SOA Protection by Relay.

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Hi Mike,
They are on VDE/UL/CSA certification. I would help if they used their heads once in a while though. Mind you, many times the safety organisations can be fairly stupid too and force these "gifts" on us.

If these parts go open (and they will in a fault), it will guarantee excessive current in the output stages. Like tons of uncontrolled current. There would be high current in a failure, but not like this unless an output shorted.

They will probably not discolour and confound a technician without experience, or the poor guy without a diagram (thanks by the way!).

-Chris
 
It gets worse...

Sony's last so-called ''current feedback'' ''high-end'' offering uses a crude shortcircuit-only arrangement, which is supposed to VERY prematurely limit each of five pairs/channel of 2SK1530/2SJ201 MOSFETs to just 6.7A regardless of Vds (but doesn't in practice because of the relay's drop-out time-constant), leaving the MOSFETs unprotected for Vds>20V and Id<=6.7A.

Abominable!
 
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