POWER SUPPLY KIT

MODEL XP-15K

Instruction & Assembly Manual

ELENCO

®

Copyright © 2012, 1991 by ELENCO ® All rights reserved. Revised 2012 REV-P

No part of this book shall be reproduced by any means; electronic, photocopying, or otherwise without written permission from the publisher.

753015

INTRODUCTION

Assembly of your XP-15K Regulated Variable Power Supply Kit will prove to be an exciting project and give much satisfaction and personal achievement. If you have experience in soldering and wiring technique, you should have no problem in the assembly of this kit. Care must be given to identifying the proper components and in good soldering habits.

Above all, take your time and follow the easy step-by-step instructions. Remember, “An ounce of prevention is worth a pound of cure”. Avoid making mistakes and no problems will occur.

USE SAFETY GOGGLES WHEN ASSEMBLING THIS KIT!!

SPECIFICATIONS FOR XP-15K POWER SUPPLY

Output Voltage

Output Current

Load Regulation

Line Regulation

0 - 15VDC

0.3A @ 12V, 0.2A @ 15V

0.1V

0.1V

Ripple Max.

0.01V rms

Short Protection IC THERMO

Output Impedance 0.3

Ω

PARTS LIST

If you are a student, and any parts are missing or damaged, please see instructor or bookstore. If you purchased this kit from a distributor, catalog, etc., please contact ELENCO ® (address/phone/e-mail is at the back of this manual) for additional assistance, if needed. DO NOT contact your place of purchase as they will not be able to help you.

Qty.

r 1 r 2 r 1

Qty.

r 1 r 1 r 1 r 1

Qty.

r 8 r 1 r 1

Qty.

r 1 r 1 r 1 r 1 r 1 r 1 r 1 r 1 r 2 r 2 r 1 r 4 r 1

Symbol

R2

R1, R4

R3

Symbol

C2

C4

C3

C1

Symbol

D1-8

U1

D9

Description

Transformer YD-1485

PC board

Heat sink

Knob

Case top

Case bottom

Strain relief 2-wire

Binding post black

Nut binding post

Lockwasher binding post

Binding post red

Screw 2.8 x 8mm

Screw 4-40 x 1/4”

Description

150

Ω 5% 1/4W

2.2k

Ω 5% 1/4W

2k

Ω Potentiometer

RESISTORS

Color Code brown-green-brown-gold red-red-red-gold

CAPACITORS

Description

4.7

μF 50V Electrolytic

220

μF 16V Electrolytic

470

μF 35V Electrolytic

2,200

μF 35V Electrolytic

SEMICONDUCTORS

Description

1N4001 Diode

LM317 Regulator

LED Red

Part #

440111

510002

615009

622009

623061

623062

624002

625031

625031HN

625031LW

625032

641102

641430

MISCELLANEOUS

Qty.

r 2 r 1 r 1 r 2 r 1 r 4 r 2 r 4 r 1 r 1 r 2” r 1

-1-

Description

Screw 6-32 x 3/8” Blk

Nut 7mm

Nut 4-40

Nut 6-32

Washer flat 8 x 14mm

Washer fiber #6

Lockwasher #6

Rubber foot

Label top

Line cord 2 wire

Shrink tubing

Solder lead-free

Part #

131500

142200

192421

Part #

264747

282244

284746

292226

Part #

314001

330317

350002

Part #

641652

644101

644400

644600

645101

645602

646600

662015

723071

862100

890120

9LF99

PARTS VERIFICATION

Before beginning the assembly process, familiarize yourself with the components and this instruction book.

Verify that all of the parts are present. This is best done by checking off the parts in the parts list.

RESISTORS CAPACITOR SEMICONDUCTORS

Carbon film

2k

Ω Potentiometer

Electrolytic (radial)

MISCELLANEOUS

Diode

LM317 Regulator LED

Case top

Transformer YD-1485

Label

Screws

PC Board

Nuts Washers

Lead-free solder

Binding posts

2.8 x 8mm

4-40 x 1/4”

6-32 x 3/8” black

7mm

4-40

6-32

Flat

8 x 14mm

Black Red

Fiber #6

Lockwasher #6

Binding post nut

Binding post lockwasher

-2-

Knob

Rubber foot

Strain relief 2-wire

Case bottom

Heat sink

Shrink tubing

CONSTRUCTION

Introduction

The most important factor in assembling your XP-15K Regulated

Variable Power Supply Kit is good soldering techniques. Using the proper soldering iron is of prime importance. A small pencil type soldering iron of 25 - 40 watts is recommended. The tip of the iron must be kept clean at all times and well-tinned.

