Memory card with latch-up protection

Claim 1

A memory card with a built-in semiconductor memory element which immediately stops an overcurrent when a latch-up phenomenon occurs, said memory card comprising: memory means including one or more writable RAMs having CMOS type electric field effect transistors; power source means including an external power source arranged in an external device and an internal power source connected across said memory means; means for connecting said power source means to said memory means including a power source line connecting the one or more RAMs to the external power source, a ground line, an internal power feed line connecting the one or more RAMs to the internal power source, a common power source line which is connected to the power source line and the internal power feed line at a node and diodes for switching between said internal and external power sources; input and output means for inputting and outputting data signals between said memory means and said external device; switch means for connecting and disconnecting said memory means and said power source means, said switch means including two transistor switches connected respectively to the power source line and the internal feed line; a low voltage detecting circuit connected to the one or more writable RAMs said low voltage detecting circuit transmitting a standby signal to cause the one or more RAMs to enter into a standby state when the voltage of the external power source falls below a predetermined voltage; and overcurrent detecting means for detecting the current from said power source flowing through said means for connecting and for opening said switch means when the current exceeds a predetermined value, said overcurrent detecting means including a current detector connected in series with the common power source line and an overcurrent detecting circuit for transmitting an open circuit signal to open the transistor switches when the current detector detects an overcurrent.