​what is a double base diode (single junction transistor)?

what is a double base diode (single junction transistor)?

Double base diode,also known as single crystal transistor (UJT)is a three terminal semiconductor device with only one PN junction.the circuit symbol,internal structure and equivalent circuit of double base diode.

At both ends of a high resistivity N type silicon wafer,two ohm contact electrodes (very small contact resistance contact electrodes) are made, which are called the first base B and the other side of the base Be: silicon wafer near the second base pole to make a PN junction, and the electrode led on the P type semiconductor is called the emitter E. In order to facilitate the analysis of the operating characteristics of dual base diode, the N type region between two base B and B2 is usually equivalent to a pure resistance RB, called the base resistance. It is an important parameter of the dual base diode, and the RBB of the domestic dual base diode is within the range of 2~10k2. RB can also be seen as a series of two resistors in series, where RB1 is the resistance between the base Bi and the emitter E, and R12 is the resistance between the base B2 and the emitter E. When working normally, the resistance of RB1 varies with the emitter current Ip, which can be equivalent to a variable resistor. The role of PN junction is equivalent to a diode VD.

The two most important parameters of the double base diode are the base resistance R BB and the partial pressure ratio.

RBB refers to the resistance between the two base poles in the open circuit state of the emitter, that is,RB1+RB2,usually RBB between 3~10k2.

The ETA is the ratio of the voltage between the emitter E to the base B,and the voltage between the base electrode B2 and B,which is usually between 0.3~0.85.