TREAD and power supply parameters estimator

[StanRex]

Hi guys,

I've assembled a TREAD to use with a PPA, and am wondering a few things

I'm using an AC walwart to supply it. It s rated for 24VAC, 0.5A

So, I plug the AC supply in, and do the power supply testing procedure described for the TREAD.

And get something like 35V in front of the regulator (between TP 1 and 3)!

Wow!

That s more than what I was expecting.

I intended to run the TREAD at 24V, but apparently, I have quite a bit of voltage available.

That got me thinking "I can probably run the TREAD at 30V", since opamps are usually said to run better at higher voltages, it would probably be a good thing

but then , I loaded the power supply parameter estimator (http://tangentsoft.net/elec/ps-est.htmlr ) once more, and entered

power source : RAW AC
transformer unloaded voltage, 26V (measured)
rated voltage 24V
rated current 0.5A
line freq : 50Hz (i live in france)
desired regulated voltage 30V
avg output current 0.3A
and left the other parameters at default values

the estimator tells me that regulator will drop out of regulation. I must say that it surprises me a bit, because I d imagine that with something like 5V available for "regulation", it'd be ok

so I'm wondering : would it be ok to use it at 30V, or am I too optimistic on the fact that 5V will be enough to allow it not to drop out of regulation

I'll add that I m doing these measures without anything connected to the TREAD output. I dunno if having an amp connected, pumping current, would maybe decrease the high voltage I m getting in front of the regulator and explain why the estimator thinks it s a bad idea.

Thanks in advance for your answers

[JamesL]

The voltage will drop as you draw more current from it.
Keep in mind the calculator is only an estimator..
You can check to see if your TREAD's regulating properly if you measure the AC ripple between tp2 and 3.

Originally Posted by StanRex

That got me thinking "I can probably run the TREAD at 30V", since opamps are usually said to run better at higher voltages, it would probably be a good thing

Not all opamps are rated to run at 30v, so make sure your opamp is specified to run at those voltages.

[tangent]

Originally Posted by StanRex

And get something like 35V in front of the regulator (between TP 1 and 3)!

This is one of the effects of AC rectification.

avg output current 0.3A

Really?? A typical PPA only takes around 100 mA. If you want to be conservative, put in 150 mA.

and left the other parameters at default values

You'll want to change the filter cap size to 680 uF if you're using a TREAD kit. If you're supplying your own parts for a TREAD board, I still doubt that you're fitting 2000 uF here.

Also, the default heat sink it uses is for the STEPS. Unless you know you'll be using one that's the same size, you should tell the estimator its thermal resistance to get believable heat values.

would it be ok to use it at 30V

Perhaps not, but remember, there is nothing magic about 24 V or 30 V. They are just common standards. When DIYing an adjustable power supply, you have the freedom to use anything in that 6 V range, or anything outside it, for that matter. If you re-run the numbers and find that it will run at 26 V, by all means, do so if your chips will tolerate it. It will decrease waste heat in the regulator, and may make the amp sound a smidge better.

Also, keep in mind that there's going to be 1-2 V of voltage drop across the PPA's input diode and the rail regulation JFETs, so the voltage at the op-amps will be a bit lower than the TREAD's output. Even if you're using 24 V chips, you might be able to get away with a 26 V supply, for example.

[PJPro]

I'm building a TREAD but I'm having trouble finding a transformer to suit my needs. I need to supply 12 v and approximately 320 mA to power my Beresford DAC. I hoped to use a toroidal transformer but it seems that stock items will not produce a "sane configuration" when using the power supply estimator.

So, I've been looking at the Hammond transformers as recommended by Tangent. The one I'm looking at is the 266J12, which is rated at 12.6 v and 1 A. Clicky. However, despite my best efforts, I am unable to find the unloaded voltage or percent regulation to provide all the parameters for the estimator.

Does anyone know the unloaded voltage or percent regulation of this variant of Hammond transformer? Can anyone recommend a transformer (not custom) which will provide a sane configuration?

[PJPro]

I think I might have found one! It's the Amveco 62032. It's rated at 2x12 volts at 300 mA with 2x17 unloaded voltage. I'm assuming I can configure this just to provide 12 volts and 584 mA with an unloaded voltage of 17.

I'd be grateful if someone could confirm my understanding. The transformer can be found here.

[tangent]

I remember telling you about Avel-Lindberg transformers, not about Hammond. I've not even heard discussion about Hammonds in conjunction with TREADs. Plus, the one you're linking to is an EI core type. Hammond does have toroids, but still no unloaded voltage info. You could try emailing them, I guess.

As for your Amveco choice, the TREAD doesn't provide a mechanically sound way to wire dual secondaries in parallel to the board. (The YJPS (available soon!) will have that feature.) Secondaries in series is easy, because only two lines need to go to the board; the other two are tied together at the transformer. I also worry about heat when you are so far over the desired current target. Ideal would be 25% over, so 400 mA. You're more than 80% over right now.

[PJPro]

Originally Posted by PJPro

[snip].....Does anyone know the unloaded voltage or percent regulation of this variant of Hammond transformer (266J12)?.....[snip]

Rec'd a reply from Hammond today.

"The no load voltage at 117V in is 7.08 V . So the load regulation is 12.4%" (Doug Hutt)

[PJPro]

Originally Posted by tangent

I remember telling you about Avel-Lindberg transformers, not about Hammond.

Yes, agreed...although this was in relation to the YJPS.

Originally Posted by tangent

I've not even heard discussion about Hammonds in conjunction with TREADs.

The first part number supplied in your parts list for the Tread is 546-266EA24. When I plugged this into the Mouser product search it came back with this.

