Kindly explain

bertus

Joined Apr 5, 2008
22,270
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.



Greetings,
Bertus
 

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b.shahvir

Joined Jan 6, 2009
457
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.
 

hgmjr

Joined Jan 28, 2005
9,027
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
 
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