An arguably better replacement for the resistor in a CRC power supply - R21 PS module

[Vunce]

@tombo56,
Initial power-up is 20V, there is approximately a 3sec delay before psu settles at the regulated 17V5. Will this short term overvoltage damage the OPA828 on Bliss?

 

[gary s]

The TI datasheet for the OPA828 specifies it can handle +/- 20VDC max - might be an idea to up R7 and R8 on the amp card from the 47R design value as insurance. See what tombo56 has to say.

Post #35 in the amp thread mentions this - 3rd paragraph.

 

[tombo56]

Post #35 in the amp thread mentions this - 3rd paragraph.

Post #2 in this thread as well. First 2.5 seconds regulator behaves as a piece of wire. This is to allow charging any large capacitors that may be in someone’s power supply, without burning MOSFET.

+/- 20 V is max. long term supply voltage for OPA828, so it would be fine. But, I see that you have changed transformer order to 2x 15.5 V. It is not necessary and 14.5 V was perfect.

 

[gary s]

If your incoming AC mains supply is high Vunce, that could be more of a problem. You might need to add some resistance in the PSU rails to drop the voltage a bit.

 

[tombo56]

As he has power hungry loudspeakers, good option would be to use higher resistor values in opamp supply and supply amplifier with 18 -19 V.

 

[gary s]

That would be the way to go. Selection of R7 and R8 in the op amp supply to suit the incoming reg VDC.

 

[Vunce]

Most of the time my incoming AC is 119V to 121V, during the summer AC mains sag to 113V to 116V.

I should be fine with increasing resistance of R7 and R8 if needed. Thanks fellas!

 

[ItsAllInMyHead]

The Forum software doesn't let you quote the immediately preceding post, regrettably. I guess it wasn't clear that #114 was a reply to #113.

If you mouse-over and select the text from any post, including one directly preceding your own, a widow should appear with the option to "Quote" that section of text. See below for an example.

 

[tubesguy]

a widow should appear

Cool, I'm ready to reenter the dating pool.

 

[ItsAllInMyHead]

^

 

[gary s]

Most of the time my incoming AC is 119V to 121V, during the summer AC mains sag to 113V to 116V.

You have fairly consistent mains then Vunce,

 

[gary s]

@tombo56, well I have bitten the bullet and ordered the parts and the pcbs for the R21 regs. As per your post #116 where you give the SUP60061EL as a substitute for the original SUP70101EL for the pos reg, you mention you will have to test with this alt Fet to determine the compensation resistor value. Can you let us know once you have tested that and also which resistor are you talking about in the schematic?

 

[tombo56]

I have to order parts to check on the bench. It is R7 that has to change value with various MOSFETs. Regulator would work well with specified 3900Ω resistor. But, it is likely not with best possible performance.

 

[gary s]

Thanks tombo, look forward to your comments after testing with the different part, will keep an eye on this thread.

 

[TNT]

The Forum software doesn't let you quote the immediately preceding post, regrettably. I guess it wasn't clear that #114 was a reply to #113.

It does if you mark some text... if you really want to be clear if you quoted the last post....

//

 

[gary s]

@tombo56, have you had a chance yet to look at the effects of the different SUP fet as you mention in post #133?

 

[tombo56]

No worries. I received them, along with another suitable replacement part for the N MOSFET, and will check soon. You can start assembly but leave R7 position unpopulated. That is likely to be the only change.

 

[gary s]

OK, thanks Tombo for the update.

 

[tombo56]

After thorough testing that included stability, transient response under severe fast varying load and PSRR, here are some approved replacement MOSFETs with corresponding component values changes:

Positive regulator:
SUP60061EL-GE
https://hr.mouser.com/ProductDetail/Vishay-Siliconix/SUP60061EL-GE3?qs=TuK3vfAjtkWzs5EzO2t/6w==
R7 – 4K7
C5 – 47 pF

C5 can be only ceramic C0G/NP0 or film type as are:
https://hr.mouser.com/ProductDetail/TDK/FG18C0G1H470JNT06?qs=qf2ddTMq67X/%2Bcf8DqHvfw==
https://hr.mouser.com/ProductDetail/WIMA/FKP2O100471D00HO00?qs=WI052HLiD5gTYAbXe/Io1g==

Negative regulator:
SQP120N10-09_GE3
https://hr.mouser.com/ProductDetail/Vishay-Siliconix/SQP120N10-09_GE3?qs=Nn1VXUNwu%2B/dh2XamFxneg==
R7 - 3K3

SUP70040E-GE3
https://hr.mouser.com/ProductDetail...s/SUP70040E-GE3?qs=eRmS5dli9yMyw65%2BBumSlg==
R7 - 2K2

At last, MOSFETs are not a problem anymore.

 

[RickRay]

WOW, Thank you Tombo! I know how much work went into vetting these replacements and appreciate it!