Increase of environmental care forces electrical equipment makers to constantly target higher efficiency-levels.
For power-supply designers, one solution is to use electronic components based on wide bandgap materials such as silicon-carbide power Schottky rectifiers that feature no switching power-losses.
Those diodes usually come in non-isolated packages such as the usual TO-220 package, offering a good thermal performance. However, as those are usually mounted on metal heatsinks that are, in most cases, directly connected to the ground, they require the use of isolating mica-foils and rings to avoid putting them in short-circuit.
Those insulators are generally tricky to dimension and mount properly, reducing the UPH (unit-per-hour) on assembly lines. They also feature an intrinsic thermal resistance that impacts the thermal performance of the system.
Another commonly used package is the TO-220FP full-pack that has a degraded thermal performance, limiting the dissipation. SiC diodes in TO-220FP full-pack are thus generally limited in terms of current-caliber.
ST’s solution :
Offering an insulation within the package
ST now offers a range of 650 V silicon-carbide power Schottky rectifiers housed in insulated TO-220, featuring an internal 2500 Vrms ceramic isolation. Those new diodes offer a thermal resistance junction-to-case 30% better than the traditional fully-molded TO-220FP full-pack and 20% lower than that of a non-insulated TO-220 mounted with an external mica-foil, enhancing the heat dissipation through the heat-sink.
- Insulated voltage: 2500 Vrms front-side and back-side
- Typical package capacitance: 7 pF
- Rth(j-c) junction-to-case 30% lower than TO-220FP full-pack
- Rth(j-c) junction-to-case 20% lower than non-insulated TO-220 + isolation foil
This insulated TO-220 package can be mounted on a metallic heatsink connected to the ground without any isolating foil while having no risk of putting the diode in short-circuit.
Its 2500 Vrms isolation is guaranteed on all sides of the package.
Gain about 20 seconds on mounting time in production while improving the thermal performance without any isolation risk!
A thermal-resistance comparison was made between a standard noninsulated TO-220 mounted with an isolating foil and an insulated TO-220 with no external isolation. Results are shown in table 1.
|4 A, 650 V SiC diode TO-220FP full-pack||4 A, 650 V SiC diode Standard TO-220 with isolation-foil||4 A, 650 V SiC diode Insulated TO-220|
|4.3 °C/W||3.7 °C/W||3.0 °C/W|
|Current caliber (IF(AV))||TO-220AC insulated (2 legs): single SiC diodes (650 V)||TO-220AB insulated (3 legs): dual SiC diodes in series (2 x 650 V)|
Using ST’s silicon-carbide power Schottky rectifiers housed in insulated TO-220 gives SMPS designers the benefit of the unprecedented efficiency of those power components while enabling them to get rid of the external isolation that is necessary when mouting a standard TO-220 on a heatsink. It gives power-supply makers the possibility to gain mounting time and increase their UPH in production while improving the thermal performance of the system. It’s all benefits !