Diode IFSM tester up to 300Amp

[imijoon]

Hi,

I want to make a tester to test Diode IFSM parameter up to 300Amp. To know if my diode can pass this test according to it's datasheet or not. My designed circuit is attached below the post. I apply a single 20ms square pulse to MOC3063 triac driver input. It has a zero cross detection so just one single positive ac cycle passes through current step up transformer. In the secondary the amplified current passes through diode and I measured it with the Rsense and oscilloscope. At the end I check the diode if it's damaged or not.

My step up transfomer is 220v/3v-600watt.

I want to know If my design works fine and if my transformer is suitable for the secondary current up to 300amp.

 

[schmitt trigger]

If you're going to apply a current pulse in one direction only, how are you going to reset the core?

 

[FvM]

The core will reset itself, with a respective remanence flux.

A possible problem is that switching the transformer voltage at zero crossing will already cause saturation. Switching it at the peak of the preceeding negative halfwave would be a better solution. You'll use an opto triac without zero crossing logic in this case and need to synchronize the control signal to the mains voltage.

I would also add a fuse, in case the triac becomes shorted.

 

[imijoon]

I will reset it after each test by a negative pulse. A mechanism which there is a switch and a resistor in the output exactly in parallel with DUT. A negative pulse goes through primary and then secondary and then output resistor.

 

[schmitt trigger]

I will reset it after each test by a negative pulse. A mechanism which there is a switch and a resistor in the output exactly in parallel with DUT. A negative pulse goes through primary and then secondary and then output resistor.

Another thing:
at those current levels, the diode's Vf could be a couple a volts. Also even 10 milliohm of stray resistance in the cable, contacts, etc, it could cause 3 volts of drop.

Perhaps, you will require a higher voltage secondary to overcome all those drops and able to drive that much current.

 

[imijoon]

Exactly, but I can use thick and short wires to reduce the connections resistance. You said forward drop voltage of diode is couple of volts. Isn't it about 0.9v ?

 

[D.A.(Tony)Stewart]

If it is capable of 300Apk, the forward voltage drop can be predicted by piecewise linear approximation above saturation.

A Silicon diode is usually saturated at 0.7V at Tj=25'C and any voltage rise above this comes from IR drop in the bulk resistance (ESR) related to it's size and thermal capacity. In fact ESR ~ 1/Pmax for the typical package design. The maximum current depends on the bondwire fuse limit I*t which be stated as a constant for a half cycle of line frequency or some other method.


Thus if the case is capable of 100W load with suitable sink, ESR is expected to be 10mOhm

Thus Vf= 0.7 + ESR * If

Testing at high currents is best done with a good CT to amplify the signal with low drop and good CM rejection of ground shift or equally good method.

Driving the device under test (DUT) with a pulse can be done by using an air core inductor shunting the diode such as 10 to 50uH from a low RdsOn source follower using a low voltage source with low ESR and "non-Inductive" wire series shunt to act as a current limiter from a low voltage.

the peak forward voltage and current is measured easily and when load is turned off , one can measure the reverse recovery time, and charge Qrr.