Service manual

• After closing switch 'S', the linear in time increasing current IT, , will charge
capacitor C.
• Opening switch 'S' will generate a counter-e.m.f. in coil L, trying to maintain
current IT. This is possible via diode D (this diode is also called 'freewheel
diode'). So after opening 'S', the magnetic energy stored in coil L will be
transferred to electrostatic energy in capacitor C. The VIN will only supply current
during the time that 'S' is closed while a constant current is flowing through RL.
• VBAT is directly proportional with VIN and the time that 'S' is closed and reverse
proportional with period time 'T'. Therefore, by changing the duty cycle, it will be
possible to control VBAT.
Figure: Main supply circuitry