5D-i APPENDIX 5D. ANALYSIS OF POTENTIAL EFFICIENCY IMPROVE MENTS

TABLE OF CO NTENTS

5D.1 OVERVIEW

................................................................................................................. 5D-1

5D.2 METHODOLOGY

....................................................................................................... 5D-1

5D.2.1 Ballast Selection

................................ ................................ ................................ 5D-1

5D.2.2 Schematics

........................................................................................................ 5D-1

5D.2.3 Efficiency and Power Loss Measurements

....................................................... 5D-2

5D.2.4 Efficiency Improvements

.................................................................................. 5D-2

5D.2.4.1 Active Rectification

.................................................................. 5D-2

5D.2.4.2 New Circuit Designs

................................................................. 5D-3

5D.2.4.3 Improved Components .............................................................. 5D-3

5D.3 RESULTS

..................................................................................................................... 5D-4

5D.3.5 Commercial 4

- foot MBP T8 Ballasts

............................................................... 5D-4

5D.3.5.1 Schematic

.................................................................................. 5D-4

5D.3.5.2 Stage Losses and Component Substitution ............................... 5D-5

5D.3.6 Residential 4

- foot MBP T8 Ballasts

................................................................. 5D-9

5D.3.6.1 Schematic

.................................................................................. 5D-9

5D.4 CONCLUSION

........................................................................................................... 5D-11

LIST OF TABLES

Table 5D.1 Power Losses by Functional Stage, Commercial Ballast....................................... 5D-6 Table 5D.2 Measured Losses When Using Higher Current Diodes ......................................... 5D-6 Table 5D.3 Measured Losses When Using Improved Cores and Windings for Magnetics ..... 5D-7 Table 5D.4 Output Transformer Substitution ........................................................................... 5D-7 Table 5D.5 Measured Losses When Using Improved Transistors and Capacitors ................... 5D-8 Table 5D.6 Power Losses by Functional Stage, Residential Ballast ...................................... 5D-10 Table 5D.7 Measured Losses When Using Improved Magnetics ........................................... 5D-105D

- 1 APPENDIX 5D. ANALYSIS OF POTENTIAL EFFICIENCY IMPROVE MENTS

5D.1 OVERVIEW

When the U.S. Department of Energy ( DOE ) proposes to adopt or to decline to adopt an amended or new standard for a type (or class) of covered product, as part of the rulemaking

process , DOE must ‘‘determine the maximum improvement in energy efficiency or maximum reduction in energy use that is technologically feasible’’ for the product. (42 U.S.C. 6295(p)(1))

In the technology assessment, DOE identifies various technology options emplo yed in commercially available b allasts to improve efficiency. DOE then applies the four screening criteria to determine which of these options DOE consider s in the engineering analysis. In this appendix, DOE summarizes its efforts to improve ballast effici ency beyond that whi ch exists in the market today. In the following sections , DOE discusses its methodology, results , and conclusions of this analysis.

5D.2 METHODOLOGY

To determine whether a working prototype could be created at higher efficiencies than

those commercially available

, DOE analyzed some of the most efficien t ballasts on the market.

DOE create d schematics, measured losses in each functional stage of ballast, and substituted components with the goal of creating a more efficient ballast. DOE supplemented this investigat ion with information from manufacturer interviews, subject matter experts, scholarly articles, U.S. patents, and manufacturer marketing information. DOE also considered efficiency improvements used in comparable products, such as power supplies.

5D.2.1 Ballast Selection

In conducting this analysis, DOE attempted to improve the efficiency of a ballast beyond that which was available on the market. As such, DOE selected several of the most efficient ballasts, as identified by DOE test data, f or use in its analysis. Specifically, DOE analyzed 2- lamp 4 -foot MBP ballasts in the commercial and residential sectors

. DOE selected ballasts from multiple manufacturers in order to identify different designs and components that may be used to

increase ba llast efficiency.

