Project Power Supply - Lecture Notes | ECE 445, Study Guides, Projects, Research of Electrical and Electronics Engineering

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PROJECT POWER SUPPLY

by

Brian Westendorf

Andrew Van Court

Christy Westendorf

ECE 345: Senior Design

TA Julio Urbina

May 1, 2000

Project #

Abstract

The motivation behind this project was to create an ac to dc power supply that could be used

for a variety of standard dc output voltages. The power supply was designed to operate on ac

voltages ranging between 110 and 230 Vac. The output provided by the power supply provides

users with  5Vdc and  12Vdc. The total power delivery for the 12V side is 60W and 25 W for

the 5V output. Thus the total power delivery sums up to 85W. The major design issues discussed

include the transformer, LC filter, feedback and control. The performance of the power supply is

determined by the regulation of the output voltages and the overall efficiency of power conversion

from ac to dc.

ii

iv

1.0 INTRODUCTION

The chief goal of this project was to create a cheap, reliable, and safe general-purpose power supply

that could be used in various labs located on the University of Illinois campus. The end product

virtually behaves like a black box to the user. The only manual operations required include turning

the power supply on and selecting a desired output voltage. The power supply operates on varying

AC input voltages and supplies various DC outputs. A varying input voltage is useful because it

does not limit the converters usable versatility. This power supply is designed to run on standard

wall power or higher voltages provided by lab benches like the ones located in the electric machines

laboratory in the basement of Everitt Lab. Two different output voltages were chosen to provide

power for standard logic devices and for the simulation of a car battery.

The functionality of this power supply can be broken down into two separate categories. The first

category is ac-dc conversion. The input ac voltage coming off the wall or lab bench is rectified to

provide the switching converter with dc voltage. The second category represents the dc-dc

switching conversion process, which is dependent upon time and energy. The switching action

represents the time element and the ac-dc rectifier described in category one supplies the energy.

Power transfer takes place in the dc-dc conversion process because energy (joules) is being

transferred from input to output as a function of time (seconds). Thus power is represented by

joules/seconds. Manipulation of the switching “on-time” can carefully control the amount of power

that is transferred to the output. The block diagram on the next page, Figure 1, delineates the basic

operating structure of the power supply being discussed in this report.

The specifications for a fully working project power supply are as follows:

PERFORMANCE SPECIFICATIONS

 Input Voltage: 110-230 Vac @ 60Hz

 Output Voltage: ±5 Vdc and ±12 Vdc

 Output Power: 5 Volt side at 1-25 Watts, 12 Volt side at 1-60 Watts

 Voltage Ripple: ±3% for all outputs

 Efficiency: 75%

The project has already been broken down into two categories: ac-dc and dc-dc. The first category

is relatively straightforward and will not be broken down into subcategories. The second category

will be subdivided into five parts consisting of the transformer, inductor-capacitor filters, PWM

chip, feedback control and the startup circuit. The transformer provides an effective means for

stepping the voltage down. The LC filters attenuate the dc output voltages within the required

specifications. The PWM chip acts as the “brain” of the power supply by controlling the switching

action. The feedback circuit feeds a signal into the PWM chip to make adjustments for varying

voltages and loads. The startup circuit essentially “primes the pump” for beginning circuit

operation. It provides initial power to the PWM chip to get the switching action started so that the

power supply will end up functioning solely on ac input power.

2.0 Design Procedure

2.1 AC – DC Rectifier

The task of properly sizing a capacitor for the input side of the power supply involved taking into

account several factors. First of all, the voltage range our power supply could properly function at

was based on a specific range of duty ratios. Secondly, the input voltage was going to be very high;

therefore, a capacitor had to chosen that could handle the high voltages. The specifics of the input

capacitor sizing are summed up in the Design Details section. A basic full-bridge rectifier was used

for initial conversion of ac voltage to dc voltage. The full-bridge rectifier was chosen because it is

relatively cheap and efficient to implement. The ac-dc conversion process could have been

designed using SCRs (silicon controlled rectifiers) but this method would introduce additional

difficulties such as controlling the phase delay angle of the ac voltage.

