© 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.
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.
RF manufacturer orders multiple solstice plating systems
ClassOne, a provider of semiconductor electroplating and surface preparation systems, has received multiple tool orders from an unnamed RF device manufacturer.
Sponsored content by ICAPE Group
ICAPE Group Service Office in Asia
In a context where traveling can be difficult, finding a good partner for your production of electronics parts can be a real challenge. With its unique organization and a Headquarters in China where all the key services are located close to the factories and fully operational, ICAPE Group provides a global solution.
STMicro manufactures first 200mm SiC wafers in Sweden
STMicroelectronics has manufactured the first 200mm (8-inch) Silicon-Carbide (SiC) bulk wafers for prototyping next-generation power devices from its facility in Norrköping, Sweden.
SkyWater to invest $56M in Minnesota capacity expansion
SkyWater Technology's Board of Directors has approved USD 56 million in capital investments to expand the capacity and capabilities of its Minnesota facility and to accelerate the company’s entry into the 200 mm GaN market.
Silicon Labs completes sale of Infrastructure & Automotive business
Silicon Labs announces that it has completed the divestiture of its Infrastructure & Automotive business to Skyworks Solutions for USD 2.75 billion in an all-cash asset transaction.
Sponsored content by Shenzen Kinwong Electronic
The development trend of printed circuit board products and Kinwong's solution
With the rapid development of electronic technology in recent years, printed circuit board (PCB) products are pursuing higher heat dissipation capabilities, with high voltage and high current characteristics, and are developing towards high-density interconnection technology (HDI).
Strong improvement for RoodMicrotec
Semiconductor supplier RoodMicrotec's total income during the first half of 2021 amounted to EUR 7.3 million, which is 36% above the total income of the same period 2020 and 12% higher than the total income reported for the second half of 2020.
TSMC says its to early make a final decision on German expansion
Semiconductor foundry giant TSMC says that it’s too early to say whether the company will expand with new factories in Germany and that discussions are still in early stages.
Sivers Photonics invests to expand capacity
Sivers Photonics, a part of Sivers Semiconductors, is looking to expand it manufacturing capability and capacity with a fab investment of up to GBP 3 million in 2021.
Molex goes with FUJI NXT series pick-and-place machines
Molex CVS Dabendorf GmbH has decided to use the NXT III placement machine from FUJI EUROPE CORPORATION GmbH.
Inductor current measurement in switched power supplies
Question: How do you measure inductor current?
Fingerprint Cards partners with Mouser Electronics
Swedish biometrics company Fingerprint Cards has entered into a collaboration with global distributor Mouser Electronics.
GF CEO on Intel rumour: “There’s nothing to that story”
In an interview with Jon Fortt from CNBC, GlobalFoundries’ CEO Tom Caulfield sets the record straight regarding the Wall Street Journal’s report of a potential USD 30 billion acquisition by Intel.
Applied Engineering to set up JV operations with Malaysian counterpart
US-based Applied Engineering (AE) will be establishing a joint venture (JV) plant with Malaysian counterpart, QES Manufacturing Sdn. Bhd. (QES) in Batu Kawan Industrial Park, Pulau Pinang later this year.
MKS completes its acquisition of Photon Control
MKS Instruments has completed its previously announced acquisition of Photon Control Inc.
Renesas to close its Yamaguchi factory next year
Renesas says that it has decided to consolidate the Yamaguchi Factory (located in Ube, Yamaguchi Prefecture in Japan) of its wholly owned subsidiary, Renesas Semiconductor Manufacturing Co., Ltd. at the end of June 2022.
Intel looking to buy GlobalFoundries for $30 billion?
US chipmaker Intel is reportedly in talks to acquire semiconductor manufacturer GlobalFoundries for some USD 30 billion, reports the Wall Street Journal citing sources familiar with the matter.
A simple way to measure temperature using one GPIO digital interface
Question: How can I make an analog measurement if I only have a single GPIO left on the FPGA/microprocessor for my system?
New owner for crystal growth business in Eisenach
Jenoptik has sold its crystal growth business to Hellma Materials, and will continue to focus its business on photonic applications. Hellma Materials takes over all 25 employees, and continues all business activities.
Linear Integrated Systems partners with Digi-Key Electronics
Linear Integrated Systems, a designer and manufacturer of precision, high-performance, small-signal discrete semiconductors, has entered into a new partnership with Digi-Key Electronics.
Conti invests in Israeli industrial sensing start-up Feelit
Continental has acquired a minority stake in the Industry 4.0 start-up Feelit, headquartered in Tel Aviv, Israel. Both companies have agreed not to disclose the amount of the holding.
Skeleton Technologies brings in additional capital
On the first of July, Skeleton Technologies, announced the successful closing of a further EUR 29 million in its Series D financing. The total financing in Round D amounts to EUR 70.4 million.
Fingerprint receives follow-on order for its T-Shape sensor
Swedish biometrics company, Fingerprint Cards has secured an additional volume order for approximately 250,000 units of T-Shape sensor modules from one of the world’s top three card manufacturers.
Minebea Mitsumi acquires Omron’s of 8-inch fab
Minebea Mitsumi’s subsidiary Mitsumi Electric, has entered into an agreement with Omron Corporation for the acquisition of Omron's semiconductor and MEMS fabrication plant in Yasu, Shiga, Japan – as well as its MEMS product development function.
Load more news
