a power cutter , an oscillator , a counter , a s - r latch , and a hall bias are further disposed inside a dc motor driving circuit so that current consumption of the dc motor driving circuit is reduced significantly under a standby mode . when the counter detects that a received pulse width modulation signal stays at a low electrical level over a predetermined time , the counter triggers the s - r latch so as to activate a disabling signal of the power cutter for shutting down most elements until the pulse width modulation signal returns to a high electrical level . with the aid of the built - in hall bias , space for externally coupling the hall bias is saved , and moreover , a hall sensor retrieves a dynamically - adjusted power and currents so that remarkable current consumption is saved under a standby mode .