TO-92 Package lead isolation.

[BrunoARG]

Hello everyone.

I'm working on a project in which I'm bound to use a TO-92 triac.

I know it will sound strange, but the current I have to work with is not as high so the TRIAC being used doesn't have to be a power one. Its max RMS current is about 600mA, to drive some christmas lights (about 200 LEDs in three different triac).

Where I live AC line voltage is 220VRMS (about 317Vpeak), So I wonder if lead separation in those TO-92 triacs is enough to avoid a HV arc between them.

Should I use any kind of external insulator or is that gap enough?

Thank you very much, just ask if I didn't explain myself.

 

[D.A.(Tony)Stewart]

There exist some Triacs in TO-92 plastic cases with leads on 0.1" centres rated for 800V in the off state.

Using worst case package dimensions , some have a minimum gap of 0.72mm.

Best practice would use a silicon RTV or polyurethane coating to prevent dust and humidity absorption to raise the dielectric withstanding to 5kV/mm without air voids. Breakdown voltages in dry air can be as high as 3kV/mm but 1kV/mm in moist clean air and as low as 100v/mm in salt spray or <500V in dust "bunnies" with high RH.

So you better add conformal protection to the leads and pads if you have no better choice in case size, otherwise seal the package and hope for the best for this low consumer grade product.

It might be prudent to include an LC snubber to reduce transient line voltages as well. But then there goes your 10 cent budget.

 

[BrunoARG]

Thanks for your response.

The device is theorically designed to operate in a closed plastic box, but I am pretty sure that I'll want it to work under the rain also. Humidity may affect and decrease air resistance. The triac is designed to operate under 600V so I think its package lead separation is designed to work at that voltage.

Anyway I'll add conformal protection and it won't be a problem since I will make just one device.

Thank you for the explaination, it was really useful.