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Regulated linear supply
Regulated linear supply
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Old 21st September 2019, 08:29 PM   #1
alibear is offline alibear  United Kingdom
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Default Regulated linear supply

Hi, can anyone point me in the direction for a circuit diagram of a plus and minus 45volt regulated linear supply. Needed for the front end up to and including drivers of a class A amplifier, so only low current needed. Nothing too exotic or complicated. Thanks
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Alan
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Old 21st September 2019, 08:30 PM   #2
v4lve lover is offline v4lve lover  Netherlands
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Regulated linear supply
Do you have split windings? Cause in that case you can use two TL783
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Old 21st September 2019, 10:08 PM   #3
FauxFrench is offline FauxFrench  France
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I am so trivial and assume a symmetrical winding with mid-tap:
http://www.massmind.org/images/www/h...if/ckt21_1.gif
Replace D2 and D5 with power zeners in order to protect against dynamic over-voltages.
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Old 22nd September 2019, 09:14 AM   #4
alibear is offline alibear  United Kingdom
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Thanks for the replies.
Transformer has two secondaries, 37-0. 37-0.
I require + and - forty five volts DC, say 300mA
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Alan
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Old 22nd September 2019, 12:23 PM   #5
v4lve lover is offline v4lve lover  Netherlands
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Regulated linear supply
Then you can build two independant TL783 regulated supplies, and ground the positive end of one of them to create a negative supply.



The LM317HV Will also work in this application, The vanilla LM317 will see too much input-output differential voltage during startup and fault conditions to function properly.


Alternatively you can roll your own supply using discrete parts.


Edit 37VAC is a bit on the low end, if you take dropout voltage into account.
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Old 22nd September 2019, 02:37 PM   #6
FauxFrench is offline FauxFrench  France
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"The LM317HV Will also work in this application, The vanilla LM317 will see too much input-output differential voltage during startup and fault conditions to function properly." True, this is why I suggest to add a power zener (for each regulator) to protect the ordinary LM317 against too high voltage across input-output.

As you have two separate windings, you can use either a symmetrical regulator or two positive regulators that are stacked. Personally, I prefer a symmetrical regulator for noise reasons.
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Old 28th September 2019, 12:21 AM   #7
Vovk Z is offline Vovk Z  Ukraine
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Regulated linear supply
Fauxfrench, may be you missed the voltage level - 45 V. There isn't popular negative chips for that.
And second fact that positive regulators (317 etc.) usually have better specs. So, for noise reasons - two identical integral positive regulators have to be better.
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Old 28th September 2019, 08:20 PM   #8
FauxFrench is offline FauxFrench  France
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Quote:
Originally Posted by Vovk Z View Post
Fauxfrench, may be you missed the voltage level - 45 V. There isn't popular negative chips for that.
And second fact that positive regulators (317 etc.) usually have better specs. So, for noise reasons - two identical integral positive regulators have to be better.
I see two solutions: Either a set of LM317HV/LM337HV (the LM317HV can do 60V input-output and the LM337HV -50V input-output) OR ordinary LM317/337 with power zeners between input and output.
The power zeners I would make up of an ordinary zener (some 24V) and a darlington power transistor with the zener between base and collector and a 1K resistor between base and emitter to ensure full turn-off.
The LM317/337 have the advantage over 78XX/79XX that none of the pins are grounded. In principle, an LM317 can provide a 200V regulated output from a 220V input as long as the input-to-output voltage does at no moment exceed 37V (I am a "chicken" and have until now only tried with 42V input but no protection zener). It is the dynamic input-output voltage during start-up that is our concern. That is taken care of by the power zener circuit that reacts very fast and with large pulse current capacity if the input-output voltage momentarily exceeds some 26-27V.
Only in case of an output "hard-short-circuit" (zero output impedance instantly) with an active LM317 and fully charged power supply capacitors, the protection power zener circuit is challenged in full. How much current can the power supply capacitors provide as a surge when fully shorted? You hardly ever have a "hard-short-circuit" in an operating pre-amplifier circuit or a driver stage UNLESS you are about to make some tests and it is you creating the short-circuit. Do all testing with less than 37V input. If you are still worried, add a couple of Ohm between the power supply capacitors and the regulator for limitation of short circuit currents.

I know that many use stacked power supplies to generate symmetrical voltages and that positive regulators have slightly better specs than negative and are far more in choice. My reason to prefer symmetrical designs is that with stacked (positive) power supplies, both the ground rail and the negative rail have a direct connection to a noisy rectifier circuit (most often a bridge). My fear is that the gain in performance with only positive regulators is lost from having a negative rail with direct connection a the rectifier circuit.

Last edited by FauxFrench; 28th September 2019 at 08:29 PM.
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Old 28th September 2019, 10:25 PM   #9
FauxFrench is offline FauxFrench  France
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I forgot the modified HV version with dynamic drop transistor. That modification does not hamper current protection and there are no particular surge currents.
Though we do not have many negative voltage regulators, with simple means we can modify the LM317/337 to handle higher voltages at the input.
Attached Images
File Type: jpg LM317HVMod.jpg (10.6 KB, 204 views)
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Old 29th September 2019, 10:39 AM   #10
v4lve lover is offline v4lve lover  Netherlands
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Regulated linear supply
What about adding an RC stage to isolate the negative supply leg of the negative regulator from the "Noisy" bridge rectifier? I still think the TL783 solution is more then adequate for the job at hand, if you need to feed very delicate circuits you can always add a RC filter down the line.



I have the schematics of a complex bipolar based supply somewhere, but that would need a completely new PCB design, that is relatively complex in comparison to two regulators.
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