Hi, I've designed a boost converter with UC3842.
You see the electrical circuit below.
The problem is that the output should be set to 21 volts, but the output goes to much higher values.
My other problem is to calculate the parts that I have drawn around the green line.
Another problem is that when the formula in the datasheet set is:
F = 1.72 / CR
Calculating the frequency is not the same as what is in the software.

Circuit Profile:
VIN (min)=9v
VIN(max)=18v
VIN(nom)=12v
VOUT=21v
Iout(max)=0.6A
fsw=344KHZ

In addition, the bode diagram of this circuit can be found in the multisim software.
If you can guide.

 

This Application Note should help with your component selection for slope compensation and stability.
Should Q3 be an NPN? I don't see how a PNP will work in that configuration.

 

Thank you for your guidance.
Yes, the Q3 is based on the datasheet type of the PNP:

What do you think is that the circuit output is not constant?
Are these tilt compensating slope parts or error amplifier compensating?

 

What do you think is that the circuit output is not constant?

How long a simulation time are you using? This sort of circuit usually takes a considerable time to stabilise. Initial transients can be large.
Q2, C8, R8 are for slope compensation.

 

As you see in the figure below, the circuit is initially stable.

Then it becomes unstable and unstable

Sometimes the software also gives an error
Multisim Convergence Assistant Log

 

Which circuit node provides the scope trace?
What do you see if the scope is DC-coupled instead of AC-coupled?
I don't use Multisim so I have no idea why the sim becomes 'unstable' or gives an error.

 

The oscilloscope shows the pulse output of uc3842, which shows only a dc line after unstable.

 

No one can help, especially drawing diagrams bode for this circuit in the multisim software