5D.2.2 Schematics

To understand the components and circuit types used in the most efficient fluorescent lamp ballasts, DOE began by opening the ballast enclosure and removing the circuit board . In some cases, DOE had to remove potting, a black tar -like substance, from the ballast casing. 1

1 Although DOE was unable to conduct a teardown for ballasts that were potted, DOE was able to perform this analysis because the potting material did not have to be completely removed in order to identify the type of component for inclusion in a circuit diagram . C omplete removal of potting was required for a teardown, but DOE found this process often damaged some connections and components such that the ballast would not properly

function

.5D

- 2 Some manufacturers use potting for temperature control and to increase product reliability. For DOE’s analysis, the potting prevented observation of the circuit board and needed to be

removed. DOE heated the b allast until the po tting softened and then removed the potting manually with tweezers. Once each ballast’s circuitry and components were exposed, DOE was able to study the ballast’s internal design. DOE developed schematics of each ballast and

identified t he various functional stages. DOE also identified the key components associated with each stage.

5D.2.3 Efficiency and Power Loss Measurements

DOE measured the efficiency of the overall ballast and the power losses associated with each functional stage . This approach identified the functional stages that contributed the greatest percentage of losses, representing the greatest potential gains in total efficiency. DOE made efficiency measurements with a resistor load to reduce testing variation between measurements. This is because DOE analyzed the ballast s on a standard laboratory bench without strict controls

on temperature variation and air movemen t. Measurements with a resistor are less sensitive to environmental conditions, reducing variation from test to test. In addition, tests with a resistor can be instantaneous while lamp measurement s are best taken after the lamp and ballast system have reached steady state. Thus, use of resistor loads helped to expedite the analysis. Once DOE identified a component change that increased overall ballast efficiency using resistor testing,

DOE would repeat the measurements using a lamp load to confirm the results

.

5D.2.4 Efficiency Improvements

The following sections discuss various ways in which DOE attempted to improve ballast efficiency, such as active rectification, new circuit designs , and improved components.

5D.2.4.1 Active Rectification

In the engineering analysis, the most efficient ballasts DOE identified were electronic ballasts. As described in the technology assessment (NOPR TSD chapter 3), the second stage of an electronic ballast is the input rectifier, which converts AC waveforms to DC. Through its research, DOE learned that commercially available ballasts use a process known as passive rectification to complete this step. A p assive rectification circuit typically consists of four diodes to rectify the AC waveform. Passive rectification is currently used in commercially available ballasts because it is simple to design, contains few parts, is reliable, and is relatively inexpen sive to manufacture. 1

With technological advancements in electronics in the past few decades and new developments in controls, metal-oxide-semiconductor field- effect transistors (MOSFETs) have become a popular component of power electronics. MOSFETs can h ave much lower electrical losses compared to diodes. Active rectification uses these MOSFETs in place of diodes to convert AC to DC current. Because MOSFETs operate in a slightly different manner than diodes, an integrated circuit is necessary to switch th e MOSFETs on and off as required. Even though this requires additional circuitry, the use of active rectification still results in an overall increase5D

- 3 in efficiency because the electrical losses of the MOSFETs are much smaller than that of the

diodes.

Af ter developing ballast schematics, DOE considered whet her it was possible to incorporate active rectification into an existing ballast design. At this step, DOE encountered several obstacles. DOE had difficulty identifying MOSFETs which would have smaller losses compared to the existing diodes, after accounting for switching losses. Furthermore, DOE was uncertain how to incorporate and optimize an integrated circui t in the overall ballast design

.

DOE calculated that only about 4 percent of overall losses were attributable to the input rectification stage in the commercial 2

- lamp 4

- foot MBP ballasts analyzed . Even if the losses from this stage were eliminated entirely, it would only lead to at most a half percent increase in overall efficiency. Because it is highly unlikely that all losses from this stage could be eliminated, actual savings from using active rectification would likely be less than a half percent – which is within the margin of error of the test procedure. In addition to these results, DOE’s research revealed that active rectification was typically only used in power supplies with input powers in the kilowatt (kW) range, which is larger than the input power of any ballast covered by this rulemaking. Based on this analysis, DOE does not believe active rectification is a possible means of improving fluorescent ballast efficiency.

