Elenco Electronics XP-620 Instruction Manual

POWER SUPPLY

MODEL XP-620

ElencoTMElectronics, Inc.

Copyright © 2002 ElencoTMElectronics, Inc. Revised 2003 REV-E 75320A

Instruction Manual

SPECIFICATIONS ON XP-620 POWER SUPPLY

Input Voltage 110-130VAC
Output Voltage 1) 1.5-15VDC @ 1A

(at 120V input) 2) –1.5 - –15VDC @ 1A

3) 5VDC @ 3A
Output Regulation 200mV each supply
Line Regulation 100mV each supply
Ripple Max 5mV RMS
Current Protection 1A limit 2-15VDC

3A limit 5VDC

Short Protection 1A limit 2-15VDC

3A limit 5VDC

Output Impedance .025W each supply

OPERATING INSTRUCTIONS

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 AC outlet.

3. Adjust the voltage control to desired voltage. Load variation will have practically no effect on the voltage
setting due to the special regulation circuit.

4. Connect the positive lead of your equipment to the red output terminal and the negative lead to the black
terminal when using the positive supplies. For the negative voltage use the yellow terminal.

5. Care must be taken not to exceed the current reading, as the supplies will turn themselves off if overheated.

6. The Model XP-620 has an added feature of having the positive and negative supplies being able to be stacked
to give up to 30V at 1 ampere. Simply use the negative 1.5 to 15V output (yellow jack) as your minus supply
connection. For the positive connection, use the positive 1.5 to 15V red terminal. This will allow you to obtain
a variable 3V to 30V at up to 1 ampere out.

-1-

CIRCUIT DESCRIPTION

Introduction

Congratulations on your purchase of a very versatile power supply. Our engineers have carefully designed the
XP-620 to give you years of trouble-free performance.

The Model XP-620 Power Supply features three solid-state DC power supplies. The first supply gives a variable
output of positive 1.5 to 15 volts at up to 1 ampere. The second gives a negative 1.5 to 15 volts at 1 ampere.
The third has a fixed 5V at 3 amperes. All supplies are fully regulated. A special IC circuit keeps the output
voltage within .2V when going from no load to 1 ampere. The output is fully protected from short circuits. This
supply is ideal for use in school labs, service shops or anywhere a precise DC voltage is required.

The Positive 2-15V Power Supply

Figure 1 shows a simplified circuit diagram of the positive supply. It consists of a power transformer, a DC
rectifier stage and the regulator stage.

120VAC

Input

Transformer

120V to 17V

17VAC 20VDC

Simplified diagram of positive power supply

AC to DC

Converter

Figure 1

Voltage

Regulator

1.25 - 15V

Regulated

Output

Transformer

The transformer T1 serves two purposes. First, it
reduces the 120VAC input to 17VAC and 8VAC to allow
the proper voltage to enter the rectifier stages. Second,
it isolates the power supply output from the 120VAC
line. This prevents the user from dangerous voltage
shock, should the user be standing in a grounded area.

AC to DC Converter

The AC to DC converter consists of diodes D1 and D3
and capacitor C5. Transformer T1 has two secondary
windings which are 180Oout of phase. The AC output
at each winding is shown in Figure 2A and 2B.

Diodes are semiconductor devices that allow current
to flow in one direction. The arrow in Figure 3 points
to the direction that the current will flow. Only when
the transformer voltage is positive will current flow
through the diodes. Figure 3 shows the simplest
possible rectifier circuit. This circuit is known as a half­wave rectifier. Here the diode conducts only half of
the time when the AC wave is positive as shown in
Figure 2C. Use of this circuit is simple but inefficient.
The big gap between cycles require much more
filtering to obtain a smooth DC voltage.

Voltage Waveform for Supply

A) Transformer

Winding AB

B) Transformer

Winding BC

C) Output of

diode D1.

D) Output of

diode D2.

E) Total of diodes

D1 & D2.

20V

F) Output of capacitor C1

Ripple depends on load
current (expanded).

Figure 2

Half Wave Rectifier

Figure 3

Full Wave Rectifier

Figure 4

By addition of a second diode and transformer winding, we can fill in the gap between cycles as shown in Figure 4.
This circuit is called full-wave rectification. Each diode conducts when the voltage is positive. By adding the two
outputs, the voltage presented to capacitor C5 is more complete, thus easier to filter, as shown in Figure 2E. When
used in 60 cycles AC input power, the output of a full wave rectifier will be 120 cycles.

Capacitor C5 is used to store the current charges, thus smoothing the DC voltage. The larger the capacitor, the
more current is stored. In this design, 2200mF capacitors are used, which allows about 3 volts AC ripple when
one amp is drawn.

-2-