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Triac Gate sensitivity

belkzak

New Member
Hi Electronics Guys,
I hope that you are all doing well,
Among a validation plan of my triac, I need to perform a Gate sensitivity triggering test at some defined levels (triggering currents), would you please advise an appropriate circuit to do that?

Thank you in advance
 

rjenkinsgb

Well-Known Member
Most Helpful Member
Testing is simple - a variable resistor to the gate from a fixed voltage source, or a fixed resistor from a variable voltage source.

Put scope leads on the gate an A1 (the load terminal) and watch the effect as the gate is switched, increasing the current until you get reliable triggering.

However, the trigger effects will be dependant on the load, especially if inductive - and vary from device to device.
Even if you test a hundred devices, you never know if the next is slightly different.

That's why the manufacturers supply datasheets with the possible maximum and minimum of each parameter.
 

crutschow

Well-Known Member
Most Helpful Member
For ease of testing, apply a small 50-60 AC signal through a small resistor (to get an anode current above its minimum hold current), to the Triac Anode.
That will reset the Triac every half cycle so you can see the triggering sensitivity in both quadrants (it's likely different in each).
 

belkzak

New Member
Testing is simple - a variable resistor to the gate from a fixed voltage source, or a fixed resistor from a variable voltage source.

Put scope leads on the gate an A1 (the load terminal) and watch the effect as the gate is switched, increasing the current until you get reliable triggering.

However, the trigger effects will be dependant on the load, especially if inductive - and vary from device to device.
Even if you test a hundred devices, you never know if the next is slightly different.

That's why the manufacturers supply datasheets with the possible maximum and minimum of each parameter.
I have used a variable resistor to the Triac gate with a 5v square wave signale generator,
I am getting something weird, each time I decrease the resistance in order to get the sufficient current for triggering,Triac keeps getting triggered even when I slightly increase the resistance (decrease current) till I get to a specific value.

Do you know what is exactly this phenomenon?

See these two pictures taken during the test.Screenshot_2021-06-03-16-59-46-51.jpg
IMG_20210603_165908.jpg
 

crutschow

Well-Known Member
Most Helpful Member

crutschow

Well-Known Member
Most Helpful Member
If V2 is line voltage that is not isolated, that is a dangerous setup.
 

crutschow

Well-Known Member
Most Helpful Member
Please how do you isolate it
You need a transformer with the secondary isolated from the primary (not an autotransformer or Variac).
 

alec_t

Well-Known Member
Most Helpful Member
Is your ammeter designed to give accurate readings of square-wave current?
 

belkzak

New Member
If V2 is line voltage that is not isolated, that is a dangerous setup.
Could you please explain how it can be a dangerous set-up? I'm fact i have tried with this experiment several times, and in some cases i get my circuit breaker shutting down, but other cases it works. Is it about which line wire is connected to MT1 ?
 

belkzak

New Member
Testing is simple - a variable resistor to the gate from a fixed voltage source, or a fixed resistor from a variable voltage source.

Put scope leads on the gate an A1 (the load terminal) and watch the effect as the gate is switched, increasing the current until you get reliable triggering.

However, the trigger effects will be dependant on the load, especially if inductive - and vary from device to device.
Even if you test a hundred devices, you never know if the next is slightly different.

That's why the manufacturers supply datasheets with the possible maximum and minimum of each parameter.
Thank you for your reply,
I have attached the datasheet download from the website, my triac is Q8016RH4, could you please tell me what is the the minimum and maximum triggering current from the datasheet? is 35mA maximum or minimum?
 

rjenkinsgb

Well-Known Member
Most Helpful Member
35mA is the minimum current to guarantee firing under the other conditions given in the datasheet.

Note that specific part is a "three quadrant" device and will not fire in quadrant 4; ie. with gate positive of MT1 while MT2 is negative of MT1.
To guarantee firing with both MT polarities, the gate must be drive negative of MT1 or to the same polarity as MT2.

The peak gate current is in the "Absolute maximum" ratings section; 2A for 10uS.
 

belkzak

New Member
35mA is the minimum current to guarantee firing under the other conditions given in the datasheet.

Note that specific part is a "three quadrant" device and will not fire in quadrant 4; ie. with gate positive of MT1 while MT2 is negative of MT1.
To guarantee firing with both MT polarities, the gate must be drive negative of MT1 or to the same polarity as MT2.

The peak gate current is in the "Absolute maximum" ratings section; 2A for 10uS.
according to the experement that i have done, the triac has fired with only 10mA!!
Besides, can you explain what is this Igt in the following table ?
Captureqq.PNG
 

rjenkinsgb

Well-Known Member
Most Helpful Member
according to the experement that i have done, the triac has fired with only 10mA!!
The datasheet figure is the current required to guarantee firing for any device with that part number.

The datasheet covers many different types in a range & the part you show is an overview of the whole range.
The exact information is given for each individual type in the detailed specifications.

See the table on page 3 of the datasheet - "Electrical Characteristics (TJ = 25°C, unless otherwise specified) — Alternistor Triac (3 Quadrants)"

That gives the maximum gate current that could be required to guarantee firing, for each sub-type of the triac.
You say yours is the H4 suffix type, so that is in the column for 35mA

The gate current needed will vary from device to device and probably also on what quadrant is being tested - see the info at the lower left of page 3.

That's why the manufacturer provides data, so you can design a circuit that can provide the correct current or any parameters, to guarantee operation with any device ever made under that specific part number.
 

belkzak

New Member
Is your 100 Hz ( why 100 Hz?) source Synced to the Mains 50 Hz? If not, you will get non consistent readings. Remember that the Trigger current is also dependent on the voltage across the Triac.
100 hz is just a random frequency chosen, and no, it is not synchronized, i don't see why should it be, the purpose of the test is just to detect at will current value will the Triac trigger.
One more question, how can the voltage across MT1/2 affect Igt?
Thanks.
 

belkzak

New Member
The datasheet figure is the current required to guarantee firing for any device with that part number.

The datasheet covers many different types in a range & the part you show is an overview of the whole range.
The exact information is given for each individual type in the detailed specifications.

See the table on page 3 of the datasheet - "Electrical Characteristics (TJ = 25°C, unless otherwise specified) — Alternistor Triac (3 Quadrants)"

That gives the maximum gate current that could be required to guarantee firing, for each sub-type of the triac.
You say yours is the H4 suffix type, so that is in the column for 35mA

The gate current needed will vary from device to device and probably also on what quadrant is being tested - see the info at the lower left of page 3.

That's why the manufacturer provides data, so you can design a circuit that can provide the correct current or any parameters, to guarantee operation with any device ever made under that specific part number.
Under what circumstances the triggering current will take it's maximum value ?
Thanks
 

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