Bang&Olufsen
INSTRUCTION
POWER SUPPLY SN 17/18
Bang&Olufsen 2
INTRODUCTION The B&O Power Supply SN17 and SN18 are universally applicable power
supply units for application in workshops, schools, laboratories, industrial
undertakings, etc.
The two power supply units are functionally identicaI except as regards
voltage and current range; in the SN17 it is 0...30 V/0 ...2 A and in the
SN18 it is 0...60 V/0 ...1 A.
Output voltage is adjusted through a multiturn potentiometer with an
exchange ratio of approx. 1:6 or it may be resistance programmed,
possibly through the "Remote" socket
Output impedance is very small, <2 mO at DC, and random noise is
extremely low.
Both power supply units are safeguarded against short-circuiting and
overloading, and they may be connected in series or in parallel without
introduction of equalizing resistors.
3 Bang&Olufsen
TECHNICAL DATA Range 0 30 V, 0 2 A (SN17)
0 60 V, 0 1 A (SN18)
Remote Approx. 0.7 kO/V (SN17)
Approx. 1.7 kO/V (SN18)
Adjustment at ±10% alteration of
mains voltage
Constant voltage <±0.01%
Constant current <±0.1 mA
Adjustment at load 0 ...100%
Constant voltage <0.015%
Constant current <±0.1 mA
Temperature co-efficient, constant
voltage <0.002%IOC
Output impedance <0.002 O at DC
<0.2 O at 200 kHz
Ripple and noise, 20 Hz...200 kHz <100 f-lVrms (SN17)
<200 f-lVrms (SN18)
Transient Response, load
30 %-100 %-30 %, nominal
voltage ±10 mV <50 f-lsec.
Indicator instrument
Ranges 0 30 V, 0 2 A and 0 0.6 A (SN17)
0 60 V, 0 1 A and 0 0.3 A (SN18)
Accuracy ±2% of tun scale
Mains connection 110/220 V~ ±10%, 50/60 Hz
Consumption 5...90 W
Temperature range
Dimensions, W x D x H 163 x 210 x 80 mm
Weight 3.3 kg (7.3 Ibs)
Finish Silver grey and blu e enamel
Accessories 1 manual
Subject to alterations
Bang&Olufsen 4
APPLICATION The B&O Power Supply SN17 and SN18 are functionally identical except
as regards voltage and current ranges. Below, the SN17 will primarily be
in focus, and the SN18 will only be mentioned where it deviates from the
SN17. From the factory the device is mounted for 220 V~, but it may
easily be changed to 110 V~ by connecting the mains transformer's two
110 V primary windings in parallel (fig. 1).
nov 1l0V
Fig.!. Changing to 110 V mains voltage.
Device operation appears from figs. 2 and 3.
1. Permanent-magnet moving-coil instrument Full deftection corre-
sponds to indication on the "METER" switch (2).
2. Range switch for the permanent-magnet moving-coil instrument
(1). Output voltage is measured in position "30 V" (SN18:"60 V").
Output current is measured in positions "2A" and "0.6 A" (SN18:
"lA" and "0.3 A").
Fig. 2. Front view of Power Supply SN17.
3. Current adjustment/limitation. lndication corresponds to
maximum output current
4. LED for indication of current limitation.
5. Voltage adjustment with exchange ratio 1:6.
6. Output, insulated from cabinet
7. Chassis bushing connected to cabinet
8. Mains switch.
9. Remote input Output voltage may be programmed with a resistor,
connected to pins 1 and 3, of approx. 0.7 kO/V (SN18: approx.
1.7 kO/V).
10. Mains connection (Euro-plug).
5 Bang&Olufsen
Fig. 3. Rear view of Power Supply SN 17.
Figure 4 indicates the voltage as a function of the load current for
current supply according to the constant-current principle.
°
Without load (RL = 00) I = and E = EO (point A, fig. 4). When a load
resistance is connected the current increases whereas the voltage
remains constant (point B). If the load resistance is reduced the current
increases further, but the voltage remains constant until the current is
equal to lO (point C). At this state the adjustment automatically shifts
from constant voltage to constant current If the load resistanee is
reduced further the voltage drops whereas the current remains constant
(point D). If the load resistance is reduced further the voltage drops
correspondingly until the state in point K is reached, Le. short circuit By
grtdually changing the load resistance from short circuit to no-load
(R = 00) the procedure is repeated, but in the opposite order.