5D.2.4.2 New Circuit Design s

DOE also considered the possibility of creating a completely new ballast design to achieve the highest efficiency possible, regardless of cost

. This method would not limit DOE to the design choices already made for commercially available ballasts. However, given the available resources, DOE determined that this approach was not practical. DOE was also unsure if the ballast design it developed could be manufactured on a large scale, as a similar product may not exist. Therefore, DOE decided not to pursue this approach.

5D.2.4.3 Improved Components

As described in the technology assessment (NOPR TSD chapter 3), improving the quality of the components in a ballast can increase efficiency. In particular, DOE determined that diodes, transistors, transformers, inductors, and capacitors are the main components that impact efficiency. Using the selected commercially available ballast as a point of reference, DOE used

com ponent manufacturer datasheets to identify alternative components with lower electrical losses to be used in a more efficient ballast design. If more than one alternative existed, DOE chose the component that demonstrated the lowest electrical losses and t herefore had the greatest potential to impact overall efficiency. When necessary, DOE wound custom magnetic components for use as substitutes. DOE focused its efforts on the functional areas with the greatest potential for energy savings. To determine if i mproved components can reduce electrical losses and increase ballast efficiency, DOE substituted the identified alternative components for the original components in the otherwise unaltered ballasts and measured the effects of each change on ballast effici ency.5D

- 4 DOE intended to develop incremental prices for component replacements if it determined that the improved components reduced losses and increased efficiency. Because no such improved components were identified, DOE did not include incremental compon ent price calculations in this appendix.

5D.3 RESULTS

The following sections summarize the results of DOE’s analysis including descriptions of ballast schematics and efficiency changes resulting from component substitution. DOE analyzed

commercial and residen tial 4 -foot MBP T8 ballasts. For the commercial ballast, DOE presents results using both 120V and 277 V input voltage.

5D.3.5 Commercial 4-foot MBP T8 Ballasts

5D.3.5.1 Schematic

The figure below shows a sample commercial 2

- lamp 4

- foot MBP ballast schematic divided into functional stages. This sample schematic shows a current -fed design with a boost power factor correction and resonant inverter stage.

The e lectromagnetic i nterference ( EMI ) filter c ircuit includes an inductor and capacitor

connected as a second-order low- pass filter to block circuit -generated noise from conducting

back onto the AC line input. The corner frequency of the filter is selected such that the conducted noise on the AC line stays below the maximum allowable FCC limits. The low

- pass filter, together with the varistor , also helps to suppress damaging voltage transients that can occur on

the AC line. The EMI filter circuit also incl udes two Y- capacitors, each connected from the live AC voltage inputs and neutral AC voltage inputs to ground , for limiting possible lethal leakage

currents that can flow from the circuit to ground.

The bridge rectifie r circuit includes four diodes and converts the AC sinusoidal line voltage into a full- wave rectified voltage (absolute value of a sinusoid). When the AC lin e voltage is positive, two diodes provide the current path to and from the rest of the circuit located

after the rectifier. When the AC line voltage is negative, the other two diodes provide the current path. The full-wave rectified voltage at output of the rectifier is then fed to the boost power factor correction ( PFC ) circuit.

The boost PFC circuit is generally only found in commercial ballasts. It includes an

inductor , a switch

, an d a diode connected in a boost configuration that performs the necessary power factor correction of the ballast input current. As the switch is turned on and off at a given duty cycle and frequency, the current flowing through the inductor ramps up and down linearly to form a triangular -shaped current. The peak of this triangu lar shapedcurrent follows the fullwave rectified voltage envelope at the output of the rectifier. This current is then filtered by the EMI filter at the input to produce a sinusoidal input current that is in phase with the AC input voltage to give a high power factor (>0.95). The boost PFC circuit also maintains a constant DC bus voltage across the bus capacitors . During the on -time of the switch, the current flows through

the inductor and through the switch to ground causing the inductor current to charge up to a peak5D

- 5 value. During the off-time of the switch, the inductor current then discharges through the

inductor and the diode and to the DC bus capacitors. The on

- time of the switch is adjusted dynamically by a feedback loop to deliver more or less curr ent to the DC bus during each switching cycle to keep the DC bus voltage constant during all ballast line and load conditions. The boost PFC circuit is controlled by a standa rd critical -conduction mode PFC control integrated circuit ( IC ).

