BJT is nothing but the addition of two PN junction diodes.
There are two types of BJT= P-N-P or N-P-N
P-N N-P
+ or +
N-P = P-N-P P-N =N-P-N
SCR is a thyristor which is made adding two BJTs. Of course they are made of sillicon.
Exempli gratia: P-N-P
+ +
N-P-N = P-N-P-N comparison between scr bjt and mosfet Check the related link for further information.
A diode mainly consists of only 2 terminals(anode,cathode).A SCR mainly contains one more terminal called GATE.The main purpose of the gate in an SCR is just to provide pulses.The main draw back of SCR is it is not fully controllable device.
Disadvantage:Easy to damage when compared to BJT
UJT is the voltage controlled device.in which only one mejority carriers are responsible for current flowing. UJT is one junction transistor and it is three terminal emitter and two base. BJT is the current controlled device. in which both mejority and minority carrier are responsiblefor current flowing. this type of transistor consists of two junction and three terminal these are : emitter , base , collector.
silicon controlled rectifier is a 3 terminal 4 layer device which has 2 consecutive P N junctions here the three terminals called anode, cathode and gate gate controls the conduction of the scr but diode just conducts in forward bias and blocks in reverse bias
The SCR's gate electrode is used to turn the SCR on, i.e. fire it.
neither is better, it depends on purpose
== == == ==
An SCS has an additional gate - the anode gate. It is physically smaller than an SCR and has smaller leakage and holding currents than an SCR.
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A diode mainly consists of only 2 terminals(anode,cathode).A SCR mainly contains one more terminal called GATE.The main purpose of the gate in an SCR is just to provide pulses.The main draw back of SCR is it is not fully controllable device.
A BJT (bipolar junction transistor) is a general term that includes both NPN and PNP transistors. An NPN transistor has a layer of P-type semiconductor sandwiched between two N-type layers, allowing current to flow from the collector to the emitter when a small current is applied to the base.
UJT (UniJunction Transistor): It is a transistor with only one junction and three terminals: an emitter (E) and two bases (B1 and B2). BJT (Bipolar Junction Transistor): This type of transistor consists of two junctions and three terminals, namely Emitter "E", Base "B" and Collector"C". There are two types of BJT, i) PNP and ii) NPN.
Disadvantage:Easy to damage when compared to BJT
UJT is the voltage controlled device.in which only one mejority carriers are responsible for current flowing. UJT is one junction transistor and it is three terminal emitter and two base. BJT is the current controlled device. in which both mejority and minority carrier are responsiblefor current flowing. this type of transistor consists of two junction and three terminal these are : emitter , base , collector.
Bipolar junction transistor(BJT)
silicon controlled rectifier is a 3 terminal 4 layer device which has 2 consecutive P N junctions here the three terminals called anode, cathode and gate gate controls the conduction of the scr but diode just conducts in forward bias and blocks in reverse bias
because it is gcr not scr