PTC Thermistors Characteristics

PTC Thermistor Resistance vs Temperature means the relation of zero-power resistance of PTC thermistor to PTC thermistor body temperature under a specified voltage. Zero-power resistance should be measured in super slot by using pulse power supply with low output impedance an stable output amplitude. Temperature rise of PTC thernistor induced by measuring current should be so limited that it could be ignored.

Shown in Fig.1 and 2 are PTC thermistor resistance vs temperature characteristic curves for different voltages and frequencies, at the same temperature resistance value decreases dramatically as measuring voltage and voltage frequency increases.

Fig.1 PTC Thermistor resistance vs temperature curve for different voltages	Fig.2 PTC Thermistor resistance vs temperature curve for different frequencies

PTC Thermistor Voltage vs Current characteristic

PTC thermistor Voltage vs current characteristic normally means the relation of voltage across PTC thermistor to current under stable condition with thermal balance in static air of 25^oC, that is, voltage-current characteristic of PTC thermistor in actual operating state as shown in Fig.3. I is non-operating area or linear area, II is jumping area and III is breakdown area. When measuring the characteristic, ambient temperature should be kept constant as far as possible and current readings should be taken after thermistor body temperature is balanced, and measuring circuit is shown in Fig.5. Shown in Fig.4 are voltage-current characteristic curves for various temperatures of PTC thermistor.

Fig.3 PTC thermistor voltage vs current characteristic curve	Fig.4 PTC thermistor voltage vs current characteristic curve for various temperatures

PTC Thermistor Current vs Time Characteristic

PTC Thermistor Current vs Time Characteristic means current change characteristic vs. time (as shown in Fig.7). It is normally measured with memory oscilloscope by using measuring circuit as shown in Fig.6.

Fig.5 Measuring circuit of PTC Thermistor Voltage Current Characteristic	Fig.6 Measuring circuit of PTC Thermistor Current Time Characteristic

Shown in Fig.8 is PTC Thermistor relation curve of operating current to operating time. Operating time of PTC thermistor decreases dramatically as initial current increases. Furthermore the operating time is in relation to resistance temperature coefficient, applied voltage and heat capacity of PTC thermistor.

Fig.7 PTC thermistor current time characteristic curve	Fig.8 PTC thermistor operating current vs.operating time
Fig. 9 PTC thermistor Current change characteristics vs. time with voltage on.

date: 2007-7-8