The resonant inv erter circuit incl udes a resonant transformer, a resonant capacitor, and

two switches (with bipolar junction transistors (BJT) ), and converts the DC bus voltage into a high -frequency AC voltage. The two switches are turned on and off at the resonant freque ncy de termined by the transformer and capacitor . This produces a high quasi-sinusoidal AC voltage at the output node of the resonant circuit. This AC high voltage is then fed to the primary side of the output transformer.

The output transformer circuit co nsists of a step

- up transformer for increasing the input voltage (from the resonant inverter stage) up to a higher voltage that is then used to ignite and run the lamps. The transformer also provides galvanic isolation of the lamps from the rest of the

cir cuit for safety. Additional smaller third and fourth windings are included on the transformer and are used to turn the inverter switches on and off. The secondary side of the transformer then

goes to two biasing capacitors that are used to control the current through each lamp independently. A current sensing tr ansformer is used to measure the current flowing through the lamps and feedback the measurement to a fault detection circuit to protect against an open- circuit load condition (both lamps removed).

Figure 5D .1 Schematic of Commercial Ballast

5D.3.5.2 Stage Losses and Component Substitution

DOE took measurements at key junctions between the functional stages of the ballast. Using these measurements, DOE calculated the losses associated with each stage. Table 5D.1

shows the calculated power losses at each functional stage of the sample commercial 2

- lamp 4

- foot MBP ballast using a resistor load

.

DOE found that the majority of losses came at the output transformer and resonant inverter stages and concluded that improvements at these stages held the greatest potential for improving overall efficiency. These were followed by losses at the boost PFC stage. Finally, the5D

- 6 losses at the EMI fil ter and r ectifier stages were comparatively small, leading DOE to conclude that improvements at these stages had very limited potential to impact overall efficiency.

Table 5D.1 Power Losses by Functional Stag e, Commercial Ballast Stage 277V losses (W) 277 V losses as % of total

EMI 0.3 4.8

Rectifier 0.2 3.2

Boost PFC 0.8 12.9

Resonant Inverter 2.4 38.7 Output Transformer 2.5 40.3

Total 6.2 100

In the preliminary analysis, DOE proposed replacing tradit ional silicon p

- n junction diodes with silicon carbide Schottky diodes. Schottky diodes generally have a smaller forward voltage drop than p-n junction diodes, resulting in reduced losses. However, for this analysis,

DOE was not able to find suitable Schot tky replacement diodes at the voltage levels required by

the ballast . DOE also tried substituting traditional diodes that can handle higher current loads for the existing rectifier diodes but did not see any significant efficiency improvement as there was a fixed forward voltage drop between the different diode types. Table 5D.2 shows the results of diode replacement.

Table 5D.2 Measured Losses When Using Higher Current Diodes

Paramet er Units Measurements at 277 V Existing (no changes)

Pin W 57.0

Pout W 51.7

Ploss W 5.3 Change rectifier diodes from 1A to 4A

Pin W 57.0

Pout W 51.6

Ploss W 5.4

For magnetic components, DOE considered the use of improved core materials and large r core sizes to reduce core losses and improved winding materials to reduce resistive losses in the coiled wires. A higher quality core material or larger core size can decrease the losses attributable to hysteresis and eddy currents. DOE assumed magnetic s currently used in fluorescent lamp ballasts employ an inexpensive, low

