| 摘要 |
PURPOSE: To protect a field effect transistor for a power from an excess voltage while applying a large current driving capability by providing a second means for preventing a first means from supplying currents when the voltage value of a load terminal is smaller than the voltage value of a second power supply terminal, or when the second power supply terminal is detached from the second means. CONSTITUTION: When the positive supply voltage of a power supply terminal 1 is beyond the safe operational range of an H side driving circuit, the Zener drop voltage of a Zener diode 13 is increased sufficiently for generating electronic avalanche in the Zener diode 13, and voltages at the both gate and drain edges of a field effect transistor 8 for a power are limited. When the driving voltage is positive, a diode 12 separates the driving voltage of a driving node 6 from the power supply terminal 1, and when the driving voltage is negative, the Zener diode 13 prevents the driving voltage from being transmitted to the power supply terminal 1. When the size of the driving voltage is beyond the Zener drop voltage of a Zener diode 15, electronic avalanche is generated, and the destruction of the gate oxide film of the field effect transistor 8 for a power is prevented. |
