Using a triac MAC97A with Arduino

The opto-triacs are exactly what I meant - BUT - they are not intended to directly control the load and should not be used that way. Look at the data sheet, it shows how to use them as a triggering device for a bigger triac such as the ones you already have. Note also that MOC3020 devices are 'random phase', it doesn't stop you using them but one of the MOC3040 range will work better. They have a circuit inside them that stops them switching on until the next AC zero crossing occurs whicm means less strain on the main triac and less interference.

Brian.

betwixt said:

The opto-triacs are exactly what I meant - BUT - they are not intended to directly control the load and should not be used that way. Look at the data sheet, it shows how to use them as a triggering device for a bigger triac such as the ones you already have. Note also that MOC3020 devices are 'random phase', it doesn't stop you using them but one of the MOC3040 range will work better. They have a circuit inside them that stops them switching on until the next AC zero crossing occurs whicm means less strain on the main triac and less interference.

Brian.

Click to expand...

According to the data sheet those particular devices have a max output rating of 1A AC. The solenoid valve I have has a max draw of 200-300mA AC.
So they should be fine unless I am missing something.

My MOC302x series data sheet does not quote a triac current but does say: "NOTE: This optoisolator should not be used to drive a load directly.
It is intended to be a trigger device only."

For the MOC304x series it quotes a maximum current of 1A for 100uS at 120 pulses per second (60Hz), that isn't the same as continuous load and it refers to the pulses for triggering the gate of a bigger triac. Note that when wired as described in the data sheet, as soon as the main triac conducts, the voltage across the MOC is effectively shorted out so it's dissipation is very small.

Brian.

betwixt said:

My MOC302x series data sheet does not quote a triac current but does say: "NOTE: This optoisolator should not be used to drive a load directly.
It is intended to be a trigger device only."

For the MOC304x series it quotes a maximum current of 1A for 100uS at 120 pulses per second (60Hz), that isn't the same as continuous load and it refers to the pulses for triggering the gate of a bigger triac. Note that when wired as described in the data sheet, as soon as the main triac conducts, the voltage across the MOC is effectively shorted out so it's dissipation is very small.

Brian.

Click to expand...

It does? Are you looking at the same datasheet as I am? Perhaps you should post your data sheet so I can compare it with the one I have.

Hi,

It does? Are you looking at the same datasheet as I am? Perhaps you should post your data sheet so I can compare it with the one I have.

Click to expand...

My personal opinion:
It is the OP´s job to provide (the links to) the datasheets.
This reduces time for those who want to help you (for free) and avoids confusion.

Klaus

KlausST said:

Hi,


My personal opinion:
It is the OP´s job to provide (the links to) the datasheets.
This reduces time for those who want to help you (for free) and avoids confusion.

Klaus

Click to expand...

No problem Klaus. This is the datasheet I am looking at. I am not seeing where it says anything about not driving a load directly from them.

That particular datasheet doesn't mention the load but it does imply it is unsuitable for your application.
Look right in the middle of Page 5:
"Peak repetitive surge current. PW=1mS, 120pps"
Under the "Absolute Maximum Rating" section.

It can handle 1A absolute maximum for 1mS repeated at a rate of 120 pulses per second. That is a specification for producing pulses to trigger a bigger triac, not for continuous conduction. 120 pulses per second is equivalent to zero crossing rate for a 60Hz waveform.

You CAN use it as a main triac but the continuous current rating isn't specified, I would guess it is somewhere in the region of 40mA to 50mA. Its also likely you will have problems with dv/dt ratings if the AC contains any spikes.

Brian.

betwixt said:

That particular datasheet doesn't mention the load but it does imply it is unsuitable for your application.
Look right in the middle of Page 5:
"Peak repetitive surge current. PW=1mS, 120pps"
Under the "Absolute Maximum Rating" section.

It can handle 1A absolute maximum for 1mS repeated at a rate of 120 pulses per second. That is a specification for producing pulses to trigger a bigger triac, not for continuous conduction. 120 pulses per second is equivalent to zero crossing rate for a 60Hz waveform.

You CAN use it as a main triac but the continuous current rating isn't specified, I would guess it is somewhere in the region of 40mA to 50mA. Its also likely you will have problems with dv/dt ratings if the AC contains any spikes.

Brian.

Click to expand...

I missed the word 'surge'. Then what would you do with such a device? Can I drive my T092 triacs with them?

The absolute ratings are not usually to be used in designs; but if you want this pulse to drive a relay, you may need a latch.

Hi,

Then what would you do with such a device? Can I drive my T092 triacs with them?

Click to expand...

In the applications setion of the datasheet it says:

* For triggering high power thyristor and triac.

Click to expand...

and on page 9 you see the "Basic Operation Circuit"

I agree, that the Liteon datasheet is not very informative.
Thus I recommend to look at the ONSemiconductor site: https://www.onsemi.com/PowerSolutions/product.do?id=MOC3020M
There is a more detailed datasheet.
And please - have a quick - look through the three application notes.

Klaus

KlausST said:

Hi,


In the applications setion of the datasheet it says:

and on page 9 you see the "Basic Operation Circuit"

I agree, that the Liteon datasheet is not very informative.
Thus I recommend to look at the ONSemiconductor site: https://www.onsemi.com/PowerSolutions/product.do?id=MOC3020M
There is a more detailed datasheet.
And please - have a quick - look through the three application notes.

Klaus

Click to expand...

Thankyou for that. Triacs are not quite as simple to use a regular transistor......more components required.

Thankyou for that. Triacs are not quite as simple to use a regular transistor......more components required.

Click to expand...

When being used to switch inductive loads, yes that's true.
Remember that unlike a normal transistor they work on AC and require the trigger voltage (think of it a bias current in a BJT) to change polarity to turn them on, depending on the polarity across the device as a whole. That is one of the reasons a diode in series with the gate cannot possibly work as it would restrict operation to only half cycles.

Brian.

Hi,

I think triacs an bjts are about similar simple.
(As long as you compare apples with apples)

The benefit of a triac is, that it can control (switch) AC...

For ohmic loads.
* a bjt needs just a current limiting resistor to the base
* a triac needs just a current limiting resistor to the gate

For inductive loads:
* a bjt needs additional overvoltage protection
* a triac needs additional overvoltage protection.

For phase control (triac) and PWM (bjt):
* the bjt just needs a PWM generator
* the triac additiinally needs a ZCD to synchronize gate trigger with mains frequency (variably delayed)

For a dimmer:
* a triac doesn't need a PWM generator. It uses a RC delay line combined with a diac. All in all: a triac, diac, R(pot) , C...for a dirty function.
* a bjt needs the complete PWM generator... not much, but a bit more complicated than the circuit for tge triac.

When you want yo build an AC motor control with a triac .. you need extra parts..
But still less than an AC motor control with bjt...

On the other side you can't build a DC motor control with a triac, but it's easy with a bjt...

Klaus