| 摘要 |
<p>PURPOSE:To prevent finely divided components from being destructed by constituting a voltage limiting circuit with a P-channel MOSFET of diode connection to set a clamp voltage in small steps. CONSTITUTION:A clamp level of an output voltage of a voltage limit circuit is decided by the threshold voltage of a P-channel MOSFETQ1 of diode connection. Since a substrate gate of the P-channel MOSFETQ1 is connected in common to a source having a voltage higher than the gate potential at the on-state, the threshold voltage Vthp of the P-channel MOSFET is a comparatively small value and a boosting voltage Vpp' is selected by a comparatively small voltage step. In order to switch the voltage of output terminals Vcc/Vpp' depending on the operation mode, a P-channel switch MOSFETQ8 is provided between the output terminal Vcc/Vpp' and a low-voltage power supply Vcc. In turning on/off the MOSFETQ8 in response to the operating mode of an EPROM, a control voltage formed by the next level conversion circuit is supplied to the gate.</p> |
