Tweet

Posted on 30 December 2019

Modern Challenges in Distribution

Free Bodo's Power Magazines!

 

 

 

Distributors in the electronics industry have been known for about 50 years. Today, there are several types of distributors. Some companies have become very big and carry over a hundred or more different product lines in their portfolio. Due to their large and global customer base, every electronic device manufacturer, who wants to do business worldwide, has to deal with them.

By Jens Egbers and Christopher Rocneanu, Field application Engineers MEV Elektronik Service GmbH, Germany

Another type is the catalog distributor. One of its key tasks is to have all devices in stock. All big manufacturers use one or more catalog distributors to enable fast sampling and on-time availability.

MEV Elektronik Service GmbH is a medium sized distributor and has been on the market for over 20 years. The main focus is the concentration on niche markets with niche products. MEV's strengths are its customer-orientation and its offer of detailed technical support. The system selling approach completes the strategy and is adapting the customer's feedback while thinking ahead what technology the market and customer could use in the future. To see recent products and newest innovations of technologies are today's challenges for the Application team of MEV Elektronik Service GmbH.

Challenges of future technologies in Power Devices

Everybody is talking about wide band gap power electronic devices like SiC and GaN at the moment. MEV started to go with the SiC technology a long time ago and even went successfully through the maturing times of new technologies. While it is a difficult decision to anticipate which technology will last or which technology the customer will adapt to, it is important for MEV to be ahead.

Over the last few years, SiC power devices were considered expensive, but suitable for high performance applications. In fact, SiC diodes are used in PFC inverters and many more applications. Through the last years, the price dropped to approx. US$ 0.50/ Ampere and will continue to fall. CREE for example, is ready to run 6 inch wafers in production when demand increases. There is only one work step remaining for the customer to save money with a SiC diode: You have to take a detailed look at the diode's operating point (required current at your estimated operating temperature in your application) when comparing devices from different manufacturers and wanting to choose the best device in terms of performance and price. Of course MEV will help customers to choose the right device.

Second approach with SiC devices

With SiC transistors it is a different story. The first approach with SiC was to get the best efficiency out of applications. Meanwhile, in some applications you can omit the SiC Diode when you use the body diode of the MOSFET as a freewheeling diode. Furthermore you can significantly decrease system size and weight as well as inductance when you increase the switching frequency. Dieter Liesabeths, Sales Manager CREE, EMEA, says, "It is possible to reap many of the benefits of 3level topologies while staying with the simpler 2level topology by taking advantage of the low switching losses and high blocking voltages of SiC MOSFETs."

Helpful tools for the customer to evaluate SiC are Reference Designs and Demo Boards. With CREE's gate driver board CRD-001, the customer can quickly start driving the MOSFET or the module. Additionally, CREE's 60W Demo Aux Power Supply (CRD-060DD12P) is available at MEV. Without the time- consuming development of an evaluation board, the aux power supply offers a platform for, fast comparisons between CREE's 1700V 1Ohm MOSFET (C2M1000170D) and Si High Voltage devices. Target Application is auxiliary power supply for Inverters, UPS, E-meter or motor drives.

CREE Reference Design: 60W Aux Power Supply

Solution out of one hand

It is not only important to rely on the right technology. Moreover, you have to offer a full solution. Additionally, the benefit of a design-in distributor like MEV for customers is on-time technical support in power electronics.

The technical support of the application engineers at MEV Elektronik Service GmbH mostly starts with a customer visit. Talking with the design engineers face to face is a very good starting point to find out the requirements or the needs of the customer. For power electronics, the good thing is that every application needs a power supply like AC/DC or DC/DC solutions. So, every customer is interested in the latest power electronics, new topologies or new regulators to develop the power part of their application.

To have a dedicated portfolio of different power products is mandatory for a distribution company like MEV Elektronik Service GmbH. With a portfolio starting with AC/DC switching regulators, DC/DC linear and switching regulators and a lot of discrete parts like diodes and bridge rectifiers, MEV is well prepared to find the right solution for almost any application. To complete the power management product portfolio, also ready "plug and play" AC/DC power supplies, DC/DC converters or point of loads are part of the MEV portfolio. This is important to serve also customers with smaller volumes or where the development time is critical. Figure 2 shows a typical block diagram for a power supply and where MEV and its partners can offer solutions.

