Power Electronics

2011 Rectifer/Diode Review

Although they are usually limited to only two leads, rectifiers and diodes play an important role in power electronic systems. In 2011, many types of rectifier/diodes were introduced, from bridge rectifiers to Schottky types in silicon and silicon carbide (SiC). Listed below is a review of devices that were received by Power Electronics Technology this year.

Probably the busiest company in terms of introducing rectifiers/diodes in 2011 was Vishay Intertechnology. Starting in January, the company introduced several types of Trench MOS Barrier Schottky (TMBS®) rectifiers. For solar bypass applications devices offer eSMP® surface-mount and axial-leaded package options.

These rectifiers are intended to enable higher current densities in low-voltage, high-frequency inverters, and solar cell junction boxes, where they will be used as bypass diodes for photovoltaic solar cell protection.

The V10P45S and 15 A V15P45S are offered in surface-mount SMPC packages with a typical height of 1.1 mm. Designed for automated placement, the SMPC package meets MSL Level 1.

Axial-leaded rectifiers released include the 15 A VSB1545 and 20 A VSB2045 in the P600 package. The devices can handle solder dip temperatures to 275 °C for 10 seconds per JESD 22-B106, and feature a maximum junction temperature of + 150 °C.

The TMBS rectifiers combine their high forward surge capability with low VF (forward voltage) down to 0.30 V to minimize power losses. They are compliant to RoHS Directive 2002/95/EC and WEEE 2002/96/EC, and are halogen-free according to the IEC 61249-2-21 definition.

Next, Vishay expanded its TMBS® rectifiers with release of 20 more 45 V devices in four power package types and featuring a wide range of current ratings from 10 A to 60 A (Fig. 1).

The power package devices released include the dual-chip V (B, F, I) T1045C, V (B, F, I) T2045C, V (B, F, I) T3045C, V (B, F, I) T4045C, and V (B, F, I)T6045C. Each device is offered in the power TO-220AB, ITO-220AB, TO-262AA, and TO-263AB packages.

With extremely low VF down to 0.28 V, typical at 5 A , these TMBS rectifiers reduce power losses and improve efficiency in high-frequency DC/DC converters, switch-mode power supplies (SMPS), freewheeling and OR-ing diodes, and reverse battery protection in desktop PCs, servers, and LCD TVs.

The TO-263AB package offers a MSL moisture sensitivity level of 1, per J-STD-020, LF maximum peak of 245°C. The TO-220AB, ITO-220AB, and TO-262AA packages feature solder bath temperatures of 275 °C maximum, 10s, per JESD 22-B106, and are halogen-free according to the IEC 61249-2-21 definition.

Vishay added more TMBS® rectifiers with 12 more 45 V devices in three power package options that feature a wide range of current ratings from 10 A to 60 A. With extremely low forward voltage drops down to 0.33 V typical at 10 A, the rectifiers are optimized for use in solar cell junction boxes as bypass diodes for protection.

These devices include the dual-chip V(B,F)T1045CBP, V(B,F)T2045CBP, V(B,F)T3045CBP, and V(B,F)T6045CBP. Each device is offered in the power TO-220AB, ITO-220AB, and TO-263AB packages.

All rectifiers feature a maximum operation junction temperature of 150 °C and ≤ 200 °C maximum junction temperature in DC forward current without reverse bias (t ≤ 1 hour). The devices are compliant to RoHS Directive 2002/95/EC and WEEE 2002/96/EC.

The TO-263AB package offers a moisture sensitivity level (MSL) of 1, per J-STD-020, LF maximum peak of 245 °C. The TO-220AB and ITO-220AB packages feature solder bath temperatures of 275 °C maximum, 10 s, per JESD 22-B106, and are halogen-free according to the IEC 61249-2-21 definition.

Single-Phase Single In-Line Bridge Rectifiers

Vishay also released two single-phase single in-line bridge rectifiers in the GSIB-5S package with improved VF over previous-generation devices--down to 0.73 V at + 125 °C --and high forward surge current capability.

The LVB1560 offers a current rating of 15 A and low VF down to 0.73 V at 7.5 A, while the LVB2560 features a current rating of 25 A and forward voltage down to 0.76 V at 12.5 A. The devices’ low VF reduces power loss for increased power efficiency and energy savings.

