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transformer secondary ringing

J

Jamie Morken

Jan 1, 1970
0
Hi,

I am using a fullbridge SMPS, and when I scope the secondary of the
transformer I am noticing a lot of voltage ringing which is approaching
the breakdown voltage of the diodes (600VDC). I have RC snubbers across
the primary coils, but none yet across the secondary. LTspice shows
that if I remove the primary RC snubber the output ringing is reduced,
what other methods are there to reduce output ringing or to protect the
diodes besides using an RC snubber?

cheers,
Jamie
 
M

MooseFET

Jan 1, 1970
0
Hi,

I am using a fullbridge SMPS, and when I scope the secondary of the
transformer I am noticing a lot of voltage ringing which is approaching
the breakdown voltage of the diodes (600VDC).  I have RC snubbers across
the primary coils, but none yet across the secondary.  LTspice shows
that if I remove the primary RC snubber the output ringing is reduced,
what other methods are there to reduce output ringing or to protect the
diodes besides using an RC snubber?

Depending on the circuit type:

You can load the secondary with enough capacitance to keep the ringing
amplitude low enough. The current spike on the primary side can be
prevented with a circuit like this:

L1
--+----))))----+---- To primary switches
! !
--- === C1
^ D1 !
! ! L2
------------+--))))--- GND

L1 is a lowish valued high current inductor. It causes the voltage on
the switches to dip when the current tries to spike up.

C1 is a modest value highish current capacitor. It must be able to
handle the ripple current caused by the energy the is circling around
in this circuit.

L2 is a largish valued lowish current one. It just prevents there
from being any spikes in the current here.

D1 returns the energy in the current spike back onto the power rail.
 
E

Eeyore

Jan 1, 1970
0
Jamie said:
I am using a fullbridge SMPS, and when I scope the secondary of the
transformer I am noticing a lot of voltage ringing which is approaching
the breakdown voltage of the diodes (600VDC). I have RC snubbers across
the primary coils, but none yet across the secondary. LTspice shows
that if I remove the primary RC snubber the output ringing is reduced,
what other methods are there to reduce output ringing or to protect the
diodes besides using an RC snubber?

Since so much depends on the mutual and leakage inductance of the
transformer, it's hard to give much advice.

Who designed the transformer ? What are the details ?

Graham
 
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