AC/DC Power Supply Kit
DC: 0 - 18 VDC, 1A
AC: AC: 18 VAC, 1A
AK-10
www.abra-electronics.com
sales@abra-electronics.com
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18 Volts AC output and a Variable 18 volts DC output
Up to 1 Amp in current output
Simple component placement guide
On -Off switch to save power when not in use
Detailed theory on Power electronics
U.S Toll Free: 1-800-717-2272
Can. Toll Free: 1-800-361-5237
Index
I. Parts list ............................................................................ 1
II. Specifications................................................................. 2
III. Tools Required............................................................. 2
IV. Assembly Instructions...........................................3-4
V. Schematic diagram ...................................................... 4
VI. Theory of operation ........................................... 5-12
I. AC signal.................................................................. 5-7
II. Transformers....................................................... 8-9
III. Rectifiers................................................................ 10
IV. Capacitors.............................................................. 11
V. Voltage Regulator.................................................. 11
VI. Soldering................................................................. 12
VII. Troblueshooting/FAQs.................................. 12-13
VIII. About Us ................................................................... 14
Parts list
☐☐ (2x) 220µF Capacitor (C2 & C3)
☐☐ 2200µF Capacitor (C1)
☐☐ DPDT Switch On-On
☐☐ (2x) 2 pin Terminal Block (AC & DC)
☐☐ T0-220 heat sink Clip-on (HS-220C)
☐☐ Line Cord
☐☐ 36V step down transformer (TRF-170)
☐☐ LM317T
☐☐ 5000Ω ½ watt PC mount Resistor
☐☐ 2200Ω ¼ watt Resistor (R1)
☐☐ 1300Ω ½ watt Resistor (R3)
☐☐ 330Ω ¼ watt Resistor (R2)
☐☐ Green Diffused LED (L)
☐☐ (6x) 1N4004 (D1 – D6)
☐☐ ABRA Custom PCB Board
optional
* standoff
* project box
Designed by: Thushanth Sithambararajan
Rev 1.0.1
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Specs
On-off feature
up is on, down is off
Mount with standoffs
Inter changable capacitors
Included heatsink!
18 volts adjustable DC
18 volts sine wave
PC mount potentiometer with
fine precsion adjustment
Tools Required
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Pencil type soldering iron
Solder 60 tin / 40 lead recommended
Soldering station (optional)
Helping hands (optional)
Small flat head screwdriver
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Assembly Instructions
1. Please check off the parts list to ensure you have all the parts included in your kit.
2. Solder low overhead components first, by placing them into the place marker where they belong.
3. Insert Components and bend the pins slighty to hold into place when soldering
4. Solder the pin with the soldering iron, for tips on how to solder please read the “soldering” sub section in the theory of operation chapter.
5. Cut off all excess leads after soldering components in.
6. Proceed to solder high overhead components.
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Cut off the round connector end of the line cord and strip the wires 1/4 inch.
Tin both wires with solder.
Slip on length of black heat shrink on each of the two stripped wires.
Solder the two stripped line cord wires to the red wires of the transformer.
Cover the bare wire joints with the heat shrink and heat them securely in place.
Insert coming in from the bottom of the PCB throughthe large strain relief hole beside the power switch the two blue and one black transformer secondary wires.
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Solder the black wire to the center connection and the two blue wires to the outside connections.
Place on the LM317 the heat sink clip.
Solder the terminal connection blocks and flick the switch to off position (pointing downwards in reference to the Vanier logo) if not already done.
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Connect into the wall socket and check the transform for heat inspection or shortage.
Flick the switch on and test the LM317 of heat inspection and led indication light is turned on.
Measure the output of the DC signal and adjust with the potentiometer.
Turn off the switch to ensure that there is no voltage being outputted.
Turn on the switch and measure the AC voltage.
Congratulation you now have a power supply, if it didn’t work please do not panic and read the FAQ section.
