| 摘要 |
1,191,559. Facsimile apparatus; transistor amplifiers. STEWART-WARNER CORP. 26 July, 1968 [28 July, 1967], No. 35832/68. Headings H3T and H4F. In a facsimile recorder, in which a pair of electrodes electrolytically mark a recording medium, an input signal is applied to a bridge circuit which is connected to means for controlling the current through the recording electrodes in accordance with any unbalance of the bridge, and means responsive to variations in the electrode current are provided to adjust the bridge towards the balanced condition. As shown, the recorder is designed to operate with a data transmission system employed with conventional telephone lines, the data output being applied to input 20 and comprising voltages positive relative to the ground line 22. The input is applied to an emitter follower transistor 12 which together with the 12-volt positive power supply and emitter resistor 30 forms a first arm of a bridge circuit. The other arms of the bridge comprise resistors 32 and 34, resistor 40, and resistors 42 and 44. A differential amplifier 50 comprising two transistors 54 and 56 is connected to the bridge junctions 46 and 48 and its output is applied to a darling- ton-pair amplifier comprising 2 transistors 76 and 84 which control the current supplied to a movable electrode 86 which marks an electrolytic recording medium placed on a fixed electrode 88 which is grounded. The bulk of the electrode current flows through emitter resistor 44 which also forms part of one arm of the bridge so that when the input signal increases the voltage at bridge junction 46 increases, the recording electrode current increases and the voltage at bridge junction 48 increases thus providing negative feedback which tends to rebalance the bridge. |