Originally Posted by tangent

Plus, the one you're linking to is an EI core type.

Errrr, is it? I navigated from the datasheet for the one above and simply looked for one that would hopefully fit my requirements.

Originally Posted by tangent

Hammond does have toroids, but still no unloaded voltage info. You could try emailing them, I guess.

Yeah, I tried that and was surprised to get a quick reply (see previous post). However, given the 1A current, I can rule it out as an option irrespective of the regulation.

Originally Posted by tangent

As for your Amveco choice, the TREAD doesn't provide a mechanically sound way to wire dual secondaries in parallel to the board. (The YJPS (available soon!) will have that feature.) Secondaries in series is easy, because only two lines need to go to the board; the other two are tied together at the transformer.

The reason I abandoned the YJPS for my Beresford was that I couldn't get a PCB Mounted Amveco which would meet my requirements. I still intend to make a YJPS for my GS Novo once the boards are available.

With regard to the dual secondaries, how does one deal with dual primaries? I'm guessing that a connection block is used. Couldn't I use a similar approach for the secondaries? If not, I guess I could simply use a protoboard to accept the dual secondaries and have single wires from the protoboard to the TREAD. Or am I misunderstanding the issue?

Originally Posted by tangent

I also worry about heat when you are so far over the desired current target. Ideal would be 25% over, so 400 mA. You're more than 80% over right now.

OK. Assuming the issue with the dual secondaries can be overcome, the Amveco 62022 rated at 418mA would appear to be the ticket. When I plug 418mA into the estimator, the predicted temp drops from +22 to + 17 deg C over ambient. However, I now get the warning that the regulator will drop out of regulation. The parameters are...

Unloaded Voltage: 17VAC
Loaded Voltage: 12VAC
Rated Current: 0.418A
Regulator Dropout Voltage: 1.75VDC (approx on datasheet for 500mA)
Desired Voltage: 12VDC
Desired Current: 0.320A

All other parameters at default value.

To get a sane configuration using 418mA, I have to raise the unloaded voltage to 20VAC representing a regulation of 66% (seems awful high). The predicted temp is 20 deg C over ambient. I also tried raising the loaded voltage to 14V but the predicted temp leaped to 24 deg C over ambient.

Any advice which will help me select a suitable stock item or arrive at reasonable parameters to order a custom item would be gratefully rec'd.

[tangent]

Originally Posted by PJPro

Errrr, is it?

It's an awfully funny looking toroid if not.

It also doesn't look much like a split bobbin type, the other common power transformer type.

Not that EI cores are a real problem. They're the most common sort used. You just have to be careful of EMI. And, you do get some benefit: the bandwidth is a lot lower, so they'll prevent more of the hash on the AC side from getting to the DC side, so there's less reason to use a line filter.

how does one deal with dual primaries?

Paralleling the primaries is a lot easier because the power inlet jack lugs are much bigger than the holes on the TREAD board.

I guess I could simply use a protoboard to accept the dual secondaries and have single wires from the protoboard to the TREAD.

That fixes the mechanical issue, but you've traded stability for tiny little fusible links. Most protoboard uses thinner copper layers and narrower traces than I use on the TREAD and YJPS boards.

I'd probably look into things like 3M ScotchLoks if I had to do this. Better, see if you can avoid dual primaries or secondaries. AC-DC wall warts are one way out of the trap, and it fixes the EMI problem, too.

[PJPro]

I'd rather not use a wall wart if I can.

Hmmmm, this is all rather disappointing. Perhaps the Beresford is a challenge too far for the TREAD combined with my limited knowledge?

[tangent]

<shrug>

It's nice and practical to want to get things right from the start, but I wonder if that isn't also stunting your education. I think you're looking for me to give you a guaranteed works-perfect configuration, but that's unlikely given that you're far more interested in this project than I am. Perfectly natural...it's your project, so you should be the one most interested in it. You can't expect anyone else to expend more brain power on it than you are.

It might be best if you stopped worrying about the perfect configuration and just built something. Then you'd have a practical base from which to talk about improvements.

[PJPro]

Originally Posted by tangent

<shrug>

???

Quote from How to make true friends, Part 4 body language

Shoulder shrug: The simple act of a shoulder shrug can tell someone a lot about you if you use this gesture a lot. It’s basically telling the other person that you are quite submissive, you’re telling them you don’t know something and sometimes you’re saying you don’t really care. It’s also a sign of resignation and possibly that you’ve given up on something.

OK. Message received. Thanks.

Originally Posted by tangent

It's nice and practical to want to get things right from the start, but I wonder if that isn't also stunting your education. I think you're looking for me to give you a guaranteed works-perfect configuration, but that's unlikely given that you're far more interested in this project than I am. Perfectly natural...it's your project, so you should be the one most interested in it. You can't expect anyone else to expend more brain power on it than you are.

It might be best if you stopped worrying about the perfect configuration and just built something. Then you'd have a practical base from which to talk about improvements.

I have to assume that the PSPE is correct. My respect for you, your site and your contribution to the DIY community gives me the confidence that it is...despite the fact I am unable to personally validate your algorithms.

I acknowledge my own inexperience in electronics but I am from an engineering background and am respected by my peers in my own field. I have reviewed your software and it has given me a greater understanding of the influence of the parameters being used within your algorithms.

Given my design goals for the PSU, i.e. small size and relatively cheap, I have come to the conclusion that the TREAD is not suited to supplying 12v and 320mA without the use of relatively substantial heatsink. I think this was the flavour of my previous post.

Clearly, it would have been useful for me to arrive at this conclusion before buying two kits....but there you go. An education of sorts. Doubtless, I will find a use for them.

I'm sorry if I've troubled you unnecessarily.