BC637 NPN High-Current Transistor (TO-92)

Most TO-92 transistors are rated for small signal currents in the tens or low hundreds of milliamps, but the BC637 pushes that same compact package to a full 1A rating, filling a useful middle ground between standard small-signal parts and bulkier TO-220 power transistors. That makes it a practical choice for driving moderately sized relays, small motors, or LED arrays that draw more current than a BC547 or 2N3904 can handle, while still fitting into tight board layouts where a larger power transistor package wouldn't be worth the space.