2.2 DC – DC Switching Topology

Power supplies can be designed using a multitude of various techniques. These different design

topologies offer distinctive advantages and disadvantages for ranging applications. Since the power

supply provides multiple outputs, the standard buck or boost converters would be inadequate for the

desired operation. Instead of using a switching converter that only provides one output, a converter

that provides multiple outputs is needed. This type of topology can be accomplished by

implementing a flyback converter or a forward converter. Forward converters can be represented

by a number of different designs such as the full-bridge, half-bridge, single-ended, push-pull, or

clamp topologies. The push-pull forward converter topology was chosen because it provides a

means for obtaining multiple dc outputs, operates at high frequencies, and isolates the output from

the high input ac voltage. It also used fewer parts than the traditional full-bridge converter because

it takes advantage of a center-tapped transformer. Figure 2 shows the general topology of a push-

pull converter.

Fig. 2. General Push-Pull Converter Topology.

The input versus output voltage is expressed in the general equation associated this type of

converter as:

Vout = 2aD1*Vin (0)

where (a) represents the turns ratio from the primary to the secondary side of the transformer and D 1

represents the duty ratio applied to the switches. A detailed discussion of the push-pull operation is

located in APPENDIX A.

-5V

1

Switch #

4

1

2

3

+5V

1

Center Tapped

Switch #1 Transformer

2.3 Transformer

The central and most crucial part of the push pull power supply is the transformer. This device is

the delivery mechanism for getting power from the input side to the each of the six outputs. Due to

the high switching frequency (100 kHz) used in the design, this device could be constructed by the

group using a small ferrite pot core and insulated copper wire. In doing the design of the

transformer three major considerations were made: transformer saturation, wire size, and turns ratio.

Each of these will be discussed in detail in the Design Details section below.

2.4 LC Filter

One of the goals of this project was to be able to provide clean power in order to successfully power

logic devices operating at five volts. This was achieved was by attaching output filters on each of

the six outputs. These filters consisted of an inductor used to produce a triangular current ripple

that could easily be filtered with a capacitor at the end of the filter. The final result was very clean

power with a ripple of less than +/- 3%. The design of these filters will be discussed in detail in the

Design Details section.

2.5 PWM Chip

The PWM chip served as the central brain of the switching power converter. The Motorola

MC34025 PWM chip is equipped with two outputs for driving two different transistors on or off.

These two outputs can vary the duty ratio applied to the transistors by basing its operation on

voltage mode control. This simply means that the duty ratio will be a function of voltage provided

by the feedback control circuit. This control chip is also capable of operating at switching speeds in

excess of one MHz. The desired switching frequency for this power supply is 100kHz, which is

well within this chip’s operating capacity.

2.6 Feedback Circuit

The control circuitry used in this converter was designed for completely autonomous usage. The

circuitry obtains the feedback voltage from an alternate 15 V winding in the transformer stepped

down to 5.1V through a voltage divider. Since all of the windings on the transformer are

proportional, the percent deviation from the desired voltage is the same for each of the windings.

The proportionality allows for correction of the percentage error, which is reflected on all outputs.

The reference voltage used for comparison is obtained from the PWM chip. The error between the

feedback voltage and the reference voltage is sent back into the PWM chip for duty cycle

correction. Without the control circuitry, the duty cycle ratio would be adjusted manually. A

proportional-integral design is implemented for the most economic and reliable control of the

product.

2.7 Startup Circuit

A startup circuit is necessary in a completely autonomous circuit. The startup circuit provides initial

power to the PWM chip. This initial power starts the switching action, which results in an output

voltage sufficient to maintain functioning of the circuit. Without initial power, the chip would not

produce a gate pulse and the circuit would not produce power.

