BT139 without heatsink max current

[xyz9915]

Hello all,

I am using Triac BT139 in a circuit where the heatsink can not be added due to space limit. So please help me that how much maximum current can be taken without using the heatsink. The triac is 16 ampere rating and mains voltage is 220V/50Hz

(note: datasheet attached)

 

[crutschow]

OK, a little data sheet tutorial.

The data sheet states the thermal resistance of the case without a heatsink in free air gives a junction-to-ambient temperature rise of 60°C(K)/W. The maximum (Limiting) operating junction temperature of the device is stated to be 125°C. Thus the allowable power dissipation depends upon the ambient temperature. If we assume a hot day and the ambient at the device gets to 40°C then the maximum allowed temperature rise is 125 - 40 = 85°C. This gives an allowed power dissipation of only 85/60 = 1.4W

Now looking at the left side of Figure 1 you can see that the power dissipation reaches 1.4W at perhaps 1A at a 180° conduction angle, so that is your limit.

If you want to go higher than that you will need to add a heatsink. Can you attach it to the metal case or chassis of whatever you are building?

 

[xyz9915]

Dear crutschow lot of thanks for quick reply & for the help. There is no space so it can't be mounted over chassis. I want a minimum current 3 amperes so is there any solution?

 

[ronsimpson]

I think Cutschow answered your question. 1A with out a heat sink.
A second way is to look at graph 10. It shows that a typical part under 3A load will have 0.8 volts across the part. (3x0.8=2.4watts) and a worst case part will have 1.35 volts across it. (3x1.35=4watts) Because you don't know if the next SCR you pick typical or worst case you need to design for worst case. 4 watts of loss is 3 times more than the 1.4 watts Cutshow said you can withstand.

At 1.4 watts the die is at 125°C!! This is at the breaking point. It is not a good idea to run the part "at the read line". Do you drive your car with the "hot light" on or the temperature gauge at far right? Do not run the part at 125°C (internal temp)! It will die. Maybe not this week but it will fail.

 

[Grossel]

Hi.

Without a picture or any other information I just throw out this thaught:
What about to move the triac to outside of casing, and just using three wires to connect it to the printboard?

 

[ronsimpson]

The BT139 will control 360 watts and loose about 3 watts. That makes the switch 99% efficient.

 

[crutschow]

Dear crutschow lot of thanks for quick reply & for the help. There is no space so it can't be mounted over chassis. I want a minimum current 3 amperes so is there any solution?

Not if you need to use a Triac. I'm afraid you've painted yourself into a corner.

 

[ronsimpson]

Not if you need to use a Triac. I'm afraid you've painted yourself into a corner.

Cutschow, Think positive. Add freon coils. Water cooled radiator. At 125 degrees; convert water to steam. There must be a hundred things to do. Heat sink?

 

[xyz9915]

I am again thankful to ronsimpson, crutschow & others.

In my opinion it is concluded that in a free space BT139 can not deliver 3 amperes without using a proper heatsink. But in my project, I don't have enough space/chassis to mount the triac , so i have no option except stop building the circuit.