 2005, 06:37 PM   #41
diyAudio Member
 
Join Date: Dec 2002
Location: Slovenia
Hi Eva,

thanks for posting those waveforms. I got a little bit nostalgic looking at them, since my last bipolar design dates almost 20 years ago. As far as I can remember, your base current waveform looks very good, a proper textbook example.

Maybe you could consider another variant of the transformer coupled bipolar drive. I think it was proposed by Bruce Carsten, one of the old SMPS gurus. In his design, he uses grounded base and emitter is driven by secondary winding of the drive transformer. Primary of the drive transformer is driven by a current source. As far as I can remember, advantage is:

- greater sustaining off voltage (collector base is always higher than collector emitter)

-optimal turn off behaviour (negative base current equals collector current)

-automatic short circuit protection (when collector current exceeds emitter current, BJT automatically turns off)

I must confess I never really tried the idea, but it seemed to me a good one at the time when it was published.

Best regards,

Jaka Racman
  Reply With Quote
Old 1st October 2005, 05:22 AM   #42
Kmrrz is offline Kmrrz  Russian Federation
diyAudio Member
 
Join Date: Sep 2005
Hi Eva,
could you please show synchronous rectifier board schematics?
  Reply With Quote
Old 1st October 2005, 11:59 PM   #43
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
Jaka:

As you can see, 20 years later bipolar transistors still compete with MOSFETs Conduction losses are better than the ones that you will get with latest technology TO-220 MOSFETs, 1V or less voltage drop for 10A collector current, a $15 TO-247 MOSFET is required to beat a $1 TO-220 bipolar in that field. And turn-off is not slow at all, at Ic=10A without RC snubber I get a nice 50ns rise time with 10ns or so current tail. However, turn-on is slow because Ib rise slope is limited by the base drive transformer I'm considering some changes

I don't like that emitter-switched drive scheme because all the colector current has to pass through the drive transformer, this imposes even more limitations and leakage inductance requirements. Also, getting the BE junction reverse biased during crossover time becomes quite hard.


XyeMoe:

It may seem crazy but I don't have a schematic for that board, and all the schematics I've posted on that thread were actually drawn after the boards were made.

Why? Because I usually build things direcly on a breadboard and I debug them with an actual oscilloscope and a multimeter, waching true waveforms and voltages instead of simulating. When I'm happy with the circuit, I draw a PCB by hand (no automatic schematic checking) while observing the breadboard or from memory if I can remember the circuit completely.

I will post a more detailed picture of the layout of the daughter board, you will have to figure out the rest by yourself, though
  Reply With Quote
Old 2nd October 2005, 04:55 PM   #44
diyAudio Member
 
Join Date: Dec 2003
Location: Munich
Quote:
Originally posted by Eva


It may seem crazy but I don't have a schematic for that board, and all the schematics I've posted on that thread were actually drawn after the boards were made.

Why? Because I usually build things direcly on a breadboard and I debug them with an actual oscilloscope and a multimeter, waching true waveforms and voltages instead of simulating. When I'm happy with the circuit, I draw a PCB by hand (no automatic schematic checking) while observing the breadboard or from memory if I can remember the circuit completely.

You are amazing!!!
....nerd.... Schematic of the entire SMPS only in your brain !
I also prefer reality vs. simulation.... ,
But well...... usually I draw the schematic on some 'butter bread paper' first (except ultra simple things) ... !

Uhps, and there is one thing I really love to simulate, because
the simulation results match really good to reality:
OP-Amp-Filters below 100kHz.
  Reply With Quote
Old 2nd October 2005, 06:25 PM   #45
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 use simulation mostly for linear and bode stuff, but I can't simulate base drive circuits since the usual transistor models doesn't even account for charge storage phenomena or other bipolar vodoo-like effects

Also, believe it or not, I'm still unemployed and looking for a decent job since there is almost no electronics R&D here.
  Reply With Quote
Old 2nd October 2005, 07:13 PM   #46
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
Synchronous rectification daugtherboard layout:
Click the image to open in full size.

