Conformity Magazine- May 2008 - (Page 36) Model LVR005 Vr 240 Vac 240 Vdc Imax 1.0 Arms 1.0 Adc 5.5 Arms 5.5 Adc Ihold 0.05 Arms 0.05 Adc 0.40 Arms 0.40 Adc Itrip 0.12 Arms 0.12 Adc 0.90 Arms 0.90 Adc Resistance (Ω) 18.5~31 18.5~31 0.6~0.97 0.6~0.97 Heating Effects For a linear resistive device, the heating effects for the AC and DC application are the same as shown in Equation 1. However, this may not be the case for a non-linear device like the PTC. Equation 1 derives the heat dissipation for the same AC RMS and DC voltage during one cycle. The resistance of the PTC device varies with temperature, which is a function of current/voltage applied; therefore, the total heat dissipated is not necessarily the same for the same AC RMS and DC voltage. LVR040 240 Vac 240 Vdc Table 1: Ratings at 20°C for Model LVR005 and Model LVR040 used for this study Figure 1: Resistance vs. temperature curve for one sample of Model LVR005 for the 240 Vdc aging test. For tripped parts, the PTCs are typically constant-power devices in the tripped state. Since R = V2/P, and power dissipation is constant, R = kV2, where K is an experimentallydetermined constant. Maximum Voltage Stress Samples are subjected to higher maximum voltage during AC application. This effect is most predominant during the aging and thermal runaway test. In addition, conductivity of the polymer might be a function of the voltage and, therefore, a difference in peak voltage may affect the device characteristics. Phase Angle When a device is being cycled with AC voltage, there is a phase angle when the test is initiated. Depending on the cycling rate, the DC cycling test may be a more severe test to the device than that of AC. The two tests that might be affected by this factor are the overload/endurance test and the cold operational cycling test. Ion Migration Figure 2: Resistance vs. temperature curve for one sample of Model LVR005 for the 240 Vac aging test. (Note this is not the same sample as the sample shown in Figure 1.) 3 Conformity mAy 2008 Due to the uni-polar electron movement under DC application, ions will likely migrate from one electrode and deposit at the other electrode after long term exposure, such as during the aging test.
For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.