![]() ![]() To overcome this problem a capacitor, called an “Emitter Bypass Capacitor”, C E is connected across the emitter resistance as shown. Then the current flowing through the emitter resistor is calculated as: Emitter Resistance Current However, its value cannot be too small or once again the instability of the circuit will suffer. In other words, the addition of this emitter terminal resistance helps control the transistors base biasing using negative feedback, which negates any attempted change in collector current with an opposing change in the base bias voltage and so the circuit tends to be stabilised at a fixed level.Īlso, since part of the supply is dropped across R E, its value should be as small as possible so that the largest possible voltage can be developed across the load resistance, R L and therefore the output. A similar action occurs if the supply voltage and collector current try to decrease in value. Since the base voltage is held constant by the divider resistors R1 and R2, the DC voltage on the base relative to the emitter Vbe is lowered by a proportional amount thus reducing the base current drive and keeping the collector current from increasing further. This action results in a proportional increase in base voltage because V B = V E + V BE If the collector current increases, the corresponding emitter current must also increase causing the voltage drop across R E to increase. Now if the supply voltage Vcc increases, the transistors collector current Ic also increases for a given load resistance. Where: I E is the actual emitter current. The addition of this emitter resistor means that the transistors emitter terminal is no longer grounded or at zero volt potential but sits at a small potential above it given by the Ohms Law equation of: V E = I E x R E. This resistance is known as the Emitter Resistance, R E. I have searched on google but I can't 100% understand it.The amplifiers bias voltage can be stabilised by placing a single resistor in the transistors emitter circuit as shown. How this entire thing works based on voltage amplification based on my circuit. I also understood the voltage gain based on Rc and RE for example if Rc = 1k and Re = 100 ohm the gain is 10.īut I cant understand how to choose a resistor and how much current should I use how much current to amplify to amplify the voltage, and how much voltage to give to get 10V as output. I understood that the amount of voltage we give in input to the base we will get as large voltage between collector and emitter based on the resistors. Its maximum output voltage is 3.3V but I need 10V so I planned to use an NPN transistor in common emitter configuration so that I can amplify 3.3V to 10V and then I can give that to the gate of the MOSFET. I am using STM32 micro controller for controlling. I want to give 10V input to the gate of the MOSFET to get very low Rds. In my circuit I need to amplify 3.3V of my stm32 micro controller input to 10 V output to drive a Mosfet switch. I have basic knowledge about NPN transistors and I know how they work: for current gain based on the small input current in the base we are able to drive large amount of current in between collector and emitter.
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