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I was talking about the IRF3708 (linked from mosfet's doc) - I belive that's the only MOSFET that's had a datasheet linked here.
Now, the threshold voltage is not useful information if we want to control a real life load. If the load is for example 2A we will need a lot more gate voltage if we want the transistor to turn on. If we look at figure 3 we could be fooled to expect that we only need 2V gate voltage. But don't forget that this curve is showing only typical behavior and with 5V across the MOSFET. totally useless information, because 2A * 5V = 10W. the MOSFET would expire in a puff of smoke if we tried that.>
Figure 3 where? We are clearly not looking at the same device, as figure 3 of the datasheet I thought we were talking about (again, I see no datasheets for any other MOSFETs referenced, and only mosfets have a gate voltage) says nothing about behavior at 2v on the gate - the graph doesn't start until 2.7v; the IRF3708 doesn't provide any specs for Vgs lower than 2.7, other than that Vgs(th) is between 0.6 and 2.0 volts.
Re: BJT - So you have positive voltage on emitter, and want to know how much current to apply to the base to make it saturate? It looks like somewhere around 5mA with a load of 50mA, leaving a voltage drop of around 0.4v? The voltage doesn't matter.
DrAzzy-
Re: BJT - So you have positive voltage on emitter, and want to know how much current to apply to the base to make it saturate? It looks like somewhere around 5mA with a load of 50mA, leaving a voltage drop of around 0.4v? The voltage doesn't matter.
OH! lol, I always thought the .4V was the allowable voltage across the collector-emitter... not the drop out voltage... where do you see that .4V being the drop out voltage? So just to be clear, regardless of what voltage is being applied to the emitter (with the exception of voltages above 40V) it only takes 5mA on the base (which inserts 50mA to the load) to have it saturate? Say there was 10V being applied to the emitter and you only apply 4mA to the base, would that mean only 8V is allowed through the bjt?
user52526
Ok, I'm getting conflicting information again... Dr Azzy says:
Also, when I asked
I mean, the bjt's maximum voltage rating from collector/emitter is suppose to be 40V, but what amount of current would I need to apply to the base in order to allow 40V from collector/emitter given saturation ratings...