Circuit input Analysis

[rocky79]

Hello fellows,

I am having hard time understanding what the greened part of the circuit does.

Vin can change from 0 to 28v and it may experience voltage spikes.

My question is how do you analyze this circuit and what is the purpose of this darlington transistor.

Thanks in advance

 

[audioguru]

The darlington amplifies the current from the 1k resistor that feeds the 28V zener diode then sends about 26.5V to the next regulator.

 

[dougy83]

The darlington & zener limit the voltage to what audioguru said, the caps and inductor filter out a bit of the noise presented to Vin.

 

[indulis]

28Vmax feeding a 28V zener isn't going to do much. The emitter will track 2 Vbe's below Vin.

 

[rocky79]

Thanks guys, now i have to figure out the equation for that low pass rc filter.