Power Supply on March '07 N&V Issue

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Craig
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Power Supply on March '07 N&V Issue

Post by Craig »

Since it seems a few of us are going to attempt to build this PSU, and a few of us have had issues sourcing parts, I think this would be a good place to combine our efforts.

The first thing that I am trying to find is the appropriate transformer.


T1 on the parts list is described as "120V Primary, dual 44V center tap secondaries @ 1.5A". I have sourced a transformer made by Hammond Manufacturing, part number 266J48. Here are the specs:

- Primary 117/234 VAC, 50/60 Hz.
- dual secondaries.
- Secondaries can be used as; a center tapped secondary, parallel connected or used individually.
- Open style.
- Minimum 6" long leads.
- Dual bobbin design - no electrostatic shield required.
- Class B insulation (130 degrees, C) for extra protection - UL listed as a Class A (105 degree, C) design
- Hi-Pot test of 2,000V RMS.
VA = 48
Secondary VAC in Series = 48V @ 1A
Secondary VAC in Parallel = 24V @ 2A
More info at http://www.hammondmfg.com/266.htm

There is also a model (266L48) with the 48V/24V leads at 2A/4A respectively.

Would the 266J48 be what we're after for T1?


For T2 the parts list says "120V Primary, 9V secondary @ 1.5A". Hammond has one (164H10) with these specs:
- Low profile, split bobbin design.
- Dual winding secondaries, non-concentrically wound
- Units are designed so that all windings must be used
- Low primary to secondary coupling - no electrostatic shield required.
- Choice of economical single primary 115V (164 series) or universal dual primary 115/230V (162 series) - either model 50/60 Hz operation.
VA = 20
Secondary VAC in Series = 10V C.T. @ 2A
Secondary VAC in Parallel = 5V @ 4A
More info at http://www.hammondmfg.com/162.htm

Would the 164H10 be what we're after for T2?


For T3 and T4 the parts list says "120V Primary, dual 9V @ 65mA secondaries". Hammand has one (266K18) with these specs:
- Primary 117/234 VAC, 50/60 Hz.
- dual secondaries.
- Secondaries can be used as; a center tapped secondary, parallel connected or used individually.
- Open style.
- Minimum 6" long leads.
- Dual bobbin design - no electrostatic shield required.
- Class B insulation (130 degrees, C) for extra protection - UL listed as a Class A (105 degree, C) design
- Hi-Pot test of 2,000V RMS.
VA = 27
Secondary VAC in Series = 18V @ 1.5A
Secondary VAC in Parallel = 9V @ 3A
More info at http://www.hammondmfg.com/266.htm

Would this be the right one for T3 and T4? This may be overkill, but it is the only one I could find with dual secondaries.

Am I on track with these transformers?

Thanks again in advance!!
Robert Reed
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Post by Robert Reed »

The 266J48 will work fine, but you will need one transformer for each supply, and I don't know how pricey these are. Transformers deals are everywhere on the web, and I have neither the time nor the inclination to start a search right now, but here is an outfit you can try for starters -www.mpja.com.
Look at the7844-TR transformer (24V@2A). You will need two for each supply and they will be wired up as a 48V c.t. transformer for full wave operation. As mentioned in the article two 24V transformers could be used in lieu of one 48 V c.t. transformer. These transformers are relatively small and quite cheap ($4.99 ea.). They also carry suitable transformers for the 5 volt supply. As a matter of fact, these were the transformers I originally was going to use, until I went through my junk box and found the ideal match. This is also where I purchased my DPMs from. Also you can Design your supply for a higher or lower maximum output if you choose and this may influence your decision on transformer purchase.
As far as the DPM power transformers go, why would you look for anything other than was shown in the parts list? They are incredibly cheap and very very small! Or you may want to play around with RDL's suggestion from the associated post on using just one supply for all. BTW these meters only require <5 ma per unit to power up.
Robert Reed
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Post by Robert Reed »

One afterthought - I have just ordered some sample chips from Texas Instr.These are new on the market and they are 5V-5v ISOLATED DC/DC converters chips in a nice little SIP-7 package.Don't know yet what the small quantity price is or who retails them. Will test them out when received---stay tuned.
Craig
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Post by Craig »

Hi Robert,

Thanks for your replies! I was a little confused about T1, I thought it was 44V split into two 22V lines to power each adjustable supply. I figured since the voltage is adjustable from 0-20 volts, that the transformer was putting out two 22V lines rather than two 44V lines.

The reason I didn't just order the parts from the supplier(s) you mention is because I live in Canada, and a $5 part can quickly turn into a $20 part by the time shipping, taxes, and duty are added. It's only really worth it if I order a large quantity of items at one time. Also, if I can help out a local supplier I would rather do that.
Robert Reed
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Post by Robert Reed »

T1 has (2) 44V c.t. secondarys. When wired in full wave configuration, it gives you (2) 22V full wave secondaries. After rectification and filtering you end up with 30VDC give or take. So (2) small 24V transformers wired as A 48 V c.t. transformer will give you the same thing for each supply. Just make sure you increase