T
treez
Guest
Hello,
We often measure the resistance of a 0603 resistor which is connected to the current setting pin of an offline LED driver chip. (the resistor is soldered into the PCB when we measure it). We obviously do this with the circuit unpowered.
We need to do this as its too time consuming to desolder it, measure it, then solder it back on.
With our cheaper DMM meters, the resistance reading varies depending on which way round the probes are applied to the resistor. This is obviously because the ESD diode of the chip is getting slightly forward biased by the meter in one connection orientation.
Our better quality meters don’t suffer this problem, and either way round with the probes gives the same resistance measurement.
How do we find whether or not a meter has a measurement voltage above the 0.7V or so that it takes to forward bias the circuit diodes? These meters specs don’t say…eg the Tenma ones….
Tenma DMM
https://www.farnell.com/datasheets/...MIlJea_7vw4QIVy73tCh18-QmHEAAYASAAEgLMAfD_BwE
We often measure the resistance of a 0603 resistor which is connected to the current setting pin of an offline LED driver chip. (the resistor is soldered into the PCB when we measure it). We obviously do this with the circuit unpowered.
We need to do this as its too time consuming to desolder it, measure it, then solder it back on.
With our cheaper DMM meters, the resistance reading varies depending on which way round the probes are applied to the resistor. This is obviously because the ESD diode of the chip is getting slightly forward biased by the meter in one connection orientation.
Our better quality meters don’t suffer this problem, and either way round with the probes gives the same resistance measurement.
How do we find whether or not a meter has a measurement voltage above the 0.7V or so that it takes to forward bias the circuit diodes? These meters specs don’t say…eg the Tenma ones….
Tenma DMM
https://www.farnell.com/datasheets/...MIlJea_7vw4QIVy73tCh18-QmHEAAYASAAEgLMAfD_BwE