Protection my Circuit

[aryan_hr]

Hi All,
How can I protect my A/D from high voltage input? My A/D works below 10V and I want to protect it from the voltage above 10 V.

Thanks,

 

[Hero999]

The chances are your A/D will be fine up to the supply voltage.

If you're worried then add a Schottky diode from the input to power supply (cathode to positive rail, anode to input).

 

[RadioRon]

There are a few schemes commonly used.

If your A/D has a high input impedance, then you can add a series resistor to the input. This has the effect of limiting current, and it works along with the input capacitance to create a low pass filter which also helps to suppress small high frequency transients. Beware that this RC filter will also affect your bandwidth so the values must be chosen carefully.

As Hero999 teaches, you can put a diode to power supply. This can be placed on the A/D side of the series resistor or it can be placed on the other side of the resistor. If you do the former, then the diode enhances the RC filter with its capacitance, and the current passing through the diode is limited by your resistor too. Beware that many schottky diodes have relatively high capacitance at lower voltages. You can also place a reverse biased diode from input to ground to avoid damage from negative-going voltage transients.

There are a variety of other protection devices available that are commonly used in shunt with the input signal. MOVs, Varistors and others are typically available that act like very soft zener diodes. Some of these are very good at shunting high energy over-voltage transients to ground.

Protection from hgiher frequency energy, at frequencies above 50MHz is often done with ferrite beads or common-mode chokes. These are often coupled with shunt capacitors to bypass high frequency energy to ground. Sometimes only a shunt capacitor is used.