how to test diode using digital multimeter

How to find out diode is good or bad

Remember what is diode

Remove the diode from pcb (printed circuited board) than Identify Anode, Cathode 

Now set the   multimeter knob to diode test mode.

First Forward test

Remember -Diode is allow electric current in only one direction is called forward direction.

multimeter POSITIVE(+) lead put to anode side than

multemeter Negative (-) lead put to cathode side

see below the image

Now check multimeter display show some reading.

A good forward-based diode displays a voltage drop ranging from 0.5 to 0.8 volts for the most commonly used silicon diodes. Some germanium diodes have a voltage drop ranging from 0.2 to 0.3 V.

transistor circuit symbols

transistor circuit symbols

The circuit symbols for PNP and NPN transistor are shown below

pnp transistor symbol

PNP transistor

The arrow on the emitter lead pointing towards the base represents a PNP transistor. When the emitter-base junction of PNP transistor is forward biased, the direction of the conventional current flow is from emitter to base.

NPN transistor

npn transistor symbol

NPN transistor is represented by arrow on the emitter lead pointing away from the base. When the emitter base junction of a NPN transistor is forward biased, the direction of the conventional current is from base to emitter.  

BJT(bipolar junction transistor)

BJT(bipolar Junction transistor)

• Junction transistor is a solid state device,generally it is called as Bipolar Junction Transistor (BJT). 
• The BJT transistors  are formed between three layers(three terminals), these are called emitter (E), Base (B), Collector (C). 

  

  transistor

•  The BJT transistors are current-controlled devices. If small amount of current flows through the base of a BJT transistor then it causes to flow large current from emitter to collector. The BJT transistors are only the transistors which are turned ON by the input current which is given to the base. 
• 1. Base(B) layer :-
                               It is a very thin layer, the thickness is about 25 microns it is a central              region of the transistor.
  
  2. Emitter(E) layer:-
                               The emitter region is heavily doped, since emitter has to supply majority carriers.
  
  3. Collector(C) layer:-
  
                               The collector region is lightly doped. since it has to accept majority charge carriers, it is large in size hence emitter and collector can not be interchanged.
  

Type of transistor

Type of Transistor

• Transistor is semiconductor device it consists of silicon, germanium and gallium-arsenide.
• Basically the transistors are classified depending on their structure.
• Each type of transistors has their own characteristics,and advantages,disadvantages.
• Hence transistors are designed primarily for switching purpose,
• other side some are designed for amplification purpose 
• and also transistors are designed for both amplification and switching purposes. 
• transistors are  Depending on the structure.

         Basically transistor classified into 
              1. BJT (Bipolar Junction Transistor) 
              2. FET (Field Effect Transistor)

type of transistor

what is transistor

Transistor                                        

   Transistor is a semiconductor solid state device. used to amplify or switch electronic signal and electrical power. it consists of silicon or germanium crystal containing two PN junction. the two pn junction are formed between the three layers. these are called base, emitter and collector. 

transistor

1. Base(B) layer :-
                             It is a very thin layer, the thickness is about 25 microns it is a central              region of the transistor.

2. Emitter(E) layer:-
                             The emitter region is heavily doped, since emitter has to supply majority carriers.

3. Collector(C) layer:-
                             The collector region is lightly doped. since it has to accept majority charge carriers, it is large in size hence emitter and collector can not be interchanged.

smd resistor

SMD Resistor?

Surface Mount Device

·         SMD Resistor (surface mount technology),

·         SMD resistor stands for Surface Mounted Device,

·         smd resistor a type of tiny chip resistor,

·         Smd resistors not have color band,

·         Smd resistor have a numerical based resistance value,

·         Smd resistor have 3 digit value, 4digit value, and EIA-96 value.

