DC Boost regulator MC34063 circuit in LTSPICE

[rj88a]

Hi, I'm hoping someone might be able to help me.

I am trying to simulate a circuit involving the MC34063 that's illustrated in the datasheet (attached as JPG) using LTSpice. It's a simple 12V -> 28V DC-DC converter.

I downloaded the model (attached) for the MC34063 so that I could use it in LTSpice. It seems to be ok when I tell it where the files for the model are (C:\DATA)

Have also attached the LTSpice model.

The problem is that I don't get 28V at the output - I get around 11V! I'm very new to this so have probably done something silly. I'm also not sure what values the input and output capacitors should be.

Any help is very much appreciated.
Thanks

 

[D.A.(Tony)Stewart]

Pin5 is the feedback of output scaled down to match the internal Vref=1.25V
If Pin5 is 1.25V then there is an error R ratio values, otherwise something else

 

[eetech00]

hi

Try this one...it worked for me..

eT

 

[rj88a]

Thanks to you both, all working now!