# Firing circuit for triac

Discussion in 'The Projects Forum' started by snp2411, Mar 11, 2009.

1. ### snp2411 Thread Starter Member

Mar 11, 2009
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0
How do we convert the analog voltage to firing angle(proportional to the voltage)for triggering the triac....

Apr 5, 2008
17,381
3,118
Hello,

Compare a triangle/sawtooth voltage that is synchon to the AC with the DC you want to translate into the fire angle.

Greetings,
Bertus

3. ### snp2411 Thread Starter Member

Mar 11, 2009
11
0
i dint get you...in my project i convert the digital output of a microcontroller into analog voltage and with this i need to trigger the triac...this is used to improve the efficiency of a induction motor...

• ###### triac.pdf
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Last edited: Mar 11, 2009

Apr 5, 2008
17,381
3,118
Hello,

You can make a sawtooth generator that is resetted by the zerocrossing of the AC voltage.
This sawtooth voltage can be the input of one side of a comparator.
The other input of the comparator is your DC voltage.
The output of the comparator will give the fire angle,

Greetings,
Bertus

5. ### snp2411 Thread Starter Member

Mar 11, 2009
11
0
sir can u design the circuit for it and post it to me...

6. ### snp2411 Thread Starter Member

Mar 11, 2009
11
0
or do we have any IC's to do that or any websites that has this circuit design...

Apr 20, 2004
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8. ### snp2411 Thread Starter Member

Mar 11, 2009
11
0
thank you..but i need circuits which produces firing angle...which inturn improves the efficiency of the motor...can somebody help me in designing the firing circuit as in the block diagram...

• ###### triac.pdf
File size:
53 KB
Views:
37
Last edited: Mar 11, 2009
9. ### onlyvinod56 Senior Member

Oct 14, 2008
362
1
Hi
i think i can help u here right now... if u give the details of ur digital outputs of MC..
What is the supply frequency?

10. ### onlyvinod56 Senior Member

Oct 14, 2008
362
1
Use a zero crossing detector (for example MCT2E).
The pulses from ZCD can be used as interrupt signals for ur MC.
Suppose, If ur MC is giving a 3ms pulse at an instant, that cannot be directly given to the triac. Why Bcoz, if u give the 3ms pulse to triac, it conducts from 0 to 3ms (consider a 50Hz supply. time period is 20ms. half cycle period is 10ms). But if u see the operation of an AC voltage controller, when u give a pulse to the triac, it starts conducting from the instant at which the pulse is given, to natural zero point(180 degrees or 10ms here).

But your controller makes the triac to conduct from 0ms to 3ms. As usual the triac will be turned off at natural zero crossing(180 deg or 10ms). i.e., the triac is conducting for 0 - 180 and 180 - 360.
So u r not at all controlling the voltage.

So. Use a transistor logic to modify the pulse from 3ms to 10ms.

here iam attaching a small figure. check this out. If u dont get any idea, i'll send u a detailed one later

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11. ### snp2411 Thread Starter Member

Mar 11, 2009
11
0
thank you....i am getting some idea..can u post the detailed circuit...

12. ### thatoneguy AAC Fanatic!

Feb 19, 2009
6,357
725
What phase angle are the Triacs supposed to be turned on at?

Phase to Time equations:
Degrees:
$\Delta t=\frac{\theta}{2 \cdot \pi \cdot f}$

$\theta = 2\cdot \pi \cdot f \cdot \Delta t$

Angular Velocity = ω = 2πf
$\Delta t=\frac{\phi}{\omega}$

$\phi = \omega \cdot \Delta t$

Voltage at Angle:
$V=V_{Pk}\cdot sin(\theta) = \sqrt{2} \cdot V_{\footnotesize{RMS}} \cdot sin(\theta)$

13. ### onlyvinod56 Senior Member

Oct 14, 2008
362
1
what is the supply voltage and supply frequency?
I will give u the complete idea

14. ### snp2411 Thread Starter Member

Mar 11, 2009
11
0
the supply voltage is 415v and 50hz

15. ### snp2411 Thread Starter Member

Mar 11, 2009
11
0
for example, suppose the voltage to the firing circuit ranges from 0-5v then the firing angle should vary between 0-180deg...