Using all of this information along with equation 3 the value for the input capacitor was 158F.

This is only a minimum value, however, as the ripples gets better (less) as the capacitance increases.

In our actual circuit we used the only capacitor size available, which was a 270F, 400V

electrolytic capacitor. This capacitor provided more than adequate filtering for the input side of the

circuit. As stated before, this rectifier is used to convert the input ac voltage to dc voltage so that

the dc-dc converter can perform its job. The ac input voltage ranges from 110 – 230 volts so the

rectified dc equivalent will range from 155 – 325 volts. The diodes used in the bridge-rectifier will

have to be able block voltages in excess of the 325 volts. The maximum current that will be drawn

through the bridge rectifier will not exceed 2.0 A. The diode bridge-rectifier that is used in the ac –

dc conversion process has to block over 325 V and conduct up to 2.0 A. The rectifier used in this

power supply was capable of blocking 400 V and conducting 6.0 A. The final circuit diagram of

the ac – dc rectifier is located in APPENDIX B.

3.2 Transformer

Transformer saturation is one of the most crucial issues to look at when designing any transformer.

When a transformer saturates the permeability and inductance both decrease. This leads to

discontinuous mode operation, which causes rapid increases in current and inefficient or

nonfunctional operation of the power supply. It is for this reason that special care was taken to

avoid designing the transformer for saturated operation. The way that this was done was to set the

maximum volt-second rating to an acceptable level for all of our operating ranges. The maximum

volt-second rating is

V

dc

*****  t < B sat

NA

core (7)

This equation can be solved for N to obtain the minimum number of turns necessary to avoid

saturation at any given voltage. Before doing that it is necessary to discuss the values of the

variables in the equation and why they were chosen the way that they were.

The power supply was designed to work with 72V (Vdc) as the low end input voltage coming from

the rectifier/capacitor and at a 45% duty ratio. The overall period of switching action was 10s,

which came from the 100 kHz switching frequency. This particular frequency was chosen high

enough to allow for small magnetic components, but low enough to limit switching losses. The

saturation flux density was .3T for the ferrite core that was used (3622 Pot Core) and the area of the

core was 202*

m

2

It is now possible to solve equation 7 for N and determine the minimum number of turns necessary

to keep the transformer from saturating. This solution is given below.

N > V

dc

*****  t/B sat

/ A

core

= 72V.4510ms/.3T/(202***

-

m

2

) = 5.35 turns (8)

Equation 8 clearly states that the transformer must be wound such that there are more than 5.

turns on the primary side of the transformer. If this is done the transformer will never saturate

during proper operation of the circuit.

Choosing the proper size wire for each of the coils on the transformer was also a crucial aspect of

the transformer design. Wire that is sized too small will overheat at full load and cause a failure of

the circuit. Wire that is sized to large will add unnecessary cost to the circuit, be harder to work

with, and take up more space on the core. It is for this reason that the wire size was chosen to

operate with a 500A/cm^2 current density at full load.

The specifications determined which size wire was needed to obtain this current density based on

the amount of current that each winding would carry. The amount of current for the five and twelve

volt output coils is equal to five amps. This comes from the 85 Watts output specification as

follows

(5V * 5A) + (12V * 5A) = 85 Watts (9)

The primary side current can be obtained from both the output specification and the efficiency.

Assuming that the converter is 75% efficient at 72Vin^ the primary side current is

I

primary = (85W / 75%) / 72V = 1.57A (10)

Equation 10 is best described as the input power necessary to achieve full load at 75% efficiency

divided by the input voltage. The final wire size to be chosen was the 15V outputs for providing

power to the op-amps and the PWM chip. From the spec sheet we can see that both of these chips

draw 1 Watt maximum, which gives a current through the winding of

I15V = (1W + 1W) / 15V = .133A (11)

Using the data for current draw in each winding given in equations 9-11 and table 1 below we chose

the wire size as follows.

