November 2015
Battery Technology Innovations 'Smarty' DC/DC Voltage Converter Interview with Chris Dries United Silicon Carbide
United Silicon Carbide Drives Alternative Energy Technologies
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CONTENTS
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EDITORIAL STAFF Content Editor Alex Maddalena amaddalena@aspencore.com Digital Content Manager Heather Hamilton hhamilton@aspencore.com Tel | 208-639-6485 Global Creative Director Nicolas Perner nperner@aspencore.com Graphic Designer Carol Smiley csmiley@aspencore.com Audience Development Claire Hellar chellar@aspencore.com Register at EEWeb http://www.eeweb.com/register/
Published by AspenCore 950 West Bannock Suite 450 Boise, Idaho 83702 Tel | 208-639-6464
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TECH SERIES DC/DC Book of Knowledge Chapter 4: DC/DC Converter Protection TECH TRENDS Tap Tap Tech: Battery Technology PRODUCT WATCH Noise and Surge Protection from Okaya ‘Smarty’ DC-to-DC Voltage Converter from Tamura INDUSTRY INTERVIEW Silicon Carbide Breaks into the Mainstream Interview with Chris Dries – CEO of United Silicon Carbide
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Victor Alejandro Gao General Manager Executive Publisher Cody Miller Global Media Director Group Publisher
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DC/DC
Book of
KNOWLEDGE Chapter 4 By Steve Roberts Technical Director for RECOM
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TECH SERIES
DC/DC Converter Protection RECOM´s DC/DC Book of Knowledge is a detailed introduction to the various DC/DC converter topologies, feedback loops (analogue and digital), test and measurement, protection, filtering, safety, reliability, constant current drivers and DC/DC applications. The level is necessarily technical, but readable for engineers, designers and students.
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One of the primary functions of a DC/DC converter is to protect the application. At the most simple level, this protection consists of matching the load to the primary power supply and stabilizing the output voltage against input overvoltages and undervoltages, but a DC/DC converter is also a significant element ensuring system fault protection. For example, output overload limiting and short-circuit protection not only stops the converter from being damaged if the load fails, but also can protect the load from further damage by limiting the output power during a fault condition. In an application with several identical circuits or channels each separately powered by individual DC/DC converters, a fault in one output channel will not affect the other outputs, thus making the system single fault tolerant. Other converter protection features, such as overtemperature shut-down, are primarily designed to safeguard the converter from permanent damage caused by internal component overheating, but a side-effect is also to shut down the application if the ambient temperature gets too high, thus also protecting the components in the application from over-temperature failure.
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Adding isolation between input and output breaks ground loops, eliminates source of interference and increases system reliability by protecting the application against transient damage. The elimination of power supply feedback effects is an important facet of DC/ DC converter protection. For example, consider a heavy duty DC motor speed controller. The speed controller circuit needs a stable, noise-free supply to smoothly regulate the motor speed, but the high DC currents drawn by the motor can create significant voltage transients that could feed back into the speed controller regulation circuit to cause jitter or instability. An isolated DC/DC converter not only delivers a stable low-noise supply to the speed controller circuit, but by breaking the noise feedback loop also protects the motor from unwanted and erratic control signals that could damage the motor and associated drive chain. However, a DC/DC converter is also constructed from electronic components that are just susceptible to failure if used outside their voltage, current and temperature limits as any other electronic circuit. This chapter investigates protection measures that may be needed to safeguard the converter itself from damage.
TECH SERIES
The main reason why DC/DC Converters fail if reverse polarised is the body diod the FET. This substrate diode conducts when reverse connected and allows a very la current IR to flow, which can lead to the destruction of components on the primary s To avoid this potential danger, several options are available.
The main reason why DC/DC Converters fail if reverse polarized is the body diode in the FET. This substrate diode conducts when reverse connected and allows a very large current IR to flow, which can lead to the destruction of components on the primary side. To avoid this potential danger, several options are available.
