Comparison of Different Bypass Diode Technologies
Gough Yumu Lui1, Richard Corkish2
1,2
School of Photovoltaics and Renewable Energy Engineering,
The University of New South Wales
Sydney, NSW, 2052.
1
gough@student.unsw.edu.au, 2r.corkish@unsw.edu.au
ABSTRACT
Bypass diodes are used in photovoltaic modules to prevent damage from hot-spot
heating and improve safety. However, as cells have become larger and more efficient,
there are concerns that the diodes could overheat and fail under the increased current.
Qualification testing is insufficient (Wohlgemuth and Kurtz, 2011), and there is
evidence of unidentified failure modes in thermal runaway from shaded to unshaded
transitions and degradation of plastic encapsulation from long term exposure to high
temperatures (Fahrenbruch, 2010). One solution is to change to a new bypass diode
technology. There is existing literature from the companies producing these “lossless”
diodes which extol their benefits (Acciari et al., 2011) but they do not compare the
lossless diodes with other competing technologies. Preliminary testing was undertaken
to compare the performance of P-N, Schottky, Super Barrier Rectifier (SBR), Trench
MOS Barrier Schottky (TMBS) and Lossless Diodes in terms of voltage drop, power
dissipation, junction temperature rise, reverse bias leakage current, timing
characteristics and I-V characteristics to determine the suitability of these diodes. While
there were limitations in our testing procedure, it was determined that only Lossless
Diodes offer significant benefits over Schottky diodes in all tested areas. Despite the
benefits offered by Lossless Diodes, there are also potential barriers, such as the
positive temperature co-efficient of voltage drop, and their high costs. Further research
is required to fully understand the impact of the timing characteristics of some lossless
diodes and how that affects PV systems, and to understand how the lossless diodes
behave when subjected to lightning surge transients.
Keywords : bypass, diode, failures, lossless, overheating, photovoltaics
INTRODUCTION
Bypass diodes have become a standard feature of photovoltaic modules. They are
provided to protect the module from hot-spot heating in case of shading, as well as
improve energy collection in cases of shading (Wenham et al., 2006), and provide
limited protection against arcing (Spooner and Wilmot, 2008). Most modules produced
today use Schottky diodes to perform the bypass function, however, with increasing
efficiencies and wafer sizes, the increased current and self heating may cause bypass
diodes to fail prematurely from overheating (Fahrenbruch, 2010, Arp, n.d.). With the
advent of new diode technologies claiming significant benefits over the Schottky diode,
and questions about whether it is wise to change to a new bypass technology, it is
important to evaluate these new technologies for their suitability to ensure optimal
decisions.
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LITERATURE REVIEW
A literature review was completed in order to understand the concerns posed by
Fahrenbuch (2010) and Arp (n.d.). The present requirements of bypass diodes in
modules must first be identified. Secondly, field data must be assessed in order to
identify that there is a problem. Finally, the causes of failures must also be identified in
order to be able to understand whether a change of technology will solve the problem.
The Shortcomings of Qualification Testing
Qualification testing is a set of well defined, standardized accelerated stress tests which
are used to qualify modules to a minimum standard. At present, IEC 61215 Edition 2 is
the primary standard to which modules are presently qualified. This standard includes a
bypass diode thermal test, which tests to ensure the junction temperature of the bypass
diode does not exceed the manufacturer’s rating while being subjected to an ambient
temperature of 75˚C and the short-circuit current of the module. It also tests to see that
the diode is operational after applying 1.25 times the short-circuit current of the module
for an hour. Furthermore, the insulation resistance should meet the same requirements
as initial measurements and no major visual defects may occur (IEC, 2005).
Qualification testing has been criticised for being wrongly applied in ways that do not
make sense and for being wrongly taken to be the only testing required (Wohlgemuth,
1994). It is concluded that a module which passes qualification testing does not
necessarily make a reliable module (Wohlgemuth and Kurtz, 2011).
