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Can we fire a triac using 8051 ?

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baileychic

baileychic

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Can we fire a triac using 8051 ?

I want to use 8051 (AT89C51) to control o triac. I have used AT89C2051 to control triac but in that the VDD of AT89C2051 was 230V and GND was 5V less than 230V. That circuit was not designed by me but provided by my client. For that I had to write code to fire triac in 2nd and 3rd quadrants. Also 8051 series MCUs cannot detect rising edge of ZCD signal.

I want to know whether using AT89C51 with pullup resistors on P1, 2 and 3 can we fire triac in all quadrants ?

If I want to fire triac without opto triacs then I have to make VDD 230V and GND (230V - 5V), right ?
 

Useable quadrants depend on the triac type. You want to read the datasheets. Negative trigger current as in the sketched design is required for standard triacs.
 
Voltages are relative, as long as the triac has sufficient gate to A1 voltage it will fire, no matter what the absolute voltages above ground are.

Yes, as long as the output voltages at P1, P2 and P3 are high enough it should work but beware that those output voltages are relative to VSS and the three triacs may not share a common connection with VSS.

Any MCU can detect zero crossing with a suitable interface. Zero crossing point is detected by the absence of voltage, again all you need to ensure is the detector output is relative to VSS.

I'm not sure what your application does but firing in all quadrants would be difficult even with the original plan, opto-isolators make it safer and easier to implement.

Brian.
 
Hi,

Many others have done this before.
There are schematics as well as code in the internet.
Choose a reliable document and then go step by step.

If you encounter any problem, please give us (the link to ) the document you refer to.

Klaus
 

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