- grade steel. In the selected ballasts, DOE replaced the EMI filter inductor (EF20 core) with an inductor with a larger ferrite core (EF25). This change increased the length and width of the core from approximately 20 mm to 25 mm and the height from 6 mm to 7.5 mm. DOE also tried replacing the PFC stage inductor with a larger core (EF25) inductor. Finally, DOE tried replacing the resonant inductor and output transformers with higher quality cores (PC44) and hand wound litz wire. The PC44 core uses a cylindrical center bobbin compared to the rectangular bobbin of an EF type core. DOE was unable to increase ballast efficiency when making these replacements . Some substitutions resulted in

i ncreased losses because a decrease in core losses was accompanied by an increase in winding losses, or vice

- versa. Table 5D.3 summarizes the results of these substitutions.5D

- 7 Table 5D.3 Measured Losses When Using Improved Cores and Windings for Magnetics

Parameter Units Measurements at 277V Existing (no changes)

Pin W 57.0

Pout W 51.7

Ploss W 5.3 Replace EMI filter inductor with larger EF25 core

Pin W 57.1

Pout W 51.7

Ploss W 5.4 Replace EMI filter and PFC stage inductors with larger

EF25 cores

Pin W 57.6

Pout W 51.7

Ploss W 5.9 Replace EMI filter with larger EF25 core and replace resonant and output transformers with higher quality PC44 cores and hand wound litz wire (res ults at 120V)

Pin W 49.8

Pout W 43.0

Ploss W 6.8

In addition to the sample ballast discussed above, DOE also analyzed a similar ballast (hereafter ballast two) from another manufacturer. DOE found that ballast two had a slightly different output transformer with increased winding resistance on the secondary side. DOE rewound the transformer from the sample ballast to have approximately the same inductance as ballast two, but with lower winding resistance. After replacing the output transformer in ball ast two with the modified transformer from the original ballast, DOE found no improvement in efficiency. DOE also found this modification increased the output (and input) power to the ballast. After modifying the output capacitors to decrease the output po wer to the level of the original ballast, DOE found transformer substitution decreased overall ballast efficiency. Table

5D.4 summarizes the results of this substitution.

Table 5D.4 Output Transformer Substitution

Parameter Units Measurements at 277 V Existing (no changes)

Pin W 59.2

Pout W 54.5

Ploss W 4.7 Replace output transformer with redesigned output transformer from the original ballast.

Pin W 64.2

Pout W 59.35D

- 8 Ploss W 4.9 Replace output transformer with redesigned output transformer from the original ballast and modify the output capacitors to decrease output power.

Pin W 55.1

Pout W 49.7

Ploss W 5.4

For transistors and capacitors in the boost PFC and resonant in verter stages , DOE had limited success in identifying more efficient replacements. DOE found alternative MOSFETs

with reduced conduction losses (R DS_ON ), but did not locate more efficient bipolar transistors. Thus, DOE only proposed replacing existing MOSF ETS with a more efficient substitute. While MOSFETs could be used as substitutes for bipolar transistors, a circuit redesign would have been required to include an integrated circuit to control the MOSFETs. DOE chose not to undertake a significant redesign of the ballast. For MOSFETs, DOE replaced the 1 ohm PFC MOSFET with

a 0.35 ohm substitute to reduce conduction losses. DOE also substituted transistors with higher collector emitter saturation voltages for the original resonant inverter transistors. Final ly, DOE decreased the PFC gate drive resistor from 150 ohm to 47 ohm to increase the turn-on speed of the transistors to try to reduce switching losses.

For electrolytic capacitors, DOE identified two potentially more efficient components as potential replacements. First, DOE replaced the 22uF electrolytic capacitors (bus capacitors) in

the b oost PFC stage with 47uF electrolytic capacitors

. With this substitution, DOE attempted to
reduce the capacitor ripple current and DC bus ripple voltage delivered to later stage s, thereby

increas ing efficiency of downstream stages. DOE also substituted each bus capacitor with two 22 uF capacitors in parallel to reduce the equivalent series resistance

. Reducing the equivalent series resistance reduces the losses associated with a capacitor. DOE found that using the more

efficient component substitutes did not yield higher overall ballast efficiency. Table 5D.5 shows

the results of these substitutions.