+/- 5 Vside = #16 AWG = 6.543 Amps Capacity

+/- 12 Vside = #16 AWG = 6.543 Amps Capacity

+/- 15 Vside = #32 AWG = .1601 Amps Capacity

Primary = #22 AWG = 1.628 Amps Capacity

The equation that controls the size of inductor to be used is

V

L

**= L ***  i /  t (13)

In this equation, VL is the inductor voltage and can be obtained in the following manner. Referring

to Figure 1 above the voltage across the inductor during the time that the switches are on is equal to

the voltage to the left of the inductor minus the voltage on the right side of the inductor. The right

side voltage is just equal to the output, which is 5V in this case. The voltage on the left side is

equal to the input voltage from the dc source in the circuit times the turns ratio of the transformer.

For the 5-volt case the input voltage would be 72V for a duty ratio of 45% and the turns ratio is

1.5/19.0 from the above discussion on transformer design. The t variable is equal to the period of

10 s times the duty ratio of 45%. Delta I was chosen such that the current ripple was ± 50% at a 1-

Watt load. Through careful examination of equation 13 it is apparent why the 1-Watt load case was

used. As load goes down the inductor size goes up, therefore, the inductor was chosen at the low

load case of one watt to assure that it would provide adequate filtering at all loads. A sample

calculation for the five-volt side is shown below.

L

5v side

= (72V1.5/19.0 – 5V).4510*  s / (1W/5V100%) = 15.40*  H (14)

The values for each of the output inductors along with capacitors will be shown in Table 3 after the

capacitor sizing calculations have been discussed.

The capacitors were sized according to the equation below.

C =  Icdt /  Vc (15)

Referring again to Figure 1 it can be seen that when the voltage being applied across the

transformer is positive the current in the inductor will ramp upwards due to the positive voltage on

it. When the voltage goes down the voltage on the inductor is negative and the current ramps

downward. This results in an inductor current with a triangular ripple of ± 50% oscillating around

an average value. Using Kirchoff’s current law and the fact that the average capacitor current must

be zero we can quickly tell that the capacitor current looks like a triangular waveform that oscillates

about zero amps with the exact same amplitude as the inductor current. Thus, the integral in

equation 15 simplifies to an area calculation of a triangle. The change in capacitor voltage is equal

to the ± 3% ripple that was desired from our specifications. A sample calculation for the five-volt

side can be seen below.

C

5v side

= (1/2 * 5  s * .1A) / .3V = .833  F (16)

Table 3 below shows the results of both the inductor and capacitor calculations.

5V 12V 15V

Inductor 15.40 H 28.42 H 46.18 H

Capacito

r

.833F .145 F .093 F

Table 3. Inductor and Capacitor Sizes for Output Filter.

3.4 PWM Chip

The following diagram, Fig. 4, represents the simplified view of the PWM chip used for the

switching converter. The following discussion analyzes the implementation of each pin and the

circuitry associated with it. APPENDIX B depicts the final layout of the dc-dc converter including

all the pin-outs of the PWM chip. APPENDIX B and Figure 4 provide a clear picture of the

ensuing discussion.

Fig. 4. Simplified View of PWM Chip.

Starting from the top left part of Fig. 4, pin 16 is the reference voltage supplied by the chip. This

5.1V output is used for the reference voltage of the feedback control circuitry. Next, pin 4 delivers

the clock pulse signal generated by the oscillator. The oscillator operates on the RC time constant

created by the resistor in pin 5 and the capacitor located on pin 6. The value of Rt (pin 5) is 4.6k Ω

and Ct (pin 6) is 1500pF. Thus this RC time constant results in a theoretical frequency of 145kHz.

