ELECTRIC POWER APPARATUS FOR DRIVING INDUCTIVE LOAD AND PROTECTIVE APPARATUS AGAINST PARASITIC EFFECT DUE TO NEGATIVE IMPULSE OF POWER SUPPLY IN MONOLITHIC INTEGRATED CIRCUIT INCLUDING CONTROLLER FOR THE ELECTRIC POWER APPARATUS

摘要

PURPOSE: To prevent break of a parasitic transistor by providing a shield element against negative impulses of a power source voltage in its voltage limiter. CONSTITUTION: If power apparatuses Q3 and Q4 are in a conducting state and an inductor L is assumed to be in a charged state, then any negative impulse on the voltage Vs executes the extinction of the arc on the power apparatuses Q3 and Q4 at the negative base voltage of the transistor Q3. At the same time, a voltage Vc at the common collector rises up to a clamp voltage set by a Zener diode Z2, and two breakdown stresses reverse to the power apparatuses Q3 and Q4 are produced, but these stresses are prevented by a voltage limiter constituted with transistors Q2 and Q5, a resistor Rc and a Zener diode Z1. Under this condition, the transistor Q2 is kept at a negative potential at its base by a voltage Vs, so that the arc is extinguished because the base is kept at a negative potential by the voltage Vs, and a positive over-voltage Vc on the load L ignites the transistor Q5, power apparatuses Q3 and Q4 in Darlington configuration are returned to a conducting state, and a positive over-voltage is discharged to the ground. By doing this, the parasitic effect caused by the negative impulse of the power source voltage can be eliminated.