voltage doubler for linear supply

[JAY X]

Hi!

I'm considering building a dual rail psu with voltage doubler circuit, that uses half wave rectification.
The input will be a single rail ac-dc wall transformer. Vout: 15 or 18v.

I saw a circuit by douglas self, but he says that these type of supply are only suitable for circuits using bipolar opamps only.¿why? ¿ what would happen with fet opamps? or other types like line drivers and receivers?

Any comment is wellcome!!
Jay x

 

[Khron]

I'm not too sure what you've read, but under that(?) schematic in Self's "Small Signal Audio Design" book, all it says is "Since voltage-doublers use half-wave rectification, they are not suitable for high current supplies". Nowhere can i read anything about "bipolar opamps".

 

[JAY X]

Hi Khron!

Page 533, dual supplies from a single winding, second paragraph...." these voltages are suitable only for a system that uses 5532 throughout".

As the 5532 is bipolar... I ubderstood perhaps badly that voltages doublers are not suitable for bipolar opamps...

I hope to be wrong... ;D
Jay x

 

[Khron]

What does the voltage doubler have to do with the voltages it puts out, or the type of opamps it powers?

"... a +/-18 V power supply; note that these voltages are suitable only for a system that uses
5532s throughout."

Where exactly does he mention anything about the "type"of power supply used? All he's saying is that you wouldn't want to power other opamps with +/-18V, that's all.

 

[Bo Deadly]

That will not work. The "wall-wart" described in the Self book is actually just a transformer and not the typical ACDC SMPS you get with laptops and consumer electronics.

If you have two ACDC supplies (who doesn't?) then you can just "stack" them to make dual voltages. Specifically each SMPS out has a + and -. So you stack by simply connecting the - of the positive supply to the + of the negative supply and that makes your ground. Then the two ends are + and - voltages.

Using two SMPS might sound like a Kludge but it's actually not. If you have some chokes to make LC filters that will snuff out the the high frequency noise. And a standard regulator (LM317/LMN337 to make +-15 is fine for virtually all op amps but check the op amp datasheet) will take out any low frequency noise. The result should be very quiet.

It's a little kludgey to use two laptop bricks with their own AC cords. But you could buy some MeanWell supplies on Mouser (or wherever) and wire them into an enclosure with a single AC cable. Some of the MeanWell supplies have relatively low ripple even without chokes and regs.

I am apprehensive about placing SMPS inside the same enclosure as high gain audio circuitry however because they do radiate EMI. Again some ACDC switchers are probably better than others. There are folks here that say it's not a problem if done correctly. But I use a separate enclosure with several stacked SMPS to make my multi-output supply (also because I don't want to have to re-implement a PS for each project).

 

[Khron]

If you do end up stacking two SMPS, try to find 2-prong / non-earthed ones.

 

[benb]

What does the voltage doubler have to do with the voltages it puts out, or the type of opamps it powers?

"... a +/-18 V power supply; note that these voltages are suitable only for a system that uses
5532s throughout."

Where exactly does he mention anything about the "type"of power supply used? All he's saying is that you wouldn't want to power other opamps with +/-18V, that's all.

This is the thing. 5532 are rated at +/-22V absolute max, and +/-18V "operating" voltage, whereas most (almost all?) other op-amps used in audio are +/-18V absolute max, and +/-15V "operating" voltage.

 

[merlin]

I hope to be wrong... ;D

1) You can use any opamp that is rated for the voltages you are using.
2) A power supply of this type needs to have it's two rails equally loaded so the transformer does not see any net DC current (saturation). Opamps provide equal loading, of course, but discrete circuits might not.

 

[JAY X]

Hi!

So, the only limit is the voltage, not the type of opamp as i misunderstood... :
In my case i will have +/-17v. using LM317/337 regulators. With these voltages i usually supply all my opamps/line drivers/receivers, etc..

I was considering buying a wall supply  a meanwell Rs code:  1361329 But, after reading the last posts, maybe i have to go for an Rs pro rs code: 1391791. a typical wall transformer, with a bit more ripple: 100mv instead of 80mv from the meanwell model.

Another option would be to build a psu with a rail divider. In that case, ¿could i use a smps supply? 
Of the two options (voltage doubler or rail divider) ¿which one is less noisier?

¡thank you for your help!
Jay x

 

[Bo Deadly]

Another option would be to build a psu with a rail divider. In that case, ¿could i use a smps supply?

