SGS-THOMSON Microelectronics has introduced a wide range of power bipolar and MOSFET transistors housed in a new package known as TO-220FP (for Full Plastic). This is a fully isolated plastic package that is mechanically compatible with the popular ISOWATT220 package and offers the same guaranteed minimum electrical isolation of 1500V a.c. but features a simplified assembly process that leads to lower manufacturing costs, allowing TO-220FP packaged transistors to be competitively priced. The TO-220FP package does not require external electrical insulation between the back side of the package and the heatsink and the user can safely touch the body of the device when the collector is connected to a high voltage rail.

The key to the TO-220FPýs cost-effectiveness is the use of a modified mono-thickness 0.5mm lead frame, compared to the ISOWATT220ýs bi-thickness 1.27mm lead frame. The smaller copper mass of the lead frame increases the junction-to-case thermal resistance of the package but this does not have a significant application penalty as in most applications the value does not contribute significantly to the overall junction-to-ambient thermal resistance, which is largely dependent on the customer's thermal design.

TO-220FP is UL compliant, with every device tested during production to guarantee that the isolation performance meets the UL Norms.

The initial range of power devices offered in TO-220FP includes popular bipolar and MOSFET transistors for use in Automotive (power switches), Consumer (power supply, audio, power switches), Computer (power supply, peripherals) and Industrial (high volume power supply and battery chargers, electronic lighting) applications. Bipolar devices range from the 15W BD241BFP to the 25W TIP127FP and include a new device, BUH515FP, aimed at SMPS and horizontal deflection applications. Power MOSFETs include the BUZ71FP, the IRF520/530/620FP and the STPxNA and STPxNB series.

I still love the TO-220 package. I got over the TO-3 quite easily when the -220 started to appear but it was always a pain that you still had to go through the whole mica-washer/compound routine. And the fact that the parts usually seemed to be mounted quasi-vertically inevitably left more of the stuff on you. There were also some major safety issues in some of our circuits with flyback-type voltages and 80 - 100 V collector voltages on the devices.

I know I am being fairly liberal in this Editor's choice not in this case being a specific part but I think this is an idea whose time has come around, again. It also serves as a reminder to some that the higher-than-2.7 V market still exists out there and not all products are manufactured by robot-like machines on a JIT basis. And here we have SGS issuing parts with numbers I had long forgotten but, with their new package, will have a new, probably longer, life. The areas/parts chosen for initial release will save countless hours in the assembly of some products and greatly simplify servicing requirements.

Now would I be the first guy to actually touch the package of the new BUH515FP while it was sitting in circuit doing its thing? Probably not, but that's also how I survived in high-power RF work.