Surge Pulse Clamping with Ceramic Capacitors

Klaus Kragelund · 2013-05-29T21:15:58+00:00

Hi For an application I need to protect the electronics of an RS485 interface from surges (8/20us 1kV pulse) The normal way be to use a transzorb, in a SMA housing or even a SOT23 device. That is not possible since we have to be able to withstand up to 30V DC on the bus also (that is handled by a special RS485 IC) The problem is that the selected breakdown voltage of the transzorb therefore is high (>30V) and a lot of energy is dissipated into the transzorb In another product I have used a diode from the affected node to a ceramic capacitor with a bleeder resistor in parallel to clamp the energy and dissipate the energy into the bleeder and that worked fine. The diode sees very little energy and the capacitor is just charged during the pulse I never saw any problems doing that, but I would like to know if anyone here has tried the same and has any inputs into failure cases or even a better way to clamp the pulse? One "feature" of the diode-capacitor clamp is that closely spaced pulses will eventually destroy the capacitor, but anyhow closely spaced pulses in a tranzorb will also destroy that one.... Thanks Klaus

May 29, 2013 40 Replies

Rate this thread:

langwadt 13 years ago

you could put some form of inhibit on tx_enable when you see the fault condition

-Lasse

Vote

Join the Discussion

Have something to add? Share your thoughts — no account required.

Didn't find your answer?

Ask the community — no account required

Surge Pulse Clamping with Ceramic Capacitors

Related discussions

Experiences, over voltage on FET drain source

Surge Protector

Surge Capable Chip Resistors

Join the Discussion

Didn't find your answer?