Abstract: A fan driver is provided to drive a DC brushless fan. The fan driver has a pulse generator for receiving a signal indicating the phase of a rotor in the fan from a Hall element and generating two pulse signals whose phases are inverted by about 180.degree.. Two driving units activated by the two pulse signals, respectively, are provided to alternatively apply current to the two coils thereby generating magnetic fields to rotate the rotor of the fan. Two switch elements are connected to the two driving units so that anti-electromotive voltage generated by one of the two coils can be transferred to the other coil.

Abstract: A motor drive circuit includes an amplifying and comparing circuit, a multiplexer, an input control circuit and a drive pulse generator. The amplifying and comparing circuit receives an output signal from a Hall element and generates an amplified output signal. The input control circuit detects whether the Hall element is a Hall sensor or a Hall IC for controlling the multiplexer to have its output from either the Hall IC or the amplifying and comparing circuit. The drive pulse generator has an input connected to the output of the multiplexer, and has four outputs connected to four MOS transistors respectively for generating clock signals to drive the four MOS transistors to provide driving current to the motor.

Abstract: A variable length cache system keeps track of the amount of available space on an output device. The capacity of the cache system is continuously increased so long as it is less than the available output space on the output unit. Once the size of the cache system exceeds the available output space on the output unit, which is less than the total space available on the output unit by a predetermined amount, the contents of the cache memory are flushed or written to the output device and the size of the cache memory is reduced to zero.