Saturday, January 28, 2012

Transistor as a switch and amplifier

Transistors are electronic components made up of from semi-conductor material which has three legs are: base (B), collector (C) and emitter (E).Based on the semiconductor structure that shape it, the transistor can be divided into two types, namely transistor PNP and NPN transistors. To membadakan PNP and NPN transistors can be from the direction of the arrow at the foot emitornya. In the PNP transistor arrows point to the NPN transistor and the direction of arrows leading to the outside.

Transistor is also a semiconductor device that is used as an amplifier, a circuit breaker and a connector (switching), voltage stabilization, signal modulation, or as other functions.The transistor can function like an electric valve, which is based on current inputs (BJT) or input voltage (FET), enabling highly accurate power flux from the electrical source circuits.In general, the transistor has three terminals, namely the Base (B), emitter (E) and Kolektot (C). Voltage at one terminal for instance can be used to adjust the emitter current and voltage to be amplified through kolektor.Selain used for transistor amplifier can also be used as a switch. You do this by providing a large enough current to the base of the transistor to reach saturation point. In this condition, the collector and emitter are connected like a wire or a switch is closed, and vice versa if the tiny base current collector and emitter as the switch is open. By the nature of such switching transistors can be used as a gate or that we often hear the term TTL is Transistor Transistor Logic.

.      Gbr.Transistor As the switch
a. shows the circuit switching transistors.Summation of the input voltages around the loop gives:Ib.Rb + VBE - vbb = 0Ib.Rb = VBE - vbbIb = vbb - VBE
If the base current is greater than or equal to Ib (sat), working point Q is at the upper end of the load line (Fig. (b)). In this case the transistor works at the lower end of the load line, and the transistor looks like an open switch.
By adjusting the bias of a transistor until the transistor is saturated, then it will come as a short circuit between the collector and emitter. By utilizing this phenomenon, the transistor can function as an electronic switch.

In the picture looks an electronic switch circuit using a transistor NPN and PNP transistors.Looks TR3 (NPN) and TR4 (PNP) is used to turn on and turn off the LED. TR3 is used to disconnect and connect the relationship between the LED cathode to ground. So if the transistor is OFF then the LED will die and if the transistor is ON then the LED will live.Because the foot emitter connected to ground it to turn on the transistor, the position of the switch SW1 should be ON so the base of the transistor TR3 gets biased positive voltage and consequently the transistor becomes saturated (ON) and the collector and emitter connected legs. To turn off the LED should be OFF the SW1 position. TR4 is used to disconnect and connect the relationship between the LED anode to the positive voltage.So if the transistor is OFF then the LED will die and if the transistor is ON then the LED will live. Because the foot is connected to a voltage positive emitter, then to turn the transistor, the position of the switch SW2 must be ON to be the base of the transistor TR4 got a bias voltage is negative and consequently the transistor becomes saturated (ON) and then the foot emitter and the collector is connected. To turn off the LED should be OFF the SW1 position.

The principle of the transistor as a switch that isPrinciples of Transistor as a link (the switch): transistor will experience melalaui Cutoff if current is very small base so that the collector and emitter will be like an open wire, and the transistors will run into saturation when the current through the base is too large so that between the collector and emitter like a wire connected so the voltage between the collector and emitter VCE is 0 Volt of the workings of diataslah why the transistor can function as a switch.Or in pemakiannya transistors could also serve as a switch that is by utilizing the saturation (saturation) and the blockage (cut-off). In the saturation region connecting the collector emitter resistance value is ideally equal to zero or the collector is connected directly (short). This causes the collector emitter voltage VCE = 0 at the ideal state. And the area cut off, the collector emitter junction resistance value is ideally equal to infinity or the terminal is open collector and emitter voltage VCE causing equal to the voltage source Vcc.By utilizing the properties of conductivity of the transistor which depends on the voltage between base and emitter electrodes (UBE), then we can use this transistor as an electronic switch, where an electronic switch has many advantages compared to mechanical switches, sepert:a.Fisik relatively much smaller,b.Tidak noise and, at contacting sparks.c. More economical.
B. Transistor as an amplifierThe transistor is a semiconductor monokristal PN which occurred two meetings, from here can be made two series of PNP and NPN.In a normal working state, the polarity of the transistor should be given as follows:Emitter-Base 1.Pertemuan given the polarity of the forward direction base-collector 2.Pertemuan given polarity in the reverse direction
The transistor is a component that can enlarge the output signal level up to several times the input signal. Here the input signal can be either AC or DC signal. The basic principle of the transistor as an amplifier is a small stream at the base controls a larger current through the transistor from the collector. The transistor serves as a brace when the base current change. Small changes base current controls large changes in current flowing from collector to emitter. At this time the transistor to function as an amplifier.a.transistor as a current amplifierAnother function of the transistor is a current amplifier. Because this function can be used for the transistor circuit with a power supply voltage in the set. For this purpose transistors should dibias constant voltage at its base, so that the emitter voltage of a fixed exit.Usually to set the base voltage is used to keep a zener diode.

As the amplifier current Gbr.Transistor
In the image appear two regulators with output voltages of different polarity. Transistor TR5 (NPN) is used for positive voltage regulators and transistors TR6 (PNP) was used for negative voltage regulator. The voltage at the base of each transistor are kept to the value fixed by the zener diodes D3 and D4. Thus the voltage on the emitter has a flow out of the multiplication between base current and transistor HFE.b.Transistor as an AC signal amplifier (voltage)Aside from being a current amplifier, the transistor can also be used as a voltage amplifier in the AC signal. To use the transistor as a signal amplifier used some kind of refraction techniques base of the transistor. In working as an AC signal amplifier, the transistor amplifier are grouped into several types, namely: class A amplifier, amplifier class B, class AB amplifier, and class C.

In the picture it appears that R15 and R16 cooperate in regulating the bias voltage on the base of the transistor. These configurations include the type of amplifier class A. Input signal into the amplifier through the capacitor C8 to the base of the transistor. And the output signal is taken at the collector by passing through capacitor C7. The function of the capacitor at the input and output amplifier is to isolate the amplifier to the influence of an external DC voltage amplifier. It is based on the characteristics of capacitors that do not pass the DC voltage. Principles of Transistor as an amplifier (amplifier): means that the transistor works in the area between the saturation point and the condition of an open (cut off), but not in both conditions.

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