Patent ID: 7298283
Filing Date: 2007-11-20
Classification: H02P

Abstract:
1. A device for detecting disconnection for use in a stepping motor driver which comprises at least a pair of windings wound in a bifilar turn arrangement and having each one end connected to a DC power source; a pair of switching elements connected to the other end of each winding; a common current detecting resistor connected between each of said switching elements and ground, a drive circuit for forwarding drive signals to each control terminal of said switching elements; a control circuit for supplying said drive circuit with operation signals; a Pulse Width Modulation circuit for providing said drive circuit with pulse width modulated signals; a first reference voltage generator for producing a first reference voltage; and a comparator for comparing a detection voltage applied on the current detecting resistor with the first reference voltage and providing the Pulse Width Modulation circuit with a chopper signal for turning off the switching element in the on condition when detection voltage is higher than first reference voltage, said device comprising a second reference voltage generator for producing a second reference voltage lower than the first reference voltage; a decision circuit for comparing the detection voltage on the current detecting resistor with the second reference voltage to produce an alarm signal when the detection voltage is higher than the second reference voltage; and a disconnection detector for receiving the alarm signal from the decision circuit after the comparator produces the chopper signal to produce a disconnection signal when the decision circuit continues to produce the alarm signal even after the switching element in the on condition is turned off, or when said decision circuit produces the alarm signal over a predetermined period of time or when the accumulated value of the alarm signal exceeds a predetermined value after the switching element in the on condition is turned off.