Solder

For many years leaded solder was the most common type of solder used by the electronics industry, but it is now being replaced by leadfree solder for health reasons. This kit contains lead-free solder, which contains 99.3% tin, 0.7% copper, and has a rosin-flux core.

Lead-free solder is different from lead solder: It has a higher melting point than lead solder, so you need higher temperature for the solder to flow properly. Recommended tip temperature is approximately 700 O F; higher temperatures improve solder flow but accelerate tip decay. An increase in soldering time may be required to achieve good results.

Soldering iron tips wear out faster since lead-free solders are more corrosive and the higher soldering temperatures accelerate corrosion, so proper tip care is important. The solder joint finish will look slightly duller with lead-free solders.

Use these procedures to increase the life of your soldering iron tip when using lead-free solder:

• Keep the iron tinned at all times.

• Use the correct tip size for best heat transfer. The conical tip is the most commonly used.

What Good Soldering Looks Like

A good solder connection should be bright, shiny, smooth, and uniformly flowed over all surfaces.

1. Solder all components from the copper foil side only. Push the soldering iron tip against both the lead and the circuit board foil.

Soldering Iron

Component Lead

Foil

• Turn off iron when not in use or reduce temperature setting when using a soldering station.

• Tips should be cleaned frequently to remove oxidation before it becomes impossible to remove. Use Dry Tip Cleaner (Elenco

Cleaner (Elenco ®

® #SH-1025) or Tip

#TTC1). If you use a sponge to clean your tip, then use distilled water (tap water has impurities that accelerate corrosion).

Safety Procedures

• Always wear safety glasses or safety goggles to protect your eyes when working with tools or soldering iron, and during all phases of testing.

'

• Be sure there is adequate ventilation when soldering.

• Locate soldering iron in an area where you do not have to go around it or reach over it. Keep it in a safe area away from the reach of children.

• Do not hold solder in your mouth. Solder is a toxic substance.

Wash hands thoroughly after handling solder.

Assemble Components

In all of the following assembly steps, the components must be installed on the top side of the PC board unless otherwise indicated. The top legend shows where each component goes. The leads pass through the corresponding holes in the board and are soldered on the foil side.

Use only rosin core solder.

DO NOT USE ACID CORE SOLDER!

Types of Poor Soldering Connections

1. Insufficient heat - the solder will not flow onto the lead as shown.

Rosin

2. Apply a small amount of solder to the iron tip. This allows the heat to leave the iron and onto the foil.

Immediately apply solder to the opposite side of the connection, away from the iron. Allow the heated component and the circuit foil to melt the solder.

Solder

Foil

Circuit Board

Soldering Iron

Soldering iron positioned incorrectly.

2. Insufficient solder - let the solder flow over the connection until it is covered.

Use just enough solder to cover the connection.

Solder

Component Lead

Gap

Soldering Iron

3. Excessive solder - could make connections that you did not intend to between adjacent foil areas or terminals.

Solder

3. Allow the solder to flow around the connection. Then, remove the solder and the iron and let the connection cool. The solder should have flowed smoothly and not lump around the wire lead.

Solder

Foil

Soldering Iron

4. Here is what a good solder connection looks like.

4. Solder bridges - occur when solder runs between circuit paths and creates a short circuit. This is usually caused by using too much solder.

To correct this, simply drag your soldering iron across the solder bridge as shown.

Foil Drag

-3-

MOUNTING THE TRANSFORMER & BINDING POSTS

r Peel the backing off of the label and place it onto the case top, while carefully lining up the holes as shown in Figure A.

The label should fit snug within the indentation in the case.

r Install the binding posts with the colors in the order as shown in Figure B. Insert the post into the hole and fasten it with the nut and lockwasher.

Tighten down the nut with pliers.

r Install the transformer as shown in Figure B. Use a 6-32 x 3/8” screw, #6 lockwasher, 6-32 nut, and two #6 fiber washers on each side to fasten in place as shown.

r Cut the red wires on the transformer off close to the transformer.

These wires will be used on the PC board.

#6 Lockwasher

#6 Fiber washer

Cut these two wires (red)

Transformer

#6 Fiber washer

6-32 Nut

#6 Lockwasher

#6 Fiber washer

#6 Fiber washer

Binding post nuts

Binding post lockwashers

Case top

Figure A

-4-

6-32 x 3/8”

Screws

Red binding post

Black binding post

Figure B

ASSEMBLE COMPONENTS TO THE PC BOARD

Place a check mark in the box provided next to each step to indicate that the step is completed.

