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Regulated linear supply
Regulated linear supply
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Old 29th September 2019, 12:35 PM   #11
jan.didden is offline jan.didden  Europe
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Originally Posted by FauxFrench View Post
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.
I don't think that is a concern. Remember, there is no 'noise' per se on any rail, also not on any negative rail. Noise is always between two nodes - when we talk about potential we really mean potential difference.

So when we use the negative rail as the reference for the negative supply, as we would do here, by definition that negative rail is absolutely noise free.

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Old 30th September 2019, 02:43 PM   #12
Mark Tillotson is offline Mark Tillotson
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Originally Posted by alibear View Post
Thanks for the replies.
Transformer has two secondaries, 37-0. 37-0.
I require + and - forty five volts DC, say 300mA

What VA rating is the transformer? Do you want adjustable current limiting?
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Old 1st October 2019, 09:37 AM   #13
alibear is online now alibear  United Kingdom
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Hi Mark, the toroid that I have judging by the physical size is probably around 200VA, I know its much to large for what is needed but it's one I already had. I do not require current limiting, I am after simplicity.
Thanks for the replies
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Old 4th October 2019, 03:19 AM   #14
Turbowatch2 is offline Turbowatch2  Germany
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As a very practical approach, first build the rectifier/ filter cap part and measure the voltage you really get with your transformer. Should be around 55v at idle.
For a high quality power supply I would always start with a C-L-C filter. Combine the large electrolytics with some small film caps. It takes out a lot of ripple.
Then, a zener diode, darlington combination. it will only need two resistors and a capacitor to give a very stable output, even better than a simple regulator. So you have 5-6 parts that form your regulator circuit. You can add a pot to fine tune. Last, put a diode over emitter/ collector, to prevent voltage from reversing. This is a very uncritical, simple discrete regulator with high quality.
Only down side, it is not short cut protected. With a 200 VA transformer, not the best to experiment with. You can over dimension the darlington (cheap) and put a resistor between the unregulated and regulated side, to limit current for a short time protection. Not elegant, but simple and effective.
If you use 300mA, you have to be sure the power transistor can vent about 8
W of heat away.

Those values have to be adjusted to your voltages and you repeat the circuit for the negative side with the complementary PNP transistor. If you do not feel comfortable with that, ask.

maybe have a look here: Transistor-Zener Diode Regulator Circuits

and : Filter circuits - Inductor Filter, LC filter, CLC or PI filter, Capacitor filter | D&E notes
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Last edited by Turbowatch2; 4th October 2019 at 03:35 AM.
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