Part list:
C9,10 - 22u 35V
D1..D8 - 1N4148
IC1 - CD4049
Q9,11,13,15 - bc327
Q10,12,14,16,17,18,19 - bc546
R1,2,3,4,5,6,7,8 - 10
R9,10,11,12 - 47
R13 - 22
R14,15,16,17 - 100
R18,19,22,23 - 10k
R20,21,24 - 4k7

"+V" is 17 volts, could be 19V to further reduce conduction losses but the CMOS buffer may fail.

"_EN" is enable input, it's active when pulled low (an external current comparator drives it). It's pulled up by default so everything is disabled at power-up.

"A_off" and "B_off" are pulled up to turn-off the corresponding set of MOSFETs inmediately before the primary is switched in one or another direction, then the MOSFETs remain turned off until their source voltages "S" fall below the input threshold of the CMOS buffer (V+/2). These inputs are driven directly from the outputs of the main SG3525A control IC.

Q17 and Q18 are intentionally saturated in order to delay their effect.
  Reply With Quote
Old 2nd October 2005, 08:10 PM   #47
diyAudio Member
 
Join Date: Dec 2003
Location: Munich
Quote:
Originally posted by Eva
I use simulation mostly for linear and bode stuff, but I can't simulate base drive circuits since the usual transistor models doesn't even account for charge storage phenomena or other bipolar vodoo-like effects

Also, believe it or not, I'm still unemployed and looking for a decent job since there is almost no electronics R&D here.
Evita got mail.
  Reply With Quote
Old 3rd October 2005, 12:29 PM   #48
diyAudio Member
 
Join Date: Dec 2003
Location: Munich


...somehow I don't get your layout in line with the
traditional synchronous rectification circuits...

..in example like shown here:
http://focus.ti.com/lit/an/slua287/slua287.pdf

Your common source connection would match,
but you only parallel two drains...
On the other hand your A/B gate drive could match again....
Do you use a double secondary winding with separate rectification for
each? .... and parallel both behind rectification?
  Reply With Quote
Old 3rd October 2005, 01:24 PM   #49
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
There are two transformers whose primaries are connected in series, and two sets of push-pull secondaries that are obviously forced to conduct the same current, so paralelling is not required.

Also, If you try to lay out the board, you will find out that paralelling the secondaries actually makes things harder, particularly with a single sided PCB (where do you put the bridges??? and how do you get the high symmetry required between A and B banks???), and produces bigger current loops thus increasing EMI, while using independent rectificacion for each transformer makes things much simpler.

Note that the MOSFETs are laid out in an A-A-B-B-A-A-B-B fashion, and each A/B set is not turned on until the voltages at the drains of both transformers are not low enough.

Concerning current doublers, they are just a fashion thing that allows to use simpler off-the-shelf single ended transformers and lower current inductors at the expense of more than 4 times higher current ripple while employing the same amount of ferrite and copper. Increased current ripple produces much higher I^2*R and switch turn-off losses, so this topology is almost useless for high power applications, its only advantage is easier manufacturing.

PD: You've also got mail.
  Reply With Quote
Old 3rd October 2005, 07:38 PM   #50
diyAudio Member
 
Join Date: Dec 2003
Location: Munich
Quote:
Originally posted by Eva
There are two transformers whose primaries are connected in series, and two sets of push-pull secondaries that are obviously forced to conduct the same current, so paralelling is not required.

...two sets of push-pull secondaries....
..no paralleling....
How do you get a single 15V output from that, without paralleling somewhere?


Schematics make life easier...
- except for U
  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
UC3846 current mode control vs. SG3525 with average current mode control mflorin Power Supplies 35 7th June 2014 08:06 AM
Adjustable B+ and Cathode Current linestage Brit01 Tubes / Valves 2 30th July 2009 12:12 PM
forward regulation of push-pull average current mode control? zilog Power Supplies 9 19th January 2009 06:06 AM
will this average current mode controller work? zilog Power Supplies 0 23rd January 2007 09:17 PM
Can some one give me a schematic on a current source, adjustable around 3 A. Progg70 Solid State 42 17th November 2005 10:18 PM


New To Site? Need Help?

All times are GMT. The time now is 08:36 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