Thanks, I appreciate the input & analysis. I will take your point one at a time and see if that helps any. Also, is that simulation a file that you can/would share with me? I downloaded that program before, but haven't really figured how to use it. Would the simulation allow me to play with the values?

1. Since you do not know the type of AC load (resistive or inductive), use Zero crossing optos.
I figured that. In the past, I may or may not have tried switching stereo equipment with regular relays - yeah, not a good idea.
Still, though...I thought that using a triac was going to be zero-crossing as a matter of course, thus that the optocoupler action wasn't relevant. I have since been told otherwise, but don't really understand the explanation given thus far.

The OPTO controls when the TRIAC turns on/off. So it is the OPTO that needs to be a Zero crossing type.

2. The 3030 has a recommended input trigger current of 30mA. That is the MAX current limit for the LM3914. To avoid this, use the 3031, as it has a recommended trigger current of 15mA.
Hmm, that sounds reasonable. But I'm not going to buy any more optos. I already have these, and either the 3010s, or the 3030s were what this was designed for, although I don't know which. I currently gave the 3030s socketed in. With the stage active, the indicator LEDs are fairly bright. Is there a way to directly measure the current through that LED & the optocoupler? DMM in series?

Its ok to use 3030 if the trigger current is set to 30mA, but the LM3914 will degrade faster.
Otherwise, it may not trigger reliably.

3. The LM3914 programming resistors need to be adjusted to supply the required opto trigger currents. For the 3031, use R1=820, R2=470 (Sets IF=15mA, Vref=2v).
Can you elaborate on this for me? I see the section about current programming in the datasheet, can you kinda reframe that in...uh...layman's terms for me? Wouldn't changing that change the timing as well?

No, if set properly it won't change the timing, only the output current limit.

4. Change 100uf to 470u to further reduce supply ripple voltage.
That cap is actually a 1000uF. Once again, I already had it. Plus, I suspect that it was the original value anyway. The reason I have them, is because my father used those same caps for almost any linear power supply that he built. The fact that it fit perfectly in the pads is another clue.

1000uf is good.

 

Thanks, how do I calculate the resistors required for that current level?



The 3010s that I have are 15mA to trigger, and I said before that I had reason to suspect they were used in the original design. But they are also not zero-crossing models, so is that a deal-breaker here? I have yet to receive any explanation for this point that makes sense to me. I currently have another sequencer (see my only other thread) which used regular relays to switch triacs for the outputs, and there was never any issues with thumps and so on like a relay alone gave. The OFF behavior is really what I care about, switching it ON in the middle of a cycle I don't see as problematic (in this application) unless there's something that I'm just completely wrong about. If so, tell me, that's why I'm here.


I suppose I could always abandon the triac outputs and trigger some SSRs, which could be zero-crossing models, but I didn't want to spend $10 or $15 apiece for 8 of them. In that scenario, I don't really even need the optos anymore, so the whole original idea to make it the way it was kinda falls apart at that point.


Any further thoughts?

 

Thanks, how do I calculate the resistors required for that current level?

R1 sets the desired current limit value (15mA), so choose R1 first:

R1 = 12.5 / 0.015 = 833.33

choose the nearest standard value = 820 ohms

R2 will set VRef=2.0v combined with R1:

R2 = (2.0-1.25) / (1.25/R1) + 75uA = 477.278

choose the nearest standard value = 470 ohms

These are values for the 3031

The 3010s that I have are 15mA to trigger, and I said before that I had reason to suspect they were used in the original design. But they are also not zero-crossing models, so is that a deal-breaker here?

That's up to you.
Zero crossing refers to the method of controlling the TRIAC as an AC switch, not the triac itself.
Zero crossing control reduces EMI and surges when the AC switch opens/closes, since it only does so when the AC voltage is at or near Zero.

I suppose I could always abandon the triac outputs and trigger some SSRs, which could be zero-crossing models, but I didn't want to spend $10 or $15 apiece for 8 of them. In that scenario, I don't really even need the optos anymore, so the whole original idea to make it the way it was kinda falls apart at that point.
Any further thoughts?

You are already basically creating a solid state circuit to replace what would be a number of "stepped sequenced" relays.
The choice is yours.

 

R1 sets the desired current limit value (15mA), so choose R1 first:

R1 = 12.5 / 0.015 = 833.33

choose the nearest standard value = 820 ohms

This seems pretty straightforward....

R2 will set VRef=2.0v combined with R1:

R2 = (2.0-1.25) / (1.25/R1) + 75uA = 477.278

choose the nearest standard value = 470 ohms

This went entirely over my head. where did the 2 & 1.25 come from? Is that the V Ref out?

Why is the 75uA (that's pin 8, right?) added to the equation?

 

This seems pretty straightforward....




This went entirely over my head. where did the 2 & 1.25 come from? Is that the V Ref out?

Why is the 75uA (that's pin 8, right?) added to the equation?

1.25v=nominal Internal voltage reference value (constant)
75uA=nominal adjustment current out RefAdj pin (constant)
2.0v=the voltage to set at RefOut pin.

 

1.25v=nominal Internal voltage reference value (constant)
75uA=nominal adjustment current out RefAdj pin (constant)
2.0v=the voltage to set at RefOut pin.

I'm sorry but can you do that again a different way? If you are calculating for R, then why is the 75uA added? Wouldn't it be divided by ?
I feel like there's something very basic here that is eluding me.

 

I'm sorry but can you do that again a different way? If you are calculating for R, then why is the 75uA added? Wouldn't it be divided by ?
I feel like there's something very basic here that is eluding me.

I refer you to the datasheet. It mentions 125uA (max) but I used nominal. Here is an excerpt from datasheet: