What Is a TO-220 Schottky Rectifier?

A TO-220 Schottky rectifier is a two-die thermal problem: 1.6 °C/W per diode plus 0.15 °C/W of coupling. What that means for usable current.

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A TO-220 Schottky rectifier is usually a two-die part, and the second die heats the first. On ST’s 100 V, 2 × 10 A dual center-tap device the junction-to-case resistance is 1.6 °C/W per diode, but the datasheet also specifies 0.15 °C/W of thermal coupling between the two — and gives the equation to add it. Anyone who designs from the per-diode figure alone under-states the junction temperature, sometimes by more than the margin they thought they had.

Last updated: October 11, 2026

Key Takeaways

TO-220 is a through-hole power outline: a plastic body on a metal tab, mounted to a heatsink with a screw and, where needed, an insulating pad.
A Schottky junction conducts with a low forward drop and switches without minority-carrier recovery, which is why these parts hold low-voltage, high-frequency rectification duties.
Dual center-tap parts carry two dies in one package, so thermal coupling between them is part of the calculation, not a rounding error.
The insulated variant of the package — TO-220FPAB in the example here — trades thermal performance for a 2000 V RMS sine insulating voltage.
Schottky leakage is the recurring limitation: it rises with temperature and is specified at a stated junction temperature rather than at the ambient.

What the Device Is, and What the Package Does

The junction sets the forward drop; the tab sets how much of it you can use. A TO-220 Schottky rectifier is a low-forward-drop diode built for continuous current high enough that the heat has to leave through metal rather than through a PCB pad.

STMicroelectronics’ STPS20H100C is a representative device: a 100 V, dual center-tap Schottky rectifier rated 10 A average per diode and 20 A per device, with a 175 °C maximum junction temperature and a typical forward voltage of 0.59 V. It is offered in TO-220AB, D²PAK, I²PAK and TO-220FPAB — four outlines for one die set, which is exactly why the package belongs in the specification rather than in the part-number decoration.

The electrical behaviour is the familiar Schottky story. A metal-semiconductor barrier gives a low turn-on voltage and leaves essentially no stored minority charge to remove at turn-off, so recovery losses are negligible in the low-voltage rectification stages where these parts live: switch-mode supplies, DC-DC converters, battery chargers, freewheel and flyback paths, reverse-polarity protection, solar blocking and OR-ing. What the package adds is the ability to dissipate the conduction loss those currents produce.

The Dual-Die Thermal Problem, in Numbers

Read the thermal table as a network rather than a single resistor. The datasheet lists the per-diode junction-to-case resistance, the total for the device, a coupling term, and the equation that combines them.

Parameter (STPS20H100C datasheet values)	TO-220AB, D²PAK, I²PAK	TO-220FPAB (insulated)
Junction-to-case R_th(j-c), per diode	1.6 °C/W	4 °C/W
Junction-to-case R_th(j-c), total	0.9 °C/W	3.2 °C/W
Coupling between diodes, R_th(c)	0.15 °C/W	2.5 °C/W
Average forward current I_F(AV), δ = 0.5 square	10 A per diode, 20 A per device at T_C = 160 °C	10 A per diode at T_C = 145 °C; 20 A per device at 125 °C
Surge non-repetitive current I_FSM	250 A (10 ms sinusoidal)
Repetitive peak avalanche power P_{AR M}	775 W (10 µs, T_j = 125 °C)
Insulating voltage	—	2000 V RMS sine

The coupling row is the interesting one, and the equation that uses it is printed next to the table: the junction rise of one diode is its own dissipation times the per-diode junction-to-case resistance, plus the other diode’s dissipation times the coupling resistance. Assume, for the sake of a model, that each diode dissipates 6 W at equal current sharing. The first diode then rises 6 × 1.6 + 6 × 0.15 = 10.5 °C above the case, and the device as a whole dissipates 12 W against 0.9 °C/W, so the case itself sits about 10.8 °C above whatever the heatsink interface provides. The 6 W figure is an assumption to be replaced with your own measured dissipation — this is a model, not a measurement — but the coupling term is real and it only exists because two dies share one tab.

Choosing the Outline and the Insulation

The tab is usually electrically live, and that decision propagates into the mechanical design.