Schematic diagram
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Thoery of Operation
Ac Signal
Your power plant step down transformers supplies to your home 220-240 volts RMS AC (Alternating
Current), this signal is comprised of sine waves.
A sine wave can be interpreted as a sway, it moves up and down like a wave in the ocean. Below is
a graphical representation of a sine wave.
The furthest point away from the middle line is called Voltage Peak (Vpeak), either positive peak
(upper half from middle line) or negative peak (lower half from middle line), the distance between
them is referenced as a peak to peak voltage (Vpeak - Vpeak).
A period is the time lapse for something to be completed, sine waves will start at different ranges
or degrees but they often come back to where they started. For example the figure below, the
voltage offset is 0 volts. The sine wave starts at 0 volts and will end at 0v, the length of this period
is 2π or 360°.
If you analyze the previous graph, you may notice something on the y-axis called t time in Radians.
The y-axis represent time, the only confusion is “in radians”. The reason why the units are in
radians is because the sine wave is essentially a circle and radians are the mathematical method of
representing in numerical values that are easy to work with.
The usage of degrees is not a practical approach in measuring the period of any signal. Degrees
give an approximation value similar to percentage, whereas radians give us values to work with
similar to decimal points.
An example of using radians to derive the relation of degrees in a sine wave.
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Example (2)
Note:
A good example of the usage of radians; There are two sine waves that have been measured, they
have the exact same identical properties ranging from amplitude to its period. The only difference is
the second signal has a phase shift of 90°, the goal is to plot this new wave.
If you are to proceed in working with degrees, a 90° shift is only a simple matter of plotting it away
from the origin by 90° as its starting point. However if the period is 2π or π/6 it can get messy quickly by not knowing where to end. A simple way to get over this is to convert the phase shift 90° to a
radian value. With the formula below explaining how to convert degrees to radians the graph can be
drawn simply by setting the origin to the right by π/2 , the ending of the wave would be the period
added to the shift in radians.
The formula for converting degrees to radians:
degree/1 x π/180=radians Therefore 90/1 x π/180 = 1/1 x π/2 = π/2
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In North America the voltage RMS is 120v or 115v for common appliances to run on, however the
peak voltage is 120v *√2 = 170 Peak Voltage. Therefore the furthest point form the middle is not
120v AC, it is 170v AC!
RMS (root mean squared) is the terminology to best describe mathematically a constant alternating
voltage that is being delivered. Since the maximum peak will be 170 volts both positive and
negative, the average of the voltage supplied during any cycle will be below 170 volts. Therefore
the terminology of RMS acts mathematically as a steady amount of AC voltage that will be supplied
to any load.
If an incandescent light bulb is rated to for 60 volts AC and the line measured indicates it provides
60 volts peak then the RMS is 60V* 1/√2 = 42.42 volts RMS, however there is another line with a
label indicating it has a 85 volts peak then the RMS is 85V*1/√2=60.095 volts RMS. It is clear that
the 60.095 stable Volts will shine brighter than the stable 42.42 volts.
The average voltage is the representation mathematically to find the midpoint of the AC voltage or
current that is being provided during time lapse of the period. The difference between RMS and
Average is with the fact that RMS is the instantaneous value rooted and average is the instantaneous
voltage added together divided by the total number of instantaneous voltage measured in the
period. Both mathematical representations are used to describe the output AC voltage or current
compared to the DC voltage and current.
Since it was explained previously the importance of RMS in finding the actual voltage output, the
method in calculating and deriving this RMS value has been made easier for first time hobbyists by
previous mathematicians. For RMS the value is 0.707, for Average Voltage the value is 0.636, both
of these values are multiplied by the amplitude and vice versa.
Here are some formulas to find the following in a sine wave;
If you are given the peak to peak voltage and are required to calculate the peak voltage:
Vpeak = Vpeak-to-peak * 0.5
If you are given the rms voltage and are required to calculate the peak voltage:
Vpeak = Vrms * √2
If you are given the average or mean voltage and are required to calculate the peak voltage:
Vpeak = Vaverage * π/2
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Transformers
Transformers in general are useful devices that assist in converting alternating current to either
increasing or decreasing AC voltage. They achieve these results through the process of induction.
