Summary:

It is rare that a distributor of electronic parts gets involved in developing components. Endrich Bauelemente GmbH, however, has been working shoulder-to-shoulder with a manufacturer that is not widely known (CT Micro). Despite the recent silence, the developer society is eager to move forward with optocouplers. The goal was to create the thinnest device that has ever been made. This feat was achieved with the CT MICRO DMC(tm), DoubleMolded-CoPlanar technology. Phoenyx Contact was a client and market leader of Endrich who defined the technical parameters. The packaging had to be extremely low-profile, with a profile that was 25% lower than MiniFlat packaging (SOP) and 60% less than 4PDIP packaging (DIL). The Electronica show in Munich has warmly welcomed CTP17.

CTMicro: About the Company

CT Micro International Corporation was established as a customer-oriented and technology-driven company to meet the market’s most demanding requirements. The company’s founders and executives have decades of experience in marketing, sales, and development in MOSFET and optoelectronic technologies. The technical leadership and general management have been familiar with infra-red components for more than 15 years. They can respond to market demands quickly by implementing new products. The main target markets are consumer electronics, industrial equipment, and white goods. CT Micro, a world-class manufacturer of quality components and products, has implemented a world-class quality management system during the design phase.

The thinnest optocoupler transistor in the world

The challenge is to design the “thinnest”, among optocouplers, since the larger the part, the more room it provides for insulation between input and output in order to separate them safely, even if the potential difference is higher.

Customers may have special requirements for thinnest components that are not available at the moment. These solutions could be on the cutting edge of technology. CT Micro can supply such components. This new DFN package is 25% smaller than the standard Mini-Flat packaging (SOP) and 60% smaller than the 4PDIP packaging (DIL). The CT MICRO Double-Molded Co-Planar technology (DMC(tm)) allowed it to be developed. The Ultra-Flat Packaging (picture 1) allows for the development of the thinnest products that meet the latest space-saving demands on the market. The structure called co-planar is created when the IR LEDs and phototransistors are placed side by side inside the optocoupler. Some reflective material is used to create the optical link. We call the “Over-Under structure” when the LED and phototransistor face each other. In the first case, the insulation length is fixed, and therefore, the dielectric strength is higher. The common mode noise is also better suppressed because there is no capacitive charging between the input and output as opposed to “over-under.” The “over-under structure” ensures a more precise current transfer rate. The co-planar design has the additional advantage that both the LED and phototransistor can be located on the same frame. This eliminates the need to position the input and output frames.

CT-Micro engineers have managed to combine the benefits of both the over-under and co-planar structures. The receiver and transmitter are located on the same miniature PCB, allowing for a co-planar design. Even if mechanical force is applied to the lead frame, it’s possible to maintain 2.5kVRMS insulation by maintaining a physical distance greater than 0.4mm.

Internal materials that are translucent and reflective have the same thermal expansion rate, ensuring better mechanical properties. In the first phase, the translucent material is injected over the optoelectronic components, and in the second phase, the reflective filling as well as the housing are built up. Image 2 shows a design that allows for the creation of devices with 2, 4, and 8 channels. In the future, parts with higher insulation strengths or more space saving can be offered by developing the carrying materials even further. Let’s first discuss what CTR means in relation to optical behavior.

The current transfer ratio (CTR), also known as the current transfer ratio, is similar to the DC gain of transistors. (h FE). It is defined as the ratio between the output current I C and the input current I f.

CTR (%)=(I I/I (f /I ) 100

CTR is an important attribute for optocouplers, just like insulation strength. It is dependent on the following factors:

• The driving current (I and F).
• The temperature of the ambient air
• Optocouplers can be disposed of easily

CTR must be taken into consideration during the design phase, as a lack of tolerance can result in an inadequate output level and malfunctioning operation.

CT Micro ensures that the CTR will be between 100% and 300% for I f=1mA/V ce=5V in order to support low driving currents, flexibility of design, and efficiency.

The dependence of CTR for the optocoupler on these factors is shown in picture 4.

This optocoupler is designed to meet the most demanding industrial environments. Its extended temperature range from -55degC up to 125degC meets all their requirements.