Power Supplies

BD135 Transistor -Medium Power Silicon NPN Transistor

BD135 transistor is a bi-polar, medium-power, plastic nPn transistor made up of silicon. It is used in a wide range of electronic equipment especially used as an audio signal amplifier and drivers using complimentary or quasi complimentary circuits. The transistor has three regions of different conductivity with two NPN junctions. The two end regions have same conductivity known as Emitter and collector while the middle region with different conductivity is known as base.

BD135 is a general-purpose medium-power transistor that falls under the category of NPN transistors. It is mainly used for switching and audio amplification purposes. It comes with a collector current 1.5A, indicating it can drive loads under 1.5A. The BD135 is one of the transistors in the popular BD series, which also includes the BD131, BD137, and BD139, as well as their PNP counterparts.

BD135 Transistor Characteristics:

  • Audio signal amplifier
  • Polarity is NPN
  • High current (maximum 1.5A)
  • Low Voltage (maximum 80V)
  • Collector current = 1.5 A
  • Base current = 0.5A
  • Collector base voltage = 45V
  • Collector emitter voltage = 45V
  • Emitter base voltage = 5V
  • It is lead (Pb) and Halogen free

BD135 Pinout:

The transistor has three pins labeled as emitter, base, and collector as shown in fig.

bd135 Transistor

BD135 Circuit Diagram:

BD135 transistor is used in low-cost universal battery chargers. Circuits for nickel-cadmium and nickel metal hydride batteries charger contain this transistor and are best for car use. This charger has a selectable charging current. And it is able to charge phones, mp3 and video players, toys, and almost all other portable electronic devices.

Schematic Diagram:

BD135 Schematic

Circuit diagram:

BD135 circuit diagramz

Parts included:

Q1 = BD135

C1 = 220 µF

D1 = 1N4007

D2 = LED 3mm

R1 = 120 Ω

R2 = given in circuit diagram

J1 = DC input socket

Input voltage:

Input voltage varies from 6.5V (min) to 21V (max) depending upon the battery. The input selection table is given below.

BD135 suply voltage

BD135 Equivalent Transistors:

  1. BD137
  2. BD139
    bd137 Transistor       bd139 Transistor

Characteristics of BD137 and BD139:


BD137 BD139
Collector base voltage (VCBO)



Collector emitter voltage (VCEO)



Emitter base voltage(VEBO)



Collector current 1.5A


BD135 Data Sheet PDF:

A4988 Stepper motor driver circuit pdf


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