Table 5D.5 Measured Losses When Using Improved Transistors and Capacitors

Parameters Units Measurements at 277V Existing (no changes)

Pin W 57.0

Pout W 51.7

Ploss W 5.3 Upgrade boost PFC MOSFET from 1 ohm to 0.35 ohm

Pin W 57.1

Pout W 51.7

Pl oss W 5.4 Upgrade boost PFC MOSFET to 0.35 ohm, replace EMI filter inductor with larger EF25 core, and upgrade 2 boost PFC electrolytic capacitors from 22 uF to 47 uF

Pin W 57.1

Pout W 51.7

Ploss W 5.4 Upgrade boost PFC MOSFET to 0.35 ohm, replace EMI filter inductor with larger5D

- 9 EF25 core, and replace resonant inverter transistors with higher collector emitter saturation voltage transistors

Pin W 57.4

Pout W 51.6

Ploss W 5.8 Upgrade boost PFC MOSFET to 0.35 ohm, replace EMI filter inductor with lar ger EF25 core, and insert 2 additional 22uF electrolytic capacitors at boost PFC stage

Pin W 57.1

Pout W 51.6

Ploss W 5.5 Upgrade boost PFC MOSFET to 0.35 ohm, decrease PFC gate resistor to 47 ohm

Pin W 57.9

Pout W 52.0

Ploss W 5.9 Upgrade boost PF C MOSFET to 0.35 ohm, decrease PFC gate resistor to 47 ohm, substitute PFC inductor from another ballast (removed 1.3 mH, 0.75 ohm, added 1.1mH, 0.67ohm)

Pin W 57.9

Pout W 52.0

Ploss W 5.9

5D.3.6 Residential 4-foot MBP T8 Ballasts

Similar to the commercial 4-foot MBP T8 ballasts , DOE studied residential ballasts and substituted components in an effort to improve efficiency.

5D.3.6.1 Schematic

Figure 5D.2 shows a schematic of a residential 2- lamp 4 -foot MBP ballast divided into

functional st ages. The circuit includes the same functional stages as a commercial ballast with the exception of the PFC stage, which is absent in most residential ballasts. The residential ballasts contained much fewer components than comparable commercial ballasts an d used a single layer circuit board with no traces on the top side. B ecause of the absence of the PFC stage,

the residential ballast output was more sensitive to fluctuations in input voltage than commercial

ballasts.

After studying the EMI stage

, DOE fo und that the 2- lamp 4

- foot MBP residential ballasts analyzed contained the same EMI filter as their commercial counterparts. Because residential ballasts are subject to more stringent EMI regulations, DOE expected these ballasts to contain higher performan ce EMI filters that would consequently have higher losses. One potential explanation for this observation is that the PFC stage in commercial ballasts creates additional EMI, so an EMI filter that can reduce the EMI from a commercial ballast to commercial regulat ory levels may be sufficient to reduce the lower levels of EMI from a residential ballast to the more stringent residential regulatory levels. Commercial ballasts have two sources of EMI

internal to the ballast

– switches in the PFC stage and switch es in the resonant inverter stage. These switches operate at different frequencies, increasing burden on the commercial EMI filter.5D

- 10 By contrast, residential ballasts have one major source of EMI – switches in the resonant inverter. Though residential ballasts have stricter FCC EMI standards, the lower levels of EMI generated by the ballast could allow for use of a more efficient EMI filter (that filters EMI to a lesser extent)

. DOE postulates that it is more likely that the EMI filter in the commercial ball ast is carefully optimized, because commercial ballasts hold a much larger market share. If this commercial EMI filter is sufficient for the residential ballast, manufacturers would then use the same EMI filter in both ballasts to take advantage of volume discounts.

DOE also observed differences in the inverter stage when comparing the residential

ballast to the commercial ballast. The residential ballast use d a “push

- pull” topology that delivers a sinusoidal output to split primary windings on the output transformer. In contrast, the

commercial ballasts use d a current

- fed half -bridge (“totem-pole”) topology to deliver sinusoidal output to a single primary winding on the output transformer.

