What is BD136 Transistor : Pin Configuration & Its Working

A general-purpose with medium power BD136 transistor is mainly used for audio amplification & switching purposes. This kind of transistor belongs to the family of PNP. This transistor works like a switch to drive or handle a maximum of 1.5A of load continuously through 45V of load voltage. It can also be used as an amplifier within audio & signal amplification-based circuits.


The package used to manufacture this BD136 Transistor is TO126. This article discusses an overview of BD136 transistor, pin configuration, working with applications.

What is BD136 Transistor?

BD136 transistor is available with 3 terminals like emitter (E), collector (C) & base (B). This NPN transistor is composed of 3 layers where one layer is n-doped & the remaining two layers are p-doped. So, the n-doped layer is arranged in between the two p-doped layers.

Here, the n-layer signifies the base pin whereas the remaining two layers signify emitter & collector correspondingly. At the base terminal of this transistor, the small amount of input current can be used to generate a huge output current at the remaining two terminals. So this method is mainly used for amplification.

BD136 Transistor
BD136 Transistor

The current gain or amplification factor carried by this transistor ranges from 40- 250. The charge carriers play a significant role within the conductivity because, in this PNP transistor, the majority charge carriers are holes whereas, in the NPN transistor, holes are the majority charge carriers.

The base terminal of this transistor is mainly responsible for the complete transistor action in two cases. This terminal works like a valve that controls the majority of charge carriers in both the transistors like PNP & NPN.

It is very essential to observe that as compared to PNP, NPN is mostly preferred for amplification purposes as the movement of electrons is superior & faster as compared to the mobility of charge carriers within PNP.

Pin Configuration/Pin Diagram

The BD136 Transistor pin configuration is shown below. This transistor includes three pins where each pin and its function are discussed below. BD136 Transistor and its symbol is shown below.

BD136 Transistor Pin Configuration
BD136 Transistor Pin Configuration
  • Pin1 (Emitter): This terminal is used to drain out the current & it is generally connected to GND.
  • Pin2 (Collector): Current supplies throughout the collector terminal which is connected to load
  • Pin3 (Base): This pin mainly controls the transistor’s biasing mainly used to switch ON/OFF the transistor.

The three terminals of this transistor can be connected through the electrical circuit. These are dissimilar in terms of working ability & doping concentrations. The two terminals of the transistor-like base & collector are doped less as compared to the ‘E’ terminal and it holds the flow of the current of the complete transistor.

Working Principle

The BD136 Transistor’s working principle is very simple & it works like an NPN transistor. In the PNP transistor, the base pin is negative whereas, in the NPN transistor, it is positive.


The transistor is activated & both the terminals like E & C are connected in forwarding bias whenever there is no flow of current at the base terminal. When the current supplies throughout the base terminal the transistor is turned OFF and both the terminals like C & E are connected in reverse bias.

As compared to the PNP transistor, the NPN transistor is most frequently used for amplification due to the flow of electrons is superior as compared to the mobility of majority charge carriers within the PNP.

Features & Specifications

The features & specifications of the BD136 Transistor include the following.

  • Type of transistor PNP
  • Operating & storage temperature max ranges from -55 to 150 oC
  • Dissipation of collector terminal 12.5W
  • Collector current is 1.5A
  • Breakdown voltage from emitter to the base is 5V
  • Max collector current is 5A
  • Transition frequency Max ‘fT’ is 190 MHz
  • DC gain (hfe) ranges from 25 to 250
  • Available in TO126, TO225 package
  • Collector to base voltage (VCB) is 45V
  • Max voltage from emitter to base (VEB) – 5V
  • Collector to emitter voltage (VCE) is 45V
  • Collector terminal dissipation max is 5Watts
  • Simple to handle & carry
  • Saturation voltage is low
  • The operating area is High safe
  • Simple drive requirements
  • Alternative ICs of BD136 are; TIP127, BC157, TIP42, BC556, BD140, 2SA1943, 2N3906 & S8550. The equivalent transistor of BD135 is BD136 transistor.

How to Protect BD136 Transistor?

Using different components below their highest ratings can make their life longer & perform stable within electronic circuits.

To obtain lasting performance from the BD136 transistor, it is advised not to drive different loads above 1.5A & 45V throughout this transistor.

An appropriate base resistor must be used to supply the required current on its base terminal. Use an appropriate heat sink through the transistor. The storage & operating temperature must be range from -55 C & +150 C.

BD136 Transistor Circuit

The BD136 transistor application circuit like the 555 alarm sound generator is shown below. In this circuit, the BD136 transistor is used to enhance the flow of the current of the 8-ohm speaker.

This circuit operates with a 9V power supply from a battery where IC1 functions in a stable multivibrator mode. So from pin3, it generates high frequency. The output frequency of this circuit can be determined through the R1, C2 & R2 particularly C2. If the value of the capacitor is high, then the output will be less frequent.

555 Alarm Circuit using BD136
555 Alarm Circuit using BD136

The sound from pin-3 is given to the R3 resistor to restrict the flow of current for the Q1 transistor. Here ‘Q1’ is the amplifier that drives the speakers from 8 ohms to 32 ohms.

The required components to make this circuit is 555 timer IC, BD136 Q1, 100 uF

C1-Electrolytic capacitors, 0.01uF

C2 50V ceramic capacitors0.1uF , C3 50V ceramic capacitors

R1-100K, R2-4.7K, R3-100 ohms, R4-33 ohms & 8 to 32 ohms speaker. To design a buzzer sound circuit, there are many methods available but here we have used transistors to design this circuit and also 555 timer IC due to its simple design, uses less amount of current & less cost.

Advantages & Disadvantages of a Transistor

The advantages of the BD136 transistor include the following.

  • Small size
  • Uses less voltage to operate
  • Immediate action
  • high durability
  • Less cost
  • Less output impedance
  • It controls the power which is delivered to different loads

The disadvantages of the BD136 transistor include the following.

  • Responsive to temperature
  • Generates less energy
  • It can be broken because of the thermal runaway.
  • Very less reverse blocking capacity
  • The o/p voltage cannot be modified simply, so the DC o/p voltage is not modifiable.

Where to use/BD136 Transistor Applications

The applications of BD136 Transistor include the following.

  • This transistor is used in a lot of general-purpose applications
  • It is used as a switch to drive several loads at a time below 1.5A like LEDs, high power relays, transistors, devices, etc.
  • To design astable, bistable multivibrators, power supply, signal amplifier & battery charger circuit.
  • This transistor is also used at the output of raspberry pi, Arduino & other microcontrollers to drive different loads.
  • Motor driver, Darlington pair, audio amplifiers, load driver circuits, impedance buffering, current mirror circuits, drive loads below 1.5A, audio amplifier stages, H-bridge circuits, oscillator & computer circuits, amplification & switching circuits.
  • Alternatively, it can also be utilized in audio amplifier stages & also like a separate amplifier to drive a speaker directly.
  • General-purpose
  • TV Circuits
  • Audio Amplifier
  • High-Fidelity Amplifiers

Thus, this is all about an overview of the BD136 transistor datasheet. This is a 3 terminal PNP/NPN device. Here, the collector current (IC) is the main task of the base current (IB). So a transform within the base current will give an equivalent amplified transform within the collector current for a specified VCE (collector-emitter voltage.

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