??? 10/30/05 01:13 Read: times |
#103125 - ESD protection is no HV protection! Responding to: ???'s previous message |
Jeff said:
Ultimately, the resistor network is the only thing I can even think of. Ok, if you want to use a resistive voltage divider, then take care that resistors can only withstand a characteristic maximum voltage. For a 0207-resistor this maximum voltage is typically 350V. So, when choosing a maximum voltage of 300V per resistor, you will need a resistor network containing 15kV / 300V = 50 resistors! Maximum power dissipation of 0207-resistor is about 0.4W, so that the minimum resistance of each resistor of this resistor array will be R = 300V^2 / 0.4W = 225kOhm. So, you might want to use resistors in the MOhm-range to keep the loading low. In most cases you will need an OPamp as buffer. Then, using protection diodes at input of OPamp (from input to power supply rails) will be useful. Some chips have some level of HV protection, around 15kv I believe; but I doubt the Maxim 8051s do... This is no protection against static HV as in your application, but only against ESD (electrostatic discharge) events, which lasts for only some nanoseconds! Kai |
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