What Is A Curve Tracer?
Image showing a programmable curve tracer.Source: Wikimedia Commons A modern curve tracer refers to an electronic instrument that measures and analyzes characteristic curves of devices. For example, it includes semiconductor diodes, thyristors, and transistors. This electronic test device displays the component's current-voltage (I-V) dependency. Thus, it serves as a troubleshooting tool to determine if an element performs well or fails to operate. Plus, it can generate additional data that a manufacturer won't provide on a data sheet. You can utilize an I-V curve trace on various applications, including PV installations. Some models may also require curve tracer software for failure analysis. You can also use a mobile device to perform tests. Overall, curve tracers feature a wide voltage and current range valued from 3 kV/20A to 10 kV/1500A. That makes them ideal for many types of power devices. These commonly have interlocks and shields to keep a user safe from high voltages and currents. On the other hand, an inexpensive curve tracer cannot perform tests on power devices, making them less lethal for an operator.
Types Of Curve Tracers
This type can measure transistors.Source: Wikimedia Commons Three types of curve tracers exist on the market today, including:
- Pulsed current-voltage (fast IV)
- Current-voltage (IV)
- Capacitance-voltage (CV)
How Does a Curve Tracer Work?An I-V curve tracer features two terminals, which receive a swept voltage for component testing purposes. Generally, the device measures the amount of current that can flow through a component at each voltage. Afterward, you will see the voltage graph on the oscilloscope display. It shows the max voltage and applied polarity voltage.
Two terminal components, such as diodes, can be tested.Source: Wikimedia Commons Two terminal components, such as diodes, undergo a characterization process. From there, the device shows the forward voltage, reverse breakdown voltage, and reverse leakage current. Curve tracers also present the bold and reverse trigger voltages in devices like DIACs. Moreover, these display the cutoff occurring from harmful resistance devices, such as tunnel diodes. Such a technique allows professionals to determine if a device has damaged pins.
Curve Tracers FeaturesClassic curve tracers include the following features:
- Fully programmable operation
- Waveform comparison and averaging
- List sweep
- Time sampling
- Integrated cursor measurements
- Digital screen and acquisition
- Third-party hard copy printer operation
- High-res parameter measurements
- Push button for performing measurements
Simple Curve Tracer Circuit: Building Your Curve TracerBelow, we will show you a simple circuit for an I-V tracer.
Basic curve tracer circuit diagram
- 555 IC timer - 1x
- LM358 opamp - 1x
- 1K resistor - 1x
- 10K Ω resistors - 1x
- 10M resistor - 1x
- Test resistor (resistor value between 50 ohms and a few hundred Ohms) - 1x
- 10uF decoupling electrolytic capacitor - 2x
- 100nF decoupling ceramic capacitor - 1x
- 10uF electrolytic capacitor - 1x
- BC557 PNP transistor - 1x
A 555 IC timer integrates into the circuit.Source: Wikimedia Commons Overall, the 555 IC timer circuit operates as a Sawtooth waveform generator. The timing resistor connects to a constant current supply, distributing a fixed base-emitter bias voltage. In turn, this will produce a continuous collector current. The linear ramp waveform generates once a capacitor charges through a constant current. While the capacitor generates the necessary sawtooth ramp, pin 3 distributes narrow negative pulses. Moreover, the device's output comes from the capacitor's output rather than pin three. However, this creates a problem because a component will not receive any current testing purposes. For this reason, the circuit features an LM358, which operates as a voltage buffer that delivers current to the component.
The LM358 helps distribute current to a component under test.Source: Wikimedia Commons Also, the curve tracer cannot rely on this voltage to operate since the sawtooth waveform capacitor does not incline from zero. Instead, it fluctuates between 1/3 and 2/3 VCC. AC coupling the 555 timer's input to the voltage buffer input solves this issue.
The 10M resistor provides essential capabilities for this circuit.Source: Wikimedia Commons Without a 10M resistor integration, the output would otherwise shift to and remain at the VCC source. That happens because of the parasitic input capacitance and high input impedance forming an integrator. So, the 10M resistor can expel the parasitic capacitance.
What is a Curve Tracer vs. an Analog Signature Analyzer vs. an SMU?As you already know, a curve tracer shows a device's voltage vs. current characteristic. These devices differ from others: applying dual synchronized stimulus signals to the component. Also, curve tracers utilize low-rated stepped or linear voltage waveforms for DC measurements. Meanwhile, analog signature analysis involves applying a sinewave stimulus to two PCB or component pins. In effect, this will generate a voltage vs. current signature for those pins. Afterward, that signature shows up on a screen as a graph. In this case, the X-axis represents the voltage while the Y-axis represents the current. In addition, signature analysis utilizes AC over varying frequencies. This process will analyze and display a component's characteristics. The amplitude and voltage-current phase display a lumped impedance measurement for resistors, capacitors, and inductors. Then, these results can reduce to an RLC network. You can also change the test frequency for each component that undergoes testing. In this case, you can select a low frequency to measure only the network's resistive area. A low frequency means that inductors represent shorts while capacitors can represent opens. Meanwhile, higher frequencies will result in an opposite effect. A source measure unit can source power and provide measurements simultaneously. Source: Wikimedia Commons Lastly, the source measure unit (SMU) relies on a sourcing function and measurement function via an equivalent connector or pin. The SMU distributes voltage or current and simultaneously measures voltage and current. Some SMUs may feature one or two channels that can function separately.
ApplicationsYou can utilize the test equipment to measure I-V curves of varying components. Source: Wikimedia Commons Generally, you will find these utilized in various applications. We listed a few below:
- Producing data sheets
- Manufacturing tests
- Inbound inspection
- Semiconductor parameter characterization
- IC, transistor, and other component testing and manufacturing
- Quality control and process monitoring