help for MC34063 converter IC circuit

[matin-kh]

Hi everyone,
I want to use a MC34063 IC to convert 20 vdc to 8 vdc, but my problem is that I can't calculate the parameters. according to attached picture I have the equations but I don't know what is "ton" or "toff" or "fmin" and what is the Vripple of my circuit!, could you please help me?
Regards
Matin

 

[KlausST]

Hi,


As with every IC: The manunfacturer give enough ducumentation, information, software, calcuation examples:

MC34063A is from ON Semiconductor.

goto their website: https://www.onsemi.com/PowerSolutions/product.do?id=MC34063A

then go through: "Technical Documentation & Design Resources "

And:
A switch mode controller is not a simple circuit. Not for beginners. You need a lot of experience and follow the design rules.
Forget to run it on a breadboard.

Klaus

 

[smijesh]

Your requirement is step down conversion (20VDC to 8VDC)
t on/t off = duty is the duty cycle ( Duty = 50% or more generally )
fmin is the minimum frequency
Vf is the diode forward voltage drop (.5V)
CT is oscillator frequency setting capacitor you can vary the PWM frequency by varying CT value
V ripple is the ripple voltage present in the output, you can have decided the ripple by varying Co(output capacitor)
L min is the minimum inductance required
Hope it will help you

Read the data sheet carefully everything is given