A primary coil is feed with AC voltage, a non-conductive magnetic core or alternatively known
as a ferrite core is the housing for the wires to coil onto. The secondary coil that is parallel to the
primary coil which is not connected to the primary coil act as output for the transformer. The
electromagnetic forces moves the electrons and creates a flow of current and voltage that is either
higher or lower by the amount of windings that is in the primary and secondary wiring. If the
primary coil has fewer wires than the secondary coil it becomes a step up transformer with a low
current and high voltage output. In the case of the step down transformer the primary coil has
more windings than the secondary coil with a low voltage and high current output.
The formula used to calculate the Power of a device using the North American single phase power
is calculated in terms of Watts. Power = Volt * Current * (kW actual load power/kVA apparent load
power)
A Centered tapped transformer is what is currently supplied with this kit, they can be commonly
found outside on the power poles. A center tapped transformer is essentially as the name implies,
the secondary winding is wrapped around the ferrite housing with one end starting from the
bottom, the other end at the top and the center tapped wire is located in the middle of the winding.
Another interpretation can be seen as a pencil with wire wrapped on it, the wire starts at the eraser
end and ends at the pencil tip. A center tapped wire is located in the middle of the pencil that is glue
or fastened in at the center, almost like a potentiometer with a fixed wiper. This center cable acts
as the reference cable to reference the voltage; however in the kit the center line acts as the return
wire.
Here are some common wiring for transformers that are available in the market.
Common two wire in and
out transformer
Center tapped transformer
(Either 16v from top to middle or 16v middle to
bottom or 32 V across, same current)
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Dual output transformer (series connection)Less
current more voltage
Dual input transformer (parallel connection)
Very versatile for 110v or 220v application,
one transformer.
Dual output transformer (parallel connection)
more current less voltage
Dual input transformer (series connection)
Dual input and Output transformer
(all the same configurations mentioned above in one package)
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Rectifiers
Rectifiers convert AC signal into DC signal, DC signals are required for electronics devices that need
DC power to function. A power plant provides commercially three phase power, as in there are three
independent sine waves in a line at any given time with the same; amplitude, RMS, oscillation rate
of 60Hz and etcetera for north America. A common house hold receives a single phase power line or
in some cases older homes receive dual phase power. However in the end at the output of your wall
socket you will have a single phase power that will display one sine wave on your oscilloscope. The
rectifier for this circuit would be for a single phase rectifier. There are two types of rectifiers as they
will manipulate the output as either a full wave or half wave.
Full wave rectifiers
Full wave rectifiers convert the entire waveform into one constant polarity at the output, in essence
they convert the AC to a DC wave. In some sense a half wave rectifier will requires less components
than a full wave rectifier, the full wave rectifier has a higher average voltage than its counterpart
and smoother than the half wave rectifier. Observing the sine wave in AC section of the theory
chapter, sine wave was described as a wave in the ocean the negative peaks of the sine wave are
shifted upwards to create a constant positive voltage. This is achieved by placing diodes in a bridge
configuration.
Half wave rectifiers
Half wave rectifiers eliminate the negative peaks leaving blank gaps in-between compared to the
full wave rectifier. Typical the components required for the half wave rectifiers is less than the full
wave. A half wave rectifier creates a lot of ripples and thus a better filter system is required.
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Capacitors
For this power supply circuit the capacitor has two main roles and one side effect. The first role
for the capacitor is to dampen the voltage and remove any ripple leftover. The second role for the
capacitor is to act as a decoupling capacitor to remove noise from another circuit element by acting
as a shunt and reducing the effects throughout the entire circuit. The issue that is primarily derived
from the capacitor is equivalent series resistance. The capacitors resistances comes from the leads,
furthermore it generates transient spikes that could damage your components which are current
sensitive at the output of the power supply. To remedy this problem a serial resistor can be used or
a protective parallel resistor.
