99 Washington Street
Melrose, MA 02176
Fax 781-665-0780
TestEquipmentDepot.com
B
K
PRECISION
Instruction Manual
Model 1794 High Current Power Supply
TABLE OF CONTENTS
SECTION PARTICULARS PAGE NO.
1 GENERAL INFORMATION 1
2 SPECIFICATIONS 2
3 INSTALLATION 3
4 OPERATING INSTRUCTIONS 5
5 SERVICE INSTRUCTIONS 10
6 PART LIST 16
7 SCHEMATICS 21
8 CIRCUIT DIAGRAMS 28
SECTION - 1
GENERAL INFORMATION
1.1 DESCRIPTION :
The 1794 High Current Regulated D.C. Power Supply is completely solid and suitable
for bench operation or standard 19" rack operation. It is a well regulated constant
voltage / constant current supply which delivers 0-32V at 0-20Amps and can be
adjusted continuously throughout the output range. When the supply is used as a
constant voltage source the front panel VOLTAGE controls can be used to limit the
output voltage. When the unit is used as a constant current source, the front panel
CURRENT controls can be used to limit the output current. The unit will automatically
cross over from constant voltage to current mode and vice-versa if the output
current or voltage exceeds these limits.
Output voltage and current are continuously monitored on two front panel meters.
The load terminals and remote sense terminals are provided on the front panel.
Either the positive or negative output terminal may be grounded or the power supply
can be operated floating at upto a maximum of ±300VDC above ground.
1.2 OUTPUT ON/OFF SWITCH :
The output voltage and Current can be preset without connecting the power supply
to the load. With the OUTPUT ON/OFF switch in the OFF position, the maximum
voltage and current limits can be set. Pressing the OUTPUT ON switch connects
the output of the power supply to the load.
1.3 LIMIT SETTING :
The voltage and current limits can be set when the output is not connected to the
load. With the OUTPUT ON/OFF switch in the OFF position and the LIMIT switch
pressed, the voltage and current limits can be set with the front panel VOLTAGE
and CURRENT potentiometers.
1.4 REMOTE PROGRAMMING ( With External 5K Pot ) :
The output voltage of the unit can be programmed between 0 to 32V by means
of an external remote programming voltage resistor. An external resistance
programming selector link is provided on the rear panel for this purpose.
1.5 REMOTE SENSING :
The degradation in regulation which occurs at the load due to voltage drop in the
load leads can be eliminated by using the power supply in the remote sensing
mode operation. The remote sensing mode is selected by a push switch on the
front panel.
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SECTION - 2
SPECIFICATIONS
OUTPUT VOLTAGE : 0-32V DC continuously variable with coarse
and fine voltage controls.
LOAD CURRENT : 0-30 Amp max., continuously variable with
coarse and fine controls.
CONSTANT VOLTAGE MODE
REGULATION
LINE : Less than ± 0.01% ± 2mV for ±10% change in
line voltage.
LOAD : Less than ± 0.01% ± 2mV for load change from
zero to full load.
RIPPLE & NOISE : Less than 1mV rms max.(20 Hz - 20 MHz)
CONSTANT CURRENT MODE
REGULATION
LINE : Less than ± 0.05% ±10mA for ±10% change in
line voltage.
LOAD : Less than ±0.05% ±10mA for change in output
voltage from 0 volts to maximum output voltage.
RIPPLE & NOISE : Less than 6mA rms.
OVERLOAD PROTECTION : Automatic overload and short circuit protection.
TRANSIENT RESPONSE : 100µsecs to within 10mV of set output voltage
for load change from 10% to 90%.
STABILITY :
Total drift within 8 hours,after : ± 0.2% ± 10mV in constant voltage mode.
warm up under constant line, : ± 0.5% ± 10mA in constant current mode.
load & temp.
PANEL METERS : Digital panel meters (marked V for voltmeter and
A for ammeter) are provided with an accuracy of
± 3 counts.
MODE INDICATION : Respective LED lights up when the unit is
working in CV or CC mode.
SET LIMIT/ ON-OFF : Push Switches for Limit ( V & A ) and output
CONTROLS ON/OFF setting.
OUTPUT CONTROLS : Single turn coarse and fine voltage and current
controls are provided on the front panel
EXTERNAL PROGRAMMING : Output voltage can be programmed by a variable
resistance of 5K ( Pot )
OPERATING TEMPERATURE : 0-40°C.
INPUT VOLTAGE : 120/230V AC, ± 10% 47 - 63Hz single phase.
DIMENSIONS : 19"(W ) x 15.75"(D) x 5.24"(H).
WEIGHT : 50 lbs. Net.
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Test Equipment Depot - 800.517.8431 - 99 Washington Street Melrose, MA 02176
FAX 781.665.0780 - TestEquipmentDepot.com
SECTION - 3
INSTALLATION
3.1 INITIAL INSPECTION :
As soon as the power supply 1794 unit is unpacked, inspect for any damage that
may have occurred during transit. Save all packing material until inspection is
completed. If any damage is found, notify the carriers immediately. Our authorised
representatives should also be notified.
