HP (Hewlett-Packard) 6205B ユーザーズマニュアル

4-21 Stage Q3 contains a feedback equalizer net-

work, C5 and R30, which provides for high fre-
quency roll off in the loop gain in order to stabilize
the feedback loop. Q17 establishes a stable emit-
ter bias potential for error amplifier Q3. Emitter
follower transistor(s) Q4 (and Q5) serves as the
driver (and predriver) element for the series regula-
tor.

4-22 CURRENT LIMIT CIRCUIT

4-23 The current limit circuit limits the output

current to a preset value determined by the setting
of R81. Switch S2B selects the proper sampling
resistance to maintain an equal voltage drop acress
the current sampling network in both ranges.

4-24 When S2 is set to the 20 Volt position, R54

and R55 are connected in parallel. When S2 is set
to the 40 Volt position, the current sampling net-
work consists solely of R54. Note that in the

twenty Volt range, twice as much current can be
delivered as in the forty Volt range. Since the
twenty Volt range has a sampling resistance equal

to half the value of that for the forty Volt range, an
equal sampling resistor voltage drop is obtained in
both ranges. This also applies to S2 in the 6206B.

4-25 R81 sets the bias of Q10, and thus, the

threshold point at which Q10 conducts and current

limiting begins. If this threshold is exceeded, Q10

begins to conduct, forward biasing CR16 and send-

ing a turn-down signal to the series regulater via
the driver. If the current through the current sam-

pling network decreases below the threshold point,
Q10 turns off and no longer affects the operation of
the supply.

4-27 The reference circuit (see schematic) is a

feedback power supply similar to the main supply.
It provides stable reference voltages which are
used throughout the unit. The reference voltages
are a 11 derived from smoothed dc obtained from the
full wave rectifier (CR22 and CR23) and filter cap-
acitor C10. The +6.2 and -6.2 voltages, which are
used in the constant voltage input circuit for com-
parison purposes, are developed across temperature
compensated Zener diodes VR1 and VR2. Resistor

R43 limits the current through the Zener diodes to

establish an optimum bias level.

4-28 The reference circuit consists of series reg-

ulating transistor Q9 and error amplifier Q8. Out-
put voltage changes are detected by Q8 whose base
is connected to the junction of a voltage divider

(R41, R42) connected directly across the supply.

Any error signals are amplified and inverted by Q8
and applied to the base of series transistor Q9.
The series element then alters its conduction in the
direction, and by the amount, necessary to main-
tain the voltage across VR1 and VR2 constant. Re-
sistor R46, the emitter resistor for Q8, is connected
in a manner which minimizes changes in the refer-

ence voltage caused by variations in the input line.
Output capacitor C9 stabilizes the regulator loop.

4-30 The meter circuit provides continuous indi-

cations of output voltage or current on a single

multiple range meter.

The meter can be used either

as a voltmeter or an ammeter depending upon the
position of the METER section of switch S2 on the
front panel of the supply. This switch also selects
one of two meter ranges on each scale. The meter

circuit consists 

METER-RANGE switch S2, vari-

ous multiplying resistors and the meter movement.

4-31 When measuring voltage, the meter is placed
directly across the output of the supply between

the +S and -S terminals. With the METER section
of S2A in the higher voltage position (terminals A2

and A10) multiplying resistors R60, R61, R72, and

the parallel combination of R73 and R87, are in
series with the meter. For low output voltages, the

METER switch S2A can be set to the first position

(terminals 1 and 9) which removes R61 from its

series position allowing a larger percentage of the

output voltage to be felt acress the meter.

4-32 When measuring current; the meter circuit is

connected across the current sampling resistor

network as shown on Figure 4-2 and indicates the
output current that flows through the network. The
RANGE section S2B connects the appropriate re-
sistance in series with the meter so that its maxi-
mum deflection range is full-scale in the high cur-
rent (low voltage) operating mode and half-scale in
the low current (high voltage) operating mode. This

circuit obviates the need for a dual current scale
which would be necessary since the voltages drop-
ped across the current sampling network in both
operating modes are equal for proportional currents.

4-3