Introduction to Analog Circuits: A Comprehensive Guide

Current

The unit of current is Ampere (A), 1A = 1000mA

The larger the current, the more electrons pass through in the same amount of time

A circuit is the pathway for current to flow. A battery is a special energy device that generates energy through chemical reactions. The positive terminal of the battery absorbs electrons, while the negative terminal sends out electrons.

Composition of an Electromagnetic Bulb

The negative terminal of the battery emits electrons, pushing electrons through the bulb back to the positive terminal of the battery

A large number of electrons passing through certain special materials will generate heat and light, which is the principle of a light bulb

Direction of Current

Note a small detail: Two hundred years ago, scientists who discovered electricity could not directly observe electrons. They guessed based on experimental phenomena, thinking that current flows from the positive terminal to the negative terminal. All physical point formulas are based on this assumption. In fact, the true direction of electron flow is opposite to that of current. However, this direction does not affect the calculation results.

Direct Current (DC)

Alternating Current (AC)

Open Circuit

Closed Circuit

Voltage is potential energy, measured in volts (V)

What is potential energy? It is a type of energy described by physics that indicates the energy possessed by an object

Increasing voltage makes LEDs brighter, and motors turn faster

After increasing voltage, a larger current will be generated, leading to a brighter LED and a faster motor. However, the voltage cannot be increased indefinitely; excessive voltage can generate too much current, causing the LED and motor to burn out.

Voltage creates a potential difference that drives current flow

Resistance hinders the flow of current

Ohm’s Law is one of the fundamental laws of electricity

It describes the relationship between current and voltage. The formula for Ohm’s Law is I=U/R, where I is current, U is voltage, and R is resistance. This formula indicates that, with resistance remaining constant, voltage and current are directly proportional.

Important parameters of Ohm’s Law

Answer: U = 3*2

Answer: U = 2*10

Answer: 12/(3+4+5)

Answer: I = 15/9

Answer: U = 5*10

Current relationship: I = I1 = I2

Voltage relationship: U = U1+U2

Resistance relationship: R1+R2

Voltage division relationship: U1/R1 = U2/R2

Current relationship: I = I1+I2

Voltage relationship: U = U1 = U2

Resistance relationship: 1/R = 1/R1+R2/1

Voltage division relationship: I1 * R1 = I2 * R2

The maximum current through an LED is 20mA. If we connect a 9V battery to the LED, what size resistor should we use?

If a wire is very long, it can also achieve resistance and generate heat; this is the principle of heating pads.

Packaging: Look at what the resistor looks like, whether it is through-hole or surface-mount, and its size.

Look at the resistance value, precision, and error, with errors of 1%, 5%, 10%. The higher the precision, the more expensive.

Rated power is P = I * I * R = I * U. Rated power actually limits the withstand voltage; the maximum current that the resistor can pass is fixed. The higher the rated power, the higher the withstand voltage. Exceeding the resistor’s withstand voltage will lead to its burnout.

Key Points:

A capacitor is a container for storing electricity **(if the positive and negative terminals are reversed, it will explode)**

A capacitor is a component used to store charge and energy, consisting of two conductors and a dielectric layer, which is located between the two conductor plates.

When a capacitor is connected to a circuit, negative charge is stored on the conductor plates, generating a magnetic field between the two plates.

The unit of capacitance is Farad (F), one Farad is the capacitance of a capacitor that can store one coulomb of charge at one volt of potential. Common types of capacitors include electrolytic capacitors, ceramic capacitors, aluminum electrolytic capacitors, etc.

Different dielectrics have different charge storage capacities. The charging and discharging of a capacitor is based on electrostatic force, not involving chemical reactions, making it safer than lithium batteries.

Functions of Capacitors:

Prevent voltage surges, store energy, filter (large capacitors filter low frequencies, small capacitors filter high frequencies)

Capacitors in daily life: The power light of a charger does not turn off immediately; there is a capacitor inside that slowly releases the charge.

Inferior headphones have poor filtering and produce a lot of noise.