The bridge rectifiers feature maximum peak reverse voltage ratings of 600 V. Offering an oxide planar chip structure, the devices provide high case dielectric strength of 2,500 VRMS.

The LVB1560 and LVB2560 are the ideal choice for primary side AC/DC full-wave rectification in switch-mode power supplies for high-efficiency desktop PCs, servers, telecommunication systems, home appliances, and white goods applications.

The rectifiers’ +275 °C, 10-second solder dipping process per JESD 22-B106 enables high reliability in wave soldering or manual soldering. The devices are compliant to RoHS Directive 2002/95/EC and WEEE 2002/96/EC, and are halogen-free according to the IEC 61249-2-21 definition.

600 V FRED Pt® Hyperfast and Ultrafast Rectifiers

In 2011 Vishay also launched 34 new 600 V FRED Pt® Hyperfast and Ultrafast rectifiers in six power packages (Fig. 2). Combining extremely fast and soft recovery time with low forward voltage drop and reverse recovery charge, the new devices reduce switching and conduction losses in high-efficiency SMPS PFC (power factor correction) applications.

Applications include PFC in SMPS applications; input booster circuits; high-frequency output rectification; freewheeling diodes; and adapters. Typical end products will include desktop PCs, servers, telecom equipment, air conditioners, UPS, industrial motor drivers, and solar inverter systems.

Available in the power TO-220AC, TO-220 FULLPAK, TO-263AB (D2PAK), TO-262 (I2PAK), TO-247AC, and modified TO-247AC packages (in addition to bare die/wafers), the rectifiers feature five forward voltage classes from 1.07 V to 3.40 V at 8 A and 15 A, and 2.0 V to 2.65 V for 30 A devices.

Reverse recovery time at room temperature starts at 17 ns (at IF = 8 A, di/dt = 200 A/µs, VR = 390 V), while reverse recovery charge at + 125 °C starts at 77 nC (at IF = 8 A, di/dt = 200 A/µs, VR = 390 V).

The new rectifiers are part of Vishay’s Hyperfast “H” and “X” series and Ultrafast “L” series. In addition, the new “U” series was specifically developed for ultrafast soft recovery time. The devices feature an improved chip design for increased reliability exceeding standard requirements for resistance to moisture and IR stability over time.

The rectifiers offer a maximum operating junction temperature of +175 °C for a more robust and cost-effective design, and extremely low leakage. Compliant to RoHS Directive 2002/95/EC (the TO-247AC package is completely lead [Pb]-free), the devices are halogen- free according to the IEC 61249-2-21 definition, and designed and qualified according to JEDEC-JESD47.

Silicon Carbide Schottky Diodes

Cree, Inc. announced a new family of seven 1200V Z-Rec™ silicon carbide (SiC) Schottky diodes optimized for price and performance and available in a range of amperages and packages. Cree is advancing the adoption of silicon carbide power devices into mainstream power applications by introducing a comprehensive family of SiC diodes with a wide range of current ratings and package options.

“In order to develop the next generation of power electronics, design engineers are looking for the unique performance advantages of SiC Schottky diodes--zero reverse recovery losses, temperature-independent switching losses, higher frequency operation--all with a lower EMI signature,” said John Palmour, Cree co-founder and chief technology officer, Power and RF.

“This new family of diodes allows a higher current density and increased avalanche capability over previous generation SiC Schottky diodes with no penalty in performance. Cree’s recent innovations in device design and commitment to continuous process improvement are allowing us to offer significantly higher current ratings at lower cost per ampere.”

Cree Z-Rec diodes feature zero reverse recovery, resulting in up to a 50% reduction in switching losses versus comparable silicon diodes. They also exhibit consistent switching performance across their entire temperature range, which simplifies circuit design and reduces the need for complex thermal management. When used in conjunction with Cree’s recently-introduced 1200V SiC power MOSFETs, these SiC Schottky diodes enable the implementation of all-SiC power electronic circuits with the capability to operate at up to four times higher switching frequencies when compared to conventional silicon diodes and IGBTs. This enables a reduction in the size, complexity and cost of inverter circuitry, while achieving extremely high system efficiency. Finally, this new family has the additional benefits of higher surge ratings and avalanche capabilities than the previous generation of SiC Schottky diodes, which increases overall system reliability.

