Controlling antiparallel SCRs using Arduino

Using Arduino Project Guidance
1

Hello,

I have an existing circuit which is completely analog in nature that I would like to convert to digital using Arduino Uno R4 Minima. This is a single phase AC power controller using SCRs (Thyristors) connected in antiparallel fashion. The firing signal from the Arduino will be sent to a TIP122 darlington transistor which controls a pulse transformer as shown in the attached picture. I know that this Arduino Uno R4 Minima has one DAC pin which I was planning on using. My question is, does the signal to the base of the TIP122 transistor need to be pulsed (PWM) or an analog signal from the DAC pin output be enough to control the SCRs?

G1, K1, G2, and K2 are the gates and cathodes of SCRs 1 and 2 respectively.

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2

The transformer will stop the DC, it needs to be pulsed so the transformer can transfer energy from the primary to the secondary.

3

Why the dac? You need a digital signal ( synchronyzed with the ac mains I suppose, at double frequency )

4

That makes sense. I have one more question. To send the pulse in my specific example, does it matter if I use analogWrite or digitalWrite as I show in the following code? They both yield the same result. Is one better than the other?

  analogWrite(scrTrig, 255);                    //output high pulse for scr
  delayMicroseconds(500);                     // Pulse width for SCR trigger
  analogWrite(scrTrig, 0);                        // Stop triggering SCR

  digitalWrite(scrTrig, HIGH);
  delayMicroseconds(500); // Pulse width for SCR trigger
  digitalWrite(scrTrig, LOW);
5

These two statements are equivalent:
analogWrite(scrTrig, 255);
digitalWrite(scrTrig, HIGH);

As are these:
analogWrite(scrTrig, 0);
digitalWrite(scrTrig, LOW);

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