The circuit you originally cited from the Self book was only meant to illustrate how you could make a bipolar supply even if your transformer did not have a center tap / split secondary. But for a number of reasons that is not ideal. So if you are going to start buying parts, then you should just buy the parts necessary to make a proper power supply and not try to make something with a "rail divider" or whatever. Meaning get a transformer with a center tap or buy proper SMPS (i have used MeanWell LPC-35-1050) and stack'em. Or if this is for the bench, there are lots of cheap bench supplies that programmable (can limit current so you don't fry stuff on your breadboard as easily).

 

[JAY X]

Hi!

I think this thread i started has derailed a bit, because i was not enough clear in my initial purpose. Sorry for that!! :-[

My initial goal was to look for options to supply power to a small format compressor i'm building. The space inside the box is small, so there is no place for a toroidal trafo/ linear supply. This is why i'm considering  AC or DC input with an external transformer or smps psu.

That said, i have three options:

1) External AC transformer + voltage doubler internal psu to provide +/17v with LM317/337 regulators.

2) External smps dc output between (9-18v) (or other range) + TRACO +/-15v DC-DC CONVERTER .

3) External smps dc output between (18-24v) (or other range) + TRACO +/-24v DC-DC CONVERTER + linear post-regulator with LM317/337, to get +/- 17v. dc output.


The option 1) has been already discussed, and i see it has its weak points, thanks for your comments.

The option 2) seems more feasible and secure, despite i loose 2 volts at the output.

The option 3) i have no idea...maybe someone has an experience on this.

In the case of options 2 and 3, i suppose it is ok to use smps psu to provide the DC input for the  DC-DC converters.

Thank you for your help!

Jay x

 

[Newmarket]

Hi!

I think this thread i started has derailed a bit, because i was not enough clear in my initial purpose. Sorry for that!! :-[

My initial goal was to look for options to supply power to a small format compressor i'm building. The space inside the box is small, so there is no place for a toroidal trafo/ linear supply. This is why i'm considering  AC or DC input with an external transformer or smps psu.

That said, i have three options:

1) External AC transformer + voltage doubler internal psu to provide +/17v with LM317/337 regulators.

2) External smps dc output between (9-18v) (or other range) + TRACO +/-15v DC-DC CONVERTER .

3) External smps dc output between (18-24v) (or other range) + TRACO +/-24v DC-DC CONVERTER + linear post-regulator with LM317/337, to get +/- 17v. dc output.


The option 1) has been already discussed, and i see it has its weak points, thanks for your comments.

The option 2) seems more feasible and secure, despite i loose 2 volts at the output.

The option 3) i have no idea...maybe someone has an experience on this.

In the case of options 2 and 3, i suppose it is ok to use smps psu to provide the DC input for the  DC-DC converters.

Thank you for your help!

Jay x

But as advised if you get a suitable CT transformer  then you won't need the complication / compromise of a voltage doubler.

 

[JAY X]

Hi Newmarket!

¡¡The first option was already discussed!! Most external AC transformers come with a +V/ GND connector only, and you MUST adapt your circuitry to this fact.

Jay x

 

[Newmarket]

Hi Newmarket!

¡¡The first option was already discussed!! Most external AC transformers come with a +V/ GND connector only, and you MUST adapt your circuitry to this fact.

Jay x

Okay. I see what you mean - a ready cased ac transformer. I was thinking to get a suitable CT transformer and box it up yourself.

 

[JAY X]

Hi All!

Given the fact that i use an external ac transformer with a 2 prong connector, one aspect i forgot to comment is the chassis to AC gnd connection at the AC in barrel connector (at the audio device).  I saw  that some manufacturers place a 47pf between ac gnd and a cable with a lug to the case.

This way: AC GND --->47PF  leg 1 to ac gnd, second leg to a trace and  wire with a lug to chassis case.


Jay x

 

[Bo Deadly]

47p is just shunting RF which is probably not something that you definitely need an earth pin for. But again, you can stack two SMPS and then make your own cable in which case you would have the earth pin and then you can have something to shunt RF to. Or you can leave the ground floating. Lot's of consumer electronics do it. The ground will simply follow whatever is connected to it (eg the shield ground of the XLR cable from your console).

Or just get a Mean Well GP25A14E-R1B for $30 USD from Mouser or wherever is near you. It has +-15 and an earth ground (if you use relays or leds you might be able to take advantage of the 5V). For a compressor without lot's of sensitive high gain circuitry, you can probably get away without regulator's but you will almost certainly want LC filters very close to where the connector enters the chassis because the SMPS can make some high frequency noise. Then you'll have +-15V. Or use some fancy Low Drop-Out regulators (LDOs) maybe.