Ferrite Transformer

[asif]

Hi All,

 

In a design of a Welding Machine using Ferrite Transformer, Switching using diodes and MOSFETs and filtering using a choke,

the moment welding strike is taken, all mosfets are blown off (burnt).

 

Other machines of the same design are performing well but we are fed up of this one.

 

The moment welding strike is taken, we are not able to analyse the developments in transformer output or across the mosfets or at choke and find that mosfets are blown off.

 

I will give you the details of transformer design, but first suggest me what would be the cause, the transformer design, the choke design or supply frequency or what?

 

 

Asif

[marke]

Hello asif

 

You would need to analyse the MOSFETs to see what their mode of failure is.

 

It is possible that the problem is due to excess current, or excess voltage on the MOSFET.

 

An arc as produced by a welder can produce very high voltages and these need to be limited when applied to the MOSFETs.

I would check the voltage of the MOSFETs relative to the other units and also check the overvoltage and spike suppression around the MOSFETs.

 

If you are happy that the MOSFETs are not being damaged by the voltage, the the current may not be sufficiently limited by the reactance of the circuit. This may be due to saturation of the output inductor, or the transformer.

 

Best regards,