| 摘要 |
PURPOSE:To protect an output circuit and to obtain a two-way output signal by connecting a base of the 1st transistor (TR) and an emitter of the 2nd TR and further connecting an emitter of the 1st TR and a base of the 2nd TR. CONSTITUTION:When an input signal Vi is supplied, a TR Q11 is turned on and an output signal Vo appears at the 3rd terminal. The voltage level of the output signal Vo is lower than the level of the input signal Vi by a base- emitter voltage Vbe, a TR Q12 reaches a reverse bias and is not operative. When no input signal Vi is supplied and a voltage Va is given to the 3rd terminal, the emitter voltage Ve of the TR Q12 is decided by equation of Ve= Va-Vbe Q12, the TR Q11 is reverse-biased and not destroyed even when the voltage Va rises. When the input signal Vi is supplied, the output signal Vo is obtained and when the voltage Va is supplied, the emitter voltage Ve is obtained as the output signal and two-way signal transmission is applied.
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