It Includea the details and Circuit explanation of how a LIGHT DIMMER Circuit works. - Er. Parth Patel

1. Light Dimmer Circuit
Prepared by :-
Parth D. Patel (140110109039)
Jay j. Patel (140110109034)
Batch : C109
Basic Electronics OEP

2. The Circuit Diagram

3. The Components Used :
 Resistors : - 100 Ω - 2Watt
- 4.7 kΩ - 0.5 Watt
- 1 MΩ - 0.5Wat
 Capacitors : - 0.1 μF – 400 V
- 0.1 μF – 400 V
- 0.1 μF – 400 V
 TRIAC : TLC 22238
 DIAC : DB3
 Variable Resistance : 500 kΩ

4. The Working Of Circuit
• A light dimmer works by essentially chopping parts out of
the AC voltage. This allows only parts of the waveform to
pass to the lamp. The brightness of the lamp is determined
by the power transferred to it, so the more the waveform is
chopped, the more it dims.
• Mains power is comprised of an alternating current that
flows in one direction and then in the other, along the cable,
at the rate of 50 or 60 cycles per second (known as Hertz).
• By chopping the waveform at the zero-crossing point,
smooth dimming can be achieved without the lamp
flickering.

5. • The mains sine wave, and a phase-controlled waveform.
The Alternating
Current Wave form
The choped waveform
at zero point where
smooth dimming is
achived

6. The Imperative Components

7. The DIAC
• The DIAC is a full-wave or bi-directional semiconductor
switch that can be turned on in both forward and reverse
polarities.
• The DIAC gains its name from the contraction of the
words DIode Alternating Current.
• The DIAC is widely used to assist even triggering of a TRIAC
when used in AC switches. DIACs are
mainly used in dimmer applications
and also in starter circuits for
florescent lamps.

8.  Operation :
• The DIAC conducts a break-over voltage. When the device
excceds thr break over voltage , it enters the region of negative
dynamic resistance.
• The diode remains in its conduction state untill the current
through it drops below what is termed the holding current.
• Below the holding current , the DIAC reverts to its hhigh
resistance.
• Its behaviousr is bi-directional and therefore its operation occurs
on both halves on AC Cycle.

9. The TRIAC
• The TRIAC is a three terminal semiconductor device for
controlling current. It gains its name from the
term TRIode for Alternating Current.
• It is effectively a development of the SCR or thyristor, but
unlike the thyristor which is only able to conduct in one
direction, the TRIAC is a bidirectional device.
• The TRIAC is an ideal device to use for
AC switching applications because it
can control the current flow over both
halves of an alternating cycle.

10.  Opreation :
• It can be imagined from the circuit symbol that the TRIAC consists of
two thyristors back to back but with a common gate terminal, and
the cathode of one thyristor connected to the anode of the other,
and vice versa.
• When the voltage on the MT1 is positive with regard to MT2 and a
positive gate voltage is applied, one of the SCRs conducts. When the
voltage is reversed and a negative voltage is applied to the gate, the
other SCR conducts. This is provided that there is sufficient voltage
across the device to enable a minimum holding current to flow.

11. Thank You