Kindly explain

Discussion in 'General Electronics Chat' started by triplehdineshbabu, Feb 20, 2009.

  1. triplehdineshbabu

    Thread Starter Active Member

    Feb 5, 2009
    38
    0
    Hi all,

    In that attached PDF, Kindly explain why D3 is connected parallel to the DC Motor? and what is the USE of D1 and D2?

    Kindly explain....

    Thanks in advance
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,347
    Hello,

    Diode D3 protects the transistor against inductive kickback of the motor.
    Diodes D1 and D2 provide the charge and discharge rates for capacitor C1 through the parts of potmeter VR1.

    [​IMG]

    Greetings,
    Bertus
     
  3. b.shahvir

    Active Member

    Jan 6, 2009
    444
    0
    It is known as a 'Freewheeling Diode'. It absorbs the inductive currents produced by the energy stored in armature winding magnetic field (winding inductance).

    It is used to suppress sparking at contact point of the commutator and brushes, due to inductive nature of armature currents.... this in turn suppresses RFI (Radio Frequency Interference) disturbances in control electronics circuit.
     
  4. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    To further elaborate on the comments already supplied, D1 and D2 permit the establishment of a discharge current path that is independent of the charge current path for capacitor C1. This makes it possible to control the speed of the motor by changing the ratio between the time that T1 is on versus the time that T1 is off simply by adjusting potentiometer VR1. This control of the ratio of on-time to off-time (duty-cycle) is the essence of the technique referred to as PWM or pulse width modulation. PWM is one of the most popular and effective methods for managing motor speed.

    hgmjr
     
Loading...