Curve Tracer Circuit
ฝัง
- เผยแพร่เมื่อ 16 มิ.ย. 2024
- This is a component curve tracer circuit made with all discreet components. This design was chosen mostly for its simplicity and wide range of operation voltagewise. However, it can only test NPN bipolar transistors. It can also test almost any two-terminal device like a diode. While not being completely accurate, this circuit helps greatly in matching transistors. It gives more information about the device than an HFE meter alone could do. This circuit feeds an oscilloscope in X Y mode. (One probe the X axis, the other Y axis). Unfortunately, the curves are display mirrored on the oscilloscope screen no matter how the 'scope probe leads are attached to the circuit.
- วิทยาศาสตร์และเทคโนโลยี
Thank you for posting such instructive experiments.
In 80s, I used 7 stage counter 4024 and ladder resisitors to do the staircase. You need 3 bits only, but you can have up to 128 steps. You need a high voltage transformer to see the breakdown regions. I think the oscillation was caused because your oscillator was not synched to ac 60hz.
this is what I'm trying to do.
Place a mirror in front of the screen, then stand behind the 'scope, and the trace/graph will look like the ones on data sheets. No additional power required.
Cool you build it! That oscillation or jitter is weird, I didn't have that on mine. Maybe, if you make a print for this circuit, you can get rid of that jitter.
Ya I could not figure out where the oscillation was coming from. I think it has something to do with the power supply and decoupling. It could also be that X input is the power supply ground and at AC, the scope ground too. It may well have been a ground loop problem.
Ground loop seems plausible yes. It was telling that the oscillations went up in frequency when you upped the voltage. But it's a cool little circuit isn't it. I din't expect it to work so well when I first saw it. :)
I originally was going to do a video on a curve tracer circuit that w2aew (great youtube channel if you haven't seen it) made that used op-amps to make the stairstep signal. For some reason I could not get the thing to work (the stairstep signal was not generating), so I built a much simpler one which did end up working.
Oh I have seen that one too! I wanted to build that too but have to wait for my scope to be repaired before I can. That's a great channel. Alan I think his name is, really knows his stuff. I build a time domain reflectometer that he showed in one of his videos and it worked really well. In fact, that's how I found out my scope was faulty because I couldn't get the high risetime on channel 1 but it did work on channel 2 to 4.
:)
Looks like a triggering difficulty. Maybe trigger somewhere else ? I'm looking into building one. Is this a open source project ?
Hi friend, I did not understand where it is connected to a point between the x and y, is it a grounding same?
The grounding in this circuit is really weird. The collector of the transistor under test is connected to ground. The 0v line or battery return is connected to the X input on the oscilloscope. This is mostly why I got some bizarre oscillations going on. I ran this circuit from a power supply which had the 0v line grounded. It's actually surprising that it worked at all.
Did you ever manage to get rid of that oscillation?
No I haven't, I suspect that it has to do with the x-input being ac coupled to ground. I haven't built this circuit in a while, I wonder if using a floating or battery power supply would help.
Yes I think that would solve it because then there's no connection with the scope through ground.
Would the scope be loading the circuit?
Hi, I have a question, why do the lines get shorter as we move up the trace, I have done this with JFET and the same thing happens the lines get shorter as we move up the trace.
For BJTs, as the base current goes up, the collector current increases, the Vce voltage drop increases and the saturation region becomes more pronounced and leans over. This makes the lines at the top shorter because the of higher saturation voltage. JFETs do that for a similar reason. As Vgs is increased, the drain current goes up, there is more voltage drop over the channel and so the slope of the line gets more vertical. This is the so-called ohmic or triode region of the JFET curves. The constant current region is where the lines are flat. The lines are really short at the very top due to a limited amount of drain current the circuit can provide at a given voltage.
@@thetuberoaster8321 I understand the triode and the saturation regions well, I understand why there is a slope, that doesn't answer why the lines get shorter as we move up the trace, none of the textbooks show that the lines get shorter as we move up the trace, they all show and explain the slope, but whenever you plot it on an oscilloscope the lines get shorter as we move up the trace, and I do not understand what you mean there isn't enough voltage available when the horizontal axis is the voltage.
@@whatever3041 The voltage gets lower every step up. The circuit actually "runs out" of current as the bias current/voltage increases. The lines near the top won't plot very much horizontally because at higher bias currents, the transistor will pass more current for a given Vce. In other words, it doesn't take much Vce to get a whole lot of current, so the circuit runs out fast. You can raise the voltage of the circuit to increase the current and plot the lines further, at least until the device pops. In a textbook, sometimes they draw theoretical lines that are super flat and are the same length. They also might draw where the transistor breaks down, but in real life this might destroy the transistor. This circuit is also rather simplistic. If you were to somehow create a constant voltage source to drive the transistor instead of a constant current one, the lines would plot out the same length.
@@thetuberoaster8321 Thank you for the response, I think I need to study more, the textbooks do show the slopes but yes the lines are always of the same length and on the oscilloscope they are never of the same length, there is always the same trend that the lines get shorter and they get shorter in a linear manner.
Update for anyone watching: I managed to make PNP version of this curve tracer which will show the traces in the right way because in this version the Y-channel needs to be inverted. You can see more about it here: th-cam.com/video/KKE17HjISX0/w-d-xo.html
On your schematic, the X signal should be going to Y on your scope and the Y signal on your schematic should be going to X on your scope. This is why you are having problems!! 73's Gary Grove