All You Need To Know

I'm working through The ALL YOU NEED TO KNOW series. These are my notes.

There is a Learn Electronics Repair Discord server.

For later viewing:

• The Art Of Methodical Fault Finding - A Practical Example
• Learn electronics Repair #14 - Circuits and Components for Beginners 1. What Is Electricity?

All You Need To Know About RESISTORS To Fix Stuff!

In circuits resistors are marked with 'R'.

• 1R0 = 1.0 Ohm
• 1K0 = 1.0 K Ohm
• 1M0 = 1.0 M Ohm

Three digit code: value value multiplier
Four digit code: value value value multiplier

The reason for connecting a bunch of lower value resistors in series is to provide an aggregate resistance which can handle a higher current.

With SMD components:

• if they look black they are almost certainly resistors (but could be capacitors)
• if they look brown they are almost certainly capacitors (probably not resistors)
• if they look white they are usually capacitors
• if they look green they are usually resistors

All You Need To Know About CAPACITORS To Fix Stuff!

In circuits capacitors are marked with 'C'.

Be careful with capacitors! Use a resistor to discharge them before working on them.

Three ratings:

1. capacitance (Farads)
2. voltage (volts, this is a limit)
3. effective series resistance (ESR) (Ohms)

1,000 pF = 1 nF
1,000 nF = 1 μF

Three main uses for capacitors:

1. filtering (coupling)
2. smoothing (decoupling)
3. timing

• capacitors in parallel: double (100 + 100 = 200)
• capacitors in series: half (100 + 100 = 50)

Ripple current can cause a capacitor to fail, it can literally boil the electrolyte.

Three failure modes of caps:

1. short (burns, explodes), usually happens on surface mount capacitors, Multi Layer Ceramic Capacitors (MLCC), the changing temperature can cause them to crack, also mechanical stress (being dropped) can cause fracture
2. leaky (passes DC current), usually happens to through-hole ceramic caps
3. low capacitance, high ESR, usually happens to electrolytic caps, they age, dry out (it's possible to recondition them, but he didn't go into how)

All You Need To Know About INDUCTORS To Fix Stuff!

In circuits inductors are marked with 'L'.

Explained Back EMF with water wheel analogy.

An inductor will pass DC and block AC.

Uses for inductors:

• as a filter to block AC current
• in Voltage Regulator Modules (VRMs)
• in buck/boost regulators
  • buck decreases voltage
  • boost increases voltage
• power factor correction

Anything with a coil inside it is effectively an inductor:

• motors
• solenoids
• relays
• transformers

He noted that 'I' (for current) is from the word "intensity".

The inside of the inductor around which the wire is wound is called the "former", and it can be ferrite, cardboard, etc.

Inductors are simple and rarely fail. Failures can be from:

1. physical damage (you can usually see this)
2. it can lose enamel and short
3. it can vibrate and the joints go bad

If you see a smoking inductor the problem isn't the inductor but too much current being passed through it. This will be a short circuit caused by something else.

If your inductors are getting hot it's not the inductor the problem is the capacitor on the low side (the output side).

Test an inductor with continuity test, if it's open circuit that's a problem, should be short circuit.

You can use an LCR meter for larger inductors.

Use an ESR meter for smaller inductors.

The symbol for reactance is X_L.

X_L = R = 2πfL = 628,000L.

You can decrease the inductance by wrapping another wire around the coil.

All You Need To Know About DIODES To Fix Stuff!

In circuits diodes are marked with 'D'. 'ZD' for Zener diodes.

Electricity (conventional electricity) flows from anode to cathode (black band is the cathode, like the bar on the diode symbol).

The property of a diode whereby AC is converted to DC is called "rectification".

There are all different types of diodes but this video is about rectifier diodes.

Three types of diodes:

1. signal diodes (for very low currents)
2. rectifier diodes (for power, high current)
3. Schottky diode (a special type of rectifier)

When a diode is forward biased it is passing current. When a diode is reverse biased it is blocking current.

Voltage drop over a silicon signal/rectifier diodes from 0.5V to 0.7V. Germanium diodes around 0.2V. Schottky diode drops around 0.15V.

Before germanium diodes we had selenium diodes (50's, 60's) and prior to that thermionic diodes (vacuum tubes). There were also crystal diodes, a particular type of which were cats whistle diodes.

Two main ratings for diodes are:

1. volts
   • the voltage rating is how many volts it can block in reverse before it breaks down and passes current
2. amps
   • silicon diodes ~100 mA
   • rectifier diodes 1-10 A

A diode also has a "recovery time" which is how fast it can turn on or off. You can get diodes called "fast rectifiers" (FR). Schottky diode are fast.

Typical applications for diodes include:

• ensuring correct polarity of power supply
• to drop voltage (~0.6V each)
• isolating input voltages
• joining 5V ATX and 3.3V CMOS battery
• for Back EMF on an inductor

He also discussed how a bridge rectifier works.

Three ways diodes can fail:

1. goes short circuit (no voltage drop)
2. goes open circuit (e.g. burn out)
3. less common, with signal diodes, can become "leaky", like a resistor

You can get a diode matrix, with common cathode or common anode.