hi there, i find this link helpful to me quite often since i'm not that good with math best reguards, crippledchicken 
http://www.onlineconversion.com/electric_capacitance.htm
http://www.onlineconversion.com/electric_capacitance.htm
Snubber capacitor values
If you have a single bobbin or toroidal transformer, use a capacitor that draws about 10% of the rated winding current. This capacitor is usually large enough to cause the DC resistance of the winding to damp the transformer winding and roll off most of the audible EMI from the transformer.
On dual bobbing transformers the leakage inductance is high enough so that the DCR isn't enough to damp the ringing out. For these transformers split this capacitor into 1/3 and 2/3's. The 2/3's capacitor gets a series resistor to control the damping.
Here's a different view on damping. The web page is about audio transformers, but the trick is the same for power transformers.
http://www.siteswithstyle.com/voltsecond/Damping_ringing_XFMRS/Damping_ringing_in_xfmrs.html
If you have a single bobbin or toroidal transformer, use a capacitor that draws about 10% of the rated winding current. This capacitor is usually large enough to cause the DC resistance of the winding to damp the transformer winding and roll off most of the audible EMI from the transformer.
On dual bobbing transformers the leakage inductance is high enough so that the DCR isn't enough to damp the ringing out. For these transformers split this capacitor into 1/3 and 2/3's. The 2/3's capacitor gets a series resistor to control the damping.
Here's a different view on damping. The web page is about audio transformers, but the trick is the same for power transformers.
http://www.siteswithstyle.com/voltsecond/Damping_ringing_XFMRS/Damping_ringing_in_xfmrs.html
Hi,
Well, you'll see anything from a few nano upto a few tens of nanoF there depending on how the diode reacts.
Don't forget either you're dealing with AC voltage so the caps should be rated accordingly.
Last thought....I wouldn't dream of putting those way too good PTFE caps across my diodes.
Cheers,
Well, you'll see anything from a few nano upto a few tens of nanoF there depending on how the diode reacts.
Don't forget either you're dealing with AC voltage so the caps should be rated accordingly.
Last thought....I wouldn't dream of putting those way too good PTFE caps across my diodes.
Cheers,
Snub the schottkies.
"Are snubber caps required with shottkies?"
I say yes. This is because there are three main sources of electrical transformer noise in a transformer.
1. The diode recovery of the winding you are on.
2. The noise on the power line.
3. Voltage distortion/ noise on other windings.
Schottky's take care of #1, but not the other two.
I have a preamp at home that has Schottkies in the filament supply where the Schottkies are making the HV ring bad enough to cause noise in the output. The HV ringing is occurring when the HV diodes are not conducting.
I have a solid state power amp that you can see ringing in the windings that aren't conducting from the conduction of other windings.
Snubbing helped reduce the audible noise in both situations.
"Are snubber caps required with shottkies?"
I say yes. This is because there are three main sources of electrical transformer noise in a transformer.
1. The diode recovery of the winding you are on.
2. The noise on the power line.
3. Voltage distortion/ noise on other windings.
Schottky's take care of #1, but not the other two.
I have a preamp at home that has Schottkies in the filament supply where the Schottkies are making the HV ring bad enough to cause noise in the output. The HV ringing is occurring when the HV diodes are not conducting.
I have a solid state power amp that you can see ringing in the windings that aren't conducting from the conduction of other windings.
Snubbing helped reduce the audible noise in both situations.
Yes you can see this with a scope.
Sometimes at 20V/ div it is hard to see on the voltage rail. Especially if the trigger is not set to "line" to sync to the 115V line voltage.
1. Check the AC side of the diode bride.
2. Clip the scope probe on top of the insulation of the power transformer's leads one at a time. Set the scope to a high sensitivity like 10 mV/ div and set the sync to "line". I've seen 100's of millivolts with the scope clipped the secondary wiring.
Bricolo said:can you see this with a scope?
I looked at my supply rails once, and wasn't able to see any ringing
Sometimes at 20V/ div it is hard to see on the voltage rail. Especially if the trigger is not set to "line" to sync to the 115V line voltage.
1. Check the AC side of the diode bride.
2. Clip the scope probe on top of the insulation of the power transformer's leads one at a time. Set the scope to a high sensitivity like 10 mV/ div and set the sync to "line". I've seen 100's of millivolts with the scope clipped the secondary wiring.
Schottky diodes, eh?
They do not have the reverse recovery problem that a conventional diode does, due to lack of minority carrier recombination.
Fancy way of saying "no P-N" junction". They will dump less energy than a conventional diode, but what little they have, they will dump rather quickly.
Yeah......try a snubber with them too. A lot of designers that I work with do not like the sound of Schottkys.
Jocko
They do not have the reverse recovery problem that a conventional diode does, due to lack of minority carrier recombination.
Fancy way of saying "no P-N" junction". They will dump less energy than a conventional diode, but what little they have, they will dump rather quickly.
Yeah......try a snubber with them too. A lot of designers that I work with do not like the sound of Schottkys.
Jocko
fdegrove said:
my experience too.
they sound philosophical, deep thinking, and fundamentally rich in the middle, and universally open on both ends of the audible spectrum. just thinking about them, pure music will start to flow through your ears.
the following best describe the sound of those devices:
"The truth embodied in the
Buddhas
Of the future, present,
past;
The teaching we received
from the
Fathers of our faith
Can be found at the tip of
my stick."
Sorry to resurect this 'old' thread, but what would be the snubber values for a 'plain vanilla' 25A 400V bridge? 0.01uf ceramic or is it appropriate to go with 0.1uf ceramic//something like 47R 1watt?
Class AB, per rail: 1 diode bridge, 3x10.000 uf capacitance, 63V, min draw <300mA, I guess max 2.5A current draw (amp has limiting circuit - bleah).
Not looking for literature but for what proved to be an improvement in practice. Thanks!
Class AB, per rail: 1 diode bridge, 3x10.000 uf capacitance, 63V, min draw <300mA, I guess max 2.5A current draw (amp has limiting circuit - bleah).
Not looking for literature but for what proved to be an improvement in practice. Thanks!
From what I have heard, 0.01uF ceramic up to 0.1uF (Mark Levinson) has been used with good results.
I actually heard one company used 0.33uF but the consensus is 0.01uF to 0.1uF and it would seem these vales are quite forgiving across difference Diode/ trafo sizes.
Personally for your use, I'd go 0.01uF with 100 ohms in series
I actually heard one company used 0.33uF but the consensus is 0.01uF to 0.1uF and it would seem these vales are quite forgiving across difference Diode/ trafo sizes.
Personally for your use, I'd go 0.01uF with 100 ohms in series
janneman said:
Hi,
Snubber caps across each diode will simply slow down and relax the “snap off” (or reverse recovery) current of the diode and reduces HF noise. Good ceramic 10nF – 100nF caps will do. Regarding oscillations due to parasitic inductance, that is best death with a RC snubber across the transformer directly (or across the AC terminals of a bridge rectifier).
Cheers
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