Replacing NPN Transistors that failed with similar/better?

Question

I have done some research about this before hand(https://www.electronics-notes.com/articles/electronic_components/transistor/choosing-replacements-transistors.php). I have a switching 12v dc power supply that had been running perfectly fine for several months until it failed during a rather hot day. The power supply is passively cooled(although it will be actively cooled after I reassemble everything). Once the failure occurred, I tested the components, no bad shorted or bulged capacitors. Only failure was two e13007-2 npn transistors on the input side of the circuit(most likely heat related, as through my research that is their most common cause of failure). Replacing is not physically difficult, and with active cooling I probably could replace them with the same transistor but I am having a hard time finding it available for delivery anytime in the near future.

Since I am not too familiar with npn and pnp transistors, I am asking; would the similar, more available, 13009 npn transistor be an acceptable replacement for the e13007-2 transistor?

Answer 1

Only the designer of the power supply can tell you if you can also use a different type of transistor. Also even that designer might have to do some checks before (s)he can guarantee that it will work.

In a properly designed circuit usually the exact model of transistor doesn't matter too much as long as they're at least similar. So similar maximum voltages and current, similar beta etc. Those e13007-2 and 13009 do look "somewhat similar" in my opinion so probably you can use the 13009 and that might just work. But no guarantees!!!

Indeed improving the cooling is a good idea after the failure on a hot day.

Answer 2

MJE13007 , Ic=8.0 A, Vceo=400 V, 80W @ 25'C Rce ~ 600mΩmax =3V/5A @Tc=25'C Ic/Ib=5

MJE13009G Ic=15 A, Vceo=400 V, 100W @ 25'C Rce ~ 240mΩmax 1.2V/5A @ Tc=25'C Ic/Ib=5

PHE13007 $0.66 Ic=8A Vceo-400V, 80W @ 25'C Rce ~ 400mΩmax 2V/5A @ Tc=25'C Ic/Ib=5

2SC5071 $3.19 Ic=12 A, Vceo=400 V, 100W @ 25 Rce ~ 186mΩtyp 1.3V/7A @ Tc=25'C Ic/Ib=5

I might consider >5A ripple , low ESR Caps with a soft start ICL

Answer 3

MJE13009 does seem to be similar or marginally better replacement than the E13007-2 or MJE13007.

However, the MJE13009 may require a bit more base current to go into saturation (Figure 6. Collector Saturation Region). Considering that your previous transistor failed due to overheating, you may want to check the driver circuit for the base current it is providing for the switcher at the peak switching current (or try to simulate it by figuring out the full circuit).

Alternately, you could try to put it into an enclosure and try to measure the max temperature reached. [High voltages are involved so caution is advised.]

Either way, active cooling should help a lot.