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8 bit digital firing circuit of triac

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schnd

New Member
freinds, Iam trying to work on a firing circuit of TRIAC. I have the circuit but iam not able to analyse the circuit as i have many doubts in it.I will provide a link for the circuit and help me clearing my doubts....
1) Why is the input thru DIP switch grounded?
2) how is the firing pulses controlled thru 8 bit data entered.
3) what role does OR gates play for generation of output?

Thyristors-SCRs_and_Triacs
 

ccurtis

Well-Known Member
1) Why is the input thru DIP switch grounded?
2) how is the firing pulses controlled thru 8 bit data entered.
3) what role does OR gates play for generation of output?


I can't see the right-hand side of the schematic so I am going to ASSume that the right-hand side contains the second counter and its OR gates.

The DIP switches set the binary value that gets loaded into the counters when a load pulse appears. There should be pull-up resistors to hold an input high when a DIP switch is open, but they are not shown.

Since the counters will count down on each clock pulse from the timer IC, the binary value that gets loaded determines how long (how many clock pulses) the trigger pulse for the triac will occur after the load pulse loads the counters.

The OR gates decode the outputs of the counters so that the triac will fire after the counters reach the zero count. All those OR gates are unnecessary since the counters have borrow out outputs which can be used to decode the zero count.

I don't understand what the role of the triac is, however.
 

schnd

New Member
thats ok i think OR gates are not for decoding. The output data is already decoded na.
can u explain the relation between load pulses and clock pulses??
plz
thnks in advance for ur kind help
 

ccurtis

Well-Known Member
thats ok i think OR gates are not for decoding. The output data is already decoded na.
can u explain the relation between load pulses and clock pulses??
plz
thnks in advance for ur kind help
I can't see how load pulses are generated, so I can't answer your question. I don't see anything connected to the left side of the transformer. Unless the firing of the triac somehow generates the load pulses, there is no timing relationship between the load pulses and the clock pulses since the timer is free running. As the shematic is drawn, with nothing connected to the left side of the transformer, or no voltage source connected to the right side of the transformer, the triac will never conduct. Assuming the timer is connected as a proper astable multivibrator its output frequency is 18 Hz with a 7 ms negative going pulse, high most of the time. I can't tell what the frequency of the load pulses is since I can't see anything that generates them.
 

schnd

New Member
"I can't see how load pulses are generated, so I can't answer your question. I don't see anything connected to the left side of the transformer. Unless the firing of the triac somehow generates the load pulses, there is no timing relationship between the load pulses and the clock pulses since the timer is free running. As the shematic is drawn, with nothing connected to the left side of the transformer, or no voltage source connected to the right side of the transformer, the triac will never conduct. Assuming the timer is connected as a proper astable multivibrator its output frequency is 18 Hz with a 7 ms negative going pulse, high most of the time. I can't tell what the frequency of the load pulses is since I can't see anything that generates them."

transformer is connected to 220 v AC supply and the transformer is a 220v/6-0-6v transformer.The load pulses are generated by transistor parts and signal is transferred to counter as load pulses.I think load pulses are generated to fire the triac. the firing of triac donot generate any load pulses. Plz tell now the operation of load pulses.
 

ccurtis

Well-Known Member
The load pulses are occuring at a rate (60 Hz) greater than twice that of the clock pulses (18 Hz) and there is no defined timing relationship between those two sets of pulses.

Therefore, the triac will not conduct unless the counters are loaded with a zero (or possibly a one) to begin with, which makes the whole circuit sorta useless? :confused:
 
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