Qualification testing has also been criticised for the difficulty in equating accelerated
stresses with field lifetimes, the limited number of test samples used and limitations in
testing only for known failure mechanisms (Osterwald and McMahon, 2009). It also has
limitations with limited oversight, with certifications given despite potential changes to
module designs which may impact on their durability (Kurtz, 2011).
Failures of Bypass Diodes in the Field and in Qualification Testing
A study was undertaken into testing large scale PV systems. It was found that in 64 000
modules, 362 (0.6%) were not contributing power. Of those non contributing modules,
2% were caused by diodes (Lashway, 1988).
In a study of long term performance and reliability of crystalline silicon photovoltaic
modules, it was discovered that in a field of 60 Photowatt MU-7061 modules, three
modules had failed. In the conclusion, it was stated that “bypass diodes in three
Photowatt modules have failed due to shorting.” This is a 5 percent overall failure rate,
with 100% of failures in this particular type of module attributable to bypass diodes
(Atmaram et al., 1996).
Data from returned BP Solar and Solarex multicrystalline silicon modules since 1994
shows an overall return rate of 0.13%. Of the returns, 1.5% was put down to overheated
wires, diodes or terminal strip, and 0.2% to defective bypass diodes (Wohlgemuth et al.,
2005).
Qualification testing has shown that there are significant numbers of problems with
bypass diode thermal testing. The failure rate of qualification testing was above 30% in
2005-2007 – this was attributed to new market entrants (TamizhMani et al., 2010).
However, the numerical results shown in Fig.1 show that the diodes were operating very
close to or above their rated temperature limits. Given that they are operating so close to
their temperature limits, it is likely that the diodes will fail despite passing qualification
testing (Fahrenbruch, 2010).
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Fig. 1: Bypass Diode Thermal Test – Measured Temperatures versus Rated
Temperature (TamizhMani et al., 2008)
Bypass Diode Failure Modes
Bypass diodes can fail due to overheating. Sealed or poorly ventilated junction boxes
make it difficult for diodes to dissipate heat. Prolonged exposure to heat can also cause
degradation of the plastic encapsulation, leading to insulation failure (Fahrenbruch,
2010).
Thermal runaway from a forward-biased hot diode suddenly exposed to reverse bias in a
shaded-to-unshaded transition could result in significant leakage currents which could
continue to heat up the diode, causing its destruction (Fahrenbruch, 2010).
Lightning impulses inductively coupled into modules by the wiring cause stresses on
the diodes which can also cause them to fail. Experiments have shown that bypass
diodes can be easily destroyed by these impulses (Haeberlin and Kaempfer, 2008).
Characteristics of Improved Bypass Technologies
Historically, diodes used for bypassing were P-N junction diodes. However, as they had
a high forward voltage drop and hence high power dissipation, they were replaced with
Schottky diodes which featured much lower voltage drop. Unfortunately, Schottky
diodes also have lower thermal immunity, higher leakage current and lower surge
reliability (Diodes Incorporated, n.d.) – all of which are undesirable for bypass diode
applications.
New technologies, such as the Super Barrier Rectifier (SBR) and Trench MOS Barrier
Rectifier (TMBS) promise the robustness of P-N junction diodes with the low forward
voltage drop of Schottky diodes (Diodes Incorporated, n.d., Vishay General
Semiconductor, 2008).
Lossless diode technologies are based on MOSFET devices and promise significantly
reduced heating and forward voltage drop, as well as low leakage current and high
robustness (Pulvirenti, 2010, Microsemi Corporation, n.d.).
The operation of some lossless diodes involves the gate of a MOSFET being biased by a
circuit involving a capacitor and a charge pump (see Fig. 2). In order to replenish the
charge in the capacitor, the MOSFET is turned off, producing a voltage drop over the
internal body diode of the MOSFET which is used by the charge pump to replenish the
charge of the internal capacitor. This produces an on-off mode of operation, whose duty
cycle is determined by many variables.
