Philips PM 5167 Instruction Manual page 45

44
3.1.5.1 . - -he emitter-follower stage U6/301, 302 acts as an impedance converter.
3.1.5.2. . 'he cascode part U6/303, 305; 304, 306 inverts and amplifies the voltage. The amplification is adjusted with
potentiometer U6/626, wh ile the symmetry is adjusted by means of U6/624 .
. -he total gain (no load operation) amounts to 4.4. The bandwidth then is ca. 56 MHz which corresponds to
, rise time of ca. 20 ns (see fig . 9).
- 'he amplitude response and the step function response is optimal ly compensated by U6/751 and 507
(iee fig. 9).
3. 1.5.3. ' he driver stage consists of emitter-followers U6/307, 308.
3.1 . 5.4. i 'he power output stage operates in AB mode . The output impedance is very low and is terminated by ca.
~
O
n
by means of both series resistors U6/636, 637. A symmetrical adapted attenuator 607, 608, 609 is
c:tive when setting knob O dB/-20 dB to -20 dB .
3.1.5.5. l he d.c. offset voltage to be superimposed to the output signal is fed to the input of the cascode part via
r
~sistor
U6/608. Switch DC OFFSET serves to reverse polarity, while relevant potentiometer DC OFFSET
€
nables the offset voltage to be adjusted conti nuously.
3.1.5.6. Ildicator OVERRANGE U6/351 and lamp 821 indicates overrange of the output amplifier.
landem potentiometers 604b, 604a and 603b, 603a produce d .c. voltages proportional to the momentary
v ,lues of signal ampl itude and DC OFFSET. These d.c. voltages are added via U6/641, 642, 640. Operational
allplifier U6/351 compares the resulting voltage with the fixed reference voltage at U6/643, 644. As soon as
t le threshold value of signal and DC OFFSET 30 V, set by potentiometers AMPLITUDE and DC OFFSET, is
e<ceeded, the comparator amplifies the signal and lamp 821 lights. At lower frequencies, indicator
(iV E R RANG E I ights beforehand and warns for the expected overrange by operating potentiometers
,L.MPLlTUDE or DC OFFSET.
3.1.6.
[le
Supply unit U7
1 he DC supply unit fig. 15 contains two independent and complementary power supplies for a positive and
a negative d.c. voltage of 30 Veach. The output voltage of each power supply is kept constant by means of
a voltage regulation circuit.
-
3.1.6. 1. 1 he voltage regulation circuit for the positive supply voltage consists of:
- an adjustable voltage divider, U7/608/61 011609
- a set point section, consisting of U7/412, 607
- a voltage regulator, consisting of an amplifier U7/351 used as integrator
- a regulating element consisting of a driver transistor U7/301 and a series transistor 351 at the rear of the
instru ment.
- a low-pass filter
3.1.6.2.
f! current regulating-circuit takes over the function of the voltage regulating-circuit. It limits the charging
c ment to a maximum value in case of inadmissible low load resistances (e.g. short-circuit). The current
fl
gulating-circuit for the positive supply voltage consists of:
- a resistor U7/603, which measu res the actual cu rrent
- a stage U7/302, which determines the max. load current and at the same time serves as a reference (base­
emitter voltage)
- a regulating element and a low-pass filter, identical to those of the voltage regulating-circuit.
-
The regulating circuits for the negative supply voltage are arranged accordingly .
The supply voltages are adjusted by means of resistors U7/610 and U7/630.