Operating Instructions; Introduction; Circuit Description - Elenco Electronics XP-650 Instruction Manual

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. Set the voltage switch to 0-20V if the voltage required is under 20V. This assures cool operation of the
heat sinks. Adjust the voltage control to the 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. The power should be turned off during this operation.
5. Adjust the current limiting control to maximum counter-clockwise position. Switch your equipment on.
The overload light will glow if more than 50 milliamps is drawn. Increase this control until the light goes
out and stays out during normal use. Your equipment is now protected from high current surges. An
alternate method of adjusting current limiting is to short the output and adjust the current to a desired
value. Remove the short. This will now limit the current to your setting.

Introduction

The Model XP-650 and XP-750 are solid-state DC power supplies, continuously variable from 0 to 40 volts.
Two current ranges are available, 0-20V @ 3 amps and 0-40V @ 1.5 amps. The units are precisely held to
the desired output voltage by a special regulating circuit. Maximum output current is externally adjustable
from .05 to 3 amps. An overload indicating lamps glows when current approaches limiting conditions. This
circuit is designed to protect the power supply against shorts or excessive demand. It also protects the
equipment from possible damage due to high surge currents. This supply is ideal for use in school labs,
service shops or anywhere a precise DC voltage is required.

Circuit Description

The Elenco Models XP-650 and XP-750 use the same power and regulator circuits. The only difference is
in the display functions. The Model XP-650 uses a 0-40V and a 0-3A analog meter. Model XP-750 has two
digital meters to read voltage and current. The voltmeter has better than 1/2% accuracy. The current meter
has better than 1% accuracy.
Both models basically have two independent regulated power supplies. These supplies, when placed in
series, will give 0-40 volts @ 1.5 amps. When they are placed in parallel, the output voltage will be 0-20
volts @ 3 amps.
The basic circuits of these supplies consist of 1) The power source, 2) The regulator and 3) The readout cir-
cuits. These circuits are shown in Figure 1 and will be discussed in detail in the following paragraphs.
Figure 1 Block Diagram of 0-20V Power Supply
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