Ideally, do I want ceramic or film capacitor?
Is ceramic better in this application because they are more lossy and more heat resistant?
Is ceramic better in this application because they are more lossy and more heat resistant?
'Ideally' the ratings for the cap would be given.
'More' information about the snubber and what it is for would help, and 'more' understanding on whether you can only buy certain types of cap (with links) and 'more' information on where the cap would be located, would help too.
'More' information about the snubber and what it is for would help, and 'more' understanding on whether you can only buy certain types of cap (with links) and 'more' information on where the cap would be located, would help too.
Pardon me, I meant transformer or rectifier snubber.
I see that some used film caps, some ceramic.
There are all sorts of caps in the market, which would be too many to list.
The tip on more understanding is helpful, I did not realise that when I was asking the question.
I see that some used film caps, some ceramic.
There are all sorts of caps in the market, which would be too many to list.
The tip on more understanding is helpful, I did not realise that when I was asking the question.
you don't have really the choice. Type is defined by use. See
Safety Capacitors First: Class-X and Class-Y Capacitors - Technical Articles
Safety Capacitors First: Class-X and Class-Y Capacitors - Technical Articles
Class X or Y rated caps are not mandatory for secondary side circuits - which is likely what the OP is after (but OP has not been very definitive so far). Certainly X rated are likely a good choice, but this could be for a 1W 9VAC power supply.
Voltage of secondary? VA rating of transformer? Likely max ambient temp where the cap will be located?
The secondary snubber cap needs to be low loss at high frequencies with enough voltage rating to safely withstand the secondary volts. Film types are good but a ceramic of sufficient size and voltage rating might be a bit expansive.
I use 200V or more rated caps for 50 or 60 volt secondaries.
I use 200V or more rated caps for 50 or 60 volt secondaries.
Please read the Quasimodo thread by Mark Johnston. It works much better than snubbing the diodes and lets you tune the snubbing to match the actual circuit you are using.
Simple, no-math transformer snubber using Quasimodo test-jig
Simple, no-math transformer snubber using Quasimodo test-jig
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Typically we see a capacitor in series with a resistor.
For transformer they are applied on transformer secondary in case of transformer.
For rectifier, they are applied across each diode.
I don't have a specific application scenario. On chip amp sometimes this is provided on the PSU PCB. On tube amp it is suggested that to have 10-22n 1.5kV cap along with 200-1k ohm resistor across transformer secondary as a generic recommendation.
I was under the impression that we add the resistor to dampen the spike of switching, do we need it to be low loss?
I am aware of the Quasimodo thingie, I have no doubt that tailor made approach is better than a one size fits all recommendation.
For transformer they are applied on transformer secondary in case of transformer.
For rectifier, they are applied across each diode.
I don't have a specific application scenario. On chip amp sometimes this is provided on the PSU PCB. On tube amp it is suggested that to have 10-22n 1.5kV cap along with 200-1k ohm resistor across transformer secondary as a generic recommendation.
I was under the impression that we add the resistor to dampen the spike of switching, do we need it to be low loss?
I am aware of the Quasimodo thingie, I have no doubt that tailor made approach is better than a one size fits all recommendation.
Imho you have not identified an application or part value or voltage or operating temperature that makes either capacitor type 'better'.
About the only cap characteristic that could be worth prioritising for significantly high VA transformers is to have an X rating, to provide more confidence that a failing capacitor does not blow up or ignite.
About the only cap characteristic that could be worth prioritising for significantly high VA transformers is to have an X rating, to provide more confidence that a failing capacitor does not blow up or ignite.
more precisions in question, more accurancy in answer 😉
X, Y caps are not mandatory for secondary but I'd keep self-healing attribute
X, Y caps are not mandatory for secondary but I'd keep self-healing attribute
Hey Navyblue,
as you can see you're getting peppered with ???s; and there's a reason--it really is all about the application.
Is this power supply for a big class A heater or a semi-efficient chip amp or something in between.
That is, lets work the other way: you tell us what you're trying to do or want to accomplish and then we can tell you [and explain] which type, make, etc will fit the bill.
Deal?
🙂
So a basic schematic and layout pics/diagram is a good start.
Cheers,
Jeff
Like I said, I am not asking for anything specific, but as a general concept.
Something like this:
snubbering | DIY-Audio-Heaven
If you bother to do the math or read the link you quoted you will see that it is the resistor that critically damps the oscillation in the transformer secondary inductance with the transformer leakage capacitance.
The "snubber" is the resistor. The resistor damps the oscillation. The capacitor minimises the mains frequency current and power in the snubber resistor and should offer low Z to the high frequency disturbance. Simple.
The "snubber" is the resistor. The resistor damps the oscillation. The capacitor minimises the mains frequency current and power in the snubber resistor and should offer low Z to the high frequency disturbance. Simple.
The oscillation is the transformer secondary leakage inductance transferring its energy to anything it can - to mainly the snubber capacitor if used. The snubber is the the resistor/capacitor combo. The snubber can provide a short-cut path for the leakage inductance energy, minimising how much egresses to other circuitry such as other windings, and through the diodes and parasitic capacitances. Complex.
So in terms for performance, or reliability.
Do I want ceramic? Film? Or doesn't matter?
Or I don't know?
X/Y rated would likely win on reliability, but they only go up to the usual mains voltages. They also comes in both film and ceramic.
Then there are also both types in the kV range.
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It is easy: I use film caps for high voltage snubbers (for example >20 VAC). I usually use X2 type caps. And respectively X7R ceramic caps for low voltage snubbers (<20 VAC). A general rule is that the higher the voltage (the higher the load resistanse) - the lower the snubber rated capacity has to be. And vice versa for low voltage snubbers - they usually have to have >0.1 uF caps, so X7R 50V rated ceramics suite them well.