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Fig. 2: Schematic of a lossless diode (La Scala and Pulvirenti, 2010)
Costs of Different Bypass Technologies
In order to compare the price of different bypass technologies, three suppliers were
surveyed on 27th August 2011 for the best bulk pricing on the selected set of test diodes.
The results are presented in Tab. 1. It must be remembered that pricing is fluid and
dynamic and will change continually, it can be expected that as lossless diodes grow in
supply, the prices will begin to fall. However, it can be seen that lossless diodes
command a considerable premium above the Schottky diodes.
Tab. 1: Pricing Table for Different Bypass Technologies
Type
P-N
Schottky
SBR
TMBS
Lossless
Part Number
GP1603
PVS1545
STPS1545CT
SBR20U150CT
VBT3045CBP
SPV1001T40
SPV1002T40
LX2400
Cost Each
AU$0.31
N/A
US$0.40
US$0.65
AU$1.13
US$2.48
US$2.26
US$7.80
In a Lot of
500
N/A
2000
10000
4000
10000
10000
10000
Supplier
A
N/A
B
B
C
B
B
B
MATERIALS AND METHODS
As the testing was conducted as part of an Undergraduate Thesis program, the
experiments were undertaken within a limited budget and time frame. As a result, the
results obtained from these testing procedures are only of preliminary quality and may
have a wide margin for error. The diodes chosen for testing were specifically targeted
for PV applications or were intended for use in PV modules.
Voltage Drop, Power Dissipation, Junction Temperature Rise and Reverse
Bias Leakage Test
A test circuit, whose schematic is shown in Fig. 3, was constructed. Wires were
soldered to a diode sample and a thermocouple was epoxied to the metal tab or lead
(Diotec Semiconductor, 2011). No heatsink was provided, however, some diode
samples were pre-mounted and these were used in situ. The test sample was placed
inside a QC Solar Smartbox Junction Box and connected to the test circuit, except in the
case of the LX2400 which was placed in a larger jiffy box due to the physical size of the
evaluation board. The test circuit was connected to multimeters, a Tektronix TDS2022
Digital Storage Oscilloscope and power supplies. A current limited power supply was
set to an initial current of 1A. The temperature on the thermocouple was observed until
the change in temperature was below 1 degree Celsius per 15 minutes. The temperature
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reading was recorded, as were the ambient temperature and the voltage drop over the
diode. The switch was flipped, triggering the oscilloscope and reverse biasing the diode.
The voltage over Rsense was recorded by the oscilloscope and the peak value was
recorded. If the burden voltage was not within 0.1V to 2V, Rsense was adjusted, and the
experiment was repeated. This was converted to a leakage current by Ohm’s law. Once
the experiment was completed for a current of 1A, it was repeated for currents of 2A,
4A, 6A, 8A and 10A provided the temperature of the diode case did not exceed 160˚C.
The experiment was repeated for all diode samples.
Fig. 3: Test Circuit Schematic for Voltage Drop, Power Dissipation, Junction
Temperature Rise and Reverse Bias Leakage Test. The unit under test (UUT) is shown
between the voltmeter test points.
I-V Curve Test
The diode sample was connected as shown in Fig. 4. The current limited power supply
had its current varied from 0 to 3A smoothly while the oscilloscope captured raw data.
This data was interpreted to produce an I-V scatter plot.
Timing Characteristics Test
The diode sample was connected as shown in Fig. 4. The current limited power supply
was set to 1A. The oscilloscope was set to capture a screenshot. In the case of
observable timing disruptions, three diodes in series would be connected in place of the
single diode to determine what interactions exist between the diodes.
Fig. 4: Test Circuit Schematic for Timing Characteristics Test and I-V Curve Test
RESULTS AND DISCUSSION
Unfortunately, as the PVS1545 and LX2400 diodes both arrived with their own
heatsink, their results are not directly comparable to the other diodes or with each other.
