I have built a voltage controlled current source for a project at school and am currently trying to spec the components I need to actually build the circuit. The circuit is shown below.
I realize I should just be using an op-amp but this isn't allowed in the design nor is a voltage regulator. P.S. The small 1u resistors are just to show me current through the MOSFETS.
This is a run down of current through the mosfet / power dissipated:
X1 52mA 55mW
X2 53.4mA 1.04W <---PROBLEM
X4 26.7mA 535mW
X5 26.7mA 354mW
X3 26.7mA 25.8mW
X6 26.7mA 510mW
X7 500mA 3.75W <---PROBLEM
Since this is a differential amplifier X4 and X5 should match (ideally) as well as X3 and X6. The idea would be to buy a single N-MOSFET for X1,X2,X4, and X5 and a single P-MOSFET for X3 and X6. Obviously X7 is the largest problem with X2 a close second. The only thing i have thought of doing is adding MOSFETS in parrallel to disperse the power. The problem is even doing this I will need over 5 MOSFETS to compensate for it and thats being optimistic. I know there are power mosfets rated for 2W + but I also know this is if you had an infinite heat sink which I currently dont have . If someone could point me in the direction of a MOSFET that can handle this kind of power and ones to handle the smaller requirements that would be perfect. Thanks in advance!
I realize I should just be using an op-amp but this isn't allowed in the design nor is a voltage regulator. P.S. The small 1u resistors are just to show me current through the MOSFETS.
This is a run down of current through the mosfet / power dissipated:
X1 52mA 55mW
X2 53.4mA 1.04W <---PROBLEM
X4 26.7mA 535mW
X5 26.7mA 354mW
X3 26.7mA 25.8mW
X6 26.7mA 510mW
X7 500mA 3.75W <---PROBLEM
Since this is a differential amplifier X4 and X5 should match (ideally) as well as X3 and X6. The idea would be to buy a single N-MOSFET for X1,X2,X4, and X5 and a single P-MOSFET for X3 and X6. Obviously X7 is the largest problem with X2 a close second. The only thing i have thought of doing is adding MOSFETS in parrallel to disperse the power. The problem is even doing this I will need over 5 MOSFETS to compensate for it and thats being optimistic. I know there are power mosfets rated for 2W + but I also know this is if you had an infinite heat sink which I currently dont have . If someone could point me in the direction of a MOSFET that can handle this kind of power and ones to handle the smaller requirements that would be perfect. Thanks in advance!