H11AA1 Opto-Coupler Biasing

KatyBri

I'm planning to use an H11AA1 Opto-Coupler to sense 120 VAC and want to make sure I have the input diodes properly biased.
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The H11AA1 diode inputs will be connected across the 120 VAC line (see attachment).

The datasheet for the H11AA1 indicates a maximum continuous current for the diodes of 60 ma.
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I'll use half that as the target current, 30 ma.
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So the size of the two resistors, one on each of the two diode inputs, would be 120 VAC / 30 ma = 120 VAC / 0.030 A = 4 K ohm.
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Resistor wattage would be W = VI = 120 VAC X 0.030 A = 3.6 W
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Am I calculating these resistors correctly? Thanks

PJAllen

Any idea how hot that's going to be/get?· [noparse][[/noparse]He asked, slyly.]·
Why do you figure that you need 30ma ?
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KatyBri

I just arbitrarily chose half the max current speced. What current would you suggest? I also need to connect the output to a BS2. Should I just connect a 200 ohm resistor between the two?

JonnyMac

I've seen several reference designs using that part with two 15K, 5W resistors and have used that circuit in my own designs -- works fine. I've connected the circuit to an SX chip to provide zero-cross indication for lighting controller boards (see my column in the November issue of Nuts & Volts magazine).

Connect a pull-up to the output; you'll get a short, high-going pulse every 8.33 milliseconds (this happens near the zero-cross point when the voltage input falls below the LED threshold and the transistor stops conducting).

Post Edited (JonnyMac) : 12/8/2007 1:37:28 AM GMT

KatyBri

Thanks for your help, JonnyMac.

datacps

Jon where is the info on the light dimmer and how you use the opto for the zero crossing . I need to use the opto I think in the same way for my Inverter project.. I tried finding the Nov Nuts and Volts but I could not find it. Is it posted in the SX forum in the best threads. I looked around and could not find it.. Thanks

PJAllen

It's probably too soon for that article to be available as a Download.· (Maybe your library has a subscription to N-&-V.)

JonnyMac

See attached.

datacps

Jon
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"I've connected the circuit to an SX chip to provide zero-cross indication for lighting controller boards"

I would like to use it to read·load changes·like a ·AD convertor and send the value to the SX Comp as a load feedback for my Inverter project. It will isolate my circuit and provide load change feedback to the SX48 to adjust my PWM....

When my inverter is first turned on I can read both diode values and the have the program pick the better input of the two.. Then I can just look at every half cycle and look for the load changes·so·I can adjust the PWM to the load on the inverter leads..

Thanks

JonnyMac

It seems that you would want to put an inductive loop on your output (provides isolation), rectify and filter it, and then measure (or connect it to the comparator).

datacps

Thanks JMac

I have it like in the first·Sche and I saw the opto connected·like the second Sch. I just don't know how they did it but it does work with the opto conected like that.. I am going to look at the output of the opto that is going into the Chip.. I will look at it and see but if I can't figure it out I will use the transformer and the AD chip....Thanks again