The easiest way to protect a DC/DC converter from reverse connection damage is to add a series diode. Fig. 4.2 shows the circuit. If the supply voltage is reversed, the diode D1 blocks the4.1: negative current flow and Flow Fig. Reverse Polarity Current no fault current can flow through the input circuit of the DC/DC converter. Obviously, by replacing the diode with aSeries bridge rectifier, then the Polarity Protection 4.2.1 Diode Reverse converter will function irrespectively The easiest way to protect a DC/DC converter from reverse connection damage of the input voltage polarity.
DC / DC converter are not protected against reverse polarity connection. Swapping the VIN+ and VIN- terminals will almost certainly cause immediate failure, so care must be taken to ensure that any input connectors or battery connections are polarized. If the primary supply is transformer, then a rectification diode failure could cause a negativegoing output that would then also cause the DC/DC converters to fail.
Series Diode Reverse Polarity Protection
Reverse Polarity Protection
add a series diode. Fig. 4.2 shows the circuit. If the supply voltage is reversed, the d D1 blocks the negative current flow and no fault current can flow through the input ci of the DC/DC converter. Obviously, by replacing the diode with a bridge rectifier, t the converter will function irrespectively of the input voltage polarity.
The main reason why DC/DC Converters fail if reverse polarised is the body diode in the FET. This substrate diode conducts when reverse connected and allows a very large current IR to flow, which can lead to the destruction of components on the primary side. To avoid this potential danger, several options are available. Fig. 4.2: Series Diode Reverse Polarity Protection
The series diode protection has a disadvantage, especially at low input voltages, du Fig. 4.2.Series diode reverse polarity protection the voltage drop across the diode. Depending on the choice of diode, a forward volt drop of 0.2V to 0.7V can be expected, with an associated power loss = VF Ă— IIN, w reduces both the conversion efficiency and the usable input voltage range. If the in current is 1A, then a standard power diode with VF = 0.5V dissipates 0.5W, equa about a quarter of the dissipated power of a typical 15W converter, thus reducing overall efficiency by 20%.
Fig. 4.1: Reverse Polarity Current Flow
Fig. 4.1. Reverse polarity current flow
In some applications, the voltage drop across the diode is an advantage. Rally cars o use a 16V battery to increase the brightness of the headlamps. The alternator is mod to deliver 11 - 20V, outside the range of a standard 9 - 18V DC/DC converter. By u three diodes in series, the effective input range can be dropped to match the stand 18V input voltage range.
4.2.1 Series Diode Reverse Polarity Protection
The easiest way to protect a DC/DC converter from reverse connection damage is to add a series diode. Fig. 4.2 shows the circuit. If the supply voltage is reversed, the diode D1 blocks the negative current flow and no fault current can flow through the input circuit of the DC/DC converter. Obviously, by replacing the diode with a bridge rectifier, then the converter will function irrespectively of the input voltage polarity.
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Shunt Diode Reverse Polarity Protection
The series diode protection has a disadvantage, especially at low input voltages, due to the voltage drop across the diode. Depending on the choice of diode, a forward voltage drop of 0.2V to 0.7V can be expected, with an associated power loss = VF Ă— IIN, which reduces both the conversion efficiency and the usable input voltage range. If the input current is 1A, then a standard power diode with VF = 0.5V dissipates 0.5W, equal to about a quarter of the dissipated power of a typical 15W converter, thus reducing the overall efficiency by 20%.