E max. --------------------------1
I
I
I
A (no-load)
Constant voltage I
B C l
l
l
Constant current I
I
I
l
D I
I
I
K (short circuit) I
0,0
lO lmax.
Fig. 4. Load characteristic according to the constant-current principle
Line inclination between any operating point on the rectangular characte-
ristic and the point 0.0 is proportional to the size of the load resistance.
The "critical" value of this, RL = RC = EO/IO, may be chosen at random
between O and 00 by a combination of output voltage ("Voltage") and
short circuit current ("Current"). If the resistanee is greater than RC the
voltage remains constant whereas the current remains constant when the
resistance is less than Re.
Bang&Olufsen 6
Example 1. Constant voltage A test arrangement requires a supply voltage of 24 V, and at this voltage
it has a current consumption of approx. 1 A. Because of the speciill
components in the arrangement the current consumption must not, in
case of defects, exceed 1.5 A.
The meter switch (2) is set at position "30 V". The "VOLTAGE" poten-
tiometer (5) is adjusted to 24 V on the permanent-magnet moving-coil
instrument (1). With the meter switch in position "2 A" the output (6) is
short-circuited and the "CURRENT" potentiometer (3) is adjusted to 1.5
A on the permanent-magnet moving-coil instrument The short circuit is
removed, and then the test arrangement may be connected.
Example 2. Constant current The disengaging time for a small parcel of 100 mA fine fuses with slow-
acting characteristic is desired measured at a current of 400 mA. For the
measurement of the disengagement time an electronic counter is
connected. "Start/stop"-input maximum voltage, e.g. 10 V, mus t not be
exceeded.
The "METER" switch is set at "30 V". The ''VOLTAGE'' potentiometer is
adjusted to 10 V, this may be read on the permanent-magnet moving-coil
instrument The "METER" switch is set at "0.6 A". The output is short-
circuited, and the "CURRENT" potentiometer is adjusted to 0.4 A, which
may be read on the instrument The short circuit is removed, and then
the fuses may be connected directly over the output
Remote programming The output voltage may be resistance programmed through the
"REMOTE" input (9) at the rear of the device.
The programming constant is approx. 0.7 kO/V (SN18: approx.
1.7 kO IV).
The resistance, corresponding to the desired voltage, is mounted in a 5-
pin DIN-piug between pins 1 and 3. When the plug is plugged in, the
voltage potentiometer (5) is switched off simultaneously.
Note! The output voltage may momentarily go up to approx. 40 V (SN18:
approx. 80 V), when the remote-plug is plugged in.
Programming by potentiometer If a potentiometer of e.g. 22 kO is used instead of a permanent resis-
tance it will be possible to vary the output voltage within the range 0...30
V. The cable between the " Remote "-input and the potentiometer may
well be several metres long, but in that case it must be screened in order
to avoid too high ripple at the output (fig. 5). A voltmeter with a high
input impedance, e.g. 10 MO, may be connected over the potentiometer
to control output voltage, if necessary.
REMOTE
Fig. 5. Remote programming with a potentiometer.
Programming with a potentiometer This combination provides the possibility of a limited variation range
in series with a resistanee within the voltage range (fig. 6). A 10 kO resistance in series with a 10
kO potentiometer, for instance, produces a voltage range of approx. 7...14
V.
REMOTE
Fig. 6. Remote programming with a permanent resistance.
7 Bang&Olufsen
Connection in parallel of two or As already mentioned, the shift from constant voltage to constant current
more SNl7 units. (or the other way around) takes place automatically. This may be advan-
tageously exploited by connecting two or more units in parallel. At
increasing loads the unit with the highest output voltage will supply the
current consumption until the current limitation steps into action. Then
the unit with the second highest output voltage will supply the additional
current consumption until the current limitation for this unit steps into
action, etc.
+ - D D D
12 V 2A
?B
?C~
+ -
1,5A
1,5A
12,5 V
+
II l2V!
1,5 A 13 V 1,5 A
4,5 A
Fig. 7. Connection in parallel of three SN17 units.
Example 3. Connection in An imaginary circuit requires a supply voltage of 12 V, and it has a
parallel of three SNl7 units. current consumption of 4.5 A. Three SN17 units marked A, B and C are
available. How should output voltage and current limitation on these
three units be set in order to achieve even distribution of the current
consumption?
