SMD2440-021 is an obsolete photo-transistor with the following ratings that I used for finding an alternate:
| Specification | Value |
|---|---|
| Mounting Type | Surface Mount |
| Wavelength | 880nm |
| Package/Case | 1510(3825 Metric) |
| Voltage Collector-Emitter Breakdown | 30V |
A corresponding emitter with the same wavelength that would work for that transistor is part number 480-3609-1-ND which is also currently obsolete, here are its relevant specs:
| Specification | Value |
|---|---|
| Type | Infrared |
| Current Forward | 75mA |
| Forward Voltage | 1.5V |
| Mounting Type | Surface Mount |
| Package/Case | 2-SMD, No Lead |
For the photo-transistor, I found this close enough alternate: 1080-1389-1-ND; PT42-21B/TR8.
The major differences are size and wavelength. The package size, in this case, is 1210 which is smaller than the original. You’d have to see if that is adequate for your application though, if the pads have enough tolerance and space between them, that smaller size may adequately cross the gap. The second change is the wavelength, in this case, its center wavelength (peak performance) is 940nm. Here is a datasheet (not quite the same part, but same specs): Phototransistors - Everlight Americas Inc., our current link is broken. It shows that the effective range for wavelength is 730 to 1100nm but operates best at 940nm. Technically, the old emitter would work, but might not have the best results.
If you want a better response the cross for the emitter I found is 3147-B2151IR-20C000133U1930CT-ND; B2151IR-20C000133U1930.
This has nearly the same specs across the board, so it would work more efficiently with the transistor I found. Here are some other alternate emitters with similar specs that could work: LED Emitters - Infrared, UV, Visible | Electronic Components Distributor DigiKey
Please review the datasheets to ensure the alternative works for your application.