An alternative to the series diode is the shunt diode reverse polarity protection. The forward voltage drop across the diode is avoided, but the primary supply must either be overload protected or a series fuse must be fitted (Fig. 4.3). Although this arrangement might seem at first sight to be a better solution than the series diode form of protection, in practice it has several disadvantages. One disadvantage is that although the voltage across the converter when reverse polarity connected is limited to In some applications, the voltage drop -0.7V, even this low level of negative across the diode is an advantage. Rally voltage can be sufficient to damage cars often use a 16V battery to increase some converters. Secondly, the choice of the brightness of the headlamps. 4.2.2 Shunt Diode Reversefuse Polarity is not aProtection trivial task and its effect on The alternator is modified to deliver performance is often underestimated. An alternative to the series diode is the shunt diode reverse polarity protection. The 11 - 20V, outside forward the range of adrop standard A fuse is, in effect, a resistor that ismust either be voltage across the diode is avoided, but the primary supply overload protected a series fusedesigned must be fitted (Fig.out 4.3). arrangement 9 - 18V DC/DC converter. By usingorthree to burn at Although a certainthis current. seem at first sight to be a better solution than the series diode form of protection, diodes in series, might the effective input As with all resistors, there will be a volt in practice it has several disadvantages. One disadvantage is that although the voltage range can be dropped thewhen reversedrop across it that isiscurrent across to thematch converter polarity connected limited todependent. -0.7V, even this low standard 18V input range. A fuse may have ansome insertion loss Secondly, the levelvoltage of negative voltage can be sufficient to damage converters. choice of fuse is not a trivial task (see section 4.3) and its effect performance similar or even higher thanonthe forward is often underestimated. A fuse is, in effect, a resistor that is designed to burn out at a certain drop of a diode (see next section). current. As with all resistors, there will be a volt drop across it that is current dependent. A fuse may have an insertion loss similar or even higher than the forward drop of a diode (see next section).
Fig. 4.3: Shunt-Diode Reverse Polarity Protection
Fig. 4.3. Shunt-diode reverse polarity protection
4.2.3 P-FET Reverse Polarity Protection
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A third option for reverse polarity protection is to use a series P-FET. The FET is the most expensive solution, but it is still inexpensive in comparison to the cost of the converter. The FET must be a P-channel MOSFET with an internal body diode otherwise this solution will not work. The maximum gate-source voltage VGS should exceed the maximum supply voltage or reversed supply voltage. The FET should also have an extremely low RDS,ON resistance, around 50mΊ is an acceptable compromise between component cost and effectiveness. With the supply correctly connected, the FET is biased full on and even with an input current of over an amp it will exhibit a volt drop of
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TECH SERIES
P-FET Reverse Polarity Protection
supply voltage or reversed supply voltage. The FET should also have A third option for reverse polarity an extremely low RDS,ON resistance, protection is to use a series P-FET. The around 50mΊ is an acceptable FET is the most expensive solution, but 4.2.3 P-FET Reverse Polarity Protection compromise between component cost it is still inexpensive in comparison to effectiveness. With the supply the cost for of the converter. FET must A third option reverse polarity The protection is to use a and series P-FET. The FET is the mostbe expensive solution, but it is still inexpensive in comparison to the cost of the correctly connected, the FET is biased a P-channel MOSFET with an internal converter. The FET must be a P-channel MOSFET with an internal body diode otherwise full on and even with an input current body diode otherwise this solution will this solution will not work. The maximum gate-source voltage VGS should exceed the of over an amp it will exhibit a volt not work. The maximum gate-source maximum supply voltage or reversed supply voltage. The FET should also have an drop of compromise only a few tens of millivolts. should exceedaround the maximum voltage resistance, 50mΊ is an acceptable between extremely lowVRGS DS,ON Fig. 4.3: Shunt-Diode Reverse Polarity Protection
component cost and effectiveness. With the supply correctly connected, the FET is biased full on and even with an input current of over an amp it will exhibit a volt drop of only a few tens of millivolts.
Fig. 4.4: P-FET Reverse Polarity Protection
Fig. 4.4. P-FET reverse polarity protection
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Reverse Polarity Protection
Supply Voltage*
Converter Input Voltage
Converter Input Current
VOUT (V) IOUT(mA)
Power In
Power Out
Conversion Efficiency
No Protection
9.0V
9.0V
1561mA
11.98V 1000mA
14.05W
11.98W
85.3%
1: Series Diode (1N5400)
9.7V
8.5V
1660mA
11.98V 1000mA
16.10W
11.98W
74.4%
2: Shunt Diode + 3A Fuse
9.1V
8.5V
1667mA
11.98V 1000mA
15.17W
11.98W
78.9%
3. P-FET (IRF5305)
9.0V
8.9V
1572mA
11.98V 1000mA
14.15W
11.98W
84.7%
* 9V or minimum input voltage for a stable regulated output, whichever is the higher.
