xp-800, takietam
[ Pobierz całość w formacie PDF ]
POWER SUPPLY
MODEL XP-800
TWO AC VARIABLE VOLTAGES; 0-120V and 0-40V @ 7A,
PLUS 0-28VDC @ UP TO 10A
Instruction Manual
Elenco Electronics, Inc.
Copyright © 1991 Elenco Electronics, Inc.
Revised 2002 REV-I 753206
INTRODUCTION
The XP-800 contains three output voltages: 0 to 28VDC, 0 to 40VAC and 0 to 120VAC. The maximum current
from the 28VAC supply is 10 amps. At 10 amp load current, the maximum attainable voltage is 20VDC. The
maximum current from the 40VAC supply is 7 amps. At 5 amp load current, the maximum voltage attainable
is 38VAC. The maximum current from the 120VAC supply is 2 amps. A 10 amp circuit breaker on the back
panel protects the 28VDC supply. A 3 amp circuit breaker on the back panel protects the 120VAC supply. This
circuit breaker also protects the 40VAC supply by limiting the current to the power transformer. In addition, the
XP-800 contains a 5 amp fuse on the AC input. This fuse is located on the back panel.
All three supplies are controlled by the Voltage Adjust knob on the front panel. The unit contains two digital
meters to simultaneously display the voltage and current of any supply. Which supply is displayed is controlled
by a knob on the front panel. This knob selects only which output is displayed. All three supply voltages are
present at all times.
SAFETY PRECAUTIONS
CAUTION:
When removing cover, always disconnect the power cord from the AC socket. Service repair should
be done by qualified personnel who are knowledgeable of electrical hazards.
Certain safety precautions must be observed when this power supply is used with external circuits that are
connected to AC power lines. There is always some danger when working with electrical equipment or circuits
that operate at hazardous voltages. You should thoroughly familiarize yourself with the equipment before
working on it. High voltages may appear at unexpected points in defective equipment.
The XP-800 is equipped with a three wire line cord which grounds the chassis to the power line ground.
DO
NOT CUT OFF OR DISABLE THE GROUND PLUG.
The 28VDC and 40VAC circuits are isolated from the AC input via the power transformer. When working with
other equipment, this may not be the case. Always be familiar with the equipment rating. Keep in mind that
defective equipment can have dangerous voltages at unexpected places.
SPECIFICATIONS
Input
Input Voltage
120VAC
Current Protection
5 Amp fuse
28VDC Supply
Output Current
10 Amps max.
Output Voltage
28VDC max. for light loads
20VDC max. for 10 Amp load
Ripple
Less than .2 Volts RMS at 10 Amp load
Current Protection
10 Amp Circuit Breaker
Meter
0 to 28VDC, .1 Volt resolution
0 to 10 Amps, .1 Amp resolution
40VAC Supply
120VAC Supply
Output Current
7 Amps max.
Output Current
2 Amps max.
Output Voltage
40VAC max. for light loads
Output Voltage
120VAC max.
38VAC max. for 5 Amp load
Current Protection
3 Amp Circuit Breaker
Current Protection
3 Amp Circuit Breaker
Meter
0 to 120VAC, 1 Volt resolution
(on transformer primary)
0 to 2 Amps, .1 Amp resolution
Meter
0 to 40VAC, .1 Volt resolution
0 to 7 Amps, .1 Amp resolution
-1-
OPERATING INSTRUCTIONS
WARNING
The 28VDC output is filtered with a very large capacitor. If the DC supply is unloaded or lightly loaded, the
capacitor will maintain the voltage on the output terminals even after the voltage adjust knob is turned to zero.
Before connecting any equipment, this voltage should be checked. If any voltage is present, the capacitor
should be discharged by connecting a resistor across the output terminals. Use a 10 ohm (or greater) 5 watt
(or greater) resistor.
