buckconverterdc/dc convertermosfetnpn
I'm trying to make a buck converter that should carry a load of up to 12A. Probably no surprise, the n-channel mosfet is getting hot quick, even with a heatsink it is getting to hot. (I have currently changed the Q5 to a IRFP1405PBF)
I have then tried to parallel two mosfets (with wires). But, It seems like only one of the fets gets all the load, and gets hot. How can that be? And are there other things that I could do to get a stable buck converter?
It appears that the problem was with the shape of the traces on my PCB. The following PCB design works correctly:
Unfortunately I still do not understand the real reasons behind this well enough to explain it, but I think it has to do with parasitic capacitance and inductance of the traces at high frequencies. It appears that at 1MHz these things really do matter, which also explains why I had so much trouble with the breadboard earlier.
I will try to answer your points assuming I have read them correctly.
1) The driver for the buck circuit will generally need some kind of regulation, but this can be a low power regulator. You then use the buck circuit to step down your supply voltage and regulate it, this will provide a lower stable voltage with more current for your load.
2) If your have either a dynamic supply voltage or load then the buck converter will need to be regulated to maintain a stable voltage. This is achieved by varying the duty cycle to the power MOSFET and feedback is required to the driver circuit to determine how the duty cycle is adjusted. You can use voltage feedback and then some closed loop control circuit to alter the duty cycle pending on the feedback signal.
To summarise a buck circuit is a good way to step down and regulate a large voltage to a smaller voltage, this can then provide power to a small, medium or large load. Additional regulation is generally required for control circuitry such as a microcontroller and driver circuit, but these circuits generally have very small power requirements.
Best Answer
Add this to your gate drive:
simulate this circuit – Schematic created using CircuitLab
You need to charge and discharge the gate fast to minimize switching losses. You can also buy a real gate driver that can source or sink amperes of current quickly.
Also, the IRF530 is a bit wimpy for this application. Try getting one with about 1/10 the Rds(on). Remember Rds(on) increases significantly with temperature. For that reason you generally don't want to thermally couple paralleled MOSFETs, but you're better off just getting a better, more modern, part.