On the standard TO-220AB and D²PAK variants the tab is connected to one of the diode terminals, so mounting the part on a shared heatsink means either isolating the parts from each other or accepting that the heatsink is at circuit potential. That is where the insulated variant earns its place: the TO-220FPAB carries a 2000 V RMS sine insulating voltage, so it can be screwed directly to a common heatsink without a separate insulating pad — at the cost of a much worse thermal path, 4 °C/W per diode against 1.6 °C/W, and a correspondingly lower case temperature for the same current.

Choosing between them is therefore a trade with a clear shape. If the heatsink can be isolated and the design needs the thermal performance, the uninsulated part wins. If the mechanical design wants a common metal heatsink and a simpler assembly, the insulated variant removes a pad and a process step but removes margin with it — and the numbers above say exactly how much.

Where the Recurring Limitations Bite

Three properties of this device family decide whether a given application is a good fit.

Reverse voltage is the first. Schottky barriers do not extend far into the hundreds of volts, so these parts belong on low- and medium-voltage rails; mains rectification and high-voltage blocking need a different family. Leakage is the second, and it is temperature-dependent: a Schottky specified at tens of microamps cold can be specified an order of magnitude higher at its rated junction temperature, which matters in a battery-backed or always-on path. Package size is the third: a TO-220 is large compared with a flat-lead or DFN part, so where the board is dense and the current is moderate, a surface-mount device may deliver the same electrical result in a fraction of the area.

Where a design needs a lower forward drop than a standard Schottky provides at low voltage, the low-drop variants of the same idea are the next step. ST’s STPS1L30, for example, is a 30 V, 1 A Schottky with a typical forward voltage of 0.26 V, an avalanche rating of 110 W and junction-to-lead resistances of 30 °C/W in SMA, 20 °C/W in SMA Flat Notch and 25 °C/W in SMB — the same package-versus-thermal story, at a tenth of the current.

FAQ

What is a TO-220 Schottky rectifier used for?

Low-voltage rectification and freewheeling at currents that need a heatsink: switch-mode supply output stages, DC-DC converters, battery chargers, reverse-polarity protection, solar blocking and OR-ing circuits.

Why does the datasheet list two thermal resistances?

Because dual-diode packages contain two heat sources on one tab. The per-diode junction-to-case figure applies to that diode’s own dissipation, the total applies to the device, and a coupling term accounts for heat shared between the two.

Should I choose the insulated TO-220FPAB variant?

Only when the mechanical design benefits. It removes the need for an insulating pad on a common heatsink, but its junction-to-case resistance is 4 °C/W per diode against 1.6 °C/W for the standard outline, so it carries less current at the same case temperature.

What is the main limitation of a Schottky rectifier?

Leakage and reverse-voltage ceiling. Leakage is higher than a p-n diode’s and rises with temperature, and the blocking voltage does not reach into the high hundreds of volts, so mains-side duties belong to other device families.

What should be checked before layout?

The pin-out and tab connection, whether the heatsink needs insulation, the copper and thermal path, the creepage and clearance the application requires, and the trace current capability — then the junction temperature under worst-case load, not at nominal.

Official Resources

References

STMicroelectronics, STPS20H100C — 100 V, 20 A power Schottky rectifier, DS1216 Rev 10 — source of the 2 × 10 A ratings, the 1.6 °C/W per-diode and 0.9 °C/W total thermal resistances, the 0.15 °C/W coupling term and its equation, the TO-220FPAB variants’ 4 °C/W and 3.2 °C/W figures with the 2000 V RMS insulating voltage, 250 A surge rating and 775 W avalanche rating. st.com — STPS20H100C datasheet (PDF)
STMicroelectronics, STPS1L30 — 30 V, 1 A low drop power Schottky rectifier, DS1243 Rev 8 — source of the 0.26 V typical forward voltage, the 110 W avalanche rating and the 30 / 20 / 25 °C/W junction-to-lead resistances across SMA, SMA Flat Notch and SMB. st.com — STPS1L30 datasheet (PDF)
Nexperia, PMEG030V030EPD — 30 V, 3 A low V_F MEGA Schottky barrier rectifier — used as the surface-mount comparison point for current density in a flat-lead package. assets.nexperia.com — PMEG030V030EPD datasheet (PDF)
Vishay, TO-247 Ultrafast Recovery — package-family reference for the larger-outline comparison used in this article. vishay.com — TO-247 device family

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