To prevent use of a card by precisely detecting an illicit card, called a metal cared for putting mutual contact point terminals such as a power source terminal and a ground terminal of an IC card in an electrically continuing state.
Respective values of resistances R1 and R2 are selected, so that end-to-end voltage of the resistance R2 by an output current I1 (5 mA) of the ground terminal when the metal card is inserted and + 5 V is supplied to the power source terminal of the card 30 from a transistor Q21 slightly exceeds a voltage VBE (0.7 V) between a base and an emitter of a transistor Q4. Thus, the end-to-end voltage of the resistance R2 by the current I1 at metal card inserting time becomes VBE or more of the transistor Q4, and the transistor Q4 is turned on. The end-to-end voltage of the resistance R2 by the current I1 at normal IC card inserting time becomes VBE or less of the transistor Q4, and the transistor Q4 is turned off. Thus, correctness of the IC card can be precisely detected.
MUROI JUNICHI
WAKABAYASHI DAIKI
