© Analog Devices Inc.
Application Notes | February 26, 2021
Synchronous Rectification on the Secondary Side
Question: How can I increase the efficiency of my isolated power supply?
Answer: For most step-down regulators, also called buck regulators, it is standard in typical applications to use active switches instead of Schottky diodes. This can greatly increase conversion efficiency, especially when low output voltages are generated. And in applications where galvanic isolation is needed, synchronous rectification can be used to increase conversion efficiency as well. Figure 1 shows a forward converter with synchronous rectification on the secondary side.
Figure 1. Self-driven synchronous rectification of a forward converter.
Driving the switches for the synchronous rectification can be done in different ways. One simple concept for doing so involves driving across the transformer’s secondary winding. This is shown in Figure 1. In this example, the input voltage range may not be very wide. With the minimum input voltage, there needs to be enough voltage at the gates of SR1 and SR2 so that the switches can be reliably turned on. To ensure that the gate voltage at MOSFET SR1 and MOSFET SR2 does not exceed their maximum rated voltage, the maximum input voltage cannot be too high.
In all power supplies with synchronous rectification, a negative current may develop through the circuit. For example, if the capacitors at the output of the circuit are precharged before the circuit is turned on, current could flow from the output side to the input side. The negative current could increase the voltages at MOSFET SR1 and MOSFET SR2 in such a way that they might be damaged. Care must be taken to protect the switches in such an event.
Figure 2. Synchronous rectification of a forward converter with a dedicated driver IC.
Figure 2 shows a way to implement synchronous rectification using the LTC3900. This is a controller for driving the synchronous rectification switches SR1 and SR2 in a forward topology.
Such a concept works well. However, the LTC3900 needs to prevent negative current flow through the external switches. First, the device needs to detect a negative current quickly and then the SR1 and SR2 switches need to be rapidly turned off. This is necessary to prevent damage to the circuit during a startup or during a possible burst mode.
Figure 3. Synchronous rectification of a forward topology by complete integration with the ADP1074.
Figure 3 shows a very elegant circuit design with the new ADP1074. Output voltage information is sensed by the feedback pin. To prevent the risk of negative current flow across the SR1 and SR2 switches in certain circumstances, such as when there is precharge on the output capacitor, synchronous rectification is not activated. The body diodes of the two switches perform the rectification. In this way, damage to the switches can be prevented. The built-in iCoupler® technology in the ADP1074 enables safe operation without negative current flow.
Author: Frederik Dostal studied microelectronics at the University of Erlangen-Nuremberg, Germany. Starting work in the power management business in 2001, he has been active in various applications positions, including four years in Phoenix, Arizona, working on switch mode power supplies. He joined © Analog Devices in 2009 and works as a power management technical expert for Europe.



Author: Frederik Dostal studied microelectronics at the University of Erlangen-Nuremberg, Germany. Starting work in the power management business in 2001, he has been active in various applications positions, including four years in Phoenix, Arizona, working on switch mode power supplies. He joined © Analog Devices in 2009 and works as a power management technical expert for Europe.
InnovationLab acquires flexible printed battery technology from Evonik
German printed electronics specialist, InnovationLab, has acquired the TAeTTOOz printable battery technology from Evonik.
Sponsored content by Fusion
Manufacturers Reassess their Supply Chains
Prevailing obstacles since the COVID-19 Pandemic in 2020 have manufacturers reassessing their supply chain strategies. The following major disruptions that occurred entering 2022 added to existing setbacks, or created new ones altogether:
Motorola secures chip supply with GlobalFoundries deal
The US semiconductor foundry has entered into a long-term agreement to safeguard the supply of chip solutions for Motorola Solutions' radios, which are widely used by public safety, critical infrastructure and enterprise organisations.
Nexperia and Kyocera to develop GaN automotive power modules
Nexperia and Kyocera AVX Components (Salzburg) GmbH, have entered into a partnership with a focus on power components – the companies aims to jointly developing GaN applications for electric vehicles.
Intel invests $700 million in new Oregon mega lab
The US chipmaker plans to invest more than USD 700 million for a 200,000 square-foot, research and development mega lab focused on data center technologies and addressing areas such as heating, cooling and water usage.
