Posts tagged ‘PTC’

Non-destructive Testing of Fuses

A fuse is a sacrificial device for the protection the rest of the circuit in an over-current situation. There are situations we need to know with some reasonable confidence what the actual maximum current is for a given fuse without destroying it. This is beneficial when the specifications for the fuse at hand is unknown (e.g. with cheap no-name brand fuse), or the circuitry to be protected is so critical that the interrupt current level must be specified precisely.

Continue reading ‘Non-destructive Testing of Fuses’ »

Thermistor Parameter Measurement — II

Last time I showed a simple circuit that can be used to measure unknown thermistor parameters. The circuit is basically just a power MOSFET using a voltage and duty cycle controlled PWM signal to drive the gate and thus generates a temperature reference which is measured by both the unknown thermistor and the precision temperature sensor LM335. By measuring the voltage drop across the thermistor at different temperatures, we can obtain the R-T curve of the thermistor and thus estimate the parameters that define the R-T curve using some known models. Continue reading ‘Thermistor Parameter Measurement — II’ »

Thermistor Parameter Measurement — I

Over the years, I have gathered quite a few NTC and PTC thermistors. But most of them are unmarked so it would be difficult to use them in an accurate way without knowing the parameters. So I decided to build a simple circuit that can be used to trace the temperature-resistance curve, and the parameters can then be estimated using the measured data points. Continue reading ‘Thermistor Parameter Measurement — I’ »