Contents
What is the purpose of a bipolar junction transistor?
Bipolar Junction Transistor or BJT Current Mirror An often-used circuit applying the bipolar junction transistor is the so-called current mirror , which serves as a simple current regulator, supplying nearly constant current to a load over a wide range of load resistances .
What are the three modes of BJT transistor?
There are three modes in BJT – Forward-Active (Amplification), Saturation, and Cut-off. Saturation: high current conduction from the emitter to the collector. This mode corresponds to a closed switch. This could be also used for resistors simulation in small circuits.
What happens to the current in a PN junction transistor?
If you change the diode current by changing the resistance value of R bias, then the transistor’s emitter current will follow suit, because the emitter current is described by the same equation as the diode’s, and both PN junctions experience the same voltage drop.
How does a base-emitter junction maintain a constant voltage?
To maintain a constant voltage across the transistor’s base-emitter junction use a forward-biased diode to establish a constant voltage of approximately 0.7 volts, and connect it in parallel with the base-emitter junction as in Figure below. Diode junction 0.7 V maintains constant base voltage, and constant base current.
How does a bipolar mirror convert voltage to current?
The simplest bipolar current mirror (shown in Figure 1) implements this idea. It consists of two cascaded transistor stages acting accordingly as a reversed and direct voltage-to-current converters. The emitter of transistor Q1 is connected to ground. Its collector-base voltage is zero as shown.
Why is the current of a mirror greater than zero?
Parameter β 0 is the transistor β-value for VCB = 0 V. If V BC is greater than zero in output transistor Q 2, the collector current in Q 2 will be somewhat larger than for Q 1 due to the Early effect. In other words, the mirror has a finite output (or Norton) resistance given by the ro of the output transistor, namely:
How are transistors maintained in a current mirror circuit?
A current mirror is a transistor circuit that regulates the current through a load resistance, the regulation point is set by a simple resistor adjustment. Transistors in a current mirror circuit must be maintained at the same temperature for precise operation. When using discrete transistors, you may glue their cases together to do this.