SSLtech PSU question

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jrmintz

Well-known member
Joined
Jun 4, 2004
Messages
998
Location
NY
Hi All,

Would it be normal to have about 70V DC before the LM317T regulator on the phantom rail of the SSLtech power supply? Does that sound right?

Also, is there an out-of-circuit method for checking regulators like LM317 ot 78xx?

Thanks,
 
No real out-of circuit method that I know about, other than checking for shorts...

Since it's multiplied a little more efficiently in my 'full-wave' version that the more common '½-wave' version, an unloaded transformer (i.e. unloaded even on the ±18V rails) will likely stray a little higher. -If there's ever an issue, you can tuck a series resistor in the input line, just to share the load...

Keith
 
Thanks, guys. I'm using just the phantom and positive rails with a 25-0-25 transformer for +24V to power some Neve-type pres and I think I popped the LM317 with a bit of particularly deft probe work. Under the circumstances, maybe it would be a good idea to use a series resistor. The data sheet says imput-to-output voltage can't exceed 40V and this is well within that. Maybe it's just a bit stressed - I certainly am.
 
My 18-0-18 transformer becomes rectified to 27-0-27VDC. So it's roughly 1.5x. My 48V section is about 47.9V.

I think your 25-0-25 transformer is too high. Your 25-0-25 transformer will become 37-0-37VDC after rectification and filtering. For the 48V section, that becomes 37x2 = 74Volts before regulation.... and according to you, you're measuring roughly 70Volts right?

I think you need to use a lower rating transformer. I ordered some 15-0-15 trafo because even with my 18-0-18 transformer, the regulators become hot and there's not enough clearance in the PCB for 3 heatsinks. I'll let you know how the new transformer pans out.
 
Thanks Owel,

That's a really good point. I have an 18-0-18 toroid that I was thinking about putting in. Maybe I'll go ahead and try that - it might be less stress on both regulators. Please let me know how you make out.
 
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