Figure 5D .2 Sc hematic of Residential Ballast

The table below shows the losses in the EMI and r ectifier stages versus the resonant inverter and output transformer stages. DOE found the percentages of total losses by stage in the

residential ballast to be very similar to the losses in the commercial ballast at 120V. The residential ballast had a slightly higher percentage of losses in the resonant inverter and output transformer than the commercial ballast. Because the majority of losses come at the resonant

inverter and output transformer stage, DOE concluded that improvements at these stages have high est potential to improve overall ballast efficiency. DOE observed that the EMI filter was the

same for the residential and commercial ballast . Under the assumption that the EMI filter is optimized for the commercial ballast and used in the residential ballast to take advantage of volume discounts, it is possible that the EMI filter is more robust than necessary for the

residential ballast. However, DOE was not able to reduce the losses in this stage by reducing the inductance and winding resistance of the EMI filter.

Table 5D.6 Power Losses by Functional Stage, Residential Ballast

Functional Stage 120V losses (W) 120V losses as % of total

EMI f ilter and r ectifier + bus capacitor 1. 3 21.3

Resonant i nverter and o utput t ransformer 4. 8 78.7

Total 6.1 100.0

Table 5D.7 Measured Losses When Using Improved Magnetics

Parameters Units Mea surements at 120V5D

- 11 Parameters Units Mea surements at 120V Existing (no changes)

Pin W 57.3

Pout W 51.2

Ploss W 6.1 Increase bus capacitor from 47 uF to 100uF

Pin W 60.7

Pout W 53.9

Ploss W 6.8 Change EMI filter from 2x3.4 mH

– 4 ohm to 1 mH

– 1 ohm

Pin W 57.5

Pout W 50.7

Ploss W 6.8 Remove EMI filter (short)

Pin W 58

Pout W 51.7

Ploss W 6.3

5D.4 CONCLUSION

As described in the above sections, DOE identified technology options that could improve ballast efficiency beyond that of commercially available ballasts. Although DOE was

unabl e to increase the efficiency of a commercially available ballast using improv ed

components , DOE has not concluded this to be a non

- viable path to increasing efficiency. For the

commercial 2 -lamp, 4-foot T8 ballast type, DOE selected two models of slightly different efficiency for analysis. DOE was unable to increase the efficiency of either unit using more efficient components. However, because one ballast was more efficient than the other, certain design and component changes between the two units must res ult in increased efficiency. Furthermore, it is possible that substitution of components introduced a small amount of additional losses because several connections had to be cut and then reestablished using a manual soldering process.

In general, DOE con cluded that switching losses and losses associated with magnetic components offer the greatest potential for improving the efficiency of a ballast. While substituting transistors that had reduced conducted losses (R DS_ON ) did not noticeably impact overall ballast efficiency, transistors with lower capacitance could decrease switching losses

. DOE also found that increasing the size of the magnetic cores (keeping the shape and material constant) and using litz wire instead of single

- stranded wire did not incr ease overall efficiency. A

focus on substitution of cores made of higher grade materials and more efficient shapes (resulting in higher core factors) could increase ballast efficiency

.

DOE also found that 4- foot MBP commercial and residential ballasts use similar

components. However, there are a few possible improvements that are only applicable to residential products. For example, a residential ballast could be designed with an EMI filter5D

- 12 optimized for the level of EMI it generates , which could potenti ally improve efficiency. In addition, although residential ballasts do not include a boost PFC stage, a bus capacitor could be added to boost voltage to commercial ballast bus voltage levels (about 400V). This could potentially increase efficiency by minim izing conductive losses in later stages of the ballast.5D

- 13 REFERENCES

1 Santiago, Walter and Arthur G. Birchenough. Single Phase Rectification Versus Active Rectification Applied to High Power Stirling Engines . Third International Energy Conversion Engineering Conference; 2005 Aug 15 – 18; San Francisco, California. Maryland: NASA Center for Aerospace Information; 2006. p. 1-12.