A short pull-out from manufacturers who offer suitable devices in above AC/DC power supply block diagram: CREE, Power Integration, Micrel, Itacoil, MS Schmelzer

After the customer visit and the discussed possible power management solutions, the next step begins for the application engineers at MEV. Especially for developments of discrete AC/DC power supplies, the distributor can help in different design stages, e.g. starting by defining the right regulations IC and sometimes ending with a complete prototype which will be developed in the MEV laboratory.

For most design engineers, it is very important to see the complete solution of their power supply from the beginning. This means for example that not only a switching regulator is interesting, but also the corresponding parts which are required are important to calculate the complete bill of materials and to see the complete solution. For this reason, the engineers at MEV provide the complete diagram, bill of materials and the transformer design for a discrete AC/DC solution. Figure 3 shows a typical 12W AC/DC solution based on a switching regulator from MEV's partner company Power Integrations.

A 12W power supply based on a flyback topology

All important parts are included in the published diagram. It starts with the AC 85-265V input, continuing with the primary rectification and the EMI components, followed by the galvanic isolation of the transformer and the secondary regulation with the feedback network/ output stage. Having a schematic BOM and the transformer design at the beginning of the development is a big benefit for the customer. After that, he may use this diagram or he may fine-tune it to fit his requirements.

Transformers, EMI and other technical requirements

In addition to the diagram, the transformer design plays a big role in the AC/DC power supply. A proper transformer design helps the customer to save a lot of money. For example the efficiency, safety, output regulation and the EMI behavior depend on the transformer design. This means that with a properly designed transformer, the customer can save further components and thus money. Especially for safety reasons, the transformer has to be designed to fulfill the required creepage and clearance distance.

The MEV application engineers also make suggestions and simulations here to support their customers. Figure 4 shows a simulation to define the transformer in terms of windings, size, cores and bobbins.

Simulation for a flyback transformer

The customer can take these simulations and go to his magnetic supplier and ask for samples according to the simulated results.

For a customer who wants to start quickly with an evaluation kit, Power Integrations offers for example a wide range of reference design kits for almost any switching regulator family. The kit consists of a complete ready AC/DC power supply with all components, a raw PCB board to assemble and test own discrete parts, several regulator samples and documentation. Figure 5 shows a PCB board of a Power Integrations reference design kit.

AC/DC evaluation board for first testing

When the design is finished at the customer, MEV is also there to double-check the design or to help when problems arise. For power supplies measurements like primary and secondary currents/voltages, EMI or temperatures are mandatory. With an own laboratory, the application engineers will also help here to find problems or check if everything is functioning properly with the power supply. Figure 6 shows for example the improvement with a primary common mode choke (highlighted in green in the diagram) at an input stage of an AC/DC power supply.

Input stage of a typical power supply

The left side of Image 7 shows the AC/DC power supply without a common mode choke at the primary side which failed the EMI test. And on the right, the passed test after improvement of the primary side with a common mode choke is illustrated.

EMI Results without and with a common mode choke at the primary side

The key EMI sources are:

  • High di/dt current waveforms in the primary and secondary loops
  • High dv/dt voltage waveforms from switching transistors
  • Charging and discharging of parasitic capacitances in the transformer windings
  • Noise generated from diodes
  • Coupling between transistor and heat sink

Image 8 shows what "noisy" and "quiet" nodes in a flyback topology are. Noisy nodes are those nodes which see high voltage switching signals. Potential on these nodes is changing over a switching period. Quiet nodes are low impedance nodes which see little switching activity. Potential on these nodes is constant over the switching period.

Nodes in a flyback topology

Apart from the technical support, the big benefit is that MEV can deliver the most important parts like regulation ICs and transformers from one source.

Summary

Challenges in distribution are not only relying on the right technology but being able to offer a complete solution to the customer. Moreover, for a medium-sized company like MEV, application support is the key feature for success. With its internal laboratory and a steady growing team of field application engineers, MEV is well prepared for another 20 years of distribution. 

 

VN:F [1.9.17_1161]
Rating: 0.0/6 (0 votes cast)

This post was written by:

- who has written 791 posts on PowerGuru - Power Electronics Information Portal.


Contact the author

Leave a Response

You must be logged in to post a comment.