Programmable Unijunction Transistors (PUT) Information

PUTProgrammable unijunction transistors (PUT) are three-terminal thyristors that are triggered into conduction when the voltage at the anode exceeds the voltage at the gate. The PUT is similar to the unijunction transistor (UJT), but its intrinsic standoff ratio can be set by two external resistors. Hence, the name "programmable" is used. A PUT is a more advanced version of a UJT. In a PUT, operating characteristics such as base-to-base resistance, intrinsic standoff voltage, valley current, and peak current can be programmed by setting the values of two external resistors.


Applications for PUTs include:

  • thyristor triggers
  • oscillators
  • pulse
  • timing circuits with frequencies up to 10 kHz

An integrated circuit can include not only an integrated circuit chip, but also a circuit transistor such as a PUT.


Performance specifications for PUT include:

  • peak current (with RG of 10K ohms and 1M ohms)
  • valley current (with RG of 10K ohms and 1M ohms)
  • gate-to-cathode forward voltage
  • gate-to-cathode reverse voltage
  • gate-to-anode reverse voltage
  • anode-to-cathode voltage
  • peak non-repetitive forward current
  • peak repetitive forward current
  • peak repetitive forward current
  • DC forward anode current
  • DC gate current
  • power dissipation
  • storage temperature
  • operating junction temperature

PUTs can be packaged individually or in standard packaging for high-volume requirements, such as automatic insertion equipment.


PUTs that meet U.S. military specifications (MIL-SPEC) are manufactured according to standards described in MIL-STD-750 (Test Method Standard for Semiconductor Devices) and MIL-HDBK-6100 (Military Handbook, List of Case Outlines and Dimensions for Discrete Semiconductor Devices). Like other components made of semiconductor material, PUTs that are marketed in European Union (EU) nations should be manufactured in compliance with the Restriction of Hazardous Substances (RoHS) and Waste Electrical and Electronic Equipment (WEEE) directives. RoHS requires all manufacturers of electronic and electrical equipment sold in Europe to demonstrate that their products contain only minimal levels of the following hazardous substances: lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyl, and polybrominated diphenyl ether. By definition, lead-free devices contain less than 1,000 ppm lead by weight.

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