Thoughts on my Dual Channel Dimmer Schematic?

Thread Starter

mriksman

Joined Aug 31, 2010
113
Hey Guys,

I'm interested to see what some experts think about my schematic before I get the circuit board made.

I have previously tested the photo-voltaic MOSFET drivers and the low-power ZCD circuit. They operate well, and give me really good dimming waveforms.

I've now added power monitoring using a DC-DC converter to isolate the power supply required for these ICs, and added opto-isolation. The power monitoring ICs output in pulses.

Is there any simplifications that could be done? Things that could be done better? Note I am REALLY out of space on my circuit board, so I'm limited to what I can add (unless a clever idea can remove some components).

Thanks.
 

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Thread Starter

mriksman

Joined Aug 31, 2010
113
Not sure I understand the difference. A quick Google shows examples that makes me believe mine is a ‘schematic’, and not a ‘wiring diagram’.

But, I don’t really care what it’s called :)

I’m interested in
  • The circuit for the power monitoring and the isolation/5V power. Any glaring issues? (As this is the new addition to my previously tested device)
  • Anything seem dangerous? Have I isolated the HV side from the LV side enough? Too much/unnecessary?
  • Any tips on simplifying any of it?
  • Any helpful ideas at all?
  • Any constructive comments?

Thanks.
 

MisterBill2

Joined Jan 23, 2018
13,773
There certainly is a whole lot more functionality to the circuit than "just a dual dimmer" would have. I did not evaluate or analyze what it is doing, but certainly it is a lot. A basic single dimmer has no more than five components, unless it is controlled by an analog voltage circuit or a digital computer.
So to even have an opinion about this circuit a description of the intended functionality will be needed.

I would not call the drawing a wiring diagram, but rather a circuit schematic. There are places that might be improved a small bit, but not worth doing a redraw. The signal/power flow is reasonable as well.
Overall it is a medium complexity circuit that needs to be explained because it is much more than just a dimmer.
 

aristo

Joined Feb 12, 2011
2
A quick look at the DataSheet for HLW8012 shows 6 x 470k resistors connected to Neutral, your circuit shows only 5 that are connected to Neutral, Is this intentional ?
If there is enough room on the PCB, I would recommend each HLW8012 has its own set of 470k resistors rather than commoned.
 

Thread Starter

mriksman

Joined Aug 31, 2010
113
A quick look at the DataSheet for HLW8012 shows 6 x 470k resistors connected to Neutral, your circuit shows only 5 that are connected to Neutral, Is this intentional ?
If there is enough room on the PCB, I would recommend each HLW8012 has its own set of 470k resistors rather than commoned.
Yes it is. Sonoff only use 5. When you do the math, I think 5 gives you a measurable range of ~960VAC. More (way more) than is required.
Why would you go separate? Considering Neutral is common between the two..?
 

RPLaJeunesse

Joined Jul 29, 2018
222
Have you looked at power MOSFET dissipation during turn-on and turn-off times? Note that the data sheet specs those times as typical at Cl=1000pF. Worst case over production and temp could be considerably longer, and the effective MOSFET input capacitance will surely be different. Not a simple task, unfortunately, but you don't want the power transistors to let any magic smoke out.
 

Thread Starter

mriksman

Joined Aug 31, 2010
113
I have chosen MOSFETs with Ciss of 555pF and low Rds, have limited total current to 1A (fuse is 2A and I have power monitoring), and am using it as a trailing-edge dimmer; the turn-on time (the slowest part due to the photovoltaic drivers) doesn't matter as it turns on at zero crossing. The turn-off time isn't too bad; ~30-40uS. So, all up, I think I should be safe from overheating.
During operation, these are barely warm to touch on the 10W LED drivers I have attached. I haven't tried a 1A/240W load yet however.
 
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