Different material dielectrics have different charge storage capacities

The unit of capacitance is Farad (F). Note: Farad is a very large unit. Other units include mF, uF, nF, pF.

Formula: t=(C * V) / I

T = discharge time (in seconds)

C = capacitance (in Farads)

V = voltage of the capacitor (in volts)

I = discharge current of the capacitor (in Amperes)

C = 1.5F

V = 2.8V

I = 20mA = 0.02A

Substituting these values into the formula calculates the discharge time

t = (1.5 * 2.8) / 0.02 ≈ 210 seconds

When we throw a stone into water, it creates ripples that spread outward from the stone; electricity and magnetism are similar. When current flows through a wire, it creates a magnetic field around it, like throwing a stone into water. When this magnetic field changes, it creates ripples that move surrounding electrons, generating a magnetic field; this is the principle of electromagnetic induction.

In motors, electric current flows through coils, generating a magnetic field that drives rotating parts (including the motor shaft); this is an application of electromagnetic induction.

Generators, in contrast, convert mechanical energy into electrical energy through rotating magnetic fields.

Key Points:

An inductor is an electronic component used to store and release energy in a circuit. It consists of a coil, usually made of copper wire, often with an iron core. When current flows through the inductor, it generates a magnetic field that stores energy. When the current stops flowing, the magnetic field collapses, causing the inductor to release the stored energy.

The main function of an inductor is to regulate the rate of change of current in a circuit. It can filter out high-frequency noise in the circuit, and the current across the inductor does not change suddenly, protecting other electronic components from electromagnetic interference.

Inductors are electromagnetic components that create magnetic fields when electricity flows, and the magnetic field resists changes in current. Unlike resistors, inductors do not dissipate energy as heat.

Inductors use enameled wire, insulated wire, etc., wound around an iron core. The unit of inductance is Henry (H).

The basic unit of inductance is H (Henry), which, like capacitance, is a very large unit. Other units include mH (millihenries), uH (microhenries), and nH (nanohenries).

The functions of inductors:

Oscillator Circuit Principle

LRC oscillator circuits are basic oscillators consisting of inductor L, resistor R, and capacitor C, capable of producing stable AC signals. In LRC oscillator circuits, inductors and capacitors interact through resonance, causing charge to flow back and forth between the capacitor and the inductor, generating periodic current and voltage signals.

The working principle of LRC oscillators is that when the capacitor discharges, the current in the inductor begins to increase while the charge in the capacitor decreases. When the capacitor’s charge reaches 0, the current in the inductor reaches its maximum and flows back to the capacitor, causing the capacitor’s charge to start increasing. When the capacitor’s charge reaches maximum again, the inductor reaches 0 and starts to oscillate back and forth again, forming a periodic AC signal.

Fuses and circuit breakers are devices used to protect circuits from overloads or electrical faults.

A fuse is an electrical component typically made of metal wire or copper foil, which disconnects current when it is overloaded to protect other components in the circuit. When the current reaches or exceeds the rated current of the fuse, the metal wire inside the fuse heats up and eventually burns out, interrupting the circuit to avoid fire hazards.

A circuit breaker is similar to a fuse but can reset and be reused. Circuit breakers usually respond to electrical faults faster than fuses, thus providing better protection for the circuit.

Tripping speed: slow, medium, fast, super fast.

Fast tripping speed: Tripping time less than 0.001 seconds.

Rated voltage: The maximum voltage it can withstand.

Rated current: The maximum current it can withstand.

Tripping characteristics: Fast tripping is suitable for situations where high protection is required, able to cut off overload or short-circuit currents in a short time, while slow tripping is suitable for situations where protection requirements are not high, able to withstand 2-3 times the rated current for a certain time.

Sound is produced by the vibration of objects; all sound-emitting objects vibrate, and different frequencies of vibration produce different pitches.

Buzzers are divided into active buzzers that sound when powered and passive buzzers that do not sound until a high voltage signal is provided.

