This circuit differs from the base bias circuit in two respects, which are: The circuit of emitter biasing for an npn transistor is shown in the figure below. Emitter Bias Method of Transistor Biasing It has a poor stabilization, since there is no means to stop the self-increasing collector current due to temperature increase and individual variations.
It is required to find out the proper value of R B so that required zero signal collector current flows in the collector circuit. The required value of zero signal base current (I B) and hence the zeo signal collector current I C = βI B ,can be made to flow by selecting proper value of base resistor R B since the supply voltage V CC is fixed. Here, the required zero signal base current is provided by the supply voltage V CC, and it flows through resistance R B. In this method, a high resistance R B is connected between the base and positive end of the supply voltage V CC. The circuit for base resistor biasing for an npn transistor is shown in the figure below. Biasing with collector-feedback resistorīase Resistor Method of Transistor Biasing.
The most commonly used methods for obtaining transistor biasing are: The basic purpose of transistor biasing is to keep the base-emitter junction forward biased and collector- base junction reverse biased at any instant of the applied signal. Transistor biasing can be defined as the proper flow of zero signal collector current and the maintenance of proper collector-emitter voltage during the passage of signal. The fulfillment of these conditions is known as transistor biasing. Transistor BiasingĪs we have already discussed, for faithful amplification, a transistor amplifier must satisfy the above three conditions. Hence, the applied signal will not be amplified properly and results in unfaithful amplification. This causes a decrease in the collector current and increase in the base current. Therefore, the collector can not attract the charge carriers emitter by the emitter, hence a grater portion of them goes to the base. When V CE is less than this value, the collector-emitter junction is not properly reverse biased. Proper Minimum Collector-Emitter Voltageįor faithful amplification, the collector-emitter voltage should be larger than 0.5 V for Ge transistor and 1 V for si transistor. If the base-emitter voltage is less than this value for any part of the applied signal, that part will be amplified lesser extent due to small collector current, which will result in unfaithful amplification. Once this potential barrier is overcome, the base current and hence the collector current increases sharply. Hence, In order to overcome this potential barrier, the base-emitter voltage should be larger than this voltage. Since, the potential barrier for Ge is 0.5 V and for Si 0.7 V. Proper Minimum Base-Emitter Voltageįor faithful amplification, the base-emitter voltage (V BE) should be larger than 0.5 V for Ge transistor and 0.7 V for Si transistor. The zero signal collector current value should be at least equal to maximum collector current due to signal alone.
Hence faithful amplification is achieved.