overvoltage protection
overvoltage protection
(OP)
I saw how helpful you all have been and was hoping I could get some help myself. I am trying to design an overvoltage protection circuit but don't know where to start. I will be sending a voltage signal ranging from -10V to +10V dc to an aircraft system. The maximum voltage it can receive without causing damage is +/-12.5V. Can someone please point me in the right direction or give me any ideas?
Thank you in advance!
Thank you in advance!





RE: overvoltage protection
RE: overvoltage protection
1. Very often the overvoltage protection is implemented by overvoltage relays (electromechanical or solid state or they are part of an integrated protection scheme). Essentially, the overvoltage relay would be set to trip at ±12.5VDC. Also, there may be some relay accuracy or manufacturing tolerance involved, e.g. 5%. This means that the overvoltage relay set point may be set at some lower set point than ±12.5VDC.
2. If a mere protection, e.g. protection against transients, is needed without any signal being sent to any circuit interrupter, then back-to-back connected zener diodes or similar nonlinear devices will suffice.
RE: overvoltage protection
Take a look at
http://www.us.st.com/stonline/books/toc/ds/index.htm
and see if you can find anything there.
Yours truly,
1346
RE: overvoltage protection
RE: overvoltage protection
With a med to lo input R, a bi-directional TVS (transzorb) that follows the input resistor and then goes to the ckt's common or chassis will work well.
With a hi input impedance the TVS may have too much capacitance and act as a filter (you may or may not desire this action), if the capacitance it too high then using the dual diode clamps to the supply rails is a good answer. An alternate config. is, the TVS can be in front of the ckt's R, if a series fuse is placed before the TVS and the input.
The relay ckt will work, but may be way to slow to prevent damage. However it can be used in conjuction with the others.
RE: overvoltage protection
RE: overvoltage protection
Solid State Relays are essentially FETs sometimes combined with optoisolators. These methods of overvoltage protection are most useful in battery chargers, yet tend to be more complicated in their implementation. The Linear Technology data sheets on the LT1510 and its related Application Note (#68), are good references for this sort of circuitry. (http://www.linear-tech.com; site search the LT1510)
For interfaces, the simplest, most effective solution is BillJ's -- using diodes clamped to a fixed reference (usually your system's local DC power supply). Adding decoupling capacitors in parallel with the diodes also help, as they provide a path for power spikes and high frequency noise that might corrupt your input signal.
Hope this helps. Enjoy.
-- Warpdrive