3.2 PHYSICAL CHECK :
This check should confirm that there are no broken knobs or connectors, that the
cabinet and panel surfaces are free of dents and scratches and the meters are not
scratched and cracked.
3.3 ELECTRICAL CHECK :
The power supply unit 1794 should be checked against electrical specifications.
An in-cabinet performance check will verify proper operation.
3.4 INSTALLATION DATA :
The power supply unit 1794 is shipped ready for bench operation. It is necessary
only to connect the unit to a rated source of power (120V AC) and it is ready for
operation.
3.5 LOCATION :
The power supply 1794 unit is fan cooled. Sufficient space should be kept around
the unit while in operation, so that unit do not remain in confined space or close to
another heating source.The ambient temperature of the area around the unit should
be less than 40°C.
3.6 RACK MOUNTING :
The unit is in rack size and can be rack mounted in a conventional rack using
standard mounting screws and the rack attachments optionally supplied.
3.7 INPUT POWER REQUIREMENTS :
The power supply 1794 unit may be operated continuously from input
voltage of 120V or 230V AC 47 - 63Hz power source. It is factory wired for 120V AC
operation.
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3.8 INPUT TAP SELECTION FOR 230V OPERATION :
In case of 230V Mains operation please ensure that shorting links on the Tap Selector
board is changed to 230V, marked on the PCB for both Mains Transformer &
Auxilary Transformer. as per the following diagram.
TAP SELECTOR BOARD
Please make sure the input varistor is replaced by 20D 361K or equivalent for
230V Mains Operation at the Input of EMI Filter located at bottom side of the unit.
3.9 REPACKAGING FOR SHIPMENT :
To ensure safe shipment of the power supply 1794 unit, it is recommended that the
package designed for the unit be used. The original packaging material is reusable.
Be sure to attach a tag to the unit specifying the owner, and the fault observed with
a brief description.
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Test Equipment Depot - 800.517.8431 - 99 Washington Street Melrose, MA 02176
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SECTION - 4
OPERATING INSTRUCTIONS
4.1 TURN ON SETTING PROCEDURE :
The following procedure describes the use of controls and indicators for
Constant Voltage and Constant Current Mode of Operation.
CONSTANT VOLTAGE (CV) MODE :
a. Set ‘POWER ON’ Switch & keep the OUTPUT ON/OFF switch to OFF
position ( ).
b. Press LIMIT switch and adjust the VOLTAGE controls till the desired voltage is
indicated on Voltmeter ( ).
c. Press OUTPUT switch to ON position and observe that CV LED lights ( )
CONSTANT CURRENT VOLTAGE (CC) MODE :
a. Turn off the suppy. Short circuit the output terminals of the power supply
& turn on the supply.
b. Keep the OUTPUT ON/OFF switch in the OFF position ( ).
c. Press LIMIT switch and adjust the CURRENT controls till the desired current is
indicated on Ammeter ( ).
d. Press OUTPUT switch ON position and observe that CC LED lights ( ).
e. Remove the short circuit.
4.2 SET LIMIT CONTROL (VOLTAGE AND CURRENT) :
To preset the output Voltage and Current, proceed as follows :
a. Set the OUTPUT switch to OFF position ( ) ( Release Position ).
b. Press the LIMIT switch and adjust the desired output voltage with the
VOLTAGE control potentiometers ( ).
c. Release the LIMIT switch, set the OUTPUT switch to ON position and check
the output voltage on the voltmeter ( ).
d. Set the OUTPUT switch to OFF position ( ).
e. Press the LIMIT switch and adjust the desired output current limit with the
CURRENT control potentiometers ( ).
f. Release the LIMIT switch, set the OUTPUT switch to ON position and check
the output current on the ammeter ( ).
g. Set the OUTPUT switch to OFF position ( ).
h. Connect the load to the Output terminals and set the OUTPUT switch to ON
position ( ).
4.3 LOAD CONNECTIONS :
The load should be connected to the power supply output terminals using separate
pairs of connecting wires. This will minimize mutual coupling effects between loads
and will retain full advantage of the low output impedance of the power supply.
Each pair of connecting wires should be as short as possible and twisted or shielded
to reduce noise pick up. (If a shielded pair is used, connect one end of the shield to
ground and leave the other end unconnected).
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4.4 Positive or negative voltage can be obtained from this supply by grounding either
one of the output terminals or one end of the load. Always use two leads to connect
load to the supply, regardless of where the setup is grounded. This will eliminate
any possibility of the output current return paths through the power source ground
which would damage the line cord plug. This supply can also be operated upto
±300V DC above ground, if neither output terminal is grounded.
4.5 REMOTE SENSING :
Warning : Do not Operate the Unit in 'REMOTE SENSE' mode without
ensuring proper 'REMOTE/ 4 TERMINAL' Connections. Serious
Damage to Unit or Equipment under test could result.
Remote sensing is used to maintain good regulation at the load and reduce the
degradation of regulation which could occur due to the voltage drop in the leads
betweeen the power supply and the load. Remote sensing is accomplished by
connnecting the load to remote sense terminals on the front panel. The leads from
the sensing( +S and -S) terminals to the load will carry much less current than the
load leads and it is not required that these leads be as heavy as the load leads.
