Semiconductor test station

Thread Starter

tonietabs44

Joined Jun 7, 2008
3
I am trying to come up with a semiconductor test station that will display output characteristics of both BJTs and FET on an oscilloscope. I need to apply a step voltage to the base and a ramp voltage as Vcc. Any suggestions on how i could do this? Would realy appreciate it. Thanks.
 

Wendy

Joined Mar 24, 2008
22,146
The BJT will need a step function as current, not voltage, IMO. It is easy to translate a voltage into current though, so the basic problem remains. Do you want to do this with descrete circuit or a computer? Either is practical.

Man I hate that digital font, am I the only one that thinks it is almost unreadable?

This thread could be a good starting point though...

http://forum.allaboutcircuits.com/showthread.php?t=11792
 

hgmjr

Joined Jan 28, 2005
9,029
I would tackle this design with an AVR microcontroller and the required number of DACs (digital to analog converters).

hgmjr
 

Wendy

Joined Mar 24, 2008
22,146
Could you show a link to a AVR microcontroller? I'm not that familar with a lot of the PIC (I assume that is what it is) families. Writing the software would be an additional level of complexity, but the end result would be more open ended.

Only reason I would go discrete components is the level of complexity is about the same, I think. A simple counter fed into a DAC, with a sawtooth generator providing the variable voltage (or current, as the case may be). Curve tracers are pretty simple devices overall.
 

hgmjr

Joined Jan 28, 2005
9,029
Could you show a link to a AVR microcontroller? I'm not that familar with a lot of the PIC (I assume that is what it is) families. Writing the software would be an additional level of complexity, but the end result would be more open ended.

Only reason I would go discrete components is the level of complexity is about the same, I think. A simple counter fed into a DAC, with a sawtooth generator providing the variable voltage (or current, as the case may be). Curve tracers are pretty simple devices overall.
Here are a few links to get you started with AVRs.

AVR Devices - device datasheets
AVRSTUDIO4 - FREE assembly language software development tool
WINAVR - FREE C-language development tool
AVR Forum - AVR dedicated Forum
AVR Tutorial site - Tutorial in assembly language coding and AVR features

hgmjr
 

SgtWookie

Joined Jul 17, 2007
22,210
Take a look at this Electronic Design Ideas article from October 2001:
"Trace voltage-current curves on your PC"
http://www.edn.com/article/CA170223.html?text=&text=&text=Curve+tracer

Download the PDF version; it has the schematics embedded. Direct link to PDF:
http://www.edn.com/contents/images/101101di.pdf

There are some other interesting ideas in that edition.

Bill,
AVR is a trademark of Atmel Corp. - I think they're #1 in microcontrollers at the moment.
http://www.atmel.com
PIC is a trademark of Microchip Corp. - they've gone from #20 to #2 in the last 10 years.
http://www.microchip.com
I have no experience with either (yet!) save for a couple of Parallax Inc's "Basic Stamps" - that actually are powered by PIC uC's, and are considerably more expensive (order of magnitude +) than the PICs. The only real "advantage" to the Basic Stamps is the relative ease of learning the Basic-like programming language. You pay for that from your wallet and with the loss of uC speed (PIC: 4MHz - 20MHz; Basic Stamp: 20kHz - 50kHz)
 
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