C4 - 220 μF Electrolytic

(see Figure D)

D5 - 1N4001 Diode

D6 - 1N4001 Diode

(see Figure C)

R4 - 2.2k

Ω 5% 1/4W Res.

(red-red-red-gold)

C3 - 470 μF Electrolytic

(see Figure D)

R1 - 2.2k

Ω 5% 1/4W Res.

(red-red-red-gold)

C2 - 4.7

μF Electrolytic

(see Figure D)

P4 - 3” Red wire

P5 - 3” Red wire

Cut two 3” wires from the cutoff red transformer wires and strip 1/4” of insulation off of each side.

Figure C

Diodes have polarity. Be sure to mount them with the band going in the same direction as marked on the PC board.

Figure D

These capacitors are polarized. Be sure to mount them with the “+” lead in the correct hole as marked on the PC board. Also, the negative lead of a radial electrolytic is shorter than the positive one.

Warning: If the capacitor is connected with incorrect polarity it may heat up and either leak or cause the capacitor to explode.

D4 - 1N4001 Diode

D3 - 1N4001 Diode

D2 - 1N4001 Diode

D1 - 1N4001 Diode

(see Figure C)

D8 - 1N4001 Diode

D7 - 1N4001 Diode

(see Figure C)

C1 - 2,200

μF Electrolytic Cap.

(see Figure D)

R2 - 150

Ω 5% 1/4W Res.

(brown-green-brown-gold)

U1 - LM317 Regulator

(see Figure E)

Figure E

Mount the regulator as shown, with the metal backing in the same direction as the marking on the PC board. Attach the heat sink using a 4-40 x ¼” screw and 4-40 nut.

Metal backing

PC board marking

1/4”

Band

4-40 x ¼”

Screw

Heat sink

Polarity marking

D9 - LED

Flat side r Mount the

LED to the copper side of the PC

(–) (+) board, spaced 3/8” off the board, with the flat side in the same direction as shown in Figure F.

Flat side

(–) (+)

LED

Long lead (+)

Figure F

Flat side

4-40 Nut

Short lead (–)

R3 - 2k Ω Potentiometer

r Mount the potentiometer to the copper side of the

PC board as shown in

Figure F. Insert the the pins through the holes so the body sits flat against the PC board, then solder in place.

3/8”

Copper side of PC board

2k

Ω Potentiometer

-5-

WIRING

Install the following wires as shown in Figure G.

r Cut the blue and both yellow transformer wires so that they are 4”. Strip 1/4” insulation off the ends.

r Solder one of the yellow wires from the transformer to PC Board P1 and the other to P3.

r Solder the blue wire from the transformer to the PC board hole P2.

r Solder the red wire from the P5 to the end of the the red binding post.

r Solder the red wire from the P4 to the end of the the black binding post.

r Install the PC Board into case by lining up the shaft of the pot and the LED with the holes in the case, and then pressing

PC board into place. Flip the case around and install the 8 x 14mm flat washer and

7mm nut as shown in Figure H.

r Turn the shaft on the pot fully counterclockwise. Push the knob onto the shaft so that the line on the knob lines up with the end of the circle on the front panel as shown in Figure I. If the knob is loose on the pot shaft, insert a screwdriver in to the slot and expand the slot slightly. If the knob has a set screw, tighten the set screw located on the side of the knob.

Figure G

Blue wire

Black binding post

Yellow wires

Red binding post

Red wires

Line on knob

7mm Nut

8 x 14mm

Flat washer

Flat head screwdriver blade

Knob

Pot shaft

Figure H

-6-

Figure I

LINE CORD ASSEMBLY

Install the following wires as shown in Figure K.

r Cut the two black wires from the transformer to

1½”. Strip ¼” of insulation off of each wire.

r Feed 2” of line cord into the hole of the chassis.

Place the line cord in the slot of the strain relief and squeeze the two sections together with pliers.

Then, insert the strain relief into the hole, as shown in Figure J.

r Separate the two line cord wires. Place 1” of shrink tubing over each black transformer wire. Twist and solder the line cord wires to the black transformer wires as shown in Figure K.

r Slide the shrink tubing up to cover the solder joints.

Shrink the tubing with the heat from your soldering iron. BE CAREFUL NOT TO TOUCH THE SHRINK

TUBING OR WIRES WITH THE IRON.

Case top in this direction

FINAL ASSEMBLY

r Remove the backing from each rubber foot and place them in the locations shown in Figure L.

r Assemble the top and bottom case sections and fasten with four 2.8 x 8mm self-tapping screws as shown in Figure L. Make sure the slots on the side line up with one another.

