I want to measure the stand-by current of the PIC, but my DVM has minimum 2000micro (u) amper switch. It shows 0 micro amps when in 2000 u amps mode. Without building circuit a complex (more than 3-4 components) circuit, how can I measure nano amps?
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3 Answers
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Put a suitable resistor in series, and your DVM (in voltage mode) over the resistor.
For instance, a current of 100 nA through a 1M resistor will give you 0.1V. Check the input impedance of your DVM, for this to work it must be >> 1M. You will probably need a switch to short the resistor for the period that your target is not yet in low-power mode.
Another way would be to use a known-sized capacitor as power supply and see how fast it discharges. Again, your measurement instrument must have a high impedance, otherwise it will disturb the measurement. You might get around this by connecting the voltmeter to measure the voltage only at specific moments.
answered Jan 24, 2015 at 10:34
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2\$\begingroup\$ I think it safe to say "You will need a switch to short the resistor . . ." \$\endgroup\$ Commented Jan 24, 2015 at 12:00
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1\$\begingroup\$ If you know the input impedance of your multimeter, you may not even need a separate resistor. Just stick the DMM in series, in voltage mode. \$\endgroup\$ Commented Jan 25, 2015 at 5:30
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Get one of those: https://www.kickstarter.com/projects/eevblog/current-gold-precision-multimeter-current-adapter. It has also been reviewed on the EEVBlog.
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3\$\begingroup\$ It was made by the EEVBlog guy!!! \$\endgroup\$ Commented Jan 24, 2015 at 12:46
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\$\begingroup\$ I've watched his videos on low current measurements ... wish I had known how to do it 10 years ago ... \$\endgroup\$– SpoonCommented Jan 24, 2015 at 20:32
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TIA opamp circuit with a FET opamp.
opa134 has ~pA of bias current.
10-100 Meg ohm feedback resistor.
Bipolar power supply.
answered Jan 24, 2015 at 20:13