
2N4870
Unijunction Transistor (UJT)
TO−92 Type Package
Description:
The 2N4870 is a PN unijunction transistor in a TO−92 type package designed for use in pulse
and timing circuits, sensing circuits and thyristor trigger circuits.
Absolute Maximum Ratings: (TA = +25C unless other specified)
RMS Power Dissipation, PD300mW.....................................................
Derate Above 25C 3.0mW/C.....................................................
RMS Emitter Current, IE50mA...........................................................
Peak−Pulse Emitter Current (Note 1), IE1.5A..............................................
Emitter Reverse Voltage, VB2E 30V.......................................................
Interbase Voltage (Note 2), VB2B1 35V....................................................
Operating Junction Temperature Range, TJ −65 to +125C.................................
Storage Temperature Range, Tstg −65 to +150C..........................................
Note 1. Duty cycle 1%, PRR = 10 PPS
Note 2. Based upon power dissipation at TA = +25C
Electrical Characteristics: (TA = +25C unless other specified)
Parameter Symbol Test Conditions Min Typ Max Unit
Intrinsic Standoff Ratio VB2B1 = 10V, Note 3 0.56 −0.76
Interbase Resistance RBB 4.0 6.0 9.1 k
Interbase Resistance Temperature Coefficient RBB VB2B1 = 3V, IE = 0,
TA = −65 to +125C
0.1 −0.9 %/C
Emitter Saturation Voltage VBE1(sat) VB2B1 = 10V, IE = 50mA, Note 4 −2.5 −V
Modulated Interbase Current IB2(Mod) VB2B1 = 10V, IE = 50mA −15 −mA
Emitter Reverse Current IEB2O VB2E = 30V, IB1 = 0 −0.005 1.0 A
Peak−Point Emitter Current IPVB2B1 = 25V −1.0 5.0 A
Valley−Point Current IVVB2B1 = 20V, RB2 = 100, Note 4 2.0 5.0 −mA
Base−One Peak Pulse Voltage VOB1 3.0 6.0 −V
Note 3. Intrinsic standoff ratio, is defined in terms of peak−point voltage, VP
, by means of the equa-
tion: VP = VB2B1 + VF
, where VF is approximately 0.49 volts at +25C @ IF = 10A and
decreases with temperature at approximately 2.5mV/C. Components R1, C1, and the UJT
form a relaxation oscillator, the remaining circuitry serves as a peak−voltage detector. The
forward drop of Diode D1 compensates for VF
. To use, the “call” button is pushed, and R3
is adjusted to make the current meter, M1, read full scale. When the “call” button is released,
the value of is read directly from the meter, if full scale on the meter reads 1.0.
Note 4. Use pulse techniques: PW 300s, duty cycle 2.0% to avoid internal heating, which may
result in erroneous readings.