Obsolescence management cannot be an afterthought
“Obsolescence has always existed. However, it usually only becomes really critical for companies when the exception mutates into the norm. And in recent years we have unfortunately experienced this unwanted development not only with semiconductor chips, but increasingly with many other components, materials and raw materials,” says IIOM President and COGD Chairman Dr Wolfgang Heinbach.
Tower record 1Q22 revenues of $421 Million, a 21% YoY
Tower Semiconductor reported first quarter 2022 revenue of USD 421 million, an increase of 21% compared to USD 347 million in the first quarter of 2021.
Gallium Semiconductor opens its Nijmegen R&D center
Gallium Semiconductor has officially held the grand opening of its European R&D center in a ceremony in Nijmegen, the Netherlands.
Ferrotec to add manufacturing capacity with new plant in Malaysia
Ferrotec, a global supplier of materials, components, and precision system solutions, is establishing a new manufacturing facility at Kulim Hi-Tech Park, Kedah, facilitated by the Malaysian Investment Development Authority (MIDA).
Sponsored content by Proval Service
Since 25 years your partner for SMT stencils and solder pallets.
25 years of experience makes Proval Service not just a supplier but your trustful and grounded partner to support you with SMT stencils and solder pallets. A qualified and unite team can satisfy every customer's need during the whole process.
Skeleton targets the Polish market – teams up with ZPUE
Supercapacitor specialist, Skeleton Technologies, and ZPUE, a Polish manufacturer of electrical devices for electrical power distribution utilities, have entered into a commercial agreement to provide energy storage solutions to the Polish market.
ERP partners with Flip to fulfill EOL and Obsolete component solutions
Flip Electronics has signed a franchised distributor partnership agreement with ERP Power (ERP) to distribute its End-of Life (EOL) semiconductor products.
Foxconn and DNeX build and operate wafer fab in Malaysia
Dagang NeXchange Berhad (DNeX) and Foxconn subsidiary Big Innovation Holdings (BIH), plan to set up a joint venture company to build and operate a new 300mm wafer fab in Malaysia.
Imec and semiconductor partners target greener chip manufacturing
Nanoelectronics research and innovation center, imec, says that it has managed to pool together stakeholders from the semiconductor value chain – from companies such as Apple and Microsoft, to suppliers, including ASM, Kurita, SCREEN and Tokyo Electron – to participate in its Sustainable Semiconductor Technologies and Systems (SSTS) research program.
SiPearl reaches milestone – 100 employees
The European chip designer has exceeded 100 employees across its six sites in France (Maisons-Laffitte, Grenoble, Massy, Sophia Antipolis), Germany (Duisburg) and Spain (Barcelona).
Arrow names Jörg Strughold as president EMEA components
Arrow Electronics announces that Jörg Strughold will take over as president of its components business in EMEA. He succeeds Martin Bielesch who has decided to leave the company.
€14 billion to attract semiconductor players to Germany
EUR 14 billion in state support is the German governments new strategy to attract more chipmakers to the country.
10 different companies have expressed interest in Toshiba
Back in April 2022, Toshiba Corporation announced that it had resolved to solicit proposals on strategic alternatives from potential investors and sponsors. The Japanese company is seeking to enhance its corporate value and has since the announcement been holding discussions with the potential partners.
Avnet breaks ground on German expansion
In order to better serve its customers’ local and global needs, Avnet is expanding in two locations in Germany. Avnet Embedded broke ground on a new manufacturing site in Eschbach and Avnet EMEA plans to build its third European logistics centre in Bernburg.
Viettel & Qualcomm team up on 5G infrastructure development
Viettel Group and Qualcomm Technologies plans to collaborate and develop a next-generation 5G Radio Unit (RU) with massive MIMO capabilities and distributed units (DUs). This focuses on helping to expedite the development and roll-out of 5G network infrastructure and services in Vietnam and globally.
Applied Materials opens Montana expansion – create 200 new jobs
The company has opened its latest expansion in Montana, a new semiconductor manufacturing center set to create 200 jobs in the Flathead Valley.
How to easily select the right frequency generation component
Question: What is the right frequency generation component for my application?
Bell Semiconductor is suing companies left and right
In late April, Bell Semiconductor, a Pennsylvania-based technology and intellectual property licensing company, filed lawsuits against Micron, Infineon, Nvidia and seven other companies alleging infringement of one of its patents.
Load more news