2.8 x 8mm

Screws

2.8 x 8mm Screws

Rubber feet

Strain relief

Figure J

Figure K

Twist and solder wires together

Shrink tubing

Pliers

Rubber feet

Bend wires over as shown

Slide tubing

Soldering iron

-7-

Figure L

Slot

TESTING THE XP-15K POWER SUPPLY

Testing the XP-15K Power Supply is very simple.

Before applying power to the unit, be sure that all of the wiring and soldering is firm. If so, obtain a digital voltmeter. Apply power to the XP-15K and vary the voltage control knob.

Next, short the output of the supply. It should turn off and recover when the short is removed. If you have a 4.7

Ω 1 watt resistor, set the voltage to 1.4 volts and place is across the output terminals. The output of the supply should not change more than 0.1 volts.

Set the output voltage to 15 volts and place a 75

Ω 5 watt resistor across the output terminals. Again, the output should not change by more than 0.1 volts. In making these tests, the voltmeter leads should be clipped directly to the output terminals and not to the load leads. This is to prevent errors due to voltage drop in the load leads.

Should any of these tests fail, refer to the troubleshooting guide.

CIRCUIT DESCRIPTION

INTRODUCTION

The XP-15K Power Supply features an output voltage variable from 0 to 15V at 0.3 ampere maximum current. The voltage is regulated to within

0.1V when going from no load to full load. Varying the input AC voltage from 110 to 130V will have practically no effect on the output voltage. This is because of the specially designed IC circuit used in the XP-15K. Severe overloading or even short circuiting the output will not damage the supply.

Special turn-off circuits in the IC sense the overload and turn off the output.

Figure 1 shows a simplified circuit diagram of the power supply. It consists of a power transformer, a

DC rectifier stage and the regulator stage.

120VAC

Input

Transformer

120V to 18V

18VAC

AC to DC

Converter

20VDC

Simplified diagram of positive power supply

Voltage

Regulator

Figure 1

0 - 15V

Regulated

Output

TRANSFORMER

The transformer T1 serves two purposes. First, it reduces the 120VAC input to

18VAC to allow the proper voltage to enter the rectifier stage. Second, it isolates the power supply output from the 120VAC line. This prevents the user from dangerous voltage shock should they be standing in a grounded area.

Voltage Waveform for Supply

A) Transformer

Winding AB

AC to DC CONVERTER

The AC to DC converter consists of diodes D1 and D3 and capacitor C1.

Transformer T1 has two secondary windings which are 180 degrees out of phase.

The AC output of 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 half wave rectifier.

Here, the diode conducts only half 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 requires much more filtering to obtain a smooth DC voltage.

By the 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.

-8-

B) Transformer

Winding BC

C) Output of diode D1.

D) Output of diode D3.

E) Total of diodes

D1 & D3.

20V

F) Output of capacitor C1

Ripple depends on load current (expanded).

Figure 2

Each diode conducts when the voltage is positive.

By adding the two outputs, the voltage presented to capacitor C1 is more complete, thus, easier to filter, as shown in Figure 2F. When used in 60 cycles AC input power, the output of a full wave rectifier will be

120 cycles.

Capacitor C1 is used to store the current charges, thus smoothing the DC voltage. The larger the capacitor, the more current is stored. In this design, a 2,200

μF capacitor is used, which allows about 2 volts of AC ripple when one half amp is drawn.

In practice, the current through the diodes is not as shown in Figure 2E. Because capacitor C1 has a charge after the first cycle, the diode will not conduct until the positive AC voltage exceeds the positive voltage in the capacitor. Figure 5 shows a better picture of what the current flow looks like, assuming no loss in the diode.

It takes a few cycles for the voltage to build up on the capacitor. This depends on the resistance of the winding and diode. After the initial start-up, there will be a charge and discharge on the capacitor depending on the current drawn by the output load. Remember, current only flows through the diode when the anode is more positive than the cathode. Thus, current will flow in short bursts as shown in Figure 5C.

The DC load current may be one ampere, but the peak diode current may be three times that.

Therefore, the diode rating must be sufficient to handle the peak current. The 1N4001 has a peak current rating of 10 amps.

A) Transformer

Winding

B) Voltage C1

C) Current through diodes

Figure 5

20V

Peak

20V

D1

C1

Half Wave Rectifier

Figure 3

D1

D3

C1

Full Wave Rectifier

Figure 4

REGULATOR CIRCUIT

The regulator circuit in the Model XP-15K Power

Supply consists of a LM317 integrated circuit. This

IC is specially designed to perform the regulation function. Figure 6 shows a simplified circuit of how the LM317 IC works.