Smd resistor calculation three digit:

   3-digit smd resistor

Surface mount Device Three Digit

·         The first two digit numbers will indicate the significant digits,

·         Third digit indicate multiplier, (power of ten 1ô) the number of zeros

·         Letter R, K, M is indicate Decimal Point, example-- 2R2 mean by 2.2Ω

·         R is indicate for smd resistor resistance value under 1000

·         K is indicate for smd resistor resistance value under 1000(kilo)

·         M is indicate for smd resistor resistance value under millions (Mega)

Examples:

·         330 = 33 x 10⁰   => 33 x 1 = 33Ω

·         100 = 10 x 10⁰   => 10 x 1 = 10Ω

·         102 = 10 × 10²   => 10 x 100 = 1000Ω or 1kΩ

·         524 = 52 x 10⁴   => 52 x 10000 = 520kΩ

·         2R2 = 2.2Ω

·         R23 = 0.23Ω

·         3M2 = 3.2mΩ

§  5.7Ω resistor value, written as--- 5R7

§  1Ω resistor value, written as -----1R or 1R0

§  0.67Ω resistor value written as -----R67or 0R67

Smd resistor calculation:four digit

4 Digit smd resistor:

Surface mount Device Four Digit

·         The first three digit numbers will indicate the significant digits,

·         Fourth digit is the multiplier, (power of ten 10^ô) the number of zeros

·         Letter R is indicate Decimal Point,

·         R is indicate for smd resistor resistance value under 1000

·         K is indicate for smd resistor resistance value under 1000(kilo

·         M is indicate for smd resistor resistance value under millions (Mega)

Examples:

·         5000 = 500 x 10⁰      => 500 x 10     = 5000 = 500Ω

·         4502 = 450 x 10²      => 450 x 100   = 45000 = 45kΩ

·         22R2   => 22.2Ω

·         R103   => 0.103Ω

      2M20  => 2.20mΩ

EIA-96, Smd resistor calculation:

·         EIA-96 SMD resistor

·         First two digit value find out in eia96 table

·         Third digit is the multiplier.

Example:

Surface mount Device 

·         26c   => 182 x 100 = 18.2kΩ

·         65f   => 464 x 100000 = 46.4mΩ

·         Note (first two digit ie 26 EIA96 value is 182 see the above table

And letter c value is 100)

EIA-96 smd resistor numerical and letter code below:-

letter codes below:-

Advantage of SMD resistor:

·         Very Smaller components.

·         Initial cost low      

·         Simply and faster automated assembly.

·         Better performance

Disadvantages of SMD resistor:

·         Repair is more difficult

·         Cannot used with breadboards

·         Damaged during the soldering

·         Unsuitable for large, high-power circuit

Click - Full lesson for resistors,what is resistor,type of resistor.

Resistor

What is resistor?

                        Resistor is a passive electrical component, that limit or regulate the flow of electrical current in an electronic circuit.

1. Resistor is a passive electrical component.

2. Main function of resistor in any circuit is to restrict the flow of electric current in an electronic circuit.

3.Resistors are used in electronic circuits,reduce current  flow, and adjust signal levels, to divide voltages   and etc.

Resistor Symbols

Add caption

Type of Resistors:-

Type of Resistor?

Resistor classified into:- 

                1. Linear resistor

                2. Non-linear resistor

1. Linear resistor

               Resistance does not vary with the flow of current through it

                         Directly proportional to the applied voltage

               In other words Resistance remains constant

Linear resistor are further classified into:-

                    1. Fixed resistor

                    2. Variable resistor

1. Fixed resistor:-

    Fixed resistor Have a constant resistance value

                      Can’t change the value of resistance

Fixed resistor is further classified into:-

                          1.     Carbon Composition Resistors

                          2.     Wire Wound Resistors

                          3.     Thick Film Resistors

                          4.     Thin Film Resistors

         

1. Carbon composition resistor:-

Made from the carbon or graphite with an insulating material,

Insulating material as a binder desired the original resistance of the resistor. 

                     Commonly available in Resistance values of 1 Ω to 25 MΩ.

                     The power rating is generally 1⁄10, 1⁄8, 1⁄4, 1⁄2, 1, up to 5 Watts.

2. Wire wound resistor:-

Wire wound resistor is made by the insulating core.

The insulating core is porcelain, Bakelite, plain pressed paper etc.

The resistive wire is wrapped around an insulating core

The resistance wire include tungsten and manganin, Nichrome etc.

The resistance of the resistor depends on the resistivity of the wire,

The resistance can be less than 1 Ω up to several thousand Ωohms

Wattage ratings from 1 Watt up to 100 Watt or more.

