Heathkit IP 27 Manual 2

Page 2

This chart is a guide to commonly used types of elec-
tronic components. The symbols and related illustra-

TYPICAL COMPONENT TYPES

tions should prove helpiul in identifying most parts and
reading the schematic diagrams.

RESISTOR

CAPACITOFfl

\PLAYE

su PPRESSOR
SCREEN
GRID
CATHODE

A /FILAMENT

m

TUBE

POTENTIOMETER :3
(CONTROL) '

ELECTROLVTIC
CAPACITOR

N

m
, v
o.
"' 1

MPH

co LLECTOR

ERMITTE
COLLECTOR

EMITTER

TRANSISTORfi

$$é§

RECTIFIER
(DIODE)

( ADJUSTABLE
CORE)

BULB

13

TRANSFORMER
I | (ADJUSTABLE
POWDERED IRON
I I CORE)ARROW 353g
I I INDICATES DIR-
ECTION 0F CORE
I | MOVEMENT To - -
INCREASE INDUCTA CE
TRANSFORMER ILLUMINA

T,

(D

POWER METER
TRANS- 51%?
FORMER W
RECEPTACLE SWITCH
INDUCTOR SPSTCTOG GLE
(COIL) , (1F
.
..__. (7*
DPDT
O
PIEZOELECTRIC SWITCH ,
CRYSTAL SPEAKER (SOTARY) I,//,/,/"%/ 35,
-o-1 i-r "gr/3, o. '77/
0
0
0.0
MICROPHONE
FUSE

W E3

GENERAL L0 OP

EARTH GROUND

D:
17477

CHASSIS GROUND

N OT
CONNECTE

CONDUCTORS

DCONNECTED SH'ELDED

Page 4

Page 2

-HEATHKIT"

INTRODUCTION

The Heathkit Model IP-27 Regulated Low Voltage
Power Supply is a convenient source of low
voltage DC power. It will furnish DC voltages
between .5 and 50 volts, and DC current up to
1.5 amperes. The large front panel meter can
be switched to measure either the output voltage
or the output current; indicator lights Show
which function is being monitored.

Output voltage is selected in 5-volt increments
by the Coarse Voltage switch, and vernier ad-
justments can be made with the Fine Voltage
control. Output current limiting is also selected
in fixed ranges by the Coarse Current switch,
and the Fine Current control is usedfor vernier
adjustments.

Output is taken from the positive (+) andnegative
(-) front panel binding posts, which are com-
pletely isolated from the chassis. A separate
binding post is provided for making connections
, to the chassis. The Power Supply is protected
against overloads by the automatic current limit-
er and the overload relay circuits.

The Power Supply is designed to match other
Heathkit equipment lines in practical, low-
profile styling, including feet for convenient
stacking, and handles on each side of the cabinet
for portability. The cabinet surface is easily
cleaned with soap and water.Since all regulation
and calibration controls are on the rear panel,
they are accessible without removing the cover.

Other features include: Meter scales that are
color matched to the Coarse Voltage andCurrent
range switch markings; the latest features in
solid-state circuitry for cool, dependable opera-
tion; and four-step current limiting, covering a
range of 50 milliamperes to 1.5 amperes. Higher
output capabilities can also be obtained by con-
necting additionalIP-27 Power Supplies in series
or parallel. The attractive styling of this Power
Supply and the excellent regulation make it an
ideal instrument for both the laboratory and the
modern repair shop.

Refer to the "Kit Builders Guide" for complete
information on unpacking, parts identification,
tools, wiring, soldering, and step-by-step as-
sembly procedures.

Page 15

-I-IE.A.THKIT

Page 37

mamms

Hannm mew-m: l v am»: sunny

of?

dummy aEfiuLAYED t v nuwffi su

Summons w
j .m

Figure 4

Set the COARSE VOLTAGE and CURRENT
switches to identical ranges on each Power
Supply. The range should match the current
and voltage to be supplied.

Place a .1 $2 resistor in series with the
positive (+) lead of each Power Supply as
shown. Do not connect the load at this time.