Power dissipation versus Forward Current is illustrated in Fig. 5. It is clear that the
lossless diodes (SPV1001T40, SPV1002T40 and LX2400) are significantly better than
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the Schottky, SBR and TMBS. As expected, the P-N diode provided the worst
performance. Of interest is the shape of the curves – the P-N, Schottky, SBR and TMBS
appear to be linear, whereas the lossless diodes are not. This is likely to be because they
are based on MOSFET technology which has a positive temperature coefficient of
RDSon. Furthermore, it is shown that the duty cycle of the SPV1001T40 and
SPV1002T40 reduces with increasing temperature, causing the diode to operate in
higher dissipation modes for a larger percentage of the time (STMicroelectronics, 2010,
STMicroelectronics, 2011).
Power Dissipation versus Forward Current
4.5
4
3.5
Power Dissipated (W)
GP1603
3
PVS1545
STPS1545CT
2.5
SBR20U150CT
VBT3045CBP
2
SPV1001T40
SPV1002T40
1.5
LX2400
1
0.5
0
0
1
2
3
4
5
6
7
8
9
10
Forward Current (A)
Fig. 5: Power Dissipation versus Forward Current
Fig. 6 shows the calculated junction temperature rise above ambient versus forward
current. This calculation accounts for the thermal resistance from junction to case or pad
using the calculation provided in IEC 61215. Similar trends can be seen, with the
lossless diodes performing best, however, the LX2400 and PVS1545 Schottky perform
extremely well due to their effective heatsinks (and hence cannot be compared directly
to the other results). A non-linear increase in junction temperature versus forward
current for the lossless diodes can be observed here as well.
Calculated Junction Temperature Rise versus Forward Current
160
Junction Temperature Rise (degrees C)
140
120
GP1603
PVS1545
100
STPS1545CT
SBR20U150CT
80
VBT3045CBP
SPV1001T40
60
SPV1002T40
LX2400
40
20
0
0
1
2
3
4
5
6
7
8
9
10
Forward Current (A)
Fig. 6: Calculated Junction Temperature Rise versus Forward Current
Fig. 7 shows the reverse leakage current versus the junction temperature. It can be seen
that the leakage current of the lossless diodes are only loosely related to temperature,
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and remain fairly low. This implies that thermal runaway from shaded to unshaded
conditions is unlikely due to the low leakage current. Noting the logarithmic scale, the
leakage currents for Schottky, SBR and TMBS diodes increase exponentially.
Reverse Leakage Current versus Junction Temperature
1.00E-01
Reverse Leakage Current (A)
1.00E-02
GP1603
PVS1545
STPS1545CT
SBR20U150CT
1.00E-03
VBT3045CBP
SPV1001T40
SPV1002T40
LX2400
1.00E-04
1.00E-05
0
20
40
60
80
100
120
140
160
180
Junction Temperature (degrees C)
Fig. 7: Reverse leakage current versus junction temperature
Fig. 8 depicts the measured I-V curve from our experiment. It can be seen that the
lossless diodes are significantly better. The performance of the TMBS and PVS1545
Schottky diodes are similar, with the STPS1545 Schottky just behind, followed by the
SBR. As expected, the P-N diode performs the worst. The I-V curves for the lossless
diodes SPV1001T40 and SPV1002T40 are split due to their on-off modes of operation.
I-V Curve
3.5
3
2.5
GP1603
Current (A)
PVS1545
2
STPS1545CT
SBR20U150CT
VBT3045CBP
1.5
SPV1001T40
SPV1002
LX2400
1
0.5
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Voltage (V)
Fig. 8: Measured I-V Curve
Fig. 9 shows the timing characteristics for the lossless diodes. It can be seen that the
SPV1001T40 (a) and the SPV1002T40 (b) suffers from abrupt changes in its forward
voltage drop (from less than 0.1V to 0.7V for approximately 6-7ms in every 100ms)
when switching between on and off modes of operation. This does not occur for the
LX2400 (c).
