Pressure sensitive resistance is one of the most used voltage limiting devices. Widely used in automotive electronics, communication, computer, consumer electronics, military electronic products and so on, especially in the voltage protection, lightning protection, suppression surge current, the absorption peak pulse, amplitude, high voltage interrupter, denoising, semiconductor components, LCD, keyboard, I / O interface, IC, MOSFET, CMOS, sensors, mobile phones, DVD, AV, ABS, motor protection control panel, MP3, PDA, USB interface and high-speed data signal line protection etc..
Prior to the use of the pressure sensitive resistor, we should first understand the following technical parameters: the nominal voltage is defined as the temperature and the DC current, the voltage value of the voltage at both ends of the voltage. The leakage current is the current value flowing through the pressure sensitive resistor VDR when the maximum continuous DC voltage is applied at 25 centigrade. Voltage is the voltage at which the voltage is present at both ends of the voltage sensitive resistor VDR, which is present at both ends of the 8/20 grade current pulse. The flux is represented by the peak current applied to the pulse current (8/20 s) waveform. Surge environment parameters include maximum surge current IPM (or maximum surge voltage VPM and inrush source impedance Zo), surge pulse width TT, two adjacent surges the minimum time interval TM and in the varistor VDR is predetermined working life, of the surge pulse total number N and so on.
The power supply voltage applied to the two ends of the pressure sensitive resistor can not exceed the maximum continuous operating voltage value listed in the specification sheet. But also fully take into account the power grid (or circuit) operating voltage fluctuations, the selection of voltage sensitive voltage value of the voltage sensitive, to be left with sufficient margin. Domestic fluctuation range is 30%. The varistor maximum inrush current should not exceed the value of the technical specification of the maximum impulse current (is the maximum flux). Taking into account the impact of multiple shocks, it should be selected to withstand more than 10 times the impact of the surge current value. The maximum varistor voltage clamping voltage must be less than the protected parts or equipment can withstand (i.e. safe voltage).
In addition, the selection must also pay attention to:
(1) it is necessary to ensure that the continuous operating voltage will not exceed the maximum allowable value in the voltage fluctuation, otherwise it will shorten the service life of the pressure sensitive resistance;
(2) in the power supply line and the earth between the use of pressure sensitive resistance VDR, and sometimes due to the bad grounding between the line and the ground voltage rise, so the use of the voltage between the line and the line is generally higher than the nominal voltage of the voltage sensitive resistor.
The surge current absorbed by the pressure sensitive resistor should be less than the maximum flow rate of the product.