Table 4.1: Measured Values using a Recom RP12-1212SA converter for
Table 4.1. Measured values using a RECOM RP12-1212SA converter different reverse polarity protection methods for different reverse polarity protection methods.
To examine the differences bewteen the three different methods of reverse polarity protection, measurements were made using a 12W converter with full load with a worst case 9V input to give a nominal 1.5A input current. As can be seen from Table 4.1, the P-FET solution efficiency is very similar to the circuit with no reverse polarity protection.
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Power Developer
To examine the differences between the three different methods of reverse polarity protection, measurements were made using a 12W converter with full load with a worst case 9V input to give a nominal 1.5A input current. As can be seen from Table 4.1, the P-FET solution efficiency is very similar to the circuit with no reverse polarity protection.
Input Fuse Whether used as an overcurrent protection (failsafe) device without a shunt diode, or used as a reverse polarity protection device with a shunt diode, an input fuse needs to be selected so that it does not blow at the worst case input current during normal operation. As fusewire becomes brittle with age, the fuse rating should be at least 1.6 times the highest input current for a long life. The inrush current during converter start up is significantly higher than the operating current, so the fuse should be of the timedelay type (slow-blow) to avoid nuisance blowing on switch-on. The combination of high fuse current rating and slow reaction time also means that during a reverse polarity fault, the diode must be dimensioned to carry the current and the power supply must also be able to deliver enough current to quickly blow the fuse. A fuse is a one-time only device. If the power supply is mistakenly crossconnected, then the fuse needs to be
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replaced before the converter can be used again. This may be an advantage if the circuit should remain permanently disconnected from the supply until the cause of the fault has been eliminated by a maintenance team, but for many other applications it would be preferably to make the application fault tolerant (auto recovery). An alternative to a conventional fuse is to use a resettable protection device, such as a polymeric PTC fuse (PPTC). This is a device similar to a positive temperature coefficient (PTC) resistor that increases its resistance with increasing temperature. Under fault conditions, a PPTC fuse rapidly gets hot until its internal granular structure melts, when it becomes a very high resistance, effectively disconnecting the converter except for a minimum holding current. When the power is removed, the device cools down and automatically resets. So far, Chapter 4 of the DC/DC Book of Knowledge has covered the various methods of polarity protection. The chapter goes on to cover types of voltage dips and other interruptions as well as methods of load limiting. To read the chapter in its entirety, http://www.recom-power.com/ visit: http://www.recom-power.com/ emea/downloads/bok.html emea/downloads/bok.html.
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TapTapTech
Sponsored by
By Josh Bishop
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TECH TRENDS
BATTERY
Technology
I
n this edition of Tap Tap Tech, we’re going to discuss battery technology. This surprisingly interesting topic has wide implications in every facet of life. From storage for renewable energy to phone battery packs, batteries are everywhere and they’re extremely important. While primary batteries are still important, secondary, or rechargeable batteries are what interest me now.
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It seems we’re always on the cusp of some new and crazy awesome battery technology. But currently, and for the last nearly twenty years, the most popular rechargeable battery types are lead acid, lithium ion, and the very similar lithium ion polymer, and nickel metal hydride. Nickel cadmium seems like its on its way out though it still is great in its niches, but other battery types besides these four don’t have much of a market share. In the world of smart phones, the LiPo battery is king but it is a somewhat despised king. According to extremely reputable sources on the Internet, battery life for most people is a highly prized, and frequently, highly aggravating part of owning a smart phone. I can certainly agree because my slightly older than two year old phone can’t go 14 hours of normal use without being charged. So, what are battery developers fighting? Why don’t we have the perfect batteries
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yet that last weeks for a phone? Or huge batteries tied to solar arrays to keep us powered throughout the night? The problem is, it’s a balancing act on top of straight-up engineering feats. Here are a few of the things that designers need to balance—power density, energy density, size, weight, time to charge, how many times it can be recharged before it dies, cost, materials used and toxicity, memory effects, and whether or not the battery will kill people if used incorrectly. Combine this with requiring an intimate knowledge of chemistry and I’m out. So, while I’m all for complaining and demanding better batteries, understand that it is not a simple matter. For me, though, I’m going to be nice to the battery designers because, once they crack the problem and make their hundreds of millions of dollars, they may remember me and invite me on their yachts. It could happen.