Pin 7 can be used for current sensing but since the chip operates in voltage mode control, it is

connected directly to pin 6. The error amplifier output (pin 3) is connected to the inverting input of

the error amplifier to create a unity gain op-amp. This way, the voltage signal being fed into pin 2,

which comes from the feedback circuit, can directly control the duty ratio of the outputs. The soft-

start pin (pin 8) is used for slowly bringing the circuit operation up to speed. Pin 10 is the signal

ground for the PWM chip. The current limit/shutdown function (pin 9) is not used in this design.

Pin 15 is used for chip power and pin 13 provides direct voltage to the gates of the two switching

transistors. Pins 14 and 11 are the outputs to the FETs. Lastly the power ground is connected to

pin 12. It is important to make sure that the power ground and the signal ground do not mix at the

wrong point. The power ground can carry as much as 2.0A of current. If this current is somehow

introduced to the signal ground, the PWM chip could be rendered useless.

3.5 Feedback Circuit

Proportional-integral control permits steady and continuous operation of the converter. Using

solely proportional control would cause problems when the feedback signal is equivalent to the

reference signal. Since the difference between the two signals is zero, the output of the circuitry

would be zero, which would drive the duty ratio to zero and turn off the circuit. A purely integral

control is also ineffective due to a problem known as “integrator windup”. If the output is driven

down quickly, the integrator (which integrates the error function over time) would accumulate error

and keep the duty cycle high for a long period of time. Doing so would overshoot the desired

R

3

2

8

4

1

V+

V-

OUT

C

Fig. 6. Integral Op-Amp.

Zener diodes were added across the capacitor in our control circuit to prevent the integrator windup

previously discussed. The gain of this op-amp can be determined using the resistive and capacitive

values of the op-amp as shown in Equation 19.

kI = - 1/RC (19)

Once again, due to the inverting configuration, the gain is negative. The final stage of the control

circuit is the summer. The summing op-amp adds the outputs of the proportional circuit and the

integrator circuit. The summing op-amp is also in the inverting configuration and since the resistors

are equivalent, the gain is –1. The output of the summer is fed into pin 2 of the PWM chip for duty

cycle control.

The control circuit is necessary for autonomous operation of the circuit. Proportional-integral

control using four op-amps is the most reliable and cost-effective implementation available today.

3.6 Startup Circuit

The initial source of power is supplied by everyday household alkaline batteries - a 9V and two-

1.5V batteries in series. The 12V is passed through a forward-biased diode into pin 15, which is the

power pin of the chip, as shown in Fig. 7 on the next page. The other input is the output of the 15V

feedback from the transformer. The battery power remains on for a split second while the circuit

turns on. Once on, however, the feedback supplies the PWM chip with power and prevents battery

power from advancing past the diode, essentially shutting the batteries off. A zener diode is

included in the circuit as a precautionary measure to ensure that the voltage to the PWM chip does

not exceed 18V.

18 V

12 V

From feedback

To pin 15

1 2

Fig. 7. Start-up Circuit.

4.0 DESIGN VERIFICATION

To reiterate the design goals of the project, a power supply was to be built that would take an input

voltage of 110-230Vac and give as outputs +5V, -5V, +12V, -12V with voltage ripples of no more

than ± 3% and an overall efficiency of at least 75%. Many of these design goals were met,

however, a few were unattainable for various reasons. The discussion that follows will verify what

worked and what didn’t.

The first thing on the list of design specifications was that the converter would be able to operate at

ac voltages up to 230V. This criteria was not met though. The converter functioned correctly at a

maximum ac voltage of 140V at one point during the testing phase, however, it only functioned for

approximately one minute before one of the FETs failed. After reconstructing the circuit it was

found that reliable operation could only be obtained at a maximum ac voltage of 110V. The noise

level in the circuit became too great above that voltage and the circuit failed after a short period of

time. The circuit was tested for proper operation at ac voltages of 90, 100, 110V, and functioned

correctly at each of these voltages for an extended period of time (approximately one half of an

hour). Thus, the maximum voltage specification was not met, but reliable operation at voltages

equal to the minimum specification and below was obtained. Please refer to Table 4 below to

verify that the proper outputs were obtained at each of the ac voltage levels.