/5
I4I3 /I /
~2,7 n
4,5 I I /
// EO612
A .10 /
I
o 2 6+ /
4+ /
2+ / L/ RL=-
,
V 14
12 I
1:
Fig. 8. Characteristic for the arrangement in fig. 7.
Output voltages and current limitations are set as indicated in fig. 7. The
units B and C will adjust for constant current and they will supply 1.5 A
each. Unit A will adjust for constant voltage, and it will supply the
remaining current consumption. At a current consumption of 5 A this
unit will also adjust for constant current (fig. 8).
Bang&Olufsen 8
Connection in series of two Two or more SN17 units may be connected in series. Total voltage
or more SN17 units compared to chassis must not exceed 300 V, however. The current
limitation is set at the same value on all units.
30V 1,5 A 30 V 1,5
1,5AA 20 V C 9
DD ID ,
----l
801,2A
V 1 tol
B
+ -
A
Fig. 9. Connection in series of three SN17 units.
Example 4. Connection in series of An imaginary circuit requires a supply voltage of 80 V, and it has a
three SN17 units current consumption of approx. 1.2 A. The current consumption must not
exceed 1.5 A. Three SN17 units are available.
Two of the units, e.g. A and B, are set at 30 Vand the third unit is set at
the remaining voltage, 20 V. The current limitation is set at 1.5 A on all
three units. The units are connected as indicated in fig. 9.
Bipolar voltage supply If two SN17 units are connected in series, as indicated in fig. 10, a so-
called bipolar voltage supply is achieved. The positive and negative
output voltages must be adjusted separately. This also applies to the
current limitation.
D
12 V
D
12 V
+ - + -
A B
+12 V
Fig. 10. Bipolar voltagesupply.
It is often desirable to have tracking between the positive and the
negative voltage. This is possible by connecting a tandem potentiometer
to both "Remote"-inputs (fig. 11).See also "Programming with potentio-
meter".
Fig. 11
Voltage drop over connecting lines The output impedance, measured under the terminal screws, is very low
«2 mG). At maximum load the internal voltage drop will consequently
be <4 mV (SN18: <2 mV), and in the great majority of cases this is
negligible.
9 Bang&Olufsen
When using test lines, on the other hand, the problem gains significant
importance. With a Cu cross-section of 0.75 mm2 the line resistance is
approx. 25 mO/m. With a line length of 1 m the voltage drop is thus
increased by 100 mV at 2 A. Consequently, this matter should be taken
into account, and it is best to use as short and heavy connecting lines as
possible.
Overloading In some instances the cooling profile will not be able to manage the
applied output AT CONTINUOUS OPERATION. This applies especially
when the voltage is <approx. 15 V (SNI8: <approx. 30 V) and the
current is AT TRE SAME TIME >approx. 1 A (SNI8: >approx. 0.5 A).
In such cases cooling profile temperature will increase quite rapidly, and
at approx. 80GC a built-in thermostatic circuit will cause the load current
to be reduced so that the temperature does not increase further.
~+ w
SN17 I SN18
~+ w
10+ ./ 20
° 0,5 1,5 2A IB
° 0,25 0,5 0,75 1A IB
Fig. 12. Load characteristic for SN17/18
In order to reduce the above mentioned limitation to the greatest
possible extent it is absolutely necessary to avoid covering the cabinet
ventilation holes. At any rate, the current supply should be placed as
freely as possible to enhance air circulation at the cooling profile.
Bang&Olufsen 10
DIAGRAM
470.uFT
e5.Æ3
4QV I T C6
cbL, 47..uF
16V
12
C2, 09
ZP05,6
Cl~ C,YCl
51
--E:J--O
TO,63A
Cl'
220V"" 100nF
275V .••• +
C12
10QnF
9/10
A.§LC4 19
122nF
Fig. 13. Diagram, Power Supply SN17
51
--E:J--O
TO,63A
Cl'
2Z0VN lQOnF
275V'"
l
A§L C4
22nF
Fig. 14. Diagram, Power Supply SN18
a:
w
::l
a:
f-
<n
<ti
'"
m
oa:
-o:
C!J
BANG & OLUFSEN a:
""
w
DK-7600 STRUER >-
a:
f-
DENMARK TELEPHONE 07·851122 . TELEX 66529 o
C!J
<Il
CABLE ADDRESS BANGOLUF >-
09-84 3538607
"
<Il
a:
'"
"
z
w
o
;;;
o
W
f-
Z
cc
<L