The audio frequency of a buzzer refers to the frequency of the sound waves it produces, measured in Hertz (Hz). The human hearing frequency range is 20-20kHz; frequencies below 20Hz are infrasound, while those above 20kHz are ultrasound. The common vibration frequency of buzzer products is 2-4kHz.

milliampere-hours (mAh) and milliwatt-hours (mWh) are two different physical quantities representing units of electric charge and energy.

Left: 3400mAh means a current of 3400mA can discharge continuously for one hour.

Right: 12580mWh means a power output of 12.580W for one hour.

For example, if an LED operates at a current of 20mA, the left battery can work continuously for: 3400/20=170 hours.

Power calculation gives milliampere = 12580mWh / 3.7V = 3400mAh.

The voltage of a AA battery is 1.5V. 1.5V multiplied by 0.8 gives 1.2Wh, indicating that a AA battery can output 1.2Wh of power for one hour. One kilowatt-hour is 1000Wh, so 1000/1.2 ≈ 833 AA batteries = one kilowatt-hour.

A switch circuit is a basic circuit that can control the flow and output of current or voltage, simply controlling the output of load current or voltage.

Switch circuits have wide applications in modern electronic technology and are an essential part of electronic circuit design and implementation.

Using electricity to control electricity is also the core principle of computer operation.

The principle of a relay is that electricity generates magnetism, which attracts the components inside the relay to connect with another circuit.

A diode is an electronic component made of two different semiconductor materials arranged to form a P-N structure, allowing current to flow in only one direction while blocking the other direction.

Because diodes only allow current to flow in one direction, they have many applications in electronics, such as making battery chargers, power adapters, and many other electronic devices.

We can compare a faucet to the circuit of a transistor; water flow is analogous to current, and the faucet switch corresponds to the control signal of the transistor.

When we turn on the faucet, water flows through the pipe. When the faucet switch is on, water flows smoothly from the faucet; when the switch is off, the water flow stops.

Similarly, when we connect the power supply in the circuit to the transistor, current will flow. When the control signal (such as a control voltage) is sent to the transistor’s base, the transistor turns on, allowing current to flow from the collector to the emitter. When the control signal disappears, the transistor turns off, stopping the current flow.

Two different switching methods made from different materials:

Differences between MOSFET and Transistor:

The NE555 was invented in the 1970s by the National Semiconductor Corporation and is still very popular today.

The NE555 is an integrated circuit, also known as the 555 timer, widely used in analog circuits. The NE555 has multiple applications, including square wave generators, multivibrators, pulse width modulators, timers, etc. It is a versatile, reliable, and economical circuit component used in various analog circuit designs.

The NE555 integrated circuit is one of the most important components in analog circuits, and its multiple applications make it widely used in various electronic devices.

The effects of output and input are the same

Operational amplifiers are circuit components that can process two electrical signals.

Operational amplifiers generally produce output signals by comparing the voltage levels of the input signals at their differential input ports, typically connecting two voltage signals, one being (+IN) and the other being (-IN). The operational amplifier amplifies and compares these two voltage signals’ relationships to produce an output voltage signal.

High and low output voltages need to be configured, and the larger the resistance, the smaller the impact of the operational amplifier on the circuit.

The output voltage value is modified within the operational amplifier component.

When the voltage at the + terminal is lower than that at the – terminal, the output is low voltage (L = low voltage, H = high voltage).

When the voltage at the + terminal is higher than that at the – terminal, the output is high voltage (L = low voltage, H = high voltage).

High voltage becomes low voltage, low voltage becomes high voltage.

A NOT gate is a type of logic gate with one input and one output; its output is the inverse of the input, meaning when the input is high, the output is low, and vice versa. Therefore, a NOT gate is sometimes referred to as an inverter.

A common component in electronic circuits.

A NOR gate is a common type of logic gate in electronic circuits. The output signal of a NOR gate depends on the state of all input signals; as long as one input signal is high, the output signal will be low. Only when all input signals are low will the output signal be high.

In other words, a NOR gate is like a large door that only opens (outputs high voltage) when all inputs are closed (low voltage); otherwise, the door remains closed (outputs low voltage).

A common component in electronic circuits.

Analog circuit, drawing