Ir2117 to drive buck converter problem

[mah]

i used ir2117 to drive mosfet for dc dc buck converter the input for the driver is pwm from microcontroller i attached the circuit but there is a problem the output from this driver is 9v pure dc not pwm like the input

[mah]

so what is the solution?

[mah]

lets talk about the last method using a transistor ? how to do this?

[mah]

will BC549 be able to do this job as BJT? I also have IRFZ48 I need to adjust the configuration to work with.

[georges80]

You need to firstly tell us what you are trying to do...

What frequency and duty cycle are you planning to drive the FET? What is the FET switching (load)?

Using a transistor as shown works fine to turn on the FET, but turnoff is based on the pullup resistor and most FETs have fairly high gate capacitance which means turns off time is slow such that the FET will spend time in the linear region. This may or may not be an issue depending on the frequency & duty cycle you are running at.

cheers,
george.

[mah]

I am trying to drive n mosfet for buck converter that's all i want to do added to all previous talk
duty cycle is changing from 0-90%
frequency =100KHZ

[georges80]

What's the load?

A Buck needs a catch diode and also an inductor which aren't shown in your schematic. You would also need voltage sense back to the uC to regulate. Overall, using a uC to create a buck driver is not optimal since you have a slow control loop (software) and only 'digital' steps in adjustment (pwm duty cycle). Typically a 'real' switcher IC uses a saw tooth ramp and comparators to enable the duty cycle to be adjusted in much finer 'steps'.

100KHz is relatively high, a npn with a pullup resistor will have quite slow turn off time and if the FET is switching high currents then the FET will dissipate more heat (loss) while switching off. You do realize FETs have high gate capacitance?

Either choose a FET that can be switched at logic levels or find a driver that has logic level inputs. Or better yet, buy an off the shelf switcher IC.

cheers,
george.