how to get a diode from a BJT

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electronics_kumar

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BASICALLY BJT has 3 region and diode is a 2 region.
can we use all possible ways from bjt to get a diode suitalbe commands are expected.
 

There are three pins from BJT : C,B, and E. Base (B) is the center of them. So, if you want to make BJT to be diode, you just take the B as one of your diode pin, and the other pin is up to you.
 

If you use NPN transistor, pretty common practice is to connect B(ase) with C(ollector) and treat it as the ANODE and E(mitter) becomes the CATHODE.
In PNP transistors the same connection can be used (B+C) but the polarity is reversed: (B+C) = CATHODE and (E) = ANODE
 

You can use any configuration possible the only thing is that each configuration as their special properties as their doping level is different for emitter and collector and their thickness.
 

You can use either the Collector-Base Junction or the Emitter-Base junction. If you use the Collector-Base junction, the breakdown voltage is Vceo. If you use the Emitter-Base junction the breakdown voltage will be Vebo (typically 7V for a silicon transistor). The lightly doped Collector-Base junction will give you a faster diode, since there are fewer minority carriers to sweep away from the juction during turn-off.
 

Hi.
I agree with IanP 100%. designers call it "diode connected" style. in this way you have a two terminal device just like a diode. and in its small-signal model you consider just one resistor (i.e. 1/gm) and one capacitor in parallel (just like a diode.) simple, isn't it?

Regards,
EZT
 

There is a question that I have been wondering about. Why is the Base collector shorted BJT diode better than a Base emitter shorted diode? I am thinking of some reasons but I want to confirm them.
 

the C and B connected by al,is a diode.
 

I think if you want to use the transistor as a fast diode, and want to have the highest operating voltages you have to connect the base B with the emiter E (Configuration 1). That is, for an NPN transistor C will be the Catode and B+E will be the anode. This configuration gives lower capacitance and higher breakdown voltage.....

I think the other configuration (Configuration 2 -B connected to C) comes from the old times when the transistors had small beta and low colector breakdown voltage. In this configuration the diode will be slower and the breakdown will be lower.....

Does anyone have other ideas about why the configuration 2 (base connected to collector) is very much used? Are there advantages for configuration 2?

S.
 

connect the base and emitter of any npn-bjt transistor you have obtained a diode
 

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