I worked on some transistors like BD139, BC337 and some other transisors I want to find their SMD version, I came to know that they have different numbers for SMD versions.
Is there some easy way to find an equalent transistor with SMD package?
The only easy way to do this is in the cases where they share the same datasheet, which I don’t see that they do in your examples.
It’s mainly just matching what specifications you desire and finding them with a parametric search.
In many cases there isnt a direct “SMD version” of a through-hole BJT, because the smaller package isn’t thermally competent… For industry generics such as the '5401, searching by the numerical part of the P/N will usually pull up the through-hole and SMD variants alike, along with some bycatch.
Hello saifan1,
That’s not an easy task, especially when dealing with medium power transistors such as the popular BD139.
As a starting point, let’s explore some of the device parameters for the currently produced BD139G:
-
I_{CE} Max = 1.5 A
-
V_{CE} Max = 80 V
-
P_D Max = 1.25 W in free air (25°C) or 12.5 W with an ideal heatsink to maintain 25°C
Finally, the DC current gain in in the neighborhood of 20 to 40 depending on test conditions.
Before moving on, we should recognize that designs with any longevity may temporarily stress the transistor in one dimension but not simultaneously in all dimensions. This statement is perhaps the key to finding a valid SMD equivalent.
For any given design, we must identify the performance boundaries of the transistor. Here are a few examples:
-
an industrial or automotive environment where the transistor must provide 300 mA while operating at 60°C
-
a class A headphone amplifier in a residential setting with large heatsinks
-
a motor driver with high starting current
In each case the transistor is stressed in different ways. The SMD equivalent must be selected by considering the application.
As a starting point, I generated this list of BD139 replacement candidates.
When you open the parametric search, please notice that a range of values are selected for each parameter. Instead of matching a particular parameter on a one-to-one basis, we select parameters that are in the same general range. That’s about the best we can do without more knowledge about your chosen application.
One final thought.
It’s true that thermal management is more complex with SMD devices. No longer can we just add a heatsink. Instead, the heatsink must be integrated into the PCB itself. With some creativity we can eliminate a considerable amount of heat. Please see the video link to see how a swarm of vias and SilPads may be used to solve your heat dissipation problems.
Best Wishes,
APDahlen
1 Like