fetpcb-designrepairsolderingto220
I messed up my PCB design when I made a change of FET-model. Now the Drain and the Source pins are swapped and it seems that there are no TO-220 models made this way (1-Gate, 2-Source, 3-Drain). Are there any pinouts like this, or do you have any other solution? Making a new PCB is too expensive, since many other components where soldered before discovering this mistake.
simulate this circuit – Schematic created using CircuitLab
If you wish to avoid holy wars you'll need to avoid making simplistic and incomplete statements :-).
Bipolar transistors are current driven.
MOSFETs are voltage driven.
In both cases the spread of parameters during manufacturing is such that a circuit will almost always rely on feedback to produce a given voltage or current gain.
MOSFETs tend to be slightly more costly at the very bottom end for "jelly bean" applications. But, for switching more than a few ~100mA, MOSFETs are usually as cheap or cheaper than functionally equivalent transistors, are easier to drive from a uC (microcontroller) as a digital switch than bipolar transistors and tend to have very significantly superior on characteristics.
An "on" bipolar transistor exhibits a saturation voltage. This can be several tenths of a volt and to get it much under 0.1V usually requires a high base to collector current ratio that is undesirably high. At 1 A a 0.1 \$V_{sat}\$ (saturation voltage) dissipates 0.1 W and is the equivalent of a R = V/I = 0.1/1 = 100 \$m\Omega\$ transistor. But at 10A the figures are 1 Watt dissipation and 10 \$m\Omega\$. The 0.1V is very difficult to achieve at higher current levels.
The \$R_{DSon}\$ (Drain-Source on resistance) of MOSFETs is typically under 0.1 \$\Omega\$ and you can get devices with 10 \$m\Omega\$ or even sub 1 \$m\Omega\$.
As switching speeds rise MOSFETs need a gate driver to charge and discharge the gate capacitance. These can be relatively cheap.
More soon ....
Here.
Throws the manual across the room
Edit: You cannot control an NFET on the high side of a load with 3.3V. The ON-ness is controlled by Vgs, which would need to be 5V+Vgs-sat, which is like 8-10V if this is a logic level FET.
I can't see a reason you need the blocking action of the FET here, unless you have a circumstance where the Raspberry Pi is getting power from somewhere else. You can slap that circuit in series with the PFET switch if it works, or get creative and combine them which I think is possible.
Best Answer
You have several options: