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 Post subject: Voltage regulator design
PostPosted: Oct Wed 28, 2020 6:48 pm 
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Location: Warner Robins, GA
I have a torroidal transformer that has two 30 volt 4.17A windings which unloaded produce 42.42Vdc peak.

I need a + and - 35Vdc 1.5A regulated supply for a project.

I actually needed +/- 35V 3A, but it would be easier to do two separate +/- 35V 1.5A supplies.

I am building the circuit in an old car audio amp chassis that is all aluminum so I have plenty of heatsinking.

I prefer the regulators be linear if at all possible and TO-220 case style as those are easier to mount.

Current will not normally be 1.5A, but wanted a little head room.

Each output will have a 1.5A fast blow fuse.

Will also need a 12 volt regulated supply at a max of 500mA. I suppose a higher voltage version of the 7812 would work for that.


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 Post subject: Re: Voltage regulator design
PostPosted: Oct Wed 28, 2020 10:17 pm 
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Location: Santa Rosa, CA
You might find an LDO (low dropout) regulator, but the high input voltage is perhaps an issue.

What AC voltage is produced when the transformer is loaded to about 3 Amps. You won't have much headroom for regulation.

Rich


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 Post subject: Re: Voltage regulator design
PostPosted: Oct Wed 28, 2020 10:20 pm 
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Hadn't thought about that.

Might see if I can find what the spec is on the transformer.

EDIT:

Here's the transformer.

https://www.parts-express.com/avel-lind ... r--122-630

Typical regulation 6.4

Max VA rating
Efficiency 93.2%
Copper loss 16.6W
Iron loss 1.6W

So the transformer is rated for a 115/230Vac input.

Doing the math I get an output of 31.307Vrms on each secondary for an input of 120Vac.

I would then have an unloaded voltage of 44.268Vdc.

Main filter caps after the rectifier would be at least 10,00uF 50V.


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 Post subject: Re: Voltage regulator design
PostPosted: Oct Thu 29, 2020 8:04 pm 
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as i say in another topic you need something like this :
https://powersupply33.com/0-30v-5a-adju ... it-diagram

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 Post subject: Re: Voltage regulator design
PostPosted: Oct Thu 29, 2020 8:15 pm 
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Location: Warner Robins, GA
Interesting circuit.

Only problem is mounting the TO-3 transistors.


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 Post subject: Re: Voltage regulator design
PostPosted: Oct Sat 31, 2020 4:53 am 
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The LM338 is a possible solution and it's available in TO-220 albeit with the tab terminal being Vout. It is capable of 35V output. Bear in mind the thermal consideration in a linear pass regulator is (Vin - Vout) * Ipass. For Vin = 42V, Vout = 35V, and Ipass = 1.5A, that's 10.5W which is doable with clean planar surfaces and some good thermal compound.

There exist LM338 based module solutions on Banggood (as of this writing) for $16 with shipping included. These have a fan bolted to a TO-3 + heatsink. Also as of this writing the LM338T (TO-220) is 2.11USD @ Mouser.

Depending on your willingness to build/hack, the classic pass regulator is a simple discrete design if one omits current sensing/limiting and only a bit more complicated if you don't. I wouldn't omit current sensing/limiting at the requested max current. The failure mode on power BJTs can be a collector to emitter short.

As someone said so elegantly elsewhere, this is power supply design. It is well-documented about the web with many examples and eminently doable as you seem to already be doing.

One note of caution if I may, do double check circuits involving bridge rectifiers. People sometimes inadvertently include a sneak path, particularly to ground, especially when multiple such circuits are employed.

Coop, aa1ww


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 Post subject: Re: Voltage regulator design
PostPosted: Oct Sat 31, 2020 5:14 am 
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Location: Warner Robins, GA
I'm assuming that's a positive regulator.

Is there a negative version?

EDIT:

Concerning transistors I have a pair of 2SA1941 and a pair of 2SC5198 I could use to either make a + and - regulator for the whole circuit or individual + and - regulators for each circuit. Basically it is two circuits requiring a +/- 35 volt supply with each individual circuit drawing a max of 1.3A on the + and on the - supply.

Doing two individual +/- regulators would be better as it would keep the regulators cooler, but is more complicated to do.

Current limiting is not necessary as each output will have a 1.5 amp fast blow fuse going to each circuit.

2SA1941

https://datasheetspdf.com/pdf-file/7372 ... /2SA1941/1

2SC5198

https://www.mouser.com/catalog/specshee ... 101102.pdf

So I suppose I could use an adjustable regulator and use those transistors as pass transistors.

EDIT:

Perhaps it would be possible to use those transistors with this circuit modified to handle a max of 50Vdc input and put out 35Vdc.

Attachment:
Regulagtor.png
Regulagtor.png [ 59.17 KiB | Viewed 129 times ]


Taken from here

https://www.ti.com/lit/ds/snvs778e/snvs ... e.com%252F


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