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Single Device – 50ms/div
Three Series Devices - SPV1001T40
and SPV1002T40, 25ms/div
(a)
(d)
(b)
(e)
(c)
(f)
Fig. 9: Timing Characteristics of Lossless Diodes - (a) SPV1001T40, (b) SPV1002T40,
(c) LX2400, (d) No Overlapping Pulses, (e) One Overlapping Pulse, (f) Two
Overlapping Pulses
Placing three of these devices in series, we can obtain the traces shown in right column
of Fig. 9. It can be seen that the phase of the voltage pulses are not correlated. In certain
cases, they may overlap and produce pulses of twice the amplitude or three times the
amplitude. These devices may act to modulate the voltage from a string when activated
and produce voltage noise on the DC bus. Further research is required to understand
how these pulses may affect PV systems and inverters.
CONCLUSION
It is shown that lossless diodes offer significant advantages in the tested areas of voltage
drop, power dissipation, temperature rise and leakage current over Schottky diodes and
have good potential as a replacement bypass diode technology. SBR and TMBS are
unable to provide such significant advantages. However, despite these advantages, there
could be price barriers against the adoption of lossless diodes. Further research is
required in order to assess the suitability of lossless diodes for the role of bypass diode
due to the unusual timing characteristics of lossless diodes. Further research is also
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required to determine the surge immunity of lossless diodes in order to make a complete
informed decision.
ACKNOWLEDGEMENTS
I would like to acknowledge the assistance of STMicroelectronics and Microsemi for
providing diode test samples for this research; Silex Solar in providing junction boxes
and bypass diode data; and Suntech for providing bypass diode data for our experiment.
I would also like to acknowledge the School of Electrical Engineering and the School of
Photovoltaics and Renewable Energy Engineering of UNSW for providing the facilities
which make this research possible.
REFERENCES
ACCIARI, G., GRACI, D. & LA SCALA, A. 2011. Higher PV Module Efficiency by a
Novel CBS Bypass. Power Electronics, IEEE Transactions on, 26, 1333-1336.
ARP, J. n.d. Quality of solar modules and module certification, November 5th, Poona,
India
[Online].
Available:
http://indien.ahk.de/fileadmin/ahk_indien/Dokumente/Solar_Delegation/Photov
oltaik-Institut__Dr.-Ing._J._Arp__small.pdf [Accessed 10/07/2011].
ATMARAM, G. H., VENTRE, G. G., MAYTROTT, C. W., DUNLOP, J. P. &
SWAMY, R. 1996. Long-term performance and reliability of crystalline silicon
photovoltaic modules. Photovoltaic Specialists Conference, 1996., Conference
Record of the Twenty Fifth IEEE.
DIODES INCORPORATED. n.d. Super Barrier Rectifier: An Evolution in Power
Rectifier
Technology
[Online].
Diodes
Incorporated.
Available:
http://www.diodes.com/products/sbr_product_information.html
[Accessed
26/03/2011].
DIOTEC SEMICONDUCTOR. 2011. Thermal Measurements on Bypass Diodes
[Online].
Diotec
Semiconductor.
Available:
http://www.diotec.com/service/files/thermal-measurements-on-bypassdiodes.pdf [Accessed 10/07/2011].
FAHRENBRUCH, S. A. 2010. Solar bypass diodes: Then and now. Solar. A PV
Management Magazine.
HAEBERLIN, H. & KAEMPFER, M. 2008. Measurement of Damages at Bypass
Diodes by Induced Voltages and Currents in PV Modules Caused by Nearby
Lightning Currents with Standard Waveform. 23rd European Photovoltaic Solar
Energy Conference. Valencia, Spain.
IEC 2005. IEC 61215 Edition 2.0 2005-04 Crystalline silicon terrestrial photovoltaic
(PV) modules - Design qualification and type approval.
KURTZ, S. 2011. International Quality Assurance Standards PV Module Reliability
Workshop
[Online].
NREL.
Available:
http://www.nrel.gov/docs/fy11osti/51123.pdf [Accessed 12/06/2011].
LA SCALA, A. & PULVIRENTI, F. 2010. By-pass diode structure for strings of series
connected cells of a photovoltaic panel, European Patent EP 2 141 746 A2.
