# Using TRIAC for switching load

Joined Dec 23, 2021
35
Hey.Sorry for my bad English. I'm using TRIAC and Opto-Coupler to switch loads(it can be laptop charger, lamps, and etc...).
The problem is that when i plug laptop charger to output , triac will switch on by itself. anybody have any idea to fix that?
I'm using the circuit below:

#### AlbertHall

Joined Jun 4, 2014
12,202
You have the MOC3021 connected incorrectly. Below is the typical circuit from the datasheet.

Joined Dec 23, 2021
35

#### crutschow

Joined Mar 14, 2008
31,538
Low loads that may be non-ohmic, like your charger, may require a resistive load in parallel for proper operation, such as a 4 watt or greater incandescent night-light bulb.
This could also serve as a indicator that the output is on.

Joined Dec 23, 2021
35
Thanks for your answer. but i don't want to add another element on my output like 4w bulb. is there any way to simulate that on my output?(Like adding another resistor or ... ?)

#### djsfantasi

Joined Apr 11, 2010
8,792
Thanks for your answer. but i don't want to add another element on my output like 4w bulb. is there any way to simulate that on my output?(Like adding another resistor or ... ?)
…may require a resistive load in parallel for proper operation
If it does require a resistive load in parallel, how are you going to do it without adding another element?

For simulation, you could add another resistor, rated at 5-6W. You can calculate the resistance required given the voltage supplied by the supply and the current draw needed for the laptop charger to activate. That value should be on the charger’s specifications.

I use an ATX power supply which requires a >100mA current draw on its sense wire. Which is effected by a 10W 10Ω resistor.

#### crutschow

Joined Mar 14, 2008
31,538
is there any way to simulate that on my output?(Like adding another resistor or ... ?)
Yes, you could use a resistor.
But how is that different from adding the bulb?

#### LowQCab

Joined Nov 6, 2012
2,924
What is the purpose of using the Triac ?
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Joined Dec 23, 2021
35
What is the purpose of using the Triac ?
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Turning on or off 220v lamps

#### ericgibbs

Joined Jan 29, 2010
17,171
hi mn,
A Lamp is a Resistive type load.
Have you corrected the circuit as shown in post #2.?

If, yes, does it now work as expected.?
E

#### LowQCab

Joined Nov 6, 2012
2,924
A Solid-State-Relay, (SSR), is a much easier solution.
They will generally present an Input-Load that looks like an LED, ~4 to ~5-Volts at ~20ma.

And, they are available with a "Zero-Crossing" Output
so that they don't produce any Electrical-Noise when switching On or Off, or during operation.
( no Filter required, unlike an SCR )

Retail cost is around ~\$19.oo for a 25-Amp, Zero-Crossing version.
https://www.digikey.com/en/products...s=N4IgTCBcDa4MwHYCMBaAygJVUsYCsKAckQCIgC6AvkA
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Joined Dec 23, 2021
35
Sorry for late answer. Yes its work now like a charm