| 摘要 |
PURPOSE:To prevent a temperature rise by connecting the transmission transistors (TRs) of each terminal device connected in a loop in parallel and inverting the direction of the current of the loop at the transmission mode and the reception mode so as to turn on the transmission TRs during the transmission only. CONSTITUTION:When a host H transmits a data to terminal devices T1-Tn, a TR qr is turned off and a TR qs is turned on. A transmission line comprised of a constant current source I, a host transmission section Hs, a diode Dn, photo diodes D24, D1r and the TR qs is formed and then the TR qs is switched in response to the transmission data, a transmission current l2 flows and it is received (T1r, Tgr). When the host H uses a terminal device T2 for reception, the TR qs is turned off the TR qr is turned on. A reception line comprised of the constant current source 1, a reception section Hr, a diode D2 of the T2r, a transmission section T2s and the TR qr is formed, the TR Q2as is switched by a signal to flow a reception current lr for reception Hr. Thus, the TR Q2s at the terminal device is turned on during the transmission only to prevent the temperature rise.
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