MC34063 issues

[Medo]

I tried to design 24V to 5V converter around MC34063 but I have stumbled upon some problems.

By all calculations I should get easy 5V but I measure over 8...
Could it be problem that I am using only few mA usually?
Board should work from cca 1-250 mA...
I dare not put PIC on this board before I am sure that it will not go out...

Do you have some generic component values for 24->5 conversion that would work with L=150uH?


Data I calculated is:
    R1=1.2K
    R2=3.6K
    Ct=1500pF
    Rsc=0.68
    L=150uH
    Co=470uF

[Simon]

what is the frequency ?

I put your data into http://dics.voicecontrol.ro/tutorials/mc34063/calculate.php assuming 100KHz and got some very different values, you may want to recheck your calculations

[Medo]

what is the frequency ?

I put your data into http://dics.voicecontrol.ro/tutorials/mc34063/calculate.php assuming 100KHz and got some very different values, you may want to recheck your calculations

70 kHz

[Medo]

Yep, I made "factor of ten" error in my spreadsheet...

Thanks!