A circuit and method protects an emergency head-retract capacitor that regulates
initial charge current using a constant current source. The initial charge current
is applied at power-up to the capacitor until a charging voltage having a desired
threshold level is attained in the capacitor. The charging voltage is monitored
through an analog-to-digital converter by an overall controller that, upon detecting
the presence of the desired threshold level in the capacitor, deenergizes the constant
current source. A voltage pump, which includes a voltage multiplier (doubler),
is then activated to selectively apply regulated charging voltage to thereafter
maintain the desired threshold level. The pump includes a voltage pump controller
that is controlled by a voltage comparator having a reference voltage set to a
desired threshold level. That voltage comparator is also in communication with
the capacitor to measure its present input charging voltage. When the desired threshold
level is met or exceeded at the capacitor, the comparator signals the controller
to deactivate the pump. When the capacitor's charging voltage is less than the
reference voltage, the comparator signals the controller to activate the voltage
pump and, thus, pump the capacitor with regulated voltage.