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2-28
2.5.
THE POWER SUPPLY
The stabilised power supply for the oscilloscope consists of the following:
an input circuit
a converter driver
-
a flyback converter
-
-
a regulator and protection circuit
-
secondary output rectifiers
2.5.1.
Input circuit
The instrument can be set t o operate from the following mains supply voltages: 110 V, 220 V and 240 Va.c.,
these nominal voltages being selected by the mains voltage selector S25 a t the rear of the instrument.
Fuse F1402 protects the instrument against incorrect mains voltage settings or high mains fluctuations.
A thermal fuse F1403 is located in the mains transformer T1406.
The secondary winding of T I 4 0 6 is connected t o the diode bridge V1431, where the input is rectified and
smoothed by capacitor C1452.
The instrument may alternatively be powered by a battery supply of 20
connected via the d.c. input connector X7 a t the rear of the instrument.
battery supply is used, it is applied t o resistor R1460 via the POWER ON switch S21 and connector XI407
If
a
pins 6 and 8. Protection is provided by the 2 A delayed-action fuse F1401. Diode V1436 also safeguards the
input against incorrect polarity of the battery supply. This diode blocks in the event of rev,ersed input.
Resistor R1447 prevents capacitor C1452 being charged to excessive values by spikes that may be present on
the battery supply.
To reduce the current flowing the C1441
ON
switch S21.
a t switch-on, resistor
...
28 V. This battery supply must be
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