Surface Mount Transistor in Mobile Phone and Their Function

Surface Mount Transistor in Mobile Phone – SMT Transistor is SMD part made of semiconductors like silicon or germanium. Types of SMD Transistors: NPN, PNP

Surface Mount Transistor or SMT Transistor is an SMD electronic component made up of semiconductor material like silicon or germanium. There are 2 types of Surface Mount Transistors:

  1. NPN Type
  2. PNP Type

Surface Mount Transistor (SMD Transistor)

Terminals of a Transistor

There are three terminals of a surface mount transistor or thru-hole transistor:

  1. Ammeter (E) – Flows current on receipt of forward bias. Electrons are emitted in NPN transistors whereas PNP transistors emit ‘holes’.
  2. Collector (C) – The terminal of the transistor which receives the emitted electrons or holes. Collector always works or reverse bias mode.
  3. Base (B) – The layer between ammeter and collector is called base. Base displays the property of showing low resistance in ammeter junction forward bias and high in collector junction reverse bias.

Facts about Transistor

  1. Indicating Character: Q or V, TR
  2. Function: Switching, Amplification, Regulating Voltage.
  3. Unit: Transistors are identified according to the code.

Digital Surface Mount Transistor

In digital transistor, resistance in built in the base and ammeter. This transistor is also called RET (Resistance Equipped Transistor). This type of transistor is used in mobile phones for reducing the current consumption.

Field Effect Transistor (FET)

This type of transistor is controlled by voltage instead of current. Flow of working current through a semiconductor channel is switched and regulated by the effect of electrical charge in the area near channel which is called gate. This is called unipolar transistor. FET can be P-Channel type or N-Channel Type.

Metal Oxide Semiconductor (MOSFET)

MOSFET is active semiconductor components. MOSFET has 3 terminals – source, drain and gate. There are 2 types of MOSFET:

  1. P-Channel MOSFET (PMOS)
  2. N-Channel MOSFET (NMOS)

How to Read SMD Transistor Code

All SMD Transistors are Marked with Codes to denote the type of semiconductor used and use of transistor.

Here I explain How to Read SMD Transistor Code:

First Alphabet:

  • A= Germanium
  • B = Silicon
  • C = Gallium Arsenide
  • D = Indium Antimide

Second Alphabet:

  • C = Audio Frequency Amplifier
  • D = Audio Frequency Power Amplifier
  • F = Low Power Radio Frequency Amplifier
  • P = High Power Radio Frequency Amplifier

Therefore, Identification of a Transistor Marked with the Code – BC486 will be:

  • B = Silicon
  • C = Audio Frequency Amplifier
  • The Transistor = Silicon Audio Frequency Amplifier

More Examples:

  • BD 187 = B for Silicon, D for Audio Frequency Power Amplifier
  • AD 486 = A for Germanium, D for Audio Frequency Power Amplifier
  • AC 140 = A for Germanium, C for Audio Frequency Amplifier

Surface Mount Transistor FAQs

Surface Mount Transistors offer several advantages over through-hole transistors, including smaller size, lower profile, and higher density on PCBs. They also have better thermal performance, improved electrical performance, and faster assembly times.

The pinout of an SMT transistor can be identified by referring to the datasheet provided by the manufacturer. The datasheet will typically include a pinout diagram that shows the location and function of each pin.

SMT transistors are typically soldered onto a PCB using a reflow soldering process. The PCB is first coated with solder paste, which is a mixture of solder and flux. The SMT transistor is then placed onto the PCB using a pick-and-place machine, and the PCB is heated in a reflow oven to melt the solder and permanently attach the transistor to the PCB.

SMT transistors are used in a wide range of electronic applications, including mobile devices, automotive electronics, industrial automation, and consumer electronics. They are commonly used in power management circuits, switching circuits, and amplifiers.

Related Posts:

Share This:

Santosh Das

Santosh is an Electronics Geek, Blogger, Young Entrepreneur and Founder of this Mobile Phone Repairing Website. Santosh possesses vast experience in the field of electronics, telecommunication, Soldering, SMT, ESD Safety, Keep visiting for daily dose of Tips and Tutorials.

Also Read:

12 Responses

  1. Michael Gay says:

    Santosh, have a switching power supply with SMD transistors marked only “2Ay”. Any ideas as to it’s identity? Thanks!

  2. Mukund Bist says:

    Hello sir
    I have read all components inside radio but I don’t know it’s all gone inside cell phone and where it’s located??

  3. jacky says:

    you can check smd marking codes,smd code,topmark on this website.

  4. richard says:

    hello sir i realize on my tablet it went blank it shows now battery charging however current is reaching the board a found out a smd transistor get hot when i plug in the charger. I remove it and try plug the charger again it show no red light in the charger i reconnect the charger and it shows red light again but the component get hot, could it be because of the transistor the tablet shown no sigh of charging also cpu also get hot in the process when the transistor is off the cpu is ok

  5. michael says:

    Am having an issue fixing my itel p32 screen ligh

  6. Sven says:

    Do you maybe know how many SMD transistors are in cell phone? I had a discussion with a friend and It seems like you may know it.

    Thanks,
    Sven

  7. Nieuwste Adidas says:

    Greetings! This is my first comment here so I just wanted to give a quick shout out and tell you I really enjoy reading through your articles. Can you recommend any other blogs/websites/forums that cover the same topics? Thanks a ton!

  8. Alauddin Ahmed says:

    Thanks brther

  9. Najib kiggundu says:

    thanks for all your contribution to our understanding of repairing

  1. September 16, 2019

    […] Learn More: SMD Transistor […]

Leave a Reply