HP TM 11-6625-2779-14&P manual Power Supply and Series Regulator Schematic No

Section IV

4-35. Now consider the peak detection. (See Figure 7-5)When A3Q14 is turned on and A3Q17 is turned off, no current flows through the meter from the peak detector When A3Q14 is turned off and A3Q17 is turned on, the current path is as shown by the heavy lines in Figure 4-7Diodes A3CR12 and A3CR13 are included to offset the junction drop of A3CR15 and A3CR16 respectively.

4-36. When the average detection and the peak detector are combined in the proper proportion, an equivalent rms response is produced. The advantage of this type of rms detection is fast response.

4-37. POWER SUPPLY AND SERIES REGULATOR (Schematic No. 4)

4-38. The 3555B can be operated from 115V or 230V ac, the internal 48V dry cell battery or from a central office battery (tip negative). When operating from an ac source power is applied through transformer TI and the AC/BAT switch S1 to the rectifier CR1. This rectified

Model 3555B

voltage is filtered by C2 before being applied to the series regulator through J2, S3, CR1 and cable W1.

4-39. The regulator is of the conventional series type with A3Q19 acting as the sensing element and A3CR20 as the reference. Changes in the output level are amplified by differential amplifier A3Q18 and A3Q19. The output of the differential amplifier is amplified by A3Q20 and applied to A3Q21 which controls the conduction of the series transistor A3Q22. The output of this series regulator is held at - 20 volts ±1 volt. The maximum ac ripple and noise on the output voltage is 200μV rms.

4-40. It should be noted that when operating the set from either the battery or from an ac source, capacitor C2 will always be charged whether the set is turned on or not. Caution should be exercised when servicing the power supply.

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