Farnell TSV 70 - Page 9

and hence maintains zero voltage between VT5 and VT6 bases.
The output voltage Vo is therefore defined as:
Vo
Vz3 (R8 + T2). (Pl + P2)
R8.T2
70 volts 5 amps Range.
Overload protection is provided by VT1l and 12.
T4 in parallel is connected to R49 and to VTl2 base. R33 is
connected to the l0 volt auxiliary ail. When the output
current is low, the vOltage across R49 is low. VT1l is
biased off and VTl2 is biased on. As output current increases
the voltage across R49 increases, and the voltage at VTl2 base
becomes more positive. This continues until the base of
VTl2 is sufficiently positive to cause VTll to begin to conduct.
At this point, the voltage across R30 begins to increase until
D6 becomes forward biased, and feeds current to VI9 base.
drives VT9 further into conduction, and limits the drive
available to emitter follower VT7 and hence to the series
regulator transistors. This action causes a fall in output
voltage, and v)5 to be driven off. D5 then ceases to conduct
and control is now taken over by VT1l and vTl2. On further
increase of load, the output voltage falls, and output
current remains constant. The output characteristic of the
supply is therefore constant voltage for loads less than the
limit set by P3, the front panel current limit potentiometer
and Constant current for loads in excess of the limit.
P3 with
This
With switch Sl in the 70 volts 5 amps position, the
positives of capacitors C21 and 22 are connected via regulators
VTl7-23 to the positive output terminal. The negatives of
c21 and 22 are connected via fuse F2, and switch SID to the
output of regulators VT24 - 30. The positives of C25 and 26
are connected via regulators VT24 - 30 to the negatives of C21
and 22 as above. The negatives of C25 and 26 are connected
via fuse F3, resistor R67, and switch S3 to the negative output
terminal. The input to regulators VT17-23 is as before, and
the input to regulators VT24 to 30 is from Pin 12, circuit
board No.2, via SlA, Thus the two regulator systems are
connected in series and circuit board No.l controls the upper
5
The function of circuit board No,l is the same as on the
35 volt l0 amp range, and this is the master voltage and
current limit control of the suPply. The contro1 circuitry
of circuit board No.2 is merely to hold the voltage at
regulators VT2 4 - 30 output at half the terminal output
voltage.
Dl03 and l04, and ci0l are a full wave rectifier
reservoir capacitor system fed from a 36-0-36 volt trans former
winding and supplying D.C. voltage to Z101 and zl02 via Rl0l.
This provides a +10- 0- -5 volt supply for control amplifier
Consisting of VTl0l, l02,, 103, and emitter follower VTl4.
VT104 drives series regulators VT24-30 The base of vTl0l
is connected to the output of this regulator and vTl02 base
regulators VTl7-23, and circuit board No,2 controls the lower
regulators VT24-30.
is connected to the centre of the potential divider Rll3 and