the output pulses for the attached buck converter have spikes and decreased with inductive load, switching frequency is 50 khz

 

Do you have capacitors on the "load supply" at the MOSFET?

 

That's likely due to stray inductance and capacitance in the circuit.
A small resistor in series with a small capacitor from the MOSFET output to ground should minimize that.
Start with about a 50Ω resistor in series with a 100nF capacitor.
Adjust their values for minimum spike amplitude.

 

Do you have capacitors on the "load supply" at the MOSFET?

no i don't.

 

A small resistor in series with a small capacitor from the MOSFET output to ground should minimize that.

what is the output that you mean? from Mosfet Drain to ground?

 

Would that capacitor reduce the ripple in output voltage, the ripple is high 1.5 v?

 

what is the output that you mean? from Mosfet Drain to ground?

The output to the inductor, which is shown as the MOSFET Source in your schematic.
The Drain goes to the supply so why would you consider that an output?

Would that capacitor reduce the ripple in output voltage, the ripple is high 1.5 v?

No.
The output ripple is determined by the switching frequency, the value of the inductor and the output capacitor, and the load current.

 

Would that capacitor reduce the ripple in output voltage, the ripple is high 1.5 v?

No it will reduce the ripple on the input. You need a capacitor close to the MOSFET.

The ripple seems high. It is a function of Frequency L1, C6 and Rload (R1). The LC makes a low pass filter to reduce the ripple.
I don't know the voltage or current. Increasing C6 will help the ripple. Adding a second cap will cut the ripple to 1/2.

 

The output to the inductor, which is shown as the MOSFET Source in your schematic.
The Drain goes to the supply so why would you consider that an output?

but this will increase stability of the input voltage and i don't want to increase stability by adding capacitor, i increase it by controller design

 

The ripple seems high. It is a function of Frequency L1, C6 and Rload (R1). The LC makes a low pass filter to reduce the ripple.
I don't know the voltage or current. Increasing C6 will help the ripple. Adding a second cap will cut the ripple to 1/2.

why is the ripple high, it should be very small according to calculation , it should be 4.2e-4

 

You know that L and C are in the formula. Also F^2.
Please post a scope picture of the ripple.
If C6 is low quality there will be ripple. C6 has ESR which will increase the ripple. (enteral series resistance) Also it has ESL. Normally C6 is chosen for its ESR and "current rating at 100khz". Some caps have a 60hz ripple current rating and a 100khz ripple current rating.

If the inductor is under rated for current it might be saturating. This will increase the ripple!

 

If the inductor is under rated for current it might be saturating. This will increase the ripple!

the load draw around 3.5 A while the inductor didn't get hot so i think it is rated. also i reduced the current to 1 A the ripple decreased but not too much

 

What does the ripple look like? Is the noise at 50khz or 300hz?
------edited-----
I see 0.15V ripple at 50khz.

 

but this will increase stability of the input voltage and i don't want to increase stability by adding capacitor, i increase it by controller design

No.
Those small values of R and C for a snubbing circuit at the MOSFET output will have no significant effect on the loop stability.

 

R=100ohm ,c 100nf works and removed spikes.
Thanks