SMPS analysis

[philipshadow]

Please i need to know what will happen if D812 is short internally. what will be the reading of the diode on the positive and negative pin. and what happens to the neutral ground.Does it's voltage change from zero.Assume D803 is shorted internally per my analysis it wont have any effect on the cicuit. Let me know your thoughts on this also

 

[bertus]

Hello,

It will short in input at the positive phase:



Bertus

 

[philipshadow]

Thanks for your feedback. I would love to know if the 250v present at the diode will make its way to the neutal wire of the Ac Socket. i have seen an extension board with 250v at live and 250v at neutral and yet it never caught fire and i was startled.

 

[bertus]

Hello,

The drawing I made is for a shorted D812.
The short could blow R840 or the fuse.
It could be that R840 is a fusible resistor.

Bertus

 

[philipshadow]

please it seems like the D813 will block reverse current

 

[bertus]

Hello,

When D803 is shorted, the SPMS will not start, due to the fact that R816 and the coil 5 to 6 of the transformer will block the startup.
Normaly R804 will be the starter resistor, wich has a rather high value, compared with R816 and the coil.
The diode D803 will isolate the startup sequence.
When the SPMS has started, the voltage from coil 5 to 6, R816 and D803 will take over the voltage supply for the oscillator.

Bertus

 

[philipshadow]

Thank you very much for this answer. i think this is the answer to my first post. But please can you give me answer concerning the post i recently sent. The short i created with the blue pen is on D812.

 

[philipshadow]

@bertus please kindly give me an answer