Connect together the negative (-) binding
posts of all Power Supplies.

Touch the positive (+) lead of one Power
Supply to the positive lead of another Power
Supply and note whether a voltage change
occurs on either meter. Then, ifnecessary,
adjust the FINE VOLTAGE control on one of
the Supplies until there is no change in the
voltage indication, on either meter, between
the connected and disconnected condition of
the positive leads.

5.

7.

If there are more than two Power Supplies
being connected in parallel, repeat the pre-
vious step until all Power Supplies have been
adjusted for no change in the connected and
disconnected voltage indication.

Adjust the current controls on each Power
Supply so as to split the load evenlybetween
each supply, once the known load require-
ments have been established.

Connect the load as shown in Figure 4.

This is the proper operating conditionfor Power
Supplies in parallel. Remember that each time
you change the voltage setting of one of the
Power Supplies, you must also change the others
by an equal amount or one Power Supply may
load the others.

Page 20

Page 42

HEATHKIT"

SPECIFICATIONS

LoadRegulation......................

LineRegulation......................

RippleandNO'lse.....................

Transient Response .

.
.
~
~
-
.
.
o
o
.
n
.
c
u
n
.
o

Outputlmpedance....................

MeterSize.........................

Meter CurrentRanges.................

MeterVoltageRanges.................

Power Requirements..................

Dimensions........................

NetWeight.........................

Output variation less than 3:15 millivolts from
no load to full load, for output of .5 to 50 volts
DC, Can be adjusted for no variation at a given
voltage.

Less than .05% change in output voltage with a
5% change in line voltage.

250 microvolts maximum.
Less than 25 microseconds at 1 kHz.

Less than .075 Q from DC to 10 kHz.
Less than .3 (2 above 10 kHz.

3-1/2".
50 ma, 150 ma, 500 ma, 1.5 a.
15 and 50 volts.

105-125 volts, or 210-250 volts, 50/60 Hz, 135
watts at full load (50 V at 1.5 a).

5-1/8 high x 13-1/4" wide x 9" deep.

12 lbs.

C:

The Heath Company reserves the rightto discon-
tinue instruments and to change specifications at
any time without incurring any obligation to
incorporate new features in instruments pre-

viously sold.

THEORY OF OPERATION

Qualifications for a perfect power supply would
include zero internal resistance, a feature that
is theoretically ideal but not pr actically possible.
When a load is connected to the output terminals,
the voltage tends to decrease due to the increased
current flow through the internal resistance. A
common example of this loss due to the internal
resistance of a power supply can be seen when

the lights on a car dim as the engine is being
started. The automobile storage battery, which is
the power supply in this case, contains enough in-
ternal resistance to present reduced voltage to
the car duing the heavy current drainage from
the starter motor. This reduced voltage causes
the lights to dim.

Page 27

HEATHKIT

Page 45

used to adjust the current within the range selec-
ted by the switch. Note that Rcc is shown in
parallel with the Fine Current control in Figure
9 to simplify the description. The schematic
shows this to be a parallel circuit for some
ranges, and series for others.

The current limiting circuit and transistor Q1
will handle overloads that are small or at low
voltage settings. However, the heat caused by
severe overloads could quickly destroy Q1,
therefore a protective relay is used. The coil of
this relay is connected between the reference
voltage power supply and the output terminal. If
the output voltage drops, due to the limiting ac-
tion of transistor Q1, diode D8 conducts current
from the reference voltage power supply through
the relay coil. When sufficient current flows to
produce about 4 volts across the coil, the relay
contacts open the source voltage circuit aheadof
the current limiter.

When the overload is removed, or the DC switch
is changed to the Reset-Standbyposition, capac-
itor C8 charges to operating voltage from the
reference voltage power supply. Without a suf-
ficient voltage drop across the relay coil, its
contacts return to normal and reconnect the main
voltage supply to the output terminals.