These devices are ideal as boost diodes and anti-parallel diodes in solar inverters and 3-phase motor drive circuits, as well as in PFC boost circuits in power supplies and UPS equipment. They can also be used in applications where engineers typically parallel many devices to address higher power requirements.

Devices now released are rated for 2A, 5A, 10A, 20A and 40A. Dependent on current ratings, the parts are available in standard or fully-isolated TO-220 and standard TO-247 packages.

Another SiC Source

Rohm Semiconductor also announced availability of its SCS1xxAGC series of high performance silicon carbide (SiC) Schottky barrier diodes (SBD). This class of SiC diodes enables improved power conversion efficiency in applications such as PFC/power supplies, solar panel inverters, uninterruptible power supplies, air conditioners and others.

The SCS1xxAGC series (Fig. 3) maintains low VF over a wide operating temperature range, which results in lower power dissipation under actual operating conditions. For example, the 10 A rated part has a VF of 1.5 V at 25°C and 1.6 V at 150°C. Low VF reduces conduction loss, while the ultra-short reverse recovery time (15 ns, typical) enables high-speed switching and minimizes switching loss.

With its acquisition of SiCrystal AG, ROHM Semiconductor now has total manufacturing capability for SiC semiconductors from ingot formation to power device fabrication. This allows the rapid development of advanced products and complete control of raw materials for industry leading reliability and quality.

According to David Doan, Senior Technical Product Marketing Manager for ROHM Semiconductor, “SiC is the ideal material for power electronics with its high breakdown voltage, low power loss, high operating temperature and superior thermal conductivity. ROHM is not the first vendor to offer SiC SBDs, but we’re introducing devices with differentiating features such as low VF and the high current rating at 600 V (a true 600 V/20 A SBD, not dual 2x10 A). These diodes are the first ones in ROHM’s SiC product lineup.”

High-Temperature Small-Signal Diode

CISSOID of Mont-Saint-Guibert, Belgium has released the CHT-GANYMEDE, a high-temperature 80V dual series small-signal diode in a small hermetically sealed metal can TO-18 package. This device includes two diodes connected in series that can sustain a reverse voltage of 80V, have a maximum forward current of 300mA at 225°C and are suitable for operation from -55°C up to +225°C. This dual diode is a general-purpose discrete component that can be used in a variety of applications, including clamping, low-current rectification and sensing, among others.

CHT-GANYMEDE diodes have a very small junction capacitance of 8.5pF at 25V reverse voltage, making them ideal for AC signal rectification, for example in a full-bridge rectifier using two GANYMEDEs. The diodes have a forward voltage of 0.36V for a forward current of 1mA at 225°C. They present a very low leakage current of 8.9µA at 80V reverse voltage and 225°C, making GANYMEDE very suitable for high temperature voltage multipliers (charge-pump). With a forward current of 300mA for a forward voltage of 1.5V at 225°C, GANYMEDE can also be used in voltage clamping applications.

QPL-Certified Schottky Rectifiers for Space Applications

International Rectifier (IR) expanded the company’s high reliability Schottky rectifiers in accordance with the Defense Logistics Agency (DLA) Land and Maritime Qualified Products List (QPL) for space applications including satellite bus power systems and payload power supplies.

The QPL-certified devices are available in 45 V and 100 V reverse recovery voltage, rated from 15 A to 45 A current, and offered in a TO-254, TO-257, TO-258 or SMD0.5 hermetic package in a choice of single device, doubler or common cathode configurations.

Schottky rectifiers are used primarily in the output stage of a switching power supply. Delivering very low forward voltage drops (VF) and fast turn-off characteristics (trr), these new devices minimize conduction and switching losses in power supply designs.

“The new family of devices extends IR’s offering of QPL-qualified Schottky rectifiers, providing greater design flexibility for power system designers of satellite power distribution and payload power supplies. With a certified qualification and manufacturing process, the new devices eliminate the need for Source Control Drawings (SCDs) and their associated cost and time-to-market,” said Odile Ronat, discrete marketing manager, HiRel Business Unit.

The Qualified Parts List (QPL) is the U.S. Department of Defense’s list of qualified semiconductor products produced by qualified suppliers in accordance with MIL-PRF-19500 screening requirements. Suppliers are audited periodically, thus assuring that all customers receive products that meet government standards.

