2N6028 Programmable Unijunction Transistor

The 2N6028 is a programmable unijunction transistor (PUT) — not a conventional BJT, but a thyristor-like four-layer device whose intrinsic standoff ratio and trigger point are set externally with two resistors, effectively letting the designer “program” its unijunction behavior (RBB, η, IP, IV) rather than being locked to a fixed value as with a classic unijunction transistor.

With an anode, gate, and cathode in a compact TO-92 package, the 2N6028 is the classic building block for relaxation oscillators, timing and pulse generators, and thyristor trigger circuits (firing SCRs and triacs). Its anode gate also makes it usable in specialized thyristor-style applications beyond simple oscillators.

1. Programmable unijunction characteristics via external resistors
2. Ideal for relaxation oscillators and SCR/triac trigger circuits
3. Low on-state voltage — 1.5V max at IF=50mA
4. Low gate-to-anode leakage current — 10nA max
5. High peak output voltage — 11V typical
6. Compact, inexpensive TO-92 package
7. Anode gate enables special thyristor-type applications