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Power Supply Transistor Substitution (SX-950) - Verification

bayernfan

bayernfan

Active Member
Seeking verification on the following substitutions:

Replacing the following transistors on an SX-950 power supply board:

2SD313E (NPN)

2SD313E Datasheet PDF and Replacements, Transistor Equivalent Finder, Cross Reference

alltransistors.com alltransistors.com

2SB507E (PNP)

2SB507E Datasheet PDF and Replacements, Transistor Equivalent Finder, Cross Reference

alltransistors.com alltransistors.com

Would like to substitute with the following:

TIP41CG (NPN)

TIP42CG (PNP)



Replacing the following zener diodes on the same board:

WZ-140
WZ-130

Would like to substitute with:


 
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At first glance, I believe the 2 transistors look like suitable substitutes. However, the 2 zeners are 5W parts. The originals are 500mW. You’d want to stay close to that.
 
bayernfan said:
Seeking verification on the following substitutions:

Replacing the following transistors on an SX-950 power supply board:

2SD313E (NPN)

2SD313E Datasheet PDF and Replacements, Transistor Equivalent Finder, Cross Reference

alltransistors.com alltransistors.com

2SB507E (PNP)

2SB507E Datasheet PDF and Replacements, Transistor Equivalent Finder, Cross Reference

alltransistors.com alltransistors.com

Would like to substitute with the following:

TIP41CG (NPN)

TIP42CG (PNP)



Replacing the following zener diodes on the same board:

WZ-140
WZ-130

Would like to substitute with:


Click to expand...
6A is a bit overkill and those are not the right zeners. Here:

2SD313 > TIP31CG
2SB507 > TIP32CG

WZ-140 > 1N5244B
WZ-130 > 1N5243B
 
Tip 41 and 42 do work nice, I do use them in power supplies. However I bought a few hundred in bulk to get them cheap. If you're just getting what you need with a small order the cheaper ones are the way to go.
 
I already have the TIP41C/42C in stock, but I'll keep the 31/32 in mind for future.

Thanks for the correction on the zener diodes. I figured over-sizing them for wattage would be fine, I guess not. Any particular reason for this?
 
bayernfan said:
I already have the TIP41C/42C in stock, but I'll keep the 31/32 in mind for future.

Thanks for the correction on the zener diodes. I figured over-sizing them for wattage would be fine, I guess not. Any particular reason for this?
Click to expand...
Zener voltage depends on the current being pulled. A large Zener would not be sinking the correct voltage.
 
bayernfan said:
I had considered this as well, but this graph from the 5W datasheet seemed to give the impression that in the 13 to 14V range, the zener voltage was fairly independent of zener current.
Click to expand...
Still good practice. Also the 5W leads won’t even fit into the original Zener spot.
And the Zeners don’t get warm. The transistors around them do.
If you really, really want to, at least only use a 1W Zener.
 
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