# How does Bipolar junction transistor amplifies the voltage? [duplicate]

I was looking at Operational amplifier recently, so if you look at the diagram for op-amp, it's just a bunch of npn and pnp junctions. But how could they come together and work as a voltage amplifier and achieve a $$\V_{out}>>V_{supply}\$$?

How does Bipolar junction transistor amplify the voltage?

• Why do you say $V_{out}>>V_{supply}$? Do you have a reference for that? Op amps are voltage limited by their supply. – Bill N Dec 31 '19 at 14:38
• And your next question is different. Don't ask multiple questions. – Bill N Dec 31 '19 at 14:40
• @BillN it's the same question, using an non inverting setting one could easily achieve $V_{cc}>> V_{supply}$, but the entire diagram only contain transistors and resistors. (I know how the ideal op-amp works, so as stated, how does the bipolar junction transistor amplifies the voltage.) – ShoutOutAndCalculate Dec 31 '19 at 14:50
• @ShoutOutAndCalculate Show the diagram. – verdelite Dec 31 '19 at 14:58
• @verdelite It's in the operational amplifier hyperlink in the post, just look at the second diagram. – ShoutOutAndCalculate Dec 31 '19 at 14:59

The BJT or Op Amp device can never drive the output beyond the supply rails. (Vcc to Vee) Not possible. Even though they are called active devices, they are like 'servo'-controlled resistance and cannot boost the voltage like switched reactors (L) or transformers.

Transistor voltage amplifiers are voltage-control current-sinks (VCCS) which have high output impedance and thus voltage gain is proportional to the load resistance.

Since the Vbe vs IC is very nonlinear , it must be done with constant current sources for bias and done in many stages with methods that are more linear but lower gain.

The impedance is then reduced with several stages of current amplifiers or emitter followers with unity voltage gain.

• op Amp along could not boots voltage higher than $V_{cc}$, but Non-Inverting Amplifier constructed of op-AMP and resisters can. The entire diagram only contain transistors and resister.(with only one capacitor in the middle as in the example. ) – ShoutOutAndCalculate Dec 31 '19 at 18:45
• really ;)? please demonstrate – Tony Stewart Sunnyskyguy EE75 Dec 31 '19 at 18:56
• electronics-notes.com/articles/analogue_circuits/… The op-amp = transistor + resistor + one capactor. The diagram = op-amp + resistors. – ShoutOutAndCalculate Dec 31 '19 at 19:05
• That is just DC block or AC coupled. Not $V_{out}>>V_{supply}$ – Tony Stewart Sunnyskyguy EE75 Dec 31 '19 at 19:07
• "...cannot boost the voltage like switched reactors (L) or transformers." ...or capacitors. But all of these components (if present) are external to the op amp, which cannot boost voltage by itself. – Bruce Abbott Dec 31 '19 at 22:11