Choke Snubber - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

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 13th December 2002, 09:17 PM   #1
Gunders is offline Gunders  Norway
diyAudio Member
 
Join Date: Nov 2002
Location: Norway
Default Choke Snubber

I 'm just wondering how i can design a proper choke snubber for the choke placed in the power supply.
I have no experience about choke snubbers but I have seen them used a couple of times.
Can somebody tell me a little of the theory behind the snubber... why... component values etc....
  Reply With Quote
Old 13th December 2002, 11:24 PM   #2
diyAudio Moderator Emeritus
 
Bas Horneman's Avatar
 
Join Date: Apr 2002
Location: The Netherlands
Blog Entries: 18
I'll go read Valve Amplifiers by Morgan Jones and get back to you..
  Reply With Quote
Old 14th December 2002, 09:22 PM   #3
diyAudio Moderator Emeritus
 
Bas Horneman's Avatar
 
Join Date: Apr 2002
Location: The Netherlands
Blog Entries: 18
Bottom line is that you can use 0,22uF before and after the choke. That value is not very specific..does the job..almost always according to Morgan Jones.

Theory..
Because the voltage from the diode at some times drops to zero..the choke wants to maintain current and will develop a voltage.

The snubber in other words filters out the voltage spikes..

Hope this helps..
  Reply With Quote
Old 16th December 2002, 09:00 AM   #4
dhaen is offline dhaen  Europe
diyAudio Moderator Emeritus
 
dhaen's Avatar
 
Join Date: Jun 2002
Location: U.K.
It's funny how some trivial questions cause endless reams of glib replies, while a little tricky one recieves few.

I think the concept of snubbing inductors is a little confused.
There are 2 moments in time when a CR series network connected in parallel with the choke can be useful in a choke filter circuit:

1) To reduce the initial voltage peak that can be generated from the choke at turn on.
This is to reduce the chance of first capacitor, choke insulation or rectifier breakdown.

2) In a choke input circuit to reduce the peak voltage across the choke on every cycle.
This is to reduce the chance of choke insulation or rectifier breakdown. And can reduce vibration noise from the choke, though most people just add a small value cap from the choke input to ground, even though this causes a voltage rise.
Of course the correct type and rating of choke is presumed.

Bas's "rule of thumb" value of 0.22uF sounds about right from my experience. Make sure the voltage rating is at least 2x the max in circuit.
As for the resistor: You must use one. It's where the energy is going! So, consider a dissapation of several watts. And the value? I can't remember; it obviously depends on a number of factors, but since we're into "rule of thumb", I'd start with 10K and work downwards.
  Reply With Quote
Old 17th December 2002, 02:22 PM   #5
Gunders is offline Gunders  Norway
diyAudio Member
 
Join Date: Nov 2002
Location: Norway
I have now bought some 0,1 uF capacitors with a voltage rating of 2000V DC.
But do you have an idea of how I can measure the voltage peaks produced by the choke with an oscilloscope?
I have simulated the power supply with Duncan's PSU Designer and the first peak was about 3000V!!!
While the others were a bit less than 2000V peak.

In my design I'm using a mainstransformer with two secondaries with 2*260V, these windings are coupled in series giving a voltage of 520V, and then we have a brigde consisting of 12 UF4007(fast 1N4007). The filter is a LC filter with 10H/32ohm choke and two 1000uF capacitors giving 500uF.
  Reply With Quote
Old 17th December 2002, 02:43 PM   #6
dhaen is offline dhaen  Europe
diyAudio Moderator Emeritus
 
dhaen's Avatar
 
Join Date: Jun 2002
Location: U.K.
Gunderz,

Disclaimer:
Please only do this if you are responsible and comfortable with high voltages.
Ensure capacitors are fully discharged before touching anything.


The Biz:
The real-world voltages will be slightly less, but still very high.
This is because the simulator doesn't take into account all of the chokes properties - just the important ones.
To measure the peaks, you will need to make a 100:1 scope probe.
If you already have a 10:1 probe, you can modify it:
You will need 10 x 1Mohm resistors.*
Connect the resistors in series between the high voltage test-point and ground.
Connect your 10:1 probe across the resistor nearest to ground.
There will be a slight HF loss, and a 5% measurement error, but it shouldn't matter in this case.
Remember to multiply your scopes reading by 100 to get the result.

*(1.5M, or 2.2M will do, but the measurement error will be greater)

Hope this helps
  Reply With Quote
Old 17th December 2002, 02:56 PM   #7
diyAudio Moderator Emeritus
 
Bas Horneman's Avatar
 
Join Date: Apr 2002
Location: The Netherlands
Blog Entries: 18
To decrease the risk of hurting yourself, I would also add some bleeder resistors of say 300k across the caps. So that if you switch off the capacitors are slowly discharged. Don't feel safer though, because it is this feeling of safety that gets you into trouble.

Electrolytic capacitors especially tend to keep their charge quite long in my experience.

I have a 540v choke input psu..and the caps are 630volts rated and they have been fine so far..(3 months)
  Reply With Quote
Old 17th December 2002, 03:01 PM   #8
Gunders is offline Gunders  Norway
diyAudio Member
 
Join Date: Nov 2002
Location: Norway
Thanks....
Sadly I don't have a 100:1 probe, but I have a lot 1M resistors.
What's the reason for the 5% error?
I'm currently using 1% resistors.
Are there more things I shuld be aware of measuring these peaks, I don't want to detroy my scope, I have just bought an digital scope(Tektronix TDS2000) so I'm a bit anxios about "destroing" it,but I have an old one too(Tektronix 2235)


I'm aware of about high voltages and the thing about discharging capacitors.
In fact I went to a high school couple of years ago where it was an accident with charged capacitors.
It was a 2200pF capacitor holding a voltage of 10k-50kV, and this capcitor discharged through a person holding the capacitor in one hand and the other hand at a metalcabinet.
  Reply With Quote
Old 17th December 2002, 03:10 PM   #9
Gunders is offline Gunders  Norway
diyAudio Member
 
Join Date: Nov 2002
Location: Norway
I use resistors(470k) to ensure half the supply voltage over each capacitor, but maybe I should have a bleeder too?

I'm currently using two Rifa PEH200 with a voltage rating of 350V.

And for my own security I uses gloves while working, and... one hand at my back while the other is working
  Reply With Quote
Old 17th December 2002, 03:13 PM   #10
dhaen is offline dhaen  Europe
diyAudio Moderator Emeritus
 
dhaen's Avatar
 
Join Date: Jun 2002
Location: U.K.
The error is because the bottom 1M resistor will have 10M connected in parallel when you attach your 10:1 probe to it.


Quote:
Tektronix TDS2000
A scope to envy

Yes, use your old one first.

Remember, that if the ground connection of the bottom resistor becomes disonnected, your scope is dead
  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
Choke rating for choke input duty cbutterworth Tubes / Valves 14 9th November 2007 04:43 PM
Swinging Choke or Smoothing Choke danFrank Tubes / Valves 4 11th February 2007 11:05 AM
Snubber AND non-snubber ? jimbo1968 Chip Amps 10 6th December 2005 07:49 AM
Snubber s2kov Tubes / Valves 13 30th November 2004 02:09 PM
Choke-Input: How do I calculate the right snubber for high-current-low-voltage Blitz Solid State 20 24th March 2004 08:37 PM


New To Site? Need Help?

All times are GMT. The time now is 09:54 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