Super Barrier Rectifiers

Diodes Inc. expanded its portfolio of patented Super Barrier Rectifiers (SBR® ) with the introduction of 12A and 15A rated devices in the compact PowerDI®5 package (Fig. 4). The 12A rated SBR12U100P5 and SBR12U120P5 offer blocking voltage capabilities of 100V and 120V respectively and suit slim laptop, netbook adapter, LCD and LED TV applications. The 15A rated version, the SBR15U30SP5, will in addition fit next generation solar panel design, where low profile bypass diodes are mounted directly beneath the glass. As an illustration of the devices’ low VF performance, it is typically 0.63V for the SBR12U120P5, for a forward current of 12A at an operating temperature of 125ºC.

With a thermally efficient clip bond helping to achieve a higher forward surge rating, the PowerDi5 packaged SBRs also raise power supply reliability, by offering increased protection against large turn-on spikes and better overall thermal heat transfer than larger packaged rectifiers. Compared to the SMC package, the PowerDI5’s 26mm2 footprint is 41% smaller, and its height of 1.15mm is half that of the DPAK (TO252) package.

Diodes Inc. also announced the first devices in a family of Super Barrier Rectifiers intended for automotive applications. With a lower VF, improved avalanche rating and higher safe operating area (SOA) than alternative Schottky or ultra-fast diode alternatives, these rugged rectifiers enable automotive designers to increase the reliability of motor control, display panel and LED lighting circuits.

Utilizing Diodes’ patented SBR technology, the AECQ101 qualified SBR20A60CTBQ, SBR30A45CTBQ and SBR3045CTBQ rectifiers handle output currents of 20A and 30A and are provided in the industry standard TO-263 package, while the SBR1045D1Q is rated for 10A and comes in the slightly smaller TO-252 package.

The SBRs’ low VF means circuit power efficiency can be significantly improved and much cooler operation achieved. The resulting improvement in reliability is further increased by the devices’ higher reverse avalanche rating, that provides greater protection against transient voltage spikes and its lower reverse leakage that provides a higher SOA and guards against thermal runaway in high temperature operating conditions.

Qspeed Family of Diodes

Power Integrations announced availability of the Qspeed family of advanced diodes (Fig. 5). Qspeed diodes use a unique silicon-based process to combine an extremely low reverse recovery charge (QRR) with a very soft recovery waveform. Together, these features help designers optimize the efficiency and EMI performance of their power conversion circuits. In PFC circuits, Qspeed diodes can provide an overall switching performance that is comparable to silicon-carbide (SiC) diodes at much lower cost.

According to the company, the Qspeed diodes have the lowest QRR of any low-cost, silicon-based diode. They supplant ultrafast silicon diodes in PFC and rectifier applications targeting increased efficiency or temperature reduction, and they replace silicon-carbide diodes in applications with aggressive cost goals.

The reverse recovery waveform of a diode generates electrical noise (EMI) which must be filtered to low levels to prevent conduction to the AC mains, the power supply load, or radiation to nearby systems. Qspeed diodes have excellent softness--essentially a sinusoidal recovery waveform, which contains no high-frequency harmonics thus reducing conducted and radiated EMI emissions. These characteristics reduce the size, cost, weight, and complexity of a power supply’s EMI filter hardware, and reduces the prototyping and development cost associated with EMI suppression.

THREE families of Qspeed

Qspeed diodes deliver industry-leading performance without the cost of exotic materials, enabling high-efficiency and low-cost designs. Qspeed 600 V diodes are available in three families. The X Series is optimized for cost-effective high efficiency at switching frequencies below 80 kHz, and the Q and H Series are designed for use above 80 kHz. The Q Series has the highest softness, giving the best EMI performance. The H Series has the lowest VF and QRR, providing the highest efficiency. Besides the 600 V products, Qspeed 300 V diodes provide best-in-class switching for output rectification and audio applications.

Power semiconductor supplier Power Integrations, San Jose, CA, acquired Qspeed Semiconductor in December 2010. The company offers the full family of Qspeed advanced diodes. Stuart Hodge, product marketing manager at Power Integrations, said, “In addition to power factor correction circuits, Qspeed diodes are also well suited for use as output diodes--replacing Schottky diodes--particularly in high-current, high-voltage power supplies such as telecom and audio. In these applications, Qspeed diodes deliver a dramatic reduction in peak inverse voltage, and the soft recovery often allows designers to completely remove snubber circuits, lowering design cost and complexity while increasing efficiency.”

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