12V in switchmode power supplies - Page 2 - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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 28th June 2002, 04:04 AM   #11
diyAudio Member
 
Join Date: Nov 2001
Location: Harlowton, MT, USA
I think I will read a book on switchmode power supplies before I start building, as I have never worked with SMPS's before. Thanks guys.
__________________
- "With power amplifiers, negative feedback is a good thing, and positive feedback can induce destructive oscillation, but with people, positive feedback is a good thing, and negative feedback can induce destructive oscillation"
  Reply With Quote
Old 28th June 2002, 04:58 AM   #12
blmn is offline blmn  Brazil
diyAudio Member
 
blmn's Avatar
 
Join Date: Feb 2001
Location: .
Killowatt,

As Beanz recommend, the Billing's book is a very good start. See the chapter about self oscillating supplies. It's an easier way to start learning to work with high frequency transformers.

Beanz,

Since you have the book, I think you might read the chapter to see what I'm saiyng about flux imbalance, specially the last two paragraphs (2.2.5, page 45).

regards
  Reply With Quote
Old 28th June 2002, 11:08 AM   #13
e96mlo is offline e96mlo  Sweden
diyAudio Member
 
Join Date: Apr 2002
Location: Helsingborg, Sweden
I'm not a DC blocking cap will work that well. Think of the stresses and the ripple it must take!

/Marcus
  Reply With Quote
Old 28th June 2002, 07:50 PM   #14
diyAudio Member
 
Join Date: Nov 2001
Location: Harlowton, MT, USA
Yeah and the only thing messier than a burnt resistor is a blown up electrolytic!
__________________
- "With power amplifiers, negative feedback is a good thing, and positive feedback can induce destructive oscillation, but with people, positive feedback is a good thing, and negative feedback can induce destructive oscillation"
  Reply With Quote
Old 28th June 2002, 08:59 PM   #15
diyAudio Member
 
Join Date: May 2002
Location: Cincinnati, OH now Columbus,OH USA
Send a message via AIM to BeanZ
An electrolytic is not the proper choise for this application because of it polarization. A film cap should be fine in this application. It is placeed in series with the primary winding of the transformer. Dual primaries may also be desireble too. Make sure that your output filter caps are rated for the ripple current specified for the output filter inductor.

BeanZ
__________________
BeanZ
  Reply With Quote
Old 28th June 2002, 09:31 PM   #16
diyAudio Member
 
Join Date: May 2002
Location: Cincinnati, OH now Columbus,OH USA
Send a message via AIM to BeanZ
As for flux imbalance and saturation of the core: It is almost guaranteed using MOSFETs and no combatant for their different Rds(on) values. A slight difference in the Rds(on) of the transistors will lead to catastrophic failure. When the core gets into the non-linear saturation region, the core will no longer support flux and the transistors will be driving a low impedance (short circuit) load. The transistors will fail. The process is much slower however with MOSFETs which have an increasing "on" voltage with increasing temperature. This helps to minimize flux imbalance on a short-term pulse by pulse basis but over time the core will eventually walk up the hysteresis curve and make it to the non-linear region. A small primary resistance is often added in series with the power transformer primary in car audio SMPS. This will slow the process even more. But, a few billion cycles down the road...the MOSFETs will go. Unitrode (TI) has some current-mode PWM controllers. They also have PWM drivers which have internal high-current totem-pole outputs for driving the high capacitance gate charge of a MOSFET.

BeanZ
__________________
BeanZ
  Reply With Quote
Old 29th June 2002, 06:29 AM   #17
diyAudio Member
 
Join Date: Nov 2001
Location: Harlowton, MT, USA
"A small primary resistance is often added in series with the power transformer primary in car audio SMPS."

And a DC blocking capacitor would provide just that.

Anyway, I need these to be very reliable and last practically forever, so I need some way to combat this non-linear thing. I assume almost perfectly matched parts are a must here (I wonder if I could design a current mirror into the thing ). This is a push-pull SMPS, for those who don't know. Rod suggested using 6x0.4mm wires (what AWG is that?) for the primary, I think I'll use 7. Please describe how I can keep it from saturating.

Thanks
__________________
- "With power amplifiers, negative feedback is a good thing, and positive feedback can induce destructive oscillation, but with people, positive feedback is a good thing, and negative feedback can induce destructive oscillation"
  Reply With Quote
Old 29th June 2002, 06:44 AM   #18
diyAudio Member
 
Join Date: Apr 2002
Quote:
Rod suggested using 6x0.4mm wires (what AWG is that?) for the primary, I think I'll use 7.
7 AWG is too much or big. It is around 10 AWG.

0.4 mm is 26 AWG wire.
  Reply With Quote
Old 29th June 2002, 07:26 PM   #19
diyAudio Member
 
Join Date: May 2002
Location: Cincinnati, OH now Columbus,OH USA
Send a message via AIM to BeanZ
10AWG is much too big of a wire to use for the primary at 50kHz. This is a number to indicate the equivalent amount of copper cross sectional area needed to carry the primary current. Due to the skin effect at 50kHz, several smaller guage wires are used to achieve a total copper cross sectional area about that of a ten guage solid wire. There are plenty of sites on the web that will give you this information, but here is some:

10AWG=11740 circular mils or 58.13cm^2 x 10^-3
resistance=.9987 ohms/1000'
current capacity = 13840 mA@750 Circ.Mil /A
= 20768 mA@500 Circ. Mil/A


20AWG=1246 circular mils or 6.315 cm^2 x 10^-3
resistance=10.13 ohms /1000'
current capacity = 1365 mA@ 750 Circ. Mil/A
= 2050 mA@ 500 Circ. Mil/A
__________________
BeanZ
  Reply With Quote
Old 1st July 2002, 05:32 AM   #20
diyAudio Member
 
Join Date: Nov 2001
Location: Harlowton, MT, USA
Who said anything about 10AWG wire? That's huge, I'd never be able to wind it in a 1.5" toroid. I was talking about using 6 or 7 26AWG wires. I'm not sure where Electro got 10AWG from. By "I think I'll use 7" I meant 7x0.4mm wires, not 1x7AWG wire.
__________________
- "With power amplifiers, negative feedback is a good thing, and positive feedback can induce destructive oscillation, but with people, positive feedback is a good thing, and negative feedback can induce destructive oscillation"
  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
Elliott Switchmode power supply PCB red Car Audio 86 11th July 2013 05:10 PM
Switchmode power supplies - 13.5V/40W - Ideal for T-AMP Fin Group Buys 9 4th June 2008 07:43 PM
switchmode power supply Tekko The Lounge 1 9th January 2005 08:10 PM
Class AB car amp, switchmode power supply, what rails?? SkinnyBoy Solid State 4 8th December 2003 03:26 PM
Removing switchmode power supply noise ih Digital Source 1 25th April 2002 09:18 PM


New To Site? Need Help?

All times are GMT. The time now is 07:26 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