Protection diodes dual diodes vs single TVS

[mscaff]

protection diodes across the regular

Hi,

I'm trying to protect my microcontroller inputs and outputs using a series resistor
and a protection diode.
I just don't know if is better to use dual diode (like BAV99) connected across vcc, my signal and gnd,
or use a single TVS (like MMBZ6V8AL ) connected across my signal and ground.

Thanks, Mauricio

 

[thomaz]

Hi mscaff,

if you connect a dual diode across vcc, input and gnd the following could happen:
If the interference at the input is of high energy, your vcc could rise too high.
To interface the µc to 24V (for example) I use a voltage divider made of two resistors
(output voltage ca. 5 Volt) and connect a zener diode 4.7 Volt parallel to the lower
resistor. If the upper resistor and the zener are big enough, this circuit can "eat" a lot of power (burps).

thomaz

 

[Alexg]

The TVS is much better but may end up being more expensive than the voltage divider and zener. Take a look at AVX, they have some very nice varistors in SMD packages costing about us$0.20 each.

 

[aNdreiBuuu]

hehehe good point thomaz!!! :smile:

best,
//a