Which amplifier works as a constant current source?
Op-amp current sources Now the op-amp increases its output voltage to compensate for the VBE drop. The circuit is actually a buffered non-inverting amplifier driven by a constant input voltage. It keeps up this constant voltage across the constant sense resistor.
Can PNP transistor be used as amplifier?
The construction of pnp transistor is that the collector and emitter regions are doped with p-type material and the base region is doped with small layer of n-type material. The PNP transistor can act as a switch and an amplifier.
Why constant current source is used in differential amplifier?
Need of Constant Current Source: To improve CMRR we need to increase Re. But Re cannot be increased to a great extent, since the dc current will decrease which will change the Q point of the circuit. Since, we want constant current in the emitter terminal and also very high resistance in the emitter terminal.
What are the constant current sources?
A constant current source (CCS) in electronics is a device/circuit that produces a constant value of current regardless of source voltage or load resistance. Fig. 1 illustrates a common CCS circuit using a PNP bipolar transistor. A constant current circuit can also be used as a current limiter.
Is a transistor a current source?
A current source is the dual of a voltage source. Active constant current sources are often used in circuits. Often these constant current sources use transistors, although FETs and where applicable, vacuum tunes of thermionic valves can be used as well.
How transistor works as an amplifier?
A transistor acts as an amplifier by raising the strength of a weak signal. The DC bias voltage applied to the emitter base junction, makes it remain in forward biased condition. Thus a small input voltage results in a large output voltage, which shows that the transistor works as an amplifier.
What are PNP transistors used for?
PNP transistors are used to source current, i.e. current flows out of the collector. PNP transistors are used as switches. These are used in the amplifying circuits. PNP transistors are used when we need to turnoff something by push a button.
What are the current carriers in PNP transistor?
Answer: In a pnp transistor, current carriers are holes.
How does current flow in transistor?
We know that in transistors and diodes, electric current is carried by both free electrons and holes. Free electrons and holes travel in opposite directions. For example, if free electrons flow from left to right then the holes will flow from right to left.
Why constant current source is needed?
Keeping the current constant regardless of the current taken by the series pass transistor in the circuit helps maintain a much better level of regulation. Also stand-alone current sources are also needed in processes ranging including electrochemistry and electrophoresis.
What is constant current bias?
amplifier in Unit 1 value of CMRR but if RE value is increased to very large value, IE(quiescent operating current) decreases. To maintain same value of IE, the emitter supply VEE must be increased. • To get very high value of resistance RE and constant IE, constant current bias is used.
How are NPN and PNP transistors used in circuit?
One of the simplest circuits is to employ one that uses both NPN and PNP transistors. In the circuit shown, the Vbe voltage drop changes in TR1 are compensated by those in TR2. It should be noted in this circuit that R3 is a pull up resistor for the collector of TR1 because the base of TR2 can sink current but not source it.
How is the current of an op amp constant?
This voltage drop produces a current given by Ohm’s law of 1.36V / 150Ω, giving a current of 9.1 mA. Even with the addition of a negligible amount of current from the output of the Op Amp (a factor of 100 smaller), the current is constant through the transistor, so the output to the load is 9.1 mA.
Where is the arrow located in a PNP transistor?
The arrow for BJT transistors is always located on the emitter terminal and also it indicates the direction of conventional current flow. In PNP transistor this arrow indicates as ‘pointing in’ and the current direction in PNP is completely opposite to the NPN transistor.
What kind of circuit uses a constant current source?
Transistor Circuit Types Include: Active constant current sources are often used in circuits. Often these constant current sources use transistors, although FETs and where applicable, vacuum tunes of thermionic valves can be used as well.