I'm doing an experiment to investigate the relationship between frequency and capacitance. The experimental setup is to connect an aluminum electrolytic capacitor to a function generator and use an oscilloscope to measure capacitance. Is it ok to connect an electrolytic capacitor to a function generator?
1
-
\$\begingroup\$ If the function generator has no DC bias control (as mentioned in an answer below), consider obtaining a non-polarized electrolytic capacitor instead of traditional bipolar. If no (or inadequate) DC bias is applied, the bipolar will get reverse-polarized, which could result in quite the explosive confetti device popping a few inches from your face. Never fun. e.g. parts-express.com/electronic-parts/capacitors/… \$\endgroup\$– Kyle BCommented Jun 6, 2022 at 20:37
Add a comment
|
2 Answers
\$\begingroup\$
\$\endgroup\$
Short answer - yes, with caution...
It is possible that at high frequency, a capacitor placed at function generator output acts as a short circuit, so it is worthwhile to ask, "Can the function generator survive a short circuit?".
A good function generator can survive, although it is a stress that causes internal amplifiers to run hot. A good function generator has a well-defined linear output range, and a well-defined output resistance, as in a Thevenin equivalent voltage source:
simulate this circuit – Schematic created using CircuitLab
Typical function generator characteristics:
- 50 ohm output resistance (a specific audio generator may have 600 ohms)
- open circuit output voltage (no load) 20 volts peak-to-peak at full amplitude.
With a capacitor at its output as in the second circuit, much AC current flows, so that the internal 50 ohm resistance heats considerably, along with the amplifier that is represented by voltage source V2. The second circuit forms a low-pass type filter. You can reduce internal heat by running your experiments at reduced amplitude.
In addition, a function generator very often allows a DC offset to be added to the waveform. When an electrolytic capacitor is tested, the capacitor will see this DC offset voltage, which should agree with its polarity marking.
\$\begingroup\$
\$\endgroup\$
Substantially yes, it's safe if you keep the negative portion of the signal level below about 2V.
Electrolytic capacitors however are horribly non linear so expect strange behaviour, also they are not really designed for more than about 50kHz (usually). The behaviour also changes depending on the voltage bias.
There are many way to conduct your experiment, have fun.
answered Jun 6, 2022 at 12:52