P out,

Watts

Vin +5V

+5V %

Difference

-5V

-5V %

Difference

+12V

+12V %

Difference

-12V

-12V %

Difference

9.92 91.00 4.82 -3.60% -4.86 -2.80% 12.00 0.00% -12.01 0.08%

10.10 100.00 4.90 -2.00% -4.91 -1.80% 12.03 0.25% -12.10 0.83%

10.09 110.00 4.90 -2.00% -4.90 -2.00% 12.02 0.17% -12.02 0.17%

19.28 90.00 4.84 -3.20% -4.85 -3.00% 12.01 0.08% -12.00 0.00%

19.39 100.00 4.86 -2.80% -4.87 -2.60% 12.03 0.25% -12.02 0.17%

19.19 110.00 4.82 -3.60% -4.83 -3.40% 12.00 0.00% -12.00 0.00%

59.24 90.00 4.86 -2.80% -4.92 -1.60% 11.99 -0.08% -12.00 0.00%

60.04 100.00 4.93 -1.40% -4.94 -1.20% 12.03 0.25% -12.01 0.08%

59.98 110.00 4.93 -1.40% -4.94 -1.20% 12.02 0.17% -12.02 0.17%

84.70 90.00 4.97 -0.60% -4.99 -0.20% 12.00 0.00% -12.01 0.08%

86.91 100.00 5.06 1.20% -5.02 0.40% 12.13 1.08% -12.08 0.67%

85.80 110.00 5.01 0.20% -5.00 0.00% 12.07 0.58% -12.04 0.33%

Average N/A 4.91 -1.83% -4.92 -1.62% 12.03 0.23% -12.03 0.22%

Table 4. Outputs at varying loads and input voltages.

The above table shows the results of lab testing. The circuit operated at input voltages of 90, 100,

and 110V for loads of approximately 10, 20, 60, and 85 Watts. The results were averaged and a

percent difference from desired was also calculated. As can be seen from the table all individual

data points and the averages are within the ± 3% specification (6% total difference).

The output voltage ripple was examined at 60hz and 100khz. The 100khz ripple was associated

with the switching of the converter and was well within specifications. It was measured for loads

between 10 and 85 Watts and was below .25V peak to peak for all outputs and loads. This is better

than expected and easily meets the specifications laid out for the converter. Plots of the 100khz

voltage ripple can be seen in figures 8-9 below for each of the positive outputs at maximum load

and 110Vin. The graphs of the negative outputs have been omitted to save space. They are identical

to their positive counterpart and would provide no extra insight into the functioning of the circuit.

Fig. 10. +5V and +12V 60 ripple for Vin = 110V and Pout = 85 Watts.

The next design specification was the load specification. The converter was supposed to function

over the range of 1 Watt to 85 Watts. This criteria was not met, however. The circuit exhibited

unstable operation at load levels below 10 Watts, but functioned correctly at loads above this and up

to 85 Watts.

The last design specification to be met was efficiency. The goal was to attain efficiencies at or

above 75%, which was accomplished for all load cases. The efficiency was calculated as =Pin/Pout

for loads between 10-85 Watts at voltages of 90, 100, 110V. The results can be viewed in graphical

format below in figure 11.

Efficiency Versus Varying Input Voltage at Different Loads

72%

74%

76%

78%

80%

82%

84%

86%

88%

90%

92%

90.00 100.00 110.

Input Voltage

Efficiency

(^) 10 Watt Nominal Load

20 Watt Nominal Load

60 Watt Nominal Load

85 Watt Nominal Load

Figure 11: Efficiency as a Function of Load and Input Voltage.

