Winsu
Full Member level 3
Hi All,
I'm trying to find a way to protect a microcontroller from a possible wrong input voltage( backwards mainly) in one of its inputs.
The input works at TTL level or free volt, and the input is connected internally to a pull up resistor. When the user joins the cables (free volt)or apply a TTL input voltage ( max 5v) it works fine. If the input voltage is above 5V there is a clamping diode to suppress excessive voltage.
The problem is when a backward voltage is applied as a TTL input.The ground of the microprocessor would be connected to an external voltage, causing a possible fault in the microprocessor.
I could fix that problem putting a diode from the microprocessor to micro-ground and then avoid any backward TTL connection, but I will lose the free volt. Any idea??
Please see attachment to illustrate the problem.
Cheers,
Winsu
I'm trying to find a way to protect a microcontroller from a possible wrong input voltage( backwards mainly) in one of its inputs.
The input works at TTL level or free volt, and the input is connected internally to a pull up resistor. When the user joins the cables (free volt)or apply a TTL input voltage ( max 5v) it works fine. If the input voltage is above 5V there is a clamping diode to suppress excessive voltage.
The problem is when a backward voltage is applied as a TTL input.The ground of the microprocessor would be connected to an external voltage, causing a possible fault in the microprocessor.
I could fix that problem putting a diode from the microprocessor to micro-ground and then avoid any backward TTL connection, but I will lose the free volt. Any idea??
Please see attachment to illustrate the problem.
Cheers,
Winsu