The capacitors that are included in this kit are radial electrolytic with their voltage ratings. The
orientation for the capacitors are important as the wrong orientation could cause the capacitors
to exploded or leak. The composition of the polarized capacitor allows for an affordable and
inexpensive material, however do the design method the anode film and cathode film cannot be
reversely charged or else it could burn the film.
Voltage Regulator
Linear Voltage Regulators are used commonly in many power regulating circuits in the form of a
T0-220 package. A liner voltage regulator is responsible for supplying a constant output voltage
regardless of the change in input to the IC. The circuitry inside the Regulator attempts to hold
the value set by the users demand or the adjust pin. The maximum current in the input is the
maximum current that can be outputted. Essentially the system will act as a proportional, integral
and differential system (PID). When the output voltage is higher or lower than demand, the current
will adjust to meet the output required. If you are scratching your head trying to understand how
this is done, recall ohm’s law V=I*R. Increase the current and keep the same resistance, voltage
goes up. Decrease current and keep the same resistance the voltage does down.
Due to this constant regulation of voltage if a load is introduce at the output that is active and
requires current it gets harder for the regulator to do its job, especially when the voltage output
requested is low. To remedy that, a heat sink is introduced to cool the circuitry within the packaging;
aluminum is a good thermal conductor and that why you shouldn’t touch the silver back side. This
allows users to attach heat sink that are screwed onto the back of the IC or in this case clipped on.
The LM317 like any device has its limits; the maximum it can regulate is 37 Volts. The maximum
current it can handle is 1.5 amps. If you are within these operating temperatures and forgot to
place a heat sink on the regulator the chances that it might work again after cooling down is very
likely. The LM317 has a protective circuity to shut down the regulator if the temperature reaches a
very high point, that around 125°C! You can safely dissipate 0.25 watts with the LM317.
Here is the formula for finding your thermal dissipation.
Dissipated power (watts) = (Vin-Vout) * iL (Load current)
So the power supply outputting 1 volts would be (18v – 1v) * 1 Amp = 17 watts. THAT IS A LOT!
You may be wondering, when I measured the output of my power supply the maximum current
of 5 led(s) at the output was a total of 0.15 amps not 1 amp! Don’t panic, this is perfectly normal.
You will never exceed 0.5 Amps, since the regulator is responsible for regulating it only outputs
the current you need for the voltage you want and thus you may end up with a lower current.
The power supply is designed to handle 1 amp so if you did do a future project that required such
amperage, please place an appropriate heat sink.
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Soldering
When soldering ensure for maximum quality to use a soldering station with a variable temperature
control, the recommend temperature setting is 260 to 280°C. Prior to soldering, wet the tip with
solder 60% tin /40% lead and brush of the tip with a sponge. Do not dip the solder tip into the
sponge or soak the sponge with water. A sufficient moist sponge will do the trick. It is recommend
to hold the solder tip to the components for a maximum of 3 seconds. If the solder does not melt,
increase the temperature to the extent where the solder begins to melt. The longer the soldering
iron is heating the pins the chance of damaging the IC increases. Use forceps or needle nose to
hold components in place. Hold the soldering iron with the hand that is comfortable to work with
and place into stand when not in use. Feed solder to component on opposite side of the pin, do
not put excess solder into pin as it may lead to cracking or shearing of the PCB contact, in some
cases it can create a cold solder joint (something to avoid). Work in well ventilated areas. Always
solder low overhead components first, for example diodes, resistors, surface mount components
and then proceed to solder high overhead components like capacitors, potentiometers, switches
and terminal blocks.
Troubleshooting / FAQ
The LM317 is overheating?
Please read the “Voltage Regulator” Subsection in the Theory Chapter of this manual, further details in power
dissipation will explain the reason for overheating. A temporary solution is to place a heat sink on the LM317
IC.