Transistors Q1 and Q2 form a circuit known as a differential amplifier. Transistor Q1’s base is connected to a stable 1.5V reference voltage. The base of Q2 is connected to the regulator output circuit through a voltage divider network. The collector of transistor Q2 is connected to a current source. This basically is a PNP transistor biased to draw about 1mA current. Transistor Q2 sees the current source as a very high resistor of about 1 meg ohms. Thus, the gain of transistor Q2 is very high.

Transistor Q5 is called the pass transistor. It controls the current reaching the output. Transistors Q3 and

Q4 are emitter followers. Their function is to raise the impedance of the pass transistor. Note that transistor Q2, Q3, Q4, Q5 and resistor R1 form a closed loop. Also, note that the feedback to the base of Q2 is negative, that is, the output at emitter Q5 goes negative. Now, if the 1.25V output voltage goes down because of current drain at the output, the base of Q2 will drop, forcing the collector voltage of Q2 to go higher. This will bring the output voltage back to 1.25V. This is the basis of all negative feedback regulators.

Another feature of the LM317 regulator is to protect the IC against overload and output shorts. If the IC is overloaded, the junction will overheat. A transistor will sense this overheating and shut down transistor

Q5.

The LM317 IC is basically a 1.25V regulator. To be able to vary the output 0 - 15V, we stack the IC on the negative 1.25VDC voltage as shown in Figure 7.

When R3 equals 0, the output voltage is 0 volts.

Current

Source

Equalized to 1 Meg.

1.5V

Q1

Q2

Q3

Q4

Q5

1.25V

Output

R1

R2

LM-317

R2

0V - 15V

R3

–DC

Divider

Figure 6 Figure 7

-9-

TROUBLESHOOTING GUIDE

Consult your instructor or contact ELENCO ® as they will not be able to help you.

if you have any problems. DO NOT contact your place of purchase

LED Not Lit

1) Check transformer and line cord.

2) Check for 20VDC at the cathode of D1.

3) LED in backwards or defective.

No Output Voltage

1) Check AC voltage across points P1 & P2 or

P2 & P3. It should read about 18VAC.

2) Measure voltage at the output of D1 and D3.

It should read about 20VDC. If not, then check D1, D3, C1, U1, R2, R3, D7, and D8.

Poor Regulation

1) Check AC ripple at the input of the regulator.

It should be less than 2.5V.

2) If ripple is higher, check diodes D1, D3, and the filter of capacitor C1.

Copper Side of PC Board

QUIZ

1. AC voltage is supplied to the rectifier stages by the . . .

r A. step up transformer.

r B. step down transformer.

r C. 1 to 1 transformer.

r D. AC to DC transformer.

2. The secondary windings of the transformer are . . .

r A. 90

O out of phase.

r B. 180

O out of phase.

r C. 270

O out of phase.

r D. 320

O out of phase.

3. Diodes allow current to flow . . .

r A. when the anode is more negative than the cathode.

r B. when the cathode is more positive than the anode.

r C. in one direction.

r D. when a negative or positive voltage is on the anode.

4. What circuit is more efficient for rectifying AC to DC?

r A. Hartley oscillator.

r B. Half wave.

r C. Schmitt trigger.

r D. Full wave.

5. The DC voltage is smoothed by using a . . .

r A. half-wave rectification circuit.

r B. small value capacitor with a high voltage value.

r C. Large value capacitor.

r D. 90

O out of phase rectification circuit.

-10-

6. An inefficient rectification circuit usually contains . . .

r A. large gaps between cycles.

r B. twice the AC voltage needed.

r C. more diodes.

r D. all of the above.

7. The maximum current that a diode can handle is determined by . . .

r A. the transformer’s current rating.

r B. the amount of AC ripple.

r C. three times the diode rating.

r D. peak current rating.

8. The LM317 will shut down when . . .

r A. the output voltage is too high.

r B. no current is being drawn.

r C. the junction overheats.

r D. the output voltage drops to 1.25V.

9. The LM317 regulator contains . . .

r A. a pass transistor.

r B. a constant current source.

r C. a differential amplifier.

r D. all of the above.

10. The LM317 is . . .

r A. a positive voltage regulator.

r B. a 6.25V regulator.

r C. a 2.5V regulator.

r D. a negative voltage regulator.

SCHEMATIC DIAGRAM

A

C,

D, 10.

D, 5.

C, 9.

C, 4.

D, 8.

B, 3.

ELENCO

®

150 Carpenter Avenue • Wheeling, IL 60090

(847) 541-3800 • Website: www.elenco.com • e-mail: [email protected]

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6. D

1. B ers: Answ