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naumenkov123
naumenkov123
Associate
May 12, 2018
Question

Triacs control

  • May 12, 2018
  • 1 reply
  • 973 views

Posted on May 12, 2018 at 19:44

We used BT139X-600E triac. Opto triac MOC3052 used for triac's control.  Load is 230V, 50 Hz LED lamp, current is 30 mA. Current is not very nonlinear - it is short 'pulses' in the maximum of voltage 230 V.  The triac must withstand a short-circuit current of 100 A during 10 mS. The problem is that the triac sometimes does not turn on - the reason is most likely a very small current and a large current nonlinearity. We'd like to use BTA12-600BW. Maybe someone can tell what to do in this case?

TIA

Vladimir Naumenkov

www.agat.by

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1 reply

Yannick Hague_O
Yannick Hague_O
ST Employee
May 17, 2018
Posted on May 17, 2018 at 16:47

Hello,

when using an opto-Triac, as soon as the power Triac is at ON-state, there is no more current flowing inside the opto-Triac and then no current flowing inside the power Triac gate anymore.

As a consequence, the power Triac will remain ON only if its A2-A1 current is higher than its proper Holding Current (IH) parameter.

So, with a very low power LOAD like LED 30 mA, a low IH Triac is required (but maybe even not sufficient as the current inside the lamp seems far from being sinusoidal).

ST T1610T-8FP in isolated fullpack package could be tried with Max IH at 25 °C at 15 mA (or BTA12-600TW).

The other source BT139X-600E IH is 45 mA max, typical value 4 mA, 25 °C.

OR (an maybe it is the only solution) a constant gate current must be maintained at the gate terminal.

Maintaining a gate current is requiring an auxiliary power supply linked to an opto-transistor in case isolated control is required like it is in this present case.

Let us know in case of any addition input is required.

Best Regards

naumenkov123
naumenkov123Author
Associate
May 18, 2018
Posted on May 18, 2018 at 13:30

Dear Mr. Yannick Hague, good day

Thank you.

You reported: '

OR (an maybe it is the only solution) a constant gate current must be maintained at the gate terminal.

Maintaining a gate current is requiring an auxiliary power supply linked to an opto-transistor in case isolated control is required like it is in this present case.'

Please, recommend a practice circuit with an auxiliary supply for maintaining a constant gate current

.

TIA

Sincerely,

Vladimir Naumenkov

www.agat.by

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