The graph illustrates several points. For one, the efficiency goals were met. The efficiency was

between 78% and 91% depending upon the load. A trend can also be seen that the efficiency

decreases with increasing load. This was expected because as the load increases so does the power

and therefore the current increases which leads to greater losses in the switching devices. Each

device has an internal resistance associated with it, which causes I

2

R losses in the circuit.

5.0 COST

The cost of the converter reflects the price of the parts involved in the design and the labor used in the research, design and development of the project. The engineers were hired at $25.00 / hr. During the 16 weeks the project was designed, a combined 600 man-hours were spent for a total of $37,500. A breakdown of the parts used and price per part is listed in Table 6 below. The project was completed at a final cost of $37,617.82.

• 1. Introduction.....................................................................................................................
• 2. Design Procedure ...........................................................................................................
  • 2.1 AC – DC Rectifier..............................................................................................
  • 2.2 DC – DC Switching Topology...........................................................................
  • 2.3 Transformer........................................................................................................
  • 2.4 LC Filter.............................................................................................................
  • 2.5 PWM Chip.........................................................................................................
  • 2.6 Feedback Circuit................................................................................................
  • 2.7 Startup Circuit....................................................................................................
• 3. Design Details................................................................................................................
  • 3.1 AC – DC Rectifier..............................................................................................
  • 3.2 Transformer........................................................................................................
  • 3.3 LC Filter.............................................................................................................
  • 3.4 PWM Chip.........................................................................................................
  • 3.5 Feedback Circuit..............................................................................................
  • 3.6 Startup Circuit..................................................................................................
• 4. Design Verification......................................................................................................
• 5. Costs.............................................................................................................................
• 6. Conclusions..................................................................................................................
  • APPENDIX A..............................................................................................................
  • APPENDIX B..............................................................................................................
  • APPENDIX C..............................................................................................................
  • REFERENCES............................................................................................................
  • 1 C3 10 uF electrolytic Cap $0.18 $0. Part Number Quantity Part Reference Description Price Total
  • 1 D6 Diode Bridge $1.86 $1.
  • 1 C5 270uF, 400V cap $3.36 $3.
  • 1 C1 1500pF Cap $0.32 $0.
• 1N4733A 1 D4 Zener Diode $0.15 $0.
  • 1 C4 .015 uF $0.15 $0.
  • 1 R3 47 ohm $0.13 $0.
• MBR360 6 D1 Zener Diode $0.34 $2.
• MBR160 2 D3 Diode $0.55 $1.
• 1N4746A 1 D5 Zener Diode $0.15 $0.
  • 2 R2 10 ohm,1W $0.50 $1.
  • 2 R5 1000 ohm, 1/4W $0.13 $0.
  • 1 R1 22 ohm $0.13 $0.
• MTP4W80 2 Q1 Transistors $0.55 $1.
• B1045 8 D2 Diode $0.85 $6.
  • 9 C2 2.2 uF cap $0.15 $1.
  • 1 16 AWG Spool $30.00 $30.
  • 1 22 AWG Spool $30.00 $30.
  • 2 L2 Ferrite Core $2.00 $4.
  • 3 T1, L1 Ferrite Core $3.50 $10.
  • 2 L3 Ferrite Core $4.00 $8.
• MC34875 1 PWM Chip $6.00 $6.
  • 1 R4 4.6k Ohm $0.13 $0.
  • 9 R6 1k Ohm $0.13 $1.
• 1N4728A 2 D7 Zener Diode $0.16 $0.
  • 1 R7 5k Potentiometer $3.50 $3.
  • 2 AA Alkaline Battery, Start-up $0.34 $0.
  • 1 9V Alkaline Battery, Start-up $1.19 $1.
  • 2 Diode, Start-up $0.10 $0.
  • 1 Zener Diode, Start-up $0.79 $0.
  • 2 93 ohm, 1/4W, voltage divider $0.13 $0.
  • 2 230 ohm 1W, voltage divider $0.50 $1.
    • $117.