TECH TRENDS
THINGS TO CONSIDER: ✓ Power density ✓ Energy density ✓ Size / weight ✓ Time to charge / discharge (related to power density)
Why don’t we have the perfect batteries yet that last weeks for a phone?
✓ How frequently you can recharge before death (not applicable to primary batteries) ✓ Cost ✓ Materials used / toxicity ✓ Memory effects ✓ General safety ✓ NiMH and NiCd AA, AAA batteries run at 1.2V, not 1.5V, which is fine in a lot of cases, but not all cases. My wireless keyboard, for example, requires primary batteries, which drives me crazy.
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Noise and Surge Protection
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PRODUCT WATCH
Okaya is a worldwide company manufacturing noise suppression components for the electrical and electronics industry, providing proven reliable products since 1946. ISO 9000 and ISO 14001 certifications ensure we deliver only the highest quality products to our customers. Our products also meet a variety of safety standards, allowing them to be used around the world.
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Power Developer
Okaya’s EMI filters with ratings up to 500 VAC and 600 amps can ensure devices meet regulatory requirements for both conducted immunity and conducted emissions. Okaya X and Y class capacitors are available for noise suppression, including EMI and RFI filtering of the AC power line and suppressing noise generated by motors or switching power supplies. Voltage ratings range from 250 VAC to 500 VAC, and the product line includes multiple X and Y classifications and products for 3-phase applications. Snubber capacitors have voltage ratings from 250 VDC to 1600 VDC with products suited to high frequency, high current, small footprint, and PFC applications. Spark quenchers are products used to prevent the occurrence of arcing and sparking, integrating one or more highreliability film capacitors and resistors. Okaya’s EMI filters with ratings up to 500 VAC and 600 amps can ensure devices meet regulatory requirements for both conducted immunity and conducted emissions. The filters are designed to suppress noise entering the device that
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PRODUCT WATCH
Okaya’s product lines feature a range of voltages to protect against surges on AC power lines, DC supplies, and network lines. could otherwise disturb its normal operation, and suppress noise the device feeds back on to its power lines. Single-phase and three-phase filters are available, with support for standard and medical applications as well as din rail products. Gas discharge tubes and surge protection devices are designed to protect equipment against highenergy transient voltages, such as those caused by lightning strikes. Okaya’s product lines feature a range of voltages to protect against surges on AC power lines, DC supplies, and network lines. Okaya consistently innovates to meet customer needs. One example of this is the new RGF10-152-Q, providing protection to outdoor lighting applications. For more information, datasheets, okaya.com and availability, visit Okaya.com.
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MYLINK
MYLINK
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Tamura’s TCDC-7001
“Smarty” DC-to-DC
Voltage Converter Sponsored by
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PRODUCT WATCH
S
olar is becoming more popular as people are gaining a greater ecological awareness, seeking independence from grid-based power, and governments are putting forth green
initiatives. Also, photovoltaic cells are continuously decreasing in price and increasing in efficiency, and at the same time, the electronics that control them are becoming smarter. While many photovoltaic systems are “dumb grids� that have simple switches to route power and basic surge protection, the smarter controls being implemented give greater feedback on potential problems within the grid and wireless access to metrics on grid performance. Unfortunately, these smart systems require power, separate from the photovoltaic system itself.