Connect the power supply as follows:
1. Check the voltage rating of the equipment to be powered. Care must be taken not to exceed this rating.
2. Plug the line cord into a 120V 60Hz outlet.
3. With the power supply turned off, connect the load to the desired voltage output.
a.
28VDC Supply
- Connect the positive lead of your equipment to the red terminal on the front panel
and the negative lead to the black terminal.
b.
40VAC Supply
- Connect your equipment leads to the yellow terminals on the front panel.
c.
120VAC Supply
- Plug your equipment into the 3 wire power outlet located on the back panel.
The 120 Volt Supply is connected to the AC input and grounded to the chassis. The 40VAC and 28VDC are
isolated from the AC input by the power transformer. Since the 28VDC and 40VAC supplies use the same power
transformer, they must not be connected to each other.
WARNING - ANY SHORT BETWEEN EITHER
TERMINAL OF THE 28VDC SUPPLY AND EITHER TERMINAL OF THE 40VAC SUPPLY MAY RESULT IN
DAMAGE TO THE POWER SUPPLY
. If properly isolated, the different outputs may be used at the same time.
However, care must be taken that the total current does not exceed the circuit breaker ratings.
4. Set the meter switch to the supply to be monitored.
5. Turn the voltage adjust knob to zero (fully counterclockwise) and turn the power on.
6. Turn the voltage adjust knob clockwise to set the desired voltage. The numbers on the voltage adjust dial
represent percent of maximum voltage, not actual voltage.
If the power supply is overloaded, either the 3 amp or 10 amp circuit breaker may trip. When this happens, the
button in the center of the breaker will pop out. To reset the breaker, push the button back in. Both are thermal
circuit breakers so you may have to wait a while for the breaker to cool before it will reset. If the output voltage
does not return after the power supply has cooled, check the 5 amp fuse located on the back panel.
-2-
CIRCUIT DESCRIPTION
As shown in Figure 1, the basic circuits of the XP-800
Power Supply are 1) the power source, 2) the power
transformer, 3) the bridge rectifier and 4) the meter
circuits. Each of these circuits will be discussed below.
POWER
SOURCE
120VAC
POWER
TRANSFORMER
40VAC
POWER SOURCE
The power source consists of the variable transformer
T1. This transformer is fed by the input AC line. The
output of the transformer may be varied from zero to
the full 120VAC input. The output of the transformer is
fed through circuit breaker CB1 to the power outlet plug
J2. To sense the current, the shunt resistor R19 is
placed in series with the power outlet.
BRIDGE
RECTIFIER
28VAC
METER CIRCUITS
Figure 1
POWER TRANSFORMER
The power transformer T2 is a center tapped 3 to 1 step down transformer which steps the 0-120VAC from the
variable transformer down to 0-40VAC. This output is fed to the bridge rectifier BR1 and, through shunt resistors
R23 through R26, to the 0-40VAC output terminals. The power transformer also serves to isolate the 40VAC
and 28VDC from the AC input.
BRIDGE RECTIFIER
The bridge rectifier BR1 serves as a full wave rectifier to convert the center tapped 0-40VAC to 0-28VDC.
Capacitor C6 filters the bridge output and reduces the ripple, at 10 amps, to approximately .2V RMS. This
output is fed through circuit breaker CB2 to the 0-28VDC output terminals. Shunt resistors R20-R22 sense the
current in the ground circuit of the DC supply.
METER CIRCUITS
As shown in Figure 2, the meter circuits consist of 1)
the scalers, 2) the meter switch, 3) the AC - DC
converter, 4) the meter assembly and 5) the meter
power supply.
SCALERS
METER
SWITCH
AC - DC
CONVERTERS
SCALERS - There are two sets of scalers, one for
voltage and one for current. The voltage scalers divide
the various output voltages down to voltages suitable
for input to the voltmeter. Resistors R8 and R7 divide
the 28VDC output down to approximately 540MV. Similarly R4 and R5 divide the 40VAC output and R1 and R2
divide the 120VAC output. Resistors R2 and R5 are variable resistors to allow calibration of the meter. The
current scalers divide the voltage across the shunt resistors down to voltages suitable for input to the ammeter.
