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A darlington has a voltage loss of 0.8V to 1.5V. A half-decent Mosfet has an extremely low voltage loss.Andy1845c said:I need to switch a 400mA load with a PIC. Would it be better to use a logic level MOSFET or a Darlington? Are there alot of advantages one way or the other or is it more a matter of preferance in this case?
Of course that's what they show. It's more information then is contained in a line in a table. Why are you being so...ah prickly?audioguru said:Never mind the graphs because they show typical parts. You can't order a typical part, you might get a weak but passing one.
The tiny 2N7000 Mosfet has a max continuous current of only 200mA.
With 10V on the gate and 200mA through it then its max saturation voltage loss is 1V when it is cold and 1.8V when it is hot. It will be pretty warm with a current of 200mA.
With only 4.5V on its gate, it turns on poorly and has a saturation voltage loss of a little more than with a gate voltage of 10V.
Parts are cheap.Papabravo said:Of course that's what they show. It's more information then is contained in a line in a table. Why are you being so...ah prickly?
And do you suppose that you are the only one who does that?audioguru said:Parts are cheap.
I design circuits by using the minimum and maximum ratings so all my circuits work well. I don't have any circuits that don't work because the transistor passes the spec but doesn't have enough performance.
The yield from manufacturers varies as shown by the wide spread in the specs. Also, maybe somebody bought the entire "high specs" production before you got there.
I am with audioguru, I learned a long time ago when designing with bipolar transistors to use the minimum beta.Papabravo said:And do you suppose that you are the only one who does that?
Andy1845c said:I need to switch a 400mA load with a PIC. Would it be better to use a logic level MOSFET or a Darlington? Are there alot of advantages one way or the other or is it more a matter of preferance in this case?
Many guys design circuits using the typical spec's. I guess they throw away the ones that don't work. It must be frustrating to make only one and it doesn't work because of the minimum spec's.Papabravo said:And do you suppose that you are the only one who does that?
There are a lot of advantages and disadvantages to both.Originally Posted by Andy1845c
I need to switch a 400mA load with a PIC. Would it be better to use a logic level MOSFET or a Darlington? Are there alot of advantages one way or the other or is it more a matter of preferance in this case?
mneary said:If you choose a darlington (or a pair of 2N2222's) and a 680R resistor, you're done (after doing the calculations above) for about 25 cents. Your ON voltage will be about 1.2 to 1.8 volts with a good design.