Circuit and method for protecting emergency head-retract

Abstract

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.