aqua_life: Also another question... I would like to protect the the signal wire than varies from 5 to 8 Volts against short circuit to ground.
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I will use a Zener diode from the LM317 output to its input.
That means the PIC output will need to withstand 6.75V when off and I don't think it can do that.betwixt: The other method is to use a 'normal' resistor divider to set the LM317 to produce 8V then connect the ADJ pin through a resistor to the PIC output.
Normally a fuse is to protect the circuit from damage, but if the LM317 is limiting the current, why do you want to fuse to blow?So, in a case of a short circuit how could I force the circuit to blow a fuse ?
That means the PIC output will need to withstand 6.75V when off and I don't think it can do that.
How does ≈3.5V on the output translate to an exact 3V change at the resistor junction?The PIC pin has ~0V on it when an output and ~3.5V on it when an input.
I wasn't aware of that behavior for the processor, so that connection certainly does make sense now, without requiring a transistor............
The TRIS bit I referred to decides whether the PIC pin is an input or output (direction control bit). When driven low the output latch is taken to ~ground before the direction control circuits. Therefore, changing port direction either grounds the pin (output) or lets it float (input). The lower MOSFET in the PIC output driver essentially does what your external MOSFET does without any external active device being needed. It shorts out the lower resistor in the two-resistor chain from ADJ to ground but never drives a voltage into that point......
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