Buck boost using 555 timer / PWM - 555

[SZA]

Im currently using a similar circuit to drive a MOSFET. The required frequency is 50kHz, how do i achieve this (calculations / formula)?

IS there any way to obtain variable frequency? (what if we replace the 1k with pot)

[poorchava]

Why an NE555? It's good for many things, but you can make way better SMPS with dedicated chips (starting with a $0.10 MC34063).

[Psi]

TL494 is another useful PWM psu control chip.
You can often salvage them from old electronics, ATX power supplies, car amps, etc.