Curve Tracer: Scale limits?

[MagicBox]

Hi guys,

With all the mosfet matching I'm starting to become really interested in building a curve tracer. I've had plans for this as long as I worked with transistors but never had a real need to go forth with it. This is changing.

The uC, software, USB connectivity is not an issue. I'd like to know what would be a sensible maximum scale for DUTs. Personally small signal is my main need, but I understand people like to trace output devices as well.

So, what's the max Vce, Ic you'd generally test with? Personally I would be fine with 20V, 1A at most.

[ChrisA]

Originally Posted by MagicBox

Hi guys,

With all the mosfet matching I'm starting to become really interested in building a curve tracer. I've had plans for this as long as I worked with transistors but never had a real need to go forth with it. This is changing.

The uC, software, USB connectivity is not an issue. I'd like to know what would be a sensible maximum scale for DUTs. Personally small signal is my main need, but I understand people like to trace output devices as well.

So, what's the max Vce, Ic you'd generally test with? Personally I would be fine with 20V, 1A at most.

If you have an analog 'scope and a good bench type power supply and a good signal generator these are not hard to make. You simply build a very minimalist amplifier using only the DUT and some resistors. Then place a ramp function on the input. Next place the input on the 'scope X axis and output on the Y axis and adjust the scope so the curve fits on the screen.

With computers it is about the same but use a stereo sound card for the X and Y inputs. You can also make the ramp function with the sound card. You can plot using something like GNUplot.

If you are buillding a uP based device. Design it to use a external bench power supply. Many people already have a good PS and not building another one saves some cash.

[AmpliFire]

But, but, but... we are having a wonderful tracer project going here by locky_z.

Your help would be very welcome to further improve the design, interface and manual...

[MagicBox]

Hi Chris,

Thanks I wouldn't want to use the scope for that, way too combersome. I want to go to the principle where the device allows me to run a batch of 100 transistors through it, beeping when it's ready to measure the next and then allow the data to be transmitted to PC for further processing. So yes, it'll become a uC device because of the autonomous flexibility it offers.

Using an external supply would be a good plan, I'll have to figure out a maximum dissipation rating though; possibly have the module be able to select between voltage inputs similar a class G (or was it H?) does. Besides pulse testing I want to be able to do 'in-place' testing, continuously feeding the test signals to measure under heat-up its behaviour, for example, a VAS transistor's operating conditions.

The drain/collector voltage driver will be a two-quadrant push-pull class AB supply (like a mini power amp) that's controlled by the DA in the uC. The output transistors will need to be able to handle max I * max U (I design worst-case )

I think scale still has an influence on the design and need to have some upper limit.

[MagicBox]

Originally Posted by AmpliFire

But, but, but... we are having a wonderful tracer project going here by locky_z.

Your help would be very welcome to further improve the design, interface and manual...

Hi AmpliFire,

I had found the thread and it didn't align very much with what I needed myself, sorry Keep up the good work though!

[AmpliFire]

Well, I'll keep an eye on your design then. I'm building Elektor's trace curver and locky_Z' trace curver in parallel; why not a third one if it has some unique properties. I love test gear and testing stuff .