4 12V to 10V buck converter using 555 timer IC

This  buck converter is driven by 555 timer IC and converts 12V dc from a battery to 10V dc. The 555 IC  (operated in astable mode ) generates pulses of voltages of 83.3% duty cycle. This pulses turns the transitor on and off and drives the inductor L (buck converter circuit), and as a result generates 10V dc output. For this configuration,

Ra =240K

Rb =4.7K

C =10nF

Q = TIP41C or any of the same specs

Cout = 2200uF (higher the better)

You can add 1N4740A zener diode for output stability.