However, they must be twisted or shielded to minimize noise pickup.
For reasonable lengths of load leads, remote sensing greatly improves the
performance of the supply. However, if the load is located at a considerable
distance from the supply, added precautions must be observed to obtain
satisfactory operation. Notice that the voltage in the load leads subtracts directly
from the available output voltage and also reduces the amplitude of the feedback
error signals that are developed within the unit. Because of these factors, it is
recommended that the drop in each load lead does not exceed 0.5Volts.
NOTE : Due to the voltage drop in load leads, it may be necessary to
readjust the current limit in the remote sensing mode.
Observance of the precautions in para. 4.8 and 4.9 will result in a low dc output
impedance at the load. However, another factor that must be considered is the
inductance of long leads.This causes a high ac impedance and could affect the
stability of the feed back loop seriously enough to cause oscillations. If this is the
case, it is recommended that the following actions be taken:
a) Adjust R6 to remove oscillations, or to achieve best possible transient
response for given long load lead configuration.
b) If performing adjustment in step (a) above does not remove oscillation,
disconn-ect output capacitor C3 ( L1791-FP-CNT-0603 PCB ) and connect
a capacitor having similar characteristics (approximately the same capaci
tance, the same voltage rating or greater, and having good high frequency
characteristics) directly across load using short leads.
Readjust R6 as in step (a) above after making this change.
Test Equipment Depot - 800.517.8431 - 99 Washington Street Melrose, MA 02176
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4.6 OUTPUT CAPACITANCE :
Internal capacitor C3 ( L1791-FP-CNT-0603 PCB ) connected across the output
terminals of the power supply, helps to supply high current pulses of short duration
during constant voltage operation. Any capacitance added externally will improve
the pulse current capability, but will decrease the safety provided by the constant
current circuit. A high current pulse may damage load components before the
average output current is large enough to cause the constant current circuit to
operate.
The effects of the output capacitor during constant current operation are as follows:
a.The output impedance of the power supply decreases with increasing frequency
b. The recovery time of the output voltage is longer for load resistance changes.
c. A large surge current causing a high power dissipation in the load occurs
when the load resistance is reduced rapidly.
4.7 REVERSE VOLTAGE LOADING :
A diode CR1 is connected across the output terminals. Under normal operation,
the diode is reverse biased (anode connected to the negative terminal ). If a reverse
voltage is applied to the output terminals ( positive voltage applied to the negative
terminal), the diode will conduct, shunting current across the output terminals to the
forward voltage drop of the diode. This diode protects the series transistor and the
output electrolytic capacitors.
4.8 REVERSE CURRENT LOADING :
Active loads connected to the power supply may actually deliver a reverse current
to the power supply during a portion of its operating cycle.
An external source cannot be allowed to pump current into the supply without loss
of regulation and possible damage to the output capacitor. To avoid these effects,
it is necessary to preload the supply with a dummy load resistor so that the power
supply delivers current through the entire operation cycle of the load device.
4.9 EXTERNAL PROGRAMMING :
Remote external programming can be achieved changing the external program
link on rear panel and connecting a variable resistor of 5K across the terminals as
shown on the rear panel.
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OPERATORS SAFETY SUMMARY
The general safety information in this part of the summary is for both operating &
servicing personnel. Specific warnings and cautions will be found throughout the
manual where they apply, but may not appear in this summary.
TERMS IN THIS MANUAL :
CAUTION : Statements identify conditions or practices that could result in
damage to the equipment or other property.
WARNING : Statements identify conditions or practices that could result in
personal injury or loss of life.
TERMS AS MARKED ON EQUIPMENT :
CAUTION : Indicates a personal injury hazards not immediately accessible
as one reads the markings,or a hazard to property, including the
equipment itself.
DANGER : Indicates a personal injury hazard immediately accessible as one
reads the marking.
POWER SOURCE : This product is intended to operate from a power source that
does not apply more than 130V rms between the suply conductors or between
either supply conductor and ground. If the Internal Tap is selected for 230V AC
operation, then the input voltage should not be more than 250V rms. A protective ground connections by way of the grounding conductor in the power cord is
essential for safe operation.
GROUNDING THE PRODUCT : This product is grounded through the
grounding conductor of the power cord. To avoid electrical shock, plug the
power cord into a properly wired receptacle before connecting to the product
input or output terminals. A protective ground connection by way of the
grounding conductor in the power cord is essential for safe operation.
DANGER ARISING FROM LOSS OF GROUND : Upon loss of the protective
ground connection, all accessible conductive parts (including knobs and controls
that may appear to be insulating) can render an electric shock.
USE THE PROPER POWER CORD :
Use only the power cord and connector specified for your product.
Use only a power cord that is in good condition.
Refer cord and connector changes to qualified service personnel.
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Test Equipment Depot - 800.517.8431 - 99 Washington Street Melrose, MA 02176
FAX 781.665.0780 - TestEquipmentDepot.com