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Using proprietary Tamura technology, Smarty uses parasitic power, powering itself directly off the DC side of the photovoltaic array. By using this parasitic power, it is able to convert the incoming power to a usable 24 volts DC output.
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Tamura has created the TCDC-7001 “Smarty� DC-to-DC voltage converter, to lead the next generation of photovoltaic smart grids. Using proprietary Tamura technology, Smarty uses parasitic power, powering itself directly off the DC side of the photovoltaic array. By using this parasitic power, it is able to convert the incoming power to a usable 24 volts DC output. This power then can be used to power smart modules inside the control panel without requiring external power. It can also be used directly to power battery systems or for microgrids. With this high efficiency voltage conversion, Smarty can also directly provide power to arc fault detectors, devices designed to significantly reduce the risk of roof top fires. These arc fault detectors are also going to be required by upcoming NEC standards.
PRODUCT WATCH
With Smarty, the overall cost of ownership of a PV system decreases, with approximately twenty cents per watt cheaper installation costs. With all the power conversion within the panel, photovoltaic systems that use Smarty are inherently simpler, making them easier to install, easier to monitor, and easier to maintain. Smarty can be used in a variety of applications from smart combiner box assemblies, remote sensors and security power sources, radio and wireless data links, power current sensor modules, and security lighting. To learn more about how Tamura’s Smarty please visit onlinecomponenets.com onlinecomponents.com.
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Silicon Carbide Breaks into the Mainstream Interview with Chris Dries CEO of United Silicon Carbide
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INDUSTRY INTERVIEW
United Silicon Carbide Offers Key Power-saving Solutions for the Burgeoning Alternative Energy Industry The term “alternative energy” will soon become just “energy.” As with any technology sector, the advancements in the alternative energy arena—solar, wind, smartgrid—are making mass adoption more palpable. This is due, in part, to the tremendous strides made with silicon carbide (SiC), which has proven to help lower the cost of the technology while providing better quality and continuity of the power supply. At the helm of this power revolution is United Silicon Carbide, an SiC-based power supply company that is helping provide the higher-efficiency demands needed in emerging higher voltage markets. EEWeb spoke with Chris Dries, CEO of United Silicon Carbide, about the company’s industry-leading die size, the custom discrete business they are offering, and the ways in which the SiC market will grow to around $2-billion in the next ten years.
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How do you see silicon carbide positioned in the power market? Historically, the majority of the market for silicon carbide has been dominated by diodes in power factor correction. Over the last year, that momentum has shifted to include the design-in of silicon carbide transistors. It is becoming clear that the user community is rapidly adopting silicon carbide switch technology, and I think we will see a massive acceleration in the design-in activity of silicon carbide transistors. The diodes generated enough demand to mature the supply chain. Going back to the early days, there was not enough demand for substrates to support a cost structure for growth, but now the product performance and end applications are driving tremendous demand, which is creating a supply chain that is quickly becoming very diverse and raw materials are available throughout the world.
In what ways does USCi separate itself from its competitors? The fundamental thing is we based the technology of our business on the JFET, which allows USCi to leverage the cascode configuration. This gives USCi a huge differentiator in terms of die size. We just got back from the International Conference of Silicon Carbide and Related Materials in Sicily, and virtually all of the MOSFETs are sitting at a specific ON resistance in the 3to 4-mohm centimeters-squared range. Our technology, in contrast to devices running in the 3- to 4-mOhm
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centimeters-squared range, are 1.75mOhm centimeters-squared—meaning our SiC cost is half that of a SiC MOSFET supplier. We add a low-cost Si MOSFET to form the cascode configuration, which makes USCi’s devices the only SiC Switch with standard gate drive. The low Voltage MOSFET’s intrinsic diode also serves as a very-low QRR anti-parallel diode. If you look at hardswitched half-bridge configurations where our competitors would typically use a MOSFET with an anti-parallel silicon carbide Schottky diode, we have a one-package solution that performs at lower switching losses with 50-percent of the silicon carbide die area.
