Abstract: A commutation control circuit provides a substantially periodic series of commutation signals to a conventional motor sequencer. The control circuit includes a frequency-to-current converter that receives the series of commutation signals and outputs a current that has a magnitude proportional to the average period of the series of commutation signals. The proportional current is then used to charge and/or discharge a known capacitance after a back-EMF sensor determines the appropriate starting time of a delay period. The capacitance and the proportional current are selected such that the proportional current charges the capacitance to a selected voltage level to trigger a commutation signal after the appropriate delay period.

Abstract: A disconnect switch circuit for disconnecting an under-voltage battery from a hard disk drive connected between a voltage supply line and ground includes a MOSFET device connected between the battery and the voltage supply line, control means responsive to the supply voltage on the voltage supply line for generating a control signal powering the gate of the MOSFET switch. The control signal turns on the MOSFET switch when the supply voltage is in normal condition and turns off the MOSFET switch when the supply voltage drops below an under-voltage limit, thereby beginning head retract in the hard disk drive.

Abstract: A motor control circuit is used to generate positive and negative voltage supply rails. The motor control circuit contains two halfbridges, each of which contains a pair of MOSFETs connected in series, each of the MOSFETs being formed without the customary short between the source and substrate (body). In one embodiment, a common node between the MOSFETs is connected to a positive voltage supply rail, and the body regions of the MOSFETs are connected to a negative voltage supply rail. The positive and negative voltage supply rails are biased by charging respective capacitors, using the positive and negative voltage spikes that appear at the outputs of the motor control circuit as the outputs switch from a low state to a high state, and vice versa.

Abstract: A moving media storage apparatus including a head actuator driven by flyback emf generated by a spindle motor. The spindle motor is driven by V.sub.BAT, whereas the head actuator includes a head-control circuit and an H-bridge MOSFET construction which is driven by V.sub.BAT or V.sub.CC during normal operation, and a head-retract circuit which is driven by V.sub.AUX after a battery failure. A pair of bipolar transistors are provided in the head actuator for increasing the amount of time V.sub.AUX is available to drive a head-retract procedure.

Abstract: A push-pull output stage for driving a motor which provides an auxiliary power supply Vaux above supply voltage Vcc by using highside MOSFETs which do not have source-body shorts, and by connecting a capacitor to the poles of the motor through rectifying diodes which output flyback pulses to the capacitor. Damage to the highside MOSFETs is prevented by limiting the voltage on the capacitor using a zener diode. The push-pull output stage increases the driving potential applied to the motor be eliminating the need for an isolating Schottky diode between the output stage and a power source. Back emf continues to supply energy to Vaux even after Vcc is removed.

Abstract: An insulated gate bipolar transistor (IGBT) gate driver circuit with a push-pull output stage which provides current sinking to two power supply rails. Current sinking to a low impedance power supply rail (GND) via a high current NPN bipolar transistor provides fast IGBT turn off. A PNP bipolar transistor forward biased emitter-base junction in series with an N channel field effect transistor provides current-limited current sinking to a higher impedance power supply rail (V.sub.EE). The on resistance of the N channel field effect transistor can be chosen to set the maximum current drawn from the higher impedance V.sub.EE power supply rail. This current-limiting avoids the need for a second low impedance power supply. The transition of the output of the driver from ground to V.sub.EE is only a function of the output voltage output by the driver. It is not a function of any timed switching of transistors.

Abstract: A switch interface circuit provides control voltages to the gate of a power MOSFET while protecting the power MOSFET from breakdown caused by transient signals and over-voltage. In one embodiment, a large JFET acts as gate-source shunt and a small JFET serves as a current source to turn the power MOSFET off when the turn-on current is removed. The JFET gate-drain and gate-source breakdown provides a voltage limitation to protect the MOSFET from gate overvoltage. Alternatively, Zener diodes and MOS transistors are used in lieu of the JFET for shorting the power MOSFET gate to source during turn-off and limiting its gate to source voltage during turn-on.