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schematic by the manufacture produces it

This component has two diodes in one package. What is the component's function? It's seen being used just to function as two diodes, rectifying from the two || pins at the right to the output at the left.

No real image, but it looks like a FET transistor.

Is there a function other than just two diodes that makes it useful to be produced as an integrated component?

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    \$\begingroup\$ It is just two diodes. Lots of times people need two diodes, so smart manufacturers started making two-diode packages. The package itself is probably 70% of the cost and size of the part, so why not? \$\endgroup\$ Jan 19, 2023 at 13:34
  • \$\begingroup\$ Such dual diodes exist in multiple arrangements, just compare BAT54S and BAT54C for instance. See the difference? Anyway, still only just diodes. \$\endgroup\$
    – datenheim
    Jan 20, 2023 at 17:36

4 Answers 4

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These function as an inexpensive OR gate. The anodes are isolated inputs and the output is on the common cathode.

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Dual diodes are standard components. Partly for convenience, partly because of matching.

They are generally matched, either by using two selected dies in one package, or are monolithic (two diodes one chip), so they can be wired in parallel for greater current carrying capacity. In parallel, there isn't really much difference versus a single (two-pin) part, although the lead inductance can be a little lower. But you also have the option of using them separately, such as for a full-wave center-tapped rectifier, a common use case in low voltage power supplies. So the three-terminal parts are quite common, and higher quantity drives lower prices.

Other arrangements (common-anode and series) are available. Independent pairs are much less common, since the package (TO-220 or etc.) is the limiting factor. (There are however dual rectifiers in SOT-227, for example.)

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    \$\begingroup\$ Would explain ampacity, by ( ) ? \$\endgroup\$ Jan 19, 2023 at 3:48
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    \$\begingroup\$ Ampacity = current carrying capacity (more amperes) \$\endgroup\$ Jan 19, 2023 at 3:50
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    \$\begingroup\$ mean edit it by ( ) \$\endgroup\$ Jan 19, 2023 at 4:37
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    \$\begingroup\$ edit it : ..for greater ampacity ( ) \$\endgroup\$ Jan 19, 2023 at 8:47
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    \$\begingroup\$ I think he's suggesting you edit the post to include the explanation of "ampacity." (Though I would personally just change it to "current capacity," which is likely to be more clear to those not so familiar with North American English.) \$\endgroup\$
    – cjs
    Jan 19, 2023 at 21:07
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The diodes are almost identical and thermally coupled. You can use them in differential circuits where otherwise thermal runaway can cause an increasing difference in their characteristics.

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The other day I saw a pair of diodes like this in an old (probably early 1990s) +5/+12 V switching power supply, used for rectification, one on each rail. They were D10SC4M in ITO-220 packages (which appear to be very similar to TO-220) attached to a fairly hefty heat sink. The two anodes (marked '~') are both connected to the the same AC input so that the diodes are in parallel.

My theory is that devices are designed like this for greater current-carrying capacity in a more compact configuration. Current is limited by both the design of the diode itself (10 A average per-diode is given in the datasheet) and by how much heat the package can dissipate. It appears that the TO-220 package (on an appropriate heatsink) can dissipate enough heat to run two diodes at full power, so putting them both in a single package, rather than using a separate package for each diode, reduces parts count, cost and the amount of space you need on the board.

As you can see pretty clearly in the first photo below, going from two packages to four packages would require an increase in the size of the circuit board, even if separating the diodes meant that smaller packages (such as TO-126) could be used.

enter image description here enter image description here

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