The LM2907 LM2917 series are monolithic frequency to voltage converters with a high gain op amp comparator designed to operate a relay lamp or other load when the input frequency reaches or exceeds a selected rate The tachometer uses a charge pump technique and offers frequency doubling for low ripple full input protection in two versions (LM2907-8 LM2917-8) and its output swings to ground for a zero frequency input