Uses of Wire Wound Resistors

                     Used in high power rating devices

                     Used in Testing and measuring devices

                     Used in current and voltage balancing

                     Used in current sensing

Advantages:-

                      Make lower noise

                      Reliable and flexible

                      Low cost

                      Wide resistance range

                      High accuracy/ stability

Disadvantage:-

 Used only low frequency equipment,

                      Not suitable for high frequency equipment.

3. Thick film:-

Thick film resistors are manufactured using screen and stencil printing processes.

The alumina substrate is metalized then a resistive paste is deposited on top of the terminals.

It is later trimmed, coated, metalized on the edges, and plated.

Most SMD (surface mount device) resistors today are of this type.

Thick film resistor classified into:-

                    1. Metal Oxide film Resistors
                    2. Cermet Film Resistors
                    3. Fusible Resistors

Metal oxide resistor:-

                   Metal-oxide film resistors are made of metal oxides

                   Metal oxide resistor have a higher operating temperature

                   Metal oxide resistor is greater stability/reliability

Cermet film resistor:-

Cermet oxide resistors, contains on ceramic insulation materials.

A carbon or metal alloy film or layer wrapped around the resistor and then fix it in a ceramic metal

Cermet film resistor made in the square or rectangular shape

Fusible film resistor:-

                        When the power rating is exceeded. It then serves the dual functions of a fuse and a resistor to limit.

4.Thin film:-

Thin film resistors are made by sputtering (a method of vacuum deposition) the resistive material onto an insulating substrate, allowing for a much more uniform and controlled resistive element. Then undergo similar finishing steps to trim, coat, and metalize the edges.

Thin film resistors are usually specified with tolerances of 0.1, 0.2, 0.5, or 1%,

They also have much lower noise levels,

Thin film resistors are more expensive than thick film resistors.

Thin film resistor classified into:-

                   1. Carbon Film Resistors
                   2. Metal Film Resistors

Carbon film resistor:-

                Carbon film is deposited on an insulating substrate

                Carbon film resistor Power rating is 0.125 W to 5 W

                Carbon film resistor Resistances range from 1Ω to 10 megaΩ

Metal film resistor:-

               Metal film resistor construction like Carbon film resistors,

               Metal film resistor is usually coated with nickel chromium

               Metal film resistor is very tiny,

               Metal film resistor Cheap and reliable.

Variable resistor:-

      The electric resistance(R) value can be adjusted/changed, during the   operation of equipment is required.in other words said that (increase or decrease the flow of the electric current in a circuit).

Type of variable resistor:-

1.     Potentiometers

2.     Rheostats

3.     Trimmer

1. Potentiometers:-

Potentiometer is a type of variable resistor

Potentiometers resistor have a three terminals

Potentiometers also called a pot

Potentiometer is used to vary the voltage in a circuit

                                 Potentiometer have a continuously adjustable tapping point

 Tapping point controlled by rotation of a shaft or knob

Use of potentiometer:-

                  A volume control for an audio device, frequency attenuation, and more

2. Rheostats:-

                           Rheostats is a type of variable resistor

                           Rheostats resistor have a two terminals

                           Rheostats is used to vary the current in a circuit

Types of rheostats

                          Rotary type

                          Linear type

Application of Rheostats:-

                          Used in volume controller

                          Used in speed controller and more

2. Non-linear resistors:-

            The current flowing through it does not change but changes in applied voltage.  

Type of non-linear resistor:-

                         1. LDR (light dependent resistor)

                         2. VDR (voltage dependent resistor)

                         3. Thermistors

LDR (light dependent register):

LDR is light sensitive resistor and also called photo resistor

LDR is whose resistance decreases as the intensity of light they are exposed to increases.

Types of LDR:-

1                         1. Intrinsic

2                         2. Extrinsic. 
VDR (voltage dependent resistor)

                   Used to protect circuits.

Thermistors:-

Resistance value changes significantly with a change in temperature is called thermistors.

Type of thermistors:-

                 1. NTC

                 2. PTC

NTC (negative temperature coefficient)

Thermistor indicating that its resistance decreases with an increase in operating temperature.

Used in Temperature sensing and control, inrush current limiting, flow measurement

PTC (positive temperature coefficient)

Thermistor indicating that its resistance increases with an increase in operating temperature.

Used in over-current protection, self-regulating heater, time-delays, liquid level sensing.

click here full lesson for SMD(surface mount device)resistor