Electric Circuits and Semiconductor Fundamentals
Fundamentals of Electric Circuits
Fundamentals:
a) Voltage, tension, or DDP – Indicates the energy difference between points in a circuit. They are measured in volts (V).
b) Intensity or Current (I) – Number of electrons flowing through the wire. It is measured in amperes (A).
c) Resistor (R) – The opposition a material offers to current flow. It is measured in ohms (Ω).
Ohm’s Law
Fundamental law of electric circuits: Ohm’s Law
Electric power: the power consumed or dissipated in a given time. It is measured in watts (W).
In an electric circuit, it is always true:
Power generated = power consumed
Power generated = V x I (generator)
Power consumption = R x I2
Association in series and parallel resistance. (Series add)
In parallel
Semiconductor Electronics
ELECTRONICS: Electronics use semiconductors such as silicon and germanium.
They employ two types:
P-type semiconductor: doped with positive charges.
N-type semiconductor: doped with negative charges.
Diode Semiconductor
1. DIODE SEMICONDUCTOR: Semiconductors of two panes, one P-type and one N-type.
Its symbol is
Forward Bias: Occurs when we connect the anode of the battery to the diode. This allows current polarization.
Explanation: The positive pole of the battery repels the positive charges in the P crystal, approaching them to the junction of the two crystals. The same applies to the negative charges in the N crystal. Near the junction, positive and negative charges combine using a voltage threshold (0.7 V for silicon (Si), 0.3 V for germanium (Ge)). Electrons can combine with positive charges, generating electric power.
Reverse Bias: Occurs when we join the stack anode-cathode of the diode. In this case, the diode passes no current.
Explanation: This polarization removes electrons and positive charges from the junction of the crystals, making it impossible to produce electric current.
LED Diode
2. The LED diode: This is a diode that emits light when forward biased. There are fixed and intermittent LEDs. They are used to indicate ON and OFF states. They do not support a voltage greater than 1.2 V.
Bipolar Transistors
The bipolar transistor revolutionized electronics. It is formed by 3 semiconductor crystals with two P-N junctions. There are two types: PNP transistors and NPN transistors.
It has 3 terminals called: collector, base, and emitter.
The symbol of both transistors is:
NPN PNP
The smallest part of the transistor is the base (about 1 micron), then the collector is a bit bigger, and the emitter is larger.
The transistor has three areas of operation: cutoff region, saturation region, and active region.
Transistor as a Switch
TRANSISTOR 2.1 Functions as a switch:
Zone > Cutoff and saturation zones.
In these modes, the transistor acts as a switch.
-Switch open: cutoff region.
When a transistor does not receive base current, no current will pass from the collector to the emitter, acting as an open switch.
-Switch closed: saturation region.
This occurs when electrical current is injected into the base of the transistor. The transistor acts as a closed switch, allowing current to flow from the collector to the emitter.
OPERATION: If the current through the transistor base is very small, the transistor acts as an amplifier, increasing the current going from the emitter to the collector. Each transistor has an amplification factor given by the manufacturer, called Beta (β), such that Ic = β x Ib.
Bipolar transistors are normally used to amplify current, usually with a common-emitter configuration (at the input and output) to control the output current with a small current through the base.
The input voltage (VBE) is small, resulting in a small base current (Ib). The transistor acts in the active region, achieving an output voltage greater than VCE, resulting in a higher emitter current.
A bipolar transistor with a beta of 100 works in the active region under the conditions of the problem.
Characteristic curves of bipolar transistors.
The study of the performance of transistors is complex because each of its parameters is related to the others. Their characteristic curves are used for their study.