Another example of what makes us unique is the gate drive that we provide to customers. Another example of what makes us unique is the gate drive that we provide to customers. Standard silicon carbide MOSFETs have a non-standard gate drive from -5 to +20 volts. Because our devices incorporate a low-voltage MOSFET in them, they have a standard gate drive, so if someone has designed in a superjunction FET or an IGBT, they can simply take out the silicon component and drop in our silicon carbide device and it will simply work. At the same time, anyone who has designed in a silicon carbide MOSFET can also just drop in our device, as the cascode’s low-voltage MOSFET will work fine with a -5 / +20-volt gate drive. For us, it becomes a truly universal high-voltage switch no matter the
INDUSTRY INTERVIEW device that is inside it—it is driven like a silicon switch but with the benefits of a wide band gap material inside of it.
How did USCi achieve its industry-leading die size? It’s actually quite simple in the sense that we use vertical trench technology. All MOSFETs in the world right now, with a few exceptions, are all D-MOSFETs, where there is a lateral channel and then vertical current flow. We simply use the die area much more effectively as a vertical trench device. These are approaches that have been used in silicon for a couple of decades, but at USCi we are the first ones to figure out how to do it in a manufacturable way. We have the intellectual property tied to this capability.
I think the traditional areas of power supplies and renewables such as photovoltaic inverters and charging systems will be big adopters.
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Power Developer
What is your outlook for the next three to five years? What markets will adopt silicon carbide the fastest?
Could you elaborate more on the custom discrete business that USCi offers?
I think the traditional areas of power supplies and renewables such as photovoltaic inverters and charging systems will be big adopters. In the photovoltaic inverter area, we have an existing customer that builds a 30-kilowatt system using our switch technology. They were able to reduce the size of a grid-tie inverter from something that was about the size of a small, side-by-side refrigerator down to something that is now wall-mountable. When you think of the balance of system costs associated with that, I think it is one of the massive drivers of our industry; you are able to run it at a higher switching frequency, thereby reducing the size of the units with smaller inductors and capacitors—all while operating at a higher efficiency. From an installation perspective, this eliminated the need for installers to pour a concrete pad for this heavy unit to sit on—it now just mounts to a wall. This is a big accelerant for the business.
We have several different platforms: the silicon carbide Schottky diode platform and the normally on JFET platform, which can be used to form cascodes. The custom discrete business allows us to take any one of our existing platforms and serve a custom customer need. For example, we can take our Schottky diode platform and translate that up to 3.3-kilovolts, 6.5-kilovolts, or 10-kilovolts for higher voltage applications. Typically, a customer will approach us with a unique need and a particular voltage class or current rating. We are a very flexible organization and our platforms are scalable in both voltage and currents.
We have several different platforms: the silicon carbide Schottky diode platform and the normally on JFET platform, which can be used to form cascodes. 30
It is really important because we are so focused on cost. If our customer has a large volume application, instead of trying to oversize a particular die for them, we are perfectly willing to customdesign the device precisely for the customer’s application. That is a win-win for us because we can most likely lower the price for that end-customer while maintaining a good gross margin for us, and our customer wins by getting the appropriate device at the right price.
What is unique about silicon carbide with regards to circuit protection? Silicon carbide offers the ability to handle very high short circuit events, primarily because it is very effective at absorbing thermal transients. In addition, because it is a wide-band gap material, it has a very
INDUSTRY INTERVIEW low insertion loss, meaning a relatively small amount of the semiconductor can have a relatively low resistance, but still function as a self-limiting switch under high-surge current. Essentially, the current going through the device will saturate at a tailorable level. Our limits with these kinds of events turns out to be the melting point of aluminum—once the device heats, and reaches 660ºC, the aluminum top metal melts, and that is the failure mechanism. This “upper limit” makes silicon carbide very forgiving in circuit protection, especially in a severe single event. There have been a number of good academic papers and studies done in this area, and we have customers in this area that use these devices for surge suppression in various configurations.
Silicon carbide offers the ability to handle very high short circuit events, primarily because it is very effective at absorbing thermal transients.
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