| 摘要 |
PROBLEM TO BE SOLVED: To reliably detect an open trouble of an antenna of a radio transmitter. SOLUTION: An ECU 31 at a vehicle side in a vehicle smart control system actuates an H-bridge circuit 5 composed of four transistors T1-T4 to drive an antenna for radio-transmitting signals to a portable machine. The transistor T3 in the ECU 31 has a current detecting transistor T3s forming a current mirror circuit with the transistor T3. At a diagnosis execution mode, each of the transistors T1-T4 is controlled so as to make a current flow in the transistor T3 through the antenna 3, a current flowing in the current detecting transistor T3s is detected as an antenna current i using a current detecting resistor 15, and an open trouble is decided as defective in the antenna 3 if the voltage Vm across the resistor 15 is lower than a threshold voltage Vth because no antenna current i is made to flow. COPYRIGHT: (C)2008,JPO&INPIT
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