Drive circuit for brushless DC fan motor

Abstract

A drive circuit for a brushless DC fan motor for rotating a rotor (permanent magnet) by a rotating magnetic field produced by turning on/off the flow of electric current to field coils by a signal to control terminals of switch elements in which switch sections are each connected in series with the field coils. When connecting capacitors for absorbing a current spike in parallel with the switch sections of the switch elements, resistors are each connected between the field coil and switch section, through which the capacitors are connected in parallel with the switch sections. A discharge current of the capacitors which absorbed a current spike when turning on the switch elements is passed via the resistors, thereby eliminating a current spike.

What is claimed is:  
     
         1 . A drive circuit for a brushless DC fan motor, comprising: 
 a field coil provided at a stator;    a switch element in which a switch section formed between a power supply side terminal and a ground side terminal is connected in series with the field coil;    a rotor having a permanent magnet;    a capacitor connected in parallel with the switch section for absorbing a current spike; and    a resistor inserted between the field coil and the switch section for discharging the capacitor, 
 wherein the flow of electric current to the field coil is turned on or off by a signal to a control terminal of the switch element to rotate the rotor by a rotating magnetic field produced by the field coil; and  
 wherein said capacitor is connected in parallel with the switch section via the resistor.  
   
     
     
         2 . The drive circuit for a brushless DC fan motor according to  claim 1 , further comprising: 
 a Zener diode connected between a node of the field coil and the capacitor and the control terminal of the switch element or between both ends of the capacitor in a reverse direction of the polarity therebetween.