basic transistor calculation question

From what I think is correct, to calculate the base current on a bipolar trnasistor, you figure out how much current the load is going to use, then dived that by the beta of the treansistor. If the load is the gate of a mosfet, there will be no current except for maybe a little bit to charge the capacitance if the gate. ( is that correct?) Or should I just use no base resistor at all being that no current will flow through the transistor?

The base-emitter of a BJT looks like a forward biased diode so you need a resistor (or some way) to limit the base current. This base current flows independent of whatever the collector current is.

The N-MOSFET you show is connected backwards in your circuit. And even if you turn it around the circuit still will not work. To turn on a MOSFET the gate voltage needed is always referenced to the source (positive gate-source voltage for N-MOSFET and negative gate-source voltage for P-MOSFET).

Can you high-side switch the load and connect the MOSFET to ground? That will simplify your drive requirements. Note that you need a logic-level type MOSFET to fully turn on with a 5V gate-source voltage. Standard MOSFETs typically require 10V.

I see what you are saying. the npn has its emiter tied to ground. therefore makeing the base emiter junction a diode that current will flow through.

What about the pnp, will any current run through it? And while I am thinking about it, does a pnp have to have it's base grounded or just no voltage on it? I am thinking that it would have to be tied to ground so a current can flow throught the basr to turn it on.

I drew the wrong symbol for the mosfet, it is supposed to be a p type. sorry. I am just starting to fool with mosfets.

do you know the number of a logic level mosfet off the top of you head so I can google it and take a look at it?

If the PNP has it's emitter connected to a plus voltage then you would ground the base (through a resistor of course) to turn it on. A PNP is just like an NPN expect for the reversed voltage and current directions.

If you use a P-MOSFET as shown, then the gate needs to go to +48V (Vgs = 0) to turn it off. You also need to protect the gate from have more than it's maximum voltage applied (usually Vgs=20Vmax) such as would occur if you ground the gate to turn it on. A resistor and zener would do that.

Don't know of any logic-level types off-hand. Just google "logic level MOSFET".