Multi Output Instrument Power Supply
The other transformer produces an output of 12-0-12v at its secondary terminals. The centre tap is grounded like in the previous case. The other two terminals of the secondary are fed to a bridge rectifier constructed using diodes. The rectified output is filtered by using capacitor C5 and C6 fed to IC7 and IC. The IC7-8 which is are 3 pin voltage regulators gives an output of ±8v. These two voltages are fed to the signal generator. The -8v source output is fed to the temperature network, also as voltage reference.
It is also necessary to produce a +12v and -12v supply for application to operational amplifiers. This can be conveniently done by means of 12v zener diodes. The output of the bridge rectifier is clamped to +12v and -12v respectively using two zener diodes. The zener output is fed to the operational amplifier supply terminals. Since the supply to
the operational amplifiers need not be very efficiently regulated to + 12v, the use of zener diodes proves economical.
For the testing of electronic components a voltage of above 50 V is required. This can be achieved by means of a voltage quadrupler circuit. It consists of four diodes and four electrolytic capacitors. The secondary ungrounded terminal of the 12-0-12v is connected to the quadrupler circuit. The output of the quadrupler circuit is 68v with respect to ground.
The two transformers can be controlled by the power supply switch PS 1 The switch also controls a neon lamp, which lights up once the transformer supply is on. The instrument is prevented against short circuits-excessive voltages by fuses. When the a.c. power supply exceeds beyond 250 volts resulting in any overload or damage, the fuse F1 blows out thus saving the rest of the circuit within the instrument.
The a.c. power is drawn from a 3 pin plug connected to a cable of 1000 mm to activate the instrument. The ground terminal in the 3 pin plug is earthed to the chassis, while the other two terminals are connected to the primaries of the two transformers.
Errata- D7 one end should be grounded.
Power supply part of the mesureall instrument i built 20 years back, ocr errors may be there, like I - 1 and 0 - O, other errors also uncorrected, reference textbooks, appn notes, datasheets
List Of Components For Power Supply.
1. Transformers - X1-6-0-6 (500 ma), X2-12-0-12 (500ma)
2. Semiconductors - IC6-7805, IC7-7808, IC8-7908, D1 to D10-IN4007, D11 and D12 - 12v, 1W, Zener
3. Resistors. - R1 and R2 - 100E 1/2 W CFR
4. Capacitors. - C 40v , C5 and C8 - 1000 Mfd , C1 - 2200 Mfd, C5 and C7 - 0.1 Mfd, C9 to C12 - 100Mfd
5. Miscellaneous - F1-250ma, N1-Neon, 3-Pin Mains Chord.
(OCR of a Electronic Typed Project Report of mine. May have some errors)
Pages: 1· 2