| 摘要 |
<p>PURPOSE:To improve a characteristic and make a unit small-size by integration, by constituting a current supply circuit by an operational amplifier. CONSTITUTION:Terminals 1 and 2 are connected to the telephone line, and terminals 3 and 4 are connected to the earth and power source -48V respectively. The loop including operational amplifier 19, resistance R21, transistor TR9, and resistance R23 becomes a voltage follower, and input Z of the impednace Z converter dependent upon R13 and follower 15 is high, and output Z is low, and therefore, DC Z between terminals 1 and 3 is determined by R5, 7 and 11. Similarly, DC Z between terminals 2 and 4 is determined by R6, 8 and 12, and the current from the power source is flowed to the DC load between terminals 1 and 2 as a constant- voltage current supply circuit. In respect to a sound band signal, no AC current is flowed to amplifier 19 and TR19, and AC Z between terminals 1 and 3 is looked very high and has no influence upon the frequency of the sound signal transmitted and received through the telephone line. Further, since terminal 3 and the emitter of TR9 have the equal potential for power source noise, noise is not generated between terminals 1 and 2.</p> |