For the 28VDC supply, resistors R9 and R18 divide the voltage across shunt resistors R20 - R22. Similarly, R6
divides the voltage across shunt resistors R23 - R26 for the 40VAC supply and R3 divides the voltage across
shunt resistor R19 for the 120VAC supply.
Figure 2
METER
POWER
SUPPLY
METERS
METER SWITCH - The meter switch selects which supply is monitored by the voltmeter and ammeter. Switch
sections A, B and C select the proper current scaler, ground, and voltage scaler to feed to the AC - DC
converter. Switch section D selects the proper decimal point for the voltmeter.
-3-
AC - DC CONVERTER - There are two AC - DC converters, one for the voltmeter and one for the ammeter. The
voltmeter converter consists of 1/2 of a 358 op-amp U1A configured as a unity gain amplifier. Since the amplifier
is biased at ground, only the positive portion of the AC signal from the 40VAC and 120VAC voltage scalers is
passed through the amplifier. The output is then attenuated 20:1 by resistors R12 and R28, filtered by the low
pass filter R13 and C4 and fed to the voltmeter. The DC signal from the 28VDC voltage scaler passes through
the amplifier unchanged. The ammeter converter, U1B, performs the same function as the voltmeter converter.
Since the output of the 28VDC current scaler is negative, U1B is configured for a gain of –1. The output is
attenuated 52:1 by resistors R16 and R27.
METERS - Meter operation centers around the 7107 integrated circuit (IC). This chip contains a dual slope A/D
(analog to digital) converter, display latches, seven segment decoder, and display drivers.
The input of the 7107 IC is fed to an A/D converter. Here the DC voltage is changed to a digital format. The
resulting signals are processed in the decoders to light the appropriate LED segments.
Timing for the overall operation of the A/D converter is derived from a 40kHz external oscillator. The IC divides
this frequency by four and the resulting clock pulses are used to drive its decade counters. It is then further
divided to form three convert-cycle phases. The final readout is clocked at about 2.5 readings per second.
The digitized data is presented to the display as four decoded digits (seven segments) plus polarity. The decimal
point position on the display is determined by the selector switch setting.
A/D Converter - Any given measurement cycle performed by the A/D converter can be divided into three
consecutive time periods, autozero (AZ), the integrate (INTEG) and read. A counter determines the length of
the time periods. The integrate period is fixed at 1,000 clock pulses. The read period is a variable time that is
proportional to the unknown input voltage. It can vary from zero counts for zero input voltage to 2,000 counts
for a full scale input voltage. The autozero period varies from 1,000 to 3,000 counts. For an input voltage less
than full scale, autozero gets the unused portion of the read period.
During the autozero cycle, the accumulated off set voltage errors in the converter are measured and stored as
a voltage on the external autozero capacitor. This voltage is used to correct for the offset voltage errors during
the read cycle.
During the INTEG cycle, the INTEG capacitor is charged up for 1,000 clock pulses (100ms.), see Figure 3. The
charging rate is determined by the unknown input voltage. At the end of the integrate cycle, the voltage on the
capacitor is proportional to the unknown input voltage.
During the read cycle, the INTEG capacitor is discharged at a constant rate. The time required for the discharge
AZ
INTEG
READ
AZ
+.20
Figure 3
.15
Dual Slope A/D Converter
.10
.05
0
COUNTER OUTPUT
0
1000
100MS
0
500
1000
1500
2000
is therefore proportional to the unknown input voltage. This time is converted to a digital format by counting the
number of clock pulses that occur during the discharge.
METER POWER SUPPLY - The digital meters require +5VDC. This is supplied by the meter power supply
consisting of a 7805 regulator IC U2, a step down transformer T3, a diode bridge D4-D7, and filter capacitors
C1-C3.
-4-
[ Pobierz całość w formacie PDF ]