technogeek
New Member
I'm sure you've all seen this, I know it's used commonly to create reference voltages. What you do is take the output of a zener diode and feed it into a mosfet voltage follower to boost the output current without the zener overheating.
(See attached diagram)
My question is, how do you calculate all of the parameters of this circuit?
I assume the MOSFET doesn't take in any current.. so the zener and dropping resistor can be low wattage, and use minimal current. However, how do you size the fet, and do you want to pick one over another (for instance one with a lower Vgs threshold?)
For instance, if I wanted to take a 48 volt power supply and turn it into a 24v "regulated" power supply @ 4mA, what are the steps to doing this? How do I find the proper mosfet? How do I calculate the power dissipated in it (I^2*Ron?) For such a simple circuit you'd think google would have a handy calculator built in.
(See attached diagram)
My question is, how do you calculate all of the parameters of this circuit?
I assume the MOSFET doesn't take in any current.. so the zener and dropping resistor can be low wattage, and use minimal current. However, how do you size the fet, and do you want to pick one over another (for instance one with a lower Vgs threshold?)
For instance, if I wanted to take a 48 volt power supply and turn it into a 24v "regulated" power supply @ 4mA, what are the steps to doing this? How do I find the proper mosfet? How do I calculate the power dissipated in it (I^2*Ron?) For such a simple circuit you'd think google would have a handy calculator built in.
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