Math is not my strong suit, and college was long, long ago.
I have to select a IGBT or SCR to go into the power supply for a YAG laser. The network that powers the lamp is a LC circuit set up for critical damp ing with a period of 250 uS. 250 uS is used because it corresponds to the storage limit of the laser material.
A typical circuit might be 40 uH of series inductance, and a 80 uF cap cha rged to 1100V. The lamp is kept ionized by a current of a few hundred mA o f DC, the SCR or IGBT is in series with the cap, and is triggered to dump i t into the lamp through the inductor. This gets fun because the flashlamp's impedance changes in a non-linear way during the discharge.
So the question is, what is a good way to approximate the Di/Dt through the switch once closed. From watching a existing system on the scope, the curr ent rises following a very sharp square wave for about 5 microseconds, then follows a quasi sine curve to near the maximum current in about 20 more mi croseconds.
The limiting factor on the switch data sheet for both types of devices is the instantaneous current. So that is what I need to determine.
In my case this is to replace a Eastern Bloc component that is no longer ma de, and is pre-internet. It is a SCR in a Puck Package. The lamp power sup plies make it to 15 years and then the SCR goes soft or outright fails. Th e SCRs were made in Estonia, by the semi-conductor division of a big cold w ar era Steel plant. So tracing the actual part is impossible.
Suggestions?
Steve