schottky vs. soft/fast recovery diodes

[metebalci]

Hi,

Are schottky diodes always preferred to soft/fast recovery or stealth diodes in rectifiers as long as there are available schottky diodes with required maximum repetitive reverse voltage ?

Thanks...

MB

 

[ClassD]

Schottky diodes:

+ Low forward voltage
+ Fast recovery time
- Not available in ratings higher than about 60V
- high leakage current

Soft/Fast Recovery diodes:

+ Fast Recovery Time
+ High voltage rating
+ Low leakage current
- High foward voltage

Choose whichever is going to be more efficent in your circuit.

 

[Magura]

There is a noise aspect to this as well. Wich makes more noise?? It seems to differ from application to application.


Magura

 

[joeling39]

Seems that there are manufactureres who have managed to get round the low voltage limitation with Schottky diodes :

www.cree.com

I bought some 600V 1A ones from an online retailer a while back but have not tried them out yet.

Regards,
Joe Ling
Malaysia

 

[Magura]

Are they expensive??

Magura

 

[ClassD]

There is a noise aspect to this as well. Wich makes more noise?? It seems to differ from application to application.


Magura

Well the 'Soft Recovery' diodes were specifically designed to reduce switching noise. They have a gradual turnoff which rounds off the switching current waveform. This results in a lot less RF noise, with a small sacrifice in efficency.

However if you are using the diodes in a standard 50Hz bridge rectifier then there will really be no diffrence because the frequency is so low.

 

[till]

- Not available in ratings higher than about 60V

MBR10100

Well the 'Soft Recovery' diodes were specifically designed to reduce switching noise. They have a gradual turnoff which rounds off the switching current waveform. This results in a lot less RF noise, with a small sacrifice in efficency.

And in my understanding the schottky does this even better

 

[ClassD]

Oops, meant to write "generally not available over 60V".

 

[Circlotron]

soft turnoff.

However if you are using the diodes in a standard 50Hz bridge rectifier then there will really be no diffrence because the frequency is so low.

I used to think so too. Get your scope out and have a look at the transformer secondary voltage under load. Zoom in to where the waveform is just starting to move away from the flattened peak and head toward zero again. As a slow diode recovers it will "snap" the reverse recovery current off suddenly, causing the transformer winding to ring somewhat. Fast, ultrafast and schottky diodes (and vacuum tube rectifiers for that matter) turn off more cleanly and don't "twang" the transformer winding and generate noise in the process.

 

[joeling39]

600V 1A ones cost USD1.60

Regards,
Joe Ling

 

[Telstar]

This thread answers some of my questions. I put it up cause diodes are often neglected

 

[Damon Hill]

I've found it effective (with small transformers) to put an RC snubber on the transformer secondary, tuned to minimize ringing. Similarly, smallish and very low ESR bypass caps on each rectifier is a common practice, although I think a tuned RC there ought to be more effective at damping out the ringing, in combination with a Schottky or soft recovery device.

Even with Schottky or soft recovery devices, there is still inductive ringing; an RC snubber can deal directly with this problem, small as it may be.

 

[housing]

Has anybody used MBR40250 in their power amps?

 

[Telstar]

BTW, the CREE 600V/4A cost now €3,66.

 

[barrows]

There...

are a lot of Shottky options available these days, especially for source component power supplies. I have a question though:

"
Join Date: Apr 2004
Location: Brisbane



Schottky diodes:

+ Low forward voltage
+ Fast recovery time
- Not available in ratings higher than about 60V
- high leakage current


What are the specific drawbacks of high leakage current? Thanks to anyone who can explain this to me.

 

[abraxalito]

As a bridge rectifier, depends how high the leakage current. Not much disadvantage at all if its a few milliamps - the diode runs slightly warmer, slightly less efficient power supply.

 

[Telstar]

- Not available in ratings higher than about 60V

False.

 

[housing]

are a lot of Shottky options available these days, especially for source component power supplies. I have a question though:

"
Join Date: Apr 2004
Location: Brisbane

An externally hosted image should be here but it was not working when we last tested it.

Schottky diodes:

+ Low forward voltage
+ Fast recovery time
- Not available in ratings higher than about 60V
- high leakage current


What are the specific drawbacks of high leakage current? Thanks to anyone who can explain this to me.

All false. Please refer to the datasheets of the latest silicon carbide schottky diodes.

Forward voltage more or less the same as FRED.
Zero recovery time.
Voltage rating higher than 1000V.
Very minimal leakage current.

 

[housing]

I better rephrase my above reply as follows since I can't edit it now.

All false with the latest silicon carbide schottky diodes. Please refer to their datasheets such as:
http://www.cree.com/products/pdf/C2D10120.pdf

Forward voltage more or less the same as FRED.
Zero recovery time.
Voltage rating higher than 1000V.
Very minimal leakage current.

But I don't know whether they have any sonic benefit in audio application.

 

[goody75]

I've found it effective (with small transformers) to put an RC snubber on the transformer secondary, tuned to minimize ringing. Similarly, smallish and very low ESR bypass caps on each rectifier is a common practice, although I think a tuned RC there ought to be more effective at damping out the ringing, in combination with a Schottky or soft recovery device.

I apologize for my ignorance but could you please be more specific about the RC snubber for the transformer secondary. I guess I am particularly interested about values and placement (e.g. between the negative and the 0V?).

Thanks.