help needed about power in a 5v regulator

l7805 power supply

Hi to all!!!

I have made a board with a microchip (16f876) and a power mosfet IRF3205.
The mosfet drives a 3 A motor using a 24 V DC source. I'm using the PWM output from the PIC (0-5V) to adjust the mosfet from 0-24V. This speed control runs ok, but I'm using a L7805 to convert 24V to 5V to the PIC microcontroller. The IRF3205 is cold but the L7805 is very HOT!!!!. I know that the L7805 can only drive 1A of current but my 2 questions are:
if the mosfet is driven the motor, why the L7805 is hot? (could be hot the IRF3205...)
how can I get cold the L7805?

Thanks for your help, this is my first post.

Regards

l7805 regulator circuit

My friend, I think you missed the point!

The driving voltage of the MOSFET and the power supply of the F86 are two different things.

Note the following: The L7805 is a constant power supply to your PIC, therefore regardless the PIC operation it will continue output to the PIC. These devices are disipating a lot of power and a good approach on designing such circuits is to put an aluminum heat sink.

But you can also follow this configuration: Moving down from 24V DC to 5V DC is a 19V drop that can make your IC capable to cook eggs! Try designing a three stage voltage stepper. First step will drop voltage from 24V to 15V. Second step from 15V to 9V and third one from 9V to 5V. By using this configuraion you will have less power disipation. You will ofcource need to use aluminum heat sink to all three ICs, but now the heat will be much less. I guess that there are devices like L7815, L7809 or similar values.

Trust me, it will work.

And always remember: Your motor is drived by the MOSFET that is drived ( open/closed) by the PIC. There is no way that the voltage through the PIC is ending in the motor!

D.

19v to 5v drop resistor value needed

Yes, I know that it's true but when I use a resistor in the place of the motor the L7805 is cold, and when I use the motor then it's hot.
I will try all that you said. Thanks for you help.

irf3205 power suply

Is the resistor value resembles the resistive load of the motor? If i.e. you use a resistor of 1MΩ but the load of the motor is 300MΩ the power disipation on the L7805 will be less as less current will be flowing through the resistor.

D.