I have no voltage output.
Please check if the solder contacts were soldered properly, you may use a diode checker or continuity checker
to see if the connections are connected. Please be very careful in checking the temperature of the LM317
with your finger. A safe alternative in checking the temperature of the IC is to place the eraser tip on the IC
for a few seconds and thereafter touch the eraser end to feel the heat. If the IC is hot, unplug the cable from
the wall socket and wait at most 10 minutes to cool down, place a heat sink on the IC.
The transformer is overheating.
You may have accidently shorted both blue wires to the black wire; this creates a loop in which the transformer
is supplying voltage to itself! Disconnect the Transformer from the wall socket and let the transformer cool
down. It should still work; the chances of burning the TRF-170 are slim. The possibility of this scenario
occurring is slim; however do not attempt to short the wires to replicate this problem you may end up with
a burnt fuse and no power for the day.
My Led won’t light up but I am getting power.
The first edition power supply boards have the Led layout printed backwards, please de-solder and reconnect
in the opposite orientation.
My led won’t light up and I am not getting any power.
Please check the switch is it turned on or off? If the switch is on, then proceed to troubleshooting with
transformer disconnected from the wall socket. Please check the connections from transformer to the PCB
with a continuity tester.
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Can I use an alternative transformer?
You may use an alternative transformer as long as it respects the following design constraints: The total
voltage cannot exceed 40v and the current must not exceed 1.5A. Failure in doing so will result in the
death of the LM317. You may use a center tapped or common transformer, the connection for a common
transformer would be the DC through hole as the input and center through hole as the return line. You will
not have the AC feature if you use a common 2 wire transformer and if you do change the transformer the
max voltage output will change according to the transformer rating.
Can I change the capacitor values around?
You may change the capacitors to the following values:
C2 100µF R/35V, 220µF R/35V, 470µF R/35V, 1000µF R/35V, 3300µF R/35V, 4700µF R/35V
R/35V: Rated for 35 Volts Max! The higher the capacitance the longer the discharge time.
Why is C2 circle so big?
This allows room for alternative capacitors with a maximum size of the large radial capacitor to be soldered
into, any bigger than the circle results in damaging or limiting the circuit.
For more details please read the “Capacitor subsection” in the theory chapter.
Where can I mount this?
The side holes allow you to mount the power supply with ABRA standoffs where ever you please; alternatively
you may purchase a plastic project box to house your power supply.
Do I need a heat sink for my LM317?
Please read the subsection “Voltage Regulator” in the theory chapter for more details.
Can I change the heat sink for a bigger one?
You may change the heat sink for bigger one. However the size of the current heat sink should be sufficient
if using provided components.
What version is my power supply?
If you look on the top right corner the version number should be printed, if the revision number is not
printed it is the first edition of the power supply.
What happens if I scratch the surface and I see copper?
You must not touch the copper surface when operating it is conductive! Isolate the copper with electrical
tape.
Why am I getting more than 18 volts?
Please measure the output of the transformer with AC selected and the fuse of your measuring instrument
rated at 1A or more. The result is the approximate maximum voltage you will receive at the output. Ensure
when measuring the wire orientation is the blue wire and return line (black wire).
Which pin do I connect for the potentiometer?
Please connect the potentiometer facing outwards.
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About Us
Abra Electronics caters to industry, schools & hobbyists with a wide variety of components,
kits and equipment. We have in stock imported products ranging from a multitude of
companies to local products, all with affordable pricing.
Feel Free to call us on our toll free numbers indicated below. You will be greeted with our
knowledgeable and courteous staff members. You are also free to visit our website or drop by
to our montreal warehouse from 8:30 to 4:30, Monday to Friday.
Contact us
Phone (CAN): 1-800-361-5237
Fax (CAN): 514-731-0154
Phone (US): 1-800-717-2272
Fax (US): 1-800-898-2272
Web: www.abra-electronics.com
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