EMRFD Message Archive 14859

Message Date From Subject
14859 2018-05-30 23:23:07 rcbuckiii Possible SMT Replacement for 2N5109
Mouser has a 2SC5551AF-TD-E transistor that has better specs than the 2N5109 except for maximum current of 300 mA versus 400 mA. It is a surface mount part and I am thinking about designing a circuit board for a feedback amp just for test purposes.

I did the calculations with 12 volts feeding through a 43 ohm resistor to the transistor biased at 50 mA. The numbers indicate the device would be dissipating right at 1/2 watt. If I have a double sided, 1 oz copper board, would a 1 inch square copper pad on top and bottom with vias provide ample heat sinking? The metal tab on the back of the device isn't very large so most of the heat sinking would have to come from the copper pads on the board. Unfortunately the data sheet isn't much help on heat sink requirements.

Mouser does have a .750 x .750 copper heat sink (567-208-75CTE) that could probably be added for additional heat sinking.

14861 2018-05-31 02:44:09 Roelof Bakker Re: Possible SMT Replacement for 2N5109

Yes, in my experience the format of your heatsink pad will be OK.

On an other note, I have used for years a BFG591 as 2N5109 replacement.
Much cheaper than the 2N5109 and a bit more sturdy that the 2SC5551AF-TD-E. 

The BFG591 is now obsolute and the BFU590 is a good replacement.

Roelof, pa0rdt
14862 2018-05-31 08:29:04 rcbuckiii Re: Possible SMT Replacement for 2N5109

Thank you for your comments. I will also test the BFU590. The heat sinking appears to be better for that part than the 2SC5551AF-TD-E.

Cost is not really the issue with the 2N5109. Finding a suitable heat sink at a reasonable cost has been a problem. I did find some on Aliexpress a while back.