MC34063 frequency

Dhaval Raval

Prodigy 100 points

Other Parts Discussed in Thread: MC34063A

What frequency should i set for operating MC34063?

over 10 years ago

0 Ron Michallick over 10 years ago

TI__Guru**** 165206 points

Dhaval,

The frequency of MC34063A varies with load. Ton is set by CT cap, see figure 1 in data sheet. Ton can be cut short by current limit. Toff is variable.
Frequency should be less than 100 kHz for all expected loads. Highest frequency should occur at maximum load. There is no minimum frequency.

0 Dhaval Raval over 10 years ago in reply to Ron Michallick

Prodigy 100 points

Thanks Ron but i am confused . In calculation of Ton+Toff=1/f . so what should i choose the freq there? How to choose it?

0 Ron Michallick over 10 years ago in reply to Dhaval Raval

TI__Guru**** 165206 points

Dhaval,

The design formulas in data sheet set the operating point for minimum VIN and maximum output current to be the point where inductor current switches between continuous and discontinuous inductor current. Therefore 'f' is the maximum frequency while in regulation.

At other loads and input voltage operating frequency will be lower.

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MC34063 frequency