Protecting microcontrollers inputs with diodes

[toninlg]

I've seen some schematics where the input of a microcontroller was protected with two diodes : one from ground (A) to input (K) and the other from input (A) to power supply (K) and a limiting resistor in serie with input. If the input voltage is greater than power supply voltage + diode threshold voltage, the diode will conduct limiting voltage to Vcc+06V. But there will be a current in the diode. If the power supply is a simple LM7805 regulator, there is no risk for it since it will receive a current at output?
I assume no since there is the same protection inside the microcontroller but I doon't understand why?

Thanks a lot.

 

[zajbanlik]

Hi

Usualy there is such protection in microcontrollers. They probably put it to be sure. You should also look for microcontroller's datasheet. This is because they specify the maximum voltage in ESD case. If you want to protect it against biger ESd than you have to put external protection.

Regards