voltage regulators parallel connection ?

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kambo

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can i parallel connect LM350s or any other voltage regulators in parallel ?

thanks
kambo

 
kambo said:
can i parallel connect LM350s or any other voltage regulators in parallel ?

thanks
kambo
It's not simple. You need to have load-sharing resistors that degrade the regulation. Check page 22 of the LM117 datasheet. They show an implementation where they add an opamp and a reference to improve regulation. In fact the regulators are used like power transistors, with the advantage that they have bulit-in SOA and thermal protection.
Another possibility is to use power transistors to increase the current capability. Page 17 of the same document shows how. With normal transistors, the current, SOA and thermal protections are lost, but here they use the LM195 "Ultra reliable transistors" that have these protections built-in.
But after all, depending on the application, you may not need extreme regulation.
For example, many mixers don't need a very stable PSU. They need them clean, but they use either on-board regulation or even simple distribution/protection resistors. In taht case, you may well put a battery of regulators in parallels with 0.22 ohms load-sharing resistors.
 
thank you so much for the info.
checked page 20 and all, OMG, that is a lot of work...
i guess i just switch to 6.3VAC heater supply.
 
kambo said:
thank you so much for the info.
checked page 20 and all, OMG, that is a lot of work...
i guess i just switch to 6.3VAC heater supply.
You can use multiple regulators. An LM317 can deliver about 1.5A, suitable for 5 12AX7's.
If you run heaters at 12Vdc, with 1.5A, you can heat 10 12AX7's.
Power tubes don't need DC heaters.
 
i will be using 2x6SN7 and 2x5687 at 6.3 vdc.  = 3 amp... (slowblow micpre)

i will go with 6.3VAC 6amp transformer option...
 
kambo said:
i will be using 2x6SN7 and 2x5687 at 6.3 vdc.  = 3 amp... (slowblow micpre)

i will go with 6.3VAC 6amp transformer option...


thinking again, if i connect  heaters serial on two 6SN7 for 12v(6.3+6.3=12.6), and 5687's individually  serial for 12v, then, i am at 1.5amp :)

 
kambo said:
thinking again, if i connect  heaters serial on two 6SN7 for 12v(6.3+6.3=12.6), and 5687's individually  serial for 12v, then, i am at 1.5amp :)
Just make sure you use the GTB version of 6SN7, that has controlled heater time.
Considering the low cost of LM317, I would use two regulators, one running at 600mA for the 6SN7's in series, and the other at 900mA for the 5687's in parallels. They would both run at reduced temperature and the heat dissipation would be spread on a larger area.
 
There are some regulators that are specifically designed with paralleling in mind. Great example is the LT3080, but it's far too high end for your heater needs, competing with super regulators quite equally. Go with abbeys suggestion.
 
LM338 seems like the obvious candidate for high current regulation. But it's actually tremendously difficult to dissipate the heat produced in a common 6.3vdc scenario when approaching that 5A limit. This is especially true with the TO220 package. I have failed this more than once even with huge heatsinks. Proceed with caution.

I personally don't bother with heater regulation anymore due to these safety issues. A few big caps with a big-watt dropper resistor passive configurations have performed with no noise penalties compared to regulated ones. The added safety tips the scale in favour of passive dc heaters.
 
hey Kingston,
"  A few big caps with a big-watt dropper resistor "
any example  to this ?
( not even single diode, just caps and resistor ? )
 
mjrippe said:
Personally, I can't think of a single piece of *vintage* tube audio gear with regulated filaments.  DC filaments, sure, but not regulated.


so, diode bridge, with some caps and a huge power resistor to adjust 6.3vdc ?
 
cool, thanks

ps: worst thing worst, i will add a small DC fan.
my rudetube has a small 12VDC fan inside, running at 6.3VDC, and no problem racked...
no noise, and interference...
 
12SN7 are a buck cheaper than 6SN7.

I would not worry too much about two "same" tube heaters in series. Trouble comes when you have a 100V string of 4V and 33V heaters in series. Also the controlled warm-up became nearly universal after 1963, so unless you favor very vintage bottles, odds are in your favor.

At 6V, the 0.6V drop of silicon junctions looms large. If all else is equal, stack as high as you can (but not 100V). 24V total makes your various sub-Volt drops look small.  (Ah, 5687's current makes this awkward.)
 
kambo said:
hey Kingston,
"  A few big caps with a big-watt dropper resistor "
any example  to this ?
( not even single diode, just caps and resistor ? )

Look at the orange 86 heater schemo. I just made a circuit with it and it seems like it's working great but I havent hooked it up to any tubes yet. Voltages look good thus far. You can find resistors that come in TO-220 (which you can put a heat sink on but it's a bit overkill). Maybe kingston means using a very low resistance ohm 5 or 10W wire wound resistor post rectifier bridge Pre reglulator in series between the two to ease inrush current to something like a 317.

Btw, while we're on it I'm interested a DC heater circuit with paralleled 3080's. If someone more experienced helped pioneer a schematic and select an available transformer for a paralleled 3080 circuit I would gladly make a self etch file for it and test it out on my own dime. Looks like im not the only one who might like a circuit like that floating around here. there's an LT spice version of the chip available for download. I just never got around to playing with it.
 
Kingston said:
There are some regulators that are specifically designed with paralleling in mind. Great example is the LT3080, but it's far too high end for your heater needs, competing with super regulators quite equally. Go with abbeys suggestion.
LT3080 is definitely not right for the application. Thermal resistance is likely to be about 60-65°C/W. That would put a  limit of about 1W per chip.
Due to practical considerations (availability of standard transformer, size of smoothing cap, safety margin, low mains voltage...), the unregulated voltage would be about 4 to 5 V above regulated. Best case, running heaters at 12 V, dissipation would be about 6W, meaning at least 7 chips in parallels. PCB layout would need some attention.
 
buildafriend said:
Btw, while we're on it I'm interested a DC heater circuit with paralleled 3080's.

That's like driving your cows to pasture in the front seat of your Ferrari when all you needed to do was to open the door for them. LT3080 is practically a super regulator on a chip. They are interesting for very high end audio signal chain applications. PSU's with 12-24VDC rails for your opamps and DOA's.

See the heater circuit here, http://www.michaelkingston.fi/files/Drive-1_schematic_rev2.1.pdf
It's all you need for high end tube performance and it's far more safe compared to regulated.
Here's a version with regulator: http://www.michaelkingston.fi/files/Drive-1_schematic_rev1.9.pdf
It started failing after two years and eventually the regulator chip died. It didn't help that the heat sink was huge, TO220 and big-watt do not go in the same sentence. Full story with images and measurement data in the thread: http://groupdiy.com/index.php?topic=41509.0

To sum it up for you once more, heater regulation is pointless, even unsafe.

PS. Don't use the high voltage part of that schematic for anything. It's clumsy and expensive. I've since designed something far more efficient with very low parts count and better performance.
 
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