Curve tracer

[rthorntn]

G'day,

I am looking to get a curve tracer from ebay...

A prebuilt one, it's more expensive ($130) and the power brick may be 110v, any ideas what the knob is for: http://www.ebay.com.au/itm/160891178289

A cheaper option ($45), would need a case though, and I can't see a knob: http://www.ebay.com.au/itm/140547987228 and the +-15v supply http://www.ebay.com/itm/130340589869 and a transformer: http://www.ebay.com.au/itm/320930934967

With the transformer and +-15v would I need to worry about earth, the transformer doesn't seem to have it but there is a point for it on the +-15v, maybe the transformer is wrong, could I cable earth directly between the wall plug and the +-15v supply, or is that bad?

Any ideas if one is "better" than the other?

Thanks all!

Cheers
Richard

[kg4arn]

You can build this for a few dollars, if you wish.  See the W2AEW video.

[TriodeTiger]

The knob (HOR = Horizontal) I would assume would be the voltage, as Y is current, X is voltage usually to create such useful graphs.

The kit/preassembled curve tracer appears to be for transistor testing, can you live with the extra time required to do this manually or is this useful?

The transformer you linked to appears nice, the case is plastic and I would assume double insulated (no need for earth plastic, nor introduce earth reference on the secondary side) but of course you have to deal with those 110V leads in a safe manner.

With the transformer (and current limiting resistor) you could make a nice IV curve with just about anything, as long as your devices can withstand 12Vrms, there was another post on the forums about curve tracers ("octopus curve trace" is its nickname) where we made up a few circuits :-)

EDIT: Mine was more or less this:

Code: [Select]

         1k
AC-----/\/\/\------+----o Scope X
                   |       
                   o
                   +
                  DUT
                   -
                   o
         10        |
0V-+---/\/\/\------+----o Scope Ground
   |
   +--------------------o Scope Y
12Vrms / 1000 = 12mA (on a resistor), Vpeak = 12 * sqrt(2) = ~17V (so don't run through certain things such as a silicon/shottky diode with low reverse breakdown voltage), adjust as needed. 12mA means the 10R sense resistor will output 120mV maximum, which your scope should easily be adjusted to.

Alexander.

[rthorntn]

Thanks for the info.

As you can probably tell, I'm new to electronics, I recently purchased a scope and was looking to use a curve tracer to help me understand it all.

I am working on my soldering but at the moment it's crap, so I would rather buy something that is already done and I don't want to be messing with mains voltages a lot.

Would the "Power Transistor Curve Tracer adapter XY Oscilloscopes" with the +-15v DC and the AC transformer allow me to hook up resistors, capacitors and diodes, I would be happy to pay $45 including the PSU and transformer?

https://dl.dropbox.com/u/2436853/thai_curve_tracer.jpg

Why is it so complex compared to the basic octopus circuits, what does it do that the basic circuits don't?

Thanks.

Richard

[M0BSW]

Build your own easy hang on to your dollars follow the video above by W2AEW  I did build it yourself.

[TriodeTiger]

Why is it so complex compared to the basic octopus circuits, what does it do that the basic circuits don't?

It appears to be doing multiple things for the sake of testing power transistors, you'll notice the curve goes higher each time in the eBay screenshots, this might mean a higher base current is being applied each time (I'll assume that large array of circuitry is a constant current source for the base of the transistor under test.)

For resistors and alike, you may be able to just connect collector / emitter ports to the DUT and ignore the base port, I would assume it would just scan over the same lines each "test current" and work as the others - but this bypasses the entire constant current functionality (as it is not useful to you for testing anything else) and makes the purchase a little silly.

Remember, if you look at my schematic, it just requires transformer -> resistor -> (test component) -> resistor -> ground. Stick that in a breadboard (no soldering!) and you'll be happy. The 110V leads look easy to deal with, I shouldn't suggest sticking them in the socket, but they won't short anything out if they are and pose a hazard I suppose. But as always, assume the 12V is really 120 coming out in to the DUT, you can't trust 12Vac being safe nor the transformer being of super quality (12Vac out may be higher unless loaded!), but this applies to any unknown quality thing you're exposed to.

[rthorntn]

I have the thai curve tracer, sorry mmcoffee

It appears to be working, I have put +15v, -15v and ground in to it.

Now I want to try some components in there.

So I have B C E, its actually 5 wires, I believe cable 2 and 4 are not connected.

https://dl.dropbox.com/u/2436853/thai_curve_tracer.jpg

So I have:

BLACK - Base?
WHITE - NC?
RED - Collector?
GREEN - NC?
YELLOW - Emitter?

And I have connected it to my DS1102E scope CH1 and CH2.

The curve tracer has a NPN or PNP switch.

Putting my fluke on the 5 wires above gives me roughly:

BLACK and RED = 2.2v
RED and YELLOW = 4.6v
BLACK and YELLOW = 5.5v

I am guessing these are pulses and that there is a negative voltage there somewhere.

Anyone have some instructions to allow me to connect some components to BCE and get the output on my scope like it's shown in the W2AEW video attached above?

Thanks.

Richard