Curve tracer
From Electronics Chat
a cheap and simple curve tracer is to take a small mains to 12-24v transformer and put a current-limiting resistor in series, along with a low value resistor for measuring current. the + probe goes to the current limiting resistor and the - probe goes to the current measuring resistor.
the curve tracer illustrated below were made with a 24vac transformer, 2.2k current limiting resistor, and 10 ohm current measuring resistor.
the oscilloscope is set into X-Y mode. X (left/right) represents voltage, with left of zero indicating positive voltage. Y (up/down) represents current, with above zero indicating positive current.
- Analog Signature Analysis Using a Curve Tracer
- Transistor Curve Tracer
- Transistor and FET Curve Tracer.pdf
Contents |
[edit] basic examples
[edit] open circuit
there is voltage positive and negative to full extent, but no current flows. an open circuit.
[edit] short circuit
all current and no voltage makes this a short circuit. the very low resistance of the short pulls the voltage after the current limiting resistor to nearly zero.
[edit] diode
this is a 1N5406 diode. note that in the forward voltage area, it starts conducting heavily at about 0.7v. no current flows in the reverse direction, a sign of a good diode.
[edit] schottky diode
this is a S15D40C, a dual 40V 7.5A schottky diode. the datasheet indicates the diode will start breaking down at 115% of rated voltage. this one breaks down at about 46v, and calculated breakdown is 40v*1.15=46v.
[edit] zener diode
this is a 12v zener diode. it conducts at about 0.7v forward, and breaks down in reverse at about 12v.
[edit] avalanche diode
this is a 5KP11CA, a bidirectional 11V 400A avalanche diode. it is similar in acting to two series zener diodes connected at cathodes. the function is to short when voltage exceeds 11v, as a circuit protection device. this one breaks down at about 13v.
[edit] finding pinouts
[edit] transistor
for finding pinout of a transistor, play "find the zener" with the pins. when the display mimics a zener diode, you are connected to the emitter and base leads. the pin unconnected must be the collector.
NPN: + = base, - = emitter PNP: - = base, + = emitter
here are some illustrations of some transistors.
[edit] 2SC3180
2SC3180, 80V 6A NPN transistor.
[edit] 2SA1263
2SA1263, -80V 6A PNP transistor.
[edit] MOSFET
it is possible to find the pinout of a MOSFET, but unreliable because the residual charge on the gate can make the drain-source connection look like a diode, zener diode, or short. to view this yourself, take a N-channel MOSFET and connect your curve tracer - probe to drain and + probe to source. tap the gate pin with your finger and watch the display change.
[edit] damaged parts examples
[edit] LED
these are two identical high-intensity blue T1 LEDs, one of which has suffered overheating damage due to excessive soldering iron dwell time.
[edit] good
note how the good LED looks like a good diode with a forward voltage of about 3.7V.
[edit] bad
note how the bad LED is allowing current in the reverse direction.
[edit] 2SD882 transistor
these are two identical 2SD882 30V 3A NPN transistors. one has suffered overheating damage from dissipating too much power without a heatsink over an extended period of time.
[edit] good
good transistor, looks like normal trace.
[edit] bad
bad transistor. note the slope, it is the equivalent of having a 1.2k resistor in series.
[edit] UF3002 diode
this is a failed UF3002 3A 100V diode. it now measures out as a 54.3 ohm resistor.
[edit] LM317 voltage regulator
previously identical pair of LM317KCS by texas instruments, measured between input and output. the pass transistor appears to have changed into a 2 ohm resistor.
[edit] good
[edit] bad
