Basic Analog Electronics Concepts (Beginner to Pro Foundation)

Simple, practical, and repair-focused explanation

🔶 1. Voltage (V) – Electric Pressure

Voltage is like water pressure in a pipe.

• High pressure = more force

• Low pressure = weak force

Example:

Laptop battery = 11.4V
Charger = 20V
USB port = 5V

🔶 2. Current (I) – Flow of Electrons

Current is the flow of electricity.

• Measured in Amps (A)

• High current = more power delivered

Example:

Laptop charger 20V 3.25A
Meaning: It can supply up to 3.25A of current.

🔶 3. Resistance (R) – Opposes Current

Resistance slows the flow of electricity.

• Measured in Ohms (Ω)

Example:

LED uses a 330Ω resistor to limit current.
Without resistor → LED burns.

🔶 4. Power (P) – Energy Used

P = V × I
(Watts)

Example:

20V × 3A = 60W charger
More watt = faster charging.

🔶 5. Series vs Parallel

Series Circuit

• Current same everywhere

• Voltage divides

+ → R1 → R2 → R3 → –

Parallel Circuit

• Voltage same everywhere

• Current divides

R1

+ →———|

R2

Motherboards mostly use parallel power rails.

🔶 6. Diode – One-way Door

Allows current in one direction only.

Used in:

• Adapter protection

• Charging path

• Backlight circuits

🔶 7. Zener Diode – Voltage Regulator

Keeps voltage fixed at a set value.

Example:
3.3V zener used to clamp high voltage.

🔶 8. Transistor – Electronic Switch

Small signal control big signal.

Types:

• NPN / PNP (BJT)

• MOSFET (Most used in laptop circuits)

Use:

• Enable signals

• Power switching

• Charging control

🔶 9. MOSFET – Voltage-Controlled Switch

Most important IC for power rails.

N-MOSFET

ON when Gate > Source

P-MOSFET

ON when Gate < Source

Used in:

• S5 → S3 → S0 switching

• DC-IN

• GPU/CPU power stages

🔶 10. Capacitor – Electricity Storage Tank

Stores and releases energy.

Uses:

• Filter power ripple

• Smooth DC voltage

• High-frequency stability

Types:

• Ceramic

• Electrolytic

• Tantalum

🔶 11. Inductor – Current Smoother

Stores energy in magnetic field.

Used in:

• Buck converters

• Charging circuits

• CPU/GPU power

Inductor + capacitor = Buck/Boost circuit.

🔶 12. Buck Converter – Step Down Voltage

Converts high voltage → low voltage.

Example:
20V → 12V
12V → 5V
5V → 1.2V (CPU rail)

IC Example:

• TPS51125

• ISL6259

• BQ24780S

• RT8243

🔶 13. Feedback (FB) Circuit

Controls output voltage.

If voltage drops → IC increases switching
If voltage rises → IC reduces switching

Used in:

• CPU VRM

• Backlight driver

• Charger circuit

🔶 14. Op-Amp – Error Amplifier

Compares two voltages.

Used for:

• Current sensing

• Battery charging

• Audio

Example:
BQ24780S uses op-amp for sensing ISNS across sense resistor.

🔶 15. Sense Resistor (R sense)

Low-value resistor for measuring current.

Example:
0.01Ω
Voltage drop across resistor = current measurement.

Used in:

• Charging

• CPU VRM

• Battery power-in

🔶 16. Signal vs Power Circuit

Power Section

High current, high voltage
(MOSFET, inductors, capacitors)

Signal Section

Low voltage, logic control
(Enable signals: EN, SLP_S5_L, SMC signals)

🔶 17. Analog vs Digital

Analog

Smooth, variable values
Voltage slowly changes
Used in sensors, charging, audio.

Digital

0 or 1
Signals like

• PM_SLP_S5_L

• ALL_SYS_PWRGD

• EN

Motherboards mix both.

🔶 18. Ground (GND) – Zero Reference

Common reference point for all voltages.