Sorry, I was not well so could not try out the suggestions.Thanks for the explaination, I have a few questions though.
Today i tried them out:
I did not have a 4V supply handy so tried a 5V instead. Below results are with 5V.
But this did not work. Test load(motor) did not switch off fully. However I tried two other quickies:
1. 220 ohm between VCC of MC logic to the 8051 pin : result was good and on/off was working correctly.
2. 220 ohm between Source and 8051 pin : result was motor was not fully off.
Note: 10K in place of 220 Ohm did not work.
Could you let me understand why above observation ? I would assume that changing load voltage to 5V should not matter as VGS will be 0V when both pin o/p and VSS are 5V.
But assuming at 0V MOSFET is not fully off(which it should be from transfer char) which explains load not fully off, in that case why the behaviour changes with experiment 1 above ?
Its puzzling me !!!!
Today i tried them out:
So I suggest a resistor of around 10k from the 8051 pin to the MOSFET's source (the +4V rail), a 270 ohm resistor from the 8051 pin to the MOSFET's gate, and a 5.1V (or 5.6V or 6.2V if you like) 0.5W zener diode with its anode to the gate and cathode to the source.
I did not have a 4V supply handy so tried a 5V instead. Below results are with 5V.
But this did not work. Test load(motor) did not switch off fully. However I tried two other quickies:
1. 220 ohm between VCC of MC logic to the 8051 pin : result was good and on/off was working correctly.
2. 220 ohm between Source and 8051 pin : result was motor was not fully off.
Note: 10K in place of 220 Ohm did not work.
Could you let me understand why above observation ? I would assume that changing load voltage to 5V should not matter as VGS will be 0V when both pin o/p and VSS are 5V.
But assuming at 0V MOSFET is not fully off(which it should be from transfer char) which explains load not fully off, in that case why the behaviour changes with experiment 1 above ?
Its puzzling me !!!!