OSSW/OSHW automated semiconductor analyzer

[rhb]

I've been scratching an old itch for the last few days.  I just went back and looked at a bunch of old curve tracer threads, but none was really as ambitious as what I have in mind.

I've got a Peak DCA75 which is an excellent piece of kit, but I'd like something more comprehensive.  The cheap LCR transistor testers such as the BSIDE ESR02 Pro and the nanoVNA are very powerful demonstrations of what can be done with clever design and modern parts.  When I got involved with electronics, such things were simply outside the means of a hobbyist.  I'm old now and can afford to buy a 30 year old piece of Tek or HP gear.  But I think an OSSW/OSHW design would be more valuable for the same price if it can be reproduced cheaply enough.

A general outline of what I have in mind is a device with 3 terminals.  Connect a DUT, close the lid and it probes for the type as does the BSIDE or DCA75, but in addition, measures breakdown voltages to 1000 V and every other parameter which can be accurately measured without device specific test fixtures.

At the conclusion it generates a PDF datasheet for the device.  Eventually I'd like to be able to look up the part in a database and check that the measured values are within spec.  But that's a long way off.  First I just want to measure the DUT parameters with an OSSW/OSHW  tester which could be sold on ebay for around $100 or less.

At present I'm working on a low current digitally controlled 0-1000 V PSU that can be pulsed at low duty cycles for 50-500 microseconds at various voltages to determine breakdown voltages.  I found that MOSFETS with ratings in the 1200-1500 V range are reasonably cheap, well under $1 in quantity.  The cost goes up rather quickly above that.

For the digital control of the HV supply I have in mind using PWM from an MCU to generate a variable voltage sine wave and feed that to a transformer.  There's not a lot of current needed for the breakdown tests, in fact limiting is needed.  But with a 1-2% duty cycle, just using a small capacitor should take care of that.

At the moment my "transformer" is a 380 uH ferrite choke with a single turn through it for the 2nd winding.  I've been testing it in step down mode because I don't want to damage anything.  It's 1:100, so I'm going to put a 2 turn primary on it, add a rectifier bridge, capacitor and 1 Meg load resistor and start feeding low level sine waves to it using an AWG while checking operation with a scope and DMM.

There are, of course, high current tests which are needed, but with Farad capacitors available that seems fairly tractable in pulsed operation at least up to 10 V or so.

MCUs such as the STM32F429 provide 3x 2.4 MSa/s 12 bit ADCs.  With those multiplexed to read the B, C & E currents and the voltages across the junctions,  one should be able to get 200-300 measurements during a 300 us pulse as is commonly specified in datasheets.

Reg