LASHWAY, C. 1988. Photovoltaic system testing techniques and results. Energy
Conversion, IEEE Transactions on, 3, 503-506.
MICROSEMI CORPORATION. n.d. Microsemi IDEALSolar Bypass Diode Product
Brief
LX2400
[Online].
Microsemi
Corporation.
Available:
http://www.microsemi.com/datasheets/LX2400.pdf [Accessed 26/03/2011].
th AuSES
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AuSES
Annual
Conference
Solar2011,
Annual
Conference
1
November
-2
December
2011
30th November -2nd December 2011
9 9
OSTERWALD, C. R. & MCMAHON, T. J. 2009. History of accelerated and
qualification testing of terrestrial photovoltaic modules: A literature review.
Progress in Photovoltaics: Research and Applications, 17, 11-33.
PULVIRENTI, F. 2010. Presentation of SPV1001 [Online]. ST Microelectronics.
Available:
http://www.st.com/internet/com/SALES_AND_MARKETING_RESOURCES/
MARKETING_PRESENTATIONS/TECHNOLOGY_PRESENTATION/SPI_2
010_photovoltaic.pdf [Accessed 12/05/2011].
SPOONER, E. D. & WILMOT, N. 2008. Safety Issues, Arcing and Fusing in PV
Arrays. ISES-AP.
STMICROELECTRONICS. 2010. SPV1001T40 Cool bypass switch for photovoltaic
application
[Online].
STMicroelectronics.
Available:
http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LI
TERATURE/DATASHEET/CD00287228.pdf [Accessed 08/04/2011].
STMICROELECTRONICS. 2011. SPV1002 Cool bypass switch for photovoltaic
applications
[Online].
STMicroelectronics.
Available:
http://www.dz863.com/downloadpdf-vdkimpnajump-SPV1002.pdf [Accessed
7/8/2011].
TAMIZHMANI, G., LI, B., ARENDS, T., KUITCHE, J., RAGHURAMAN, B.,
SHISLER, W., FARNSWORTH, K., GONZALES, J., VOROPAYEV, A. &
SYMANSKI, P. 2008. Failure analysis of design qualification testing: 2007 VS.
2005. Photovoltaic Specialists Conference, 2008. PVSC '08. 33rd IEEE.
TAMIZHMANI, G., LI, B., ARENDS, T., KUITCHE, J., RAGHURAMAN, B.,
SHISLER, W., FARNSWORTH, K., VOROPAYEV, A. & PARKER, D. 2010.
Failure analysis of module design qualification testing - III: 1997-2005 vs. 20052007 vs. 2007-2009. Photovoltaic Specialists Conference (PVSC), 2010 35th
IEEE.
VISHAY GENERAL SEMICONDUCTOR. 2008. Industry's First Commercial TMBS Trench MOS Barrier Schottky Rectifier Series [Online]. Vishay General
Semiconductor. Available: http://www.vishay.com/docs/89098/np-tmbs.pdf
[Accessed 28/03/2011].
WENHAM, S. R., GREEN, M. A., WATT, M. E. & CORKISH, R. 2006. Applied
Photovoltaics, University of NSW.
WOHLGEMUTH, J. H. 1994. Reliability testing of PV modules. Photovoltaic Energy
Conversion, 1994., Conference Record of the Twenty Fourth. IEEE Photovoltaic
Specialists Conference - 1994, 1994 IEEE First World Conference on.
WOHLGEMUTH, J. H., CUNNINGHAM, D. W., NGUYEN, A. M. & MILLER, J.
2005. Long Term Reliability of PV Modules [Online]. BP Solar International.
Available:
http://www.prosolarnw.com/files/Manufactures/PhotoVoltaic/BP/BP_Solar_Lon
g_Term_Performance.pdf [Accessed 20/04/2011].
WOHLGEMUTH, J. H. & KURTZ, S. 2011. Reliability testing beyond Qualification as
a key component in photovoltaic's progress toward grid parity. Reliability
Physics Symposium (IRPS), 2011 IEEE International.
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