VOLTAGE REGULATOR

In the voltage regulator circuit shown in Figure
10, the voltage from the main power supply is
compared with a constant reference voltage in
an error detector transistor. Any difference be-
tween the supply and reference voltage is ampli-
fied by transistor Q3, which controls a pair of
series regulator transistors to restore the cor-
rect voltage output.

Error detector transistor Q2 has its emitter
connected to the main supply voltage, and its
base connected to a constant reference voltage.
If the main supply voltage decreases, the col-
lector current in Q2 also decreases. This causes
a proportionate voltage decrease at the base and
emitter of Q3, and at the bases of series regu-
lator transistors Q4 and Q5. With the decreased
base voltage on these transistors, the effective
resistance (and the voltage drop) between their
emitters and collectors decreases to restore the
output voltage to nearly its original value.

An increase in the main supply voltage would
cause the opposite action to occur to reduce the
output voltage to nearly its original value. In
either case, the regulator action takes place in
a matter of microseconds.

o - '0 *
l l
c 7 2
:1; gas; 5%! REFERENCE VOLTAGE
.0I DETECTOR
BIS VOLTAGE
UNREGULATED
VOLTAGE REGUIBATED
FROM MA N SUPPLY OUT m
AMPLIFIER €323 m5
(-3 (4-)
fl
REFERENCE
POWER SUPPLY
Q 5 R
SERIES 29% 1-
REGULATOR REGULATOR
_ é R51 V
4. vV _
H52 0

Figure 10

Page 28

Page 46

An increase in current drain could still cause a
decrease in the voltage output because of the in-
ternal resistance of the regulator circuit. There-
fore, positive feedback (regeneration) is used
to further reduce the effective internal resist-
ance to zero under this condition.

The circuit shown in Figure 11 provides positive
feedback around error detector transistor Q2 in
the following manner: An increase in load current
causes a greater voltage difference across re-
sistor R24 and DC Regulation control R23. A
portion of this voltage difference is coupled
through R25 to the base of Q2 which in turn de-
creases the internal resistance of the Power
Supply by reducing the series resistance of
regulator transistors Q4 and Q5. The DC Regu-
lation control is adjusted to provide a balanced
output voltage under full current load and min-
imum current load conditions.

Resistor R28 and thermistor R29 supply the
proper bias to transistors Q4 and Q5. The ther-
mistor is physically located to sense any tem-
perature changes in Q5, and automatically ad-
justs the bias to compensate for these changes.
Resistor R51 and R52 help to equalize the emitter
currents in Q4 and Q5.

Resistor R22 and capacitor C7 form a suppressor
network to control the speed at which the error
detector reacts to a change in terminal voltage.
This prevents the regulator circuit from over-
responding to sudden momentary changes in the
output voltage. Capacitor C9 provides further
stability to the regulator circuits and reduces
the AC impedance of the output. Capacitor C10
filters any high frequencies at the output ter-
minals.

HEATHKIT
1200
DC
REGULATION R 25
n 23
R 24
. M , Q)
.33
LOAD
3
J 9
e
02
ERROR
DETECTOR
Figure 11

REFERENCE VOLTAGE POWER SUPPLY

A DC reference of 50 volts is produced by the
reference voltage power supply. Voltage regu-
lation in this supply is obtained from zener
diodes Zl, Z2, and ZS. The regulated DC volt-
age from the reference supply is usedprimarily
to furnish error detector transistor Q2 with a
reference voltage. This standard voltage is used
to sense incorrect output from the power supply
and regulate the voltage drop across transistors
Q4 and Q5.

The AC voltage from the reference voltage
winding of the power transformer is rectified
by diode D1 and filtered by capacitor C1 and re-
sistor R1. The DC voltage is first regulated at
110 volts by zener diode Z1, than at 68 volts by
zener diode Z3, and given additional filtering
by resistor R2, capacitors C2 and C3.

The stabilized voltage is applied to zener diode
Z2 through resistors R9 and R13, and Zener
Current Adjust control R3, which are in series
with the diode. The current in Z2 is adjusted to
around 5 ma, the diodes optimum operatingpoint.
R13 is a meter shunt for measuring zener cur-
rent.