Benchtop Power Supply Question

[eccerr0r]

Well, the CMOS TLC555 can go down to 2v or so, if needed?

[redwire]

You need a reference voltage for the comparators, not sure what he's using for that. Hitachi 555's are pretty ooollldddd

[jiroy]

I have almost finished a diagram's prototype for the laptops PSU project . So far , my choice went for a parallel series of LM338 , backed up by parallel diodes as illustrated in an image previously , while leaving a chance for additional ones , as necessary . Right now , I estimate LM338 power at 5A maximum , to stay on safe side , and for each another 5A , I'll add another one ..

When the project is finished , although the delays and distractions were more than to count , It will be available only for some particular friends , and through PM's .

In the meantime and for the people who liked my backups parts , my Sony Cam is back on line after some repairs , so I may re-post the previous images which were very bad , and yet , you know there are some size limits for uploads , so I'll resize them in PS as necessary .
Here's a sample of my vintage capacitors .

[stj]

that picture looks like my dustbin after a repair

parallel high current diodes doesnt work btw,
the one with the lowest voltdrop takes more of the current - then fails leaving the remaining ones overloaded.
then they fail.

happens all the time in some cheap tv psu's that try to do it.
also kills a lot of early Ryobo battery chargers

[jiroy]

Originally Posted by stj

that picture looks like my dustbin after a repair

Come on stj; I'm in the middle of hundreds of projects , including a 30 km FM transmitter , and the picture's background initially should look vintage

Originally Posted by stj

parallel high current diodes doesnt work btw,
the one with the lowest voltdrop takes more of the current - then fails leaving the remaining ones overloaded.
then they fail.

I really doubt that when they're each rated 6A. and fyi , they'll be equipped with special heatsinks similar to old CRT monitors ...
So you deserve another ...lol

[jiroy]

@stj;

That's how my dust bins look like ,

[megaraider]

Originally Posted by jiroy

Come on stj; (...) and the picture's background initially should look vintage

Originally Posted by stj

parallel high current diodes doesnt work btw,
the one with the lowest voltdrop takes more of the current - then fails leaving the remaining ones overloaded.
then they fail.
happens all the time in some cheap tv psu's that try to do it.
also kills a lot of early Ryobo battery chargers

Originally Posted by jiroy

I really doubt that when they're each rated 6A. and fyi , they'll be equipped with special heatsinks similar to old CRT monitors ...
So you deserve another ...lol

In practice what @stj claims is TRUE! You'll watch this behavior when the overall current exceeds the maximum rate per diode (plus a unknown value).

[jiroy]

Originally Posted by megaraider

In practice what @stj claims is TRUE! You'll watch this behavior when the overall current exceeds the maximum rate per diode (plus a unknown value).

It's like pushing me to reveal more secrets I would prefer to keep it hidden!! Well fine megaraider ... How the overall current would know which one is the first when the special heatsink is making them symetric with high precision ? .
Yet , I do agree that if something is arranged chaotically , of course it will rise many different problems ..

[eccerr0r]

The trick is to either go ahead and match them else current limit them, just like bjts.

[megaraider]

Originally Posted by jiroy

It's like pushing me to reveal more secrets I would prefer to keep it hidden!! (...) the special heatsink is making them symetric with high precision ? .

No secret ... IMO a great mistake.
The heatsink, no matter how 'special' it is, only works to keep the diodes under temperature limits, and if common to keep them all at about the same temperature.
Nothing else, sorry!

Originally Posted by eccerr0r

The trick is to either go ahead and match them else current limit them, just like bjts.

Yes!

[stj]

why not just use a 25A rectifier from an old pc psu?

[jiroy]

Originally Posted by megaraider

No secret ... IMO a great mistake.
The heatsink, no matter how 'special' it is, only works to keep the diodes under temperature limits, and if common to keep them all at about the same temperature.
Nothing else, sorry!



Yes!

Leave the how matter it is special , for me , and try to answer my question ... Though I won't tell you when you're right or wrong .

[jiroy]

Originally Posted by stj

why not just use a 25A rectifier from an old pc psu?

It's because I'm leaving the always possibility to add more Diodes/LMs in case I want to put more laptops on the table . When I'll draw the circuit , I'll leave that possibility for lot of other parts too . So nothing against rectifiers basically other than that ..
I left the core calculations for the last touch for such reasons .

[megaraider]

Originally Posted by jiroy

Leave the how matter it is special , for me , and try to answer my question ... Though I won't tell you when you're right or wrong .

Really No question to answer
Wishing you good luck exceeding individual max rated current using parallel diodes with you’re special heatsink…

Originally Posted by stj

why not just use a 25a rectifier from an old pc psu?

Not a problem... add more rectifiers in parallel