5D-i 

APPENDIX 5D. ANALYSIS OF POTENTIAL EFFICIENCY IMPROVEMENTS

TABLE OF CONTENTS

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-10
5D-1

APPENDIX 5D. ANALYSIS OF POTENTIAL EFFICIENCY IMPROVEMENTS

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 employed in 

commercially available ballasts to improve efficiency. DOE then applies the four screening 

criteria to determine which of these options DOE considers in the engineering analysis. In this 

appendix, DOE summarizes its efforts to improve ballast efficiency beyond that which 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 efficient ballasts on the market. 

DOE created schematics, measured losses in each functional stage of ballast, and substituted 

components with the goal of creating a more efficient ballast. DOE supplemented this 

investigation 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, for 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 ballast 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. Complete 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 ballast until the potting 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 the 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 ballasts on a standard laboratory bench without strict controls 

on temperature variation and air movement. 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 measurements 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 passive 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 

inexpensive 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 have 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 the MOSFETs on and off as required. Even though 

this requires additional circuitry, the use of active rectification still results in an overall increase 
5D-3

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

diodes. 

After developing ballast schematics, DOE considered whether 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 circuit 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 Designs 

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 

component 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 therefore 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 improved 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 efficiency.
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 component 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 residential 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 electromagnetic interference (EMI) filter circuit 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 includes 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 rectifier 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 line 

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, and 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 triangular shaped current 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 peak 
5D-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 current 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 standard critical-conduction mode PFC control 

integrated circuit (IC). 

The resonant inverter circuit includes 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 frequency 

determined 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 consists 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 

circuit 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 transformer 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, the 
5D-6

losses at the EMI filter and rectifier 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 Stage, 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 traditional 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 Schottky 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

Parameter 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 larger 

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 magnetics 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 

increased 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 (results 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 ballast 

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 power 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 59.3
5D-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 inverter stages, DOE had 

limited success in identifying more efficient replacements. DOE found alternative MOSFETs 

with reduced conduction losses (RDS_ON), but did not locate more efficient bipolar transistors. 

Thus, DOE only proposed replacing existing MOSFETS 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. Finally, 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 boost 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 stages, thereby 

increasing 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

Ploss 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 larger 
5D-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 larger 

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 PFC 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 stages. 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 and used a 

single layer circuit board with no traces on the top side. Because 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 found 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 performance 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 

regulatory 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 switches 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 ballast 

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 used a “push-pull” topology that delivers 

a sinusoidal output to split primary windings on the output transformer. In contrast, the 

commercial ballasts used a current-fed half-bridge (“totem-pole”) topology to deliver sinusoidal 

output to a single primary winding on the output transformer. 

Figure 5D.2 Schematic of Residential Ballast 

The table below shows the losses in the EMI and rectifier 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 

highest 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 filter and rectifier + bus capacitor 1.3 21.3

Resonant inverter and output transformer 4.8 78.7

Total 6.1 100.0

Table 5D.7 Measured Losses When Using Improved Magnetics

Parameters Units Measurements at 120V
5D-11

Parameters Units Measurements 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 

unable to increase the efficiency of a commercially available ballast using improved

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 result 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 concluded 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 (RDS_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 increase 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 filter 
5D-12

optimized for the level of EMI it generates, which could potentially 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 minimizing 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.