![]() R1 and R2's values were selected to strike a compromise between low current drain and compatibility. The transistor, designated Q1, is a general-purpose bipolar transistor, or a BC547, which is typically utilized in low-power switching and amplifier applications.Īny transistor that is equivalent to it (such the 2N2222, 2N4401, etc.) would work. However, the transistor activates when the proper bias is provided to the base of Q1, pushing the circuit's output low or to logic 0 (almost equal to zero potential). A NOT gate operates in such a way that if no DC bias is provided to the transistor's base (point A Q1), it will remain shut-off, resulting in a high or logic 1 (equal to V+ level) at the output (point B). Depending on how it is implemented in a particular application, the switch may be seen as either kept low or normally open.Ī simple NOT gate inverter logic gate can be created by the straightforward switching circuit shown in Fig. Making a NOT Gate with a Single TransistorĪ schematic of the transistor switch is shown in Figure 1. The basic switch circuit is a simple transistor application, which is one of the easiest designs. To avoid damaging the device or the parts that support it, suitable safety measures should be undertaken before connecting your circuit.Įven though our circuits are predominantly centered on Bipolar Junction Transistors (BJTs), they could have equally well been constructed using FET technology. The logic circuit examples explained in this article make use of bipolar NPN transistors since they are affordable and don't need special handling. Burnt components may ruin an enjoyable, creative evening of experimentation or innovation, not to forget the emotional pain of debugging. Electrostatic and general experimental misuse make FETs particularly prone to damage. Also, a bulk packet of bipolar transistors could generally be purchased for the price of a pair of FETs.įET handling necessitates significantly more care than bipolar transistor handling. ![]() Furthermore, the voltage available may decrease below the FET's optimum working range if a current-limiting or pull-down resistor is attached to the gate.Ĭonversely, bipolar switching transistors have an advantage in extremely low voltage, single battery applications since they only need 0.6 to 0.7 volts to switch on.įurthermore, the majority of common FETs, which are normally sold in bubble packs at your nearest electronics store are often costlier than bipolar transistors. Typically, the gate voltage limit is one volt or so. ![]() However, they have one limitation in extremely low-voltage applications. Additionally, they need very low gate-turn-on current. A transistorized logic gate can be customized to control heavier loads, which an IC based logic gate cannot do.įield Effect Transistors (FETs) vs bipolar transistors: which is the better option for low-voltage transistorized logic circuits? One great feature of FETs is that their "on" resistance is incredibly low.Transistorized logic gates can be operated with voltages as low as 1.5V, while the IC counterparts need a minimum of 3 V.The main advantages of logic gates built using transistors can be summarized as given below:.For each particular logic gate, just a couple of transistors are generally required, and for a typical NOT gate inverter logic, just one transistor is required. Well, then what are you going to do? Usually IC logic gates could be replaced by transistorized logic gates. However, these are not always easily accessible to the enthusiast or experimenter, and they do not work below their defined voltage specifications (generally below 2.5 volts DC).įurthermore, there might only be place for a single 1.5-volt battery in a battery-powered application. No doubt, you always have the 3-volt logic IC option. This is especially true for gadgets that run on batteries. In some electronic applications the available voltage may be inadequate to power TTL or even CMOS ICs. The main advantage of using transistor logic gates is that they can work even with voltages as low as 1.5 V. In this post we will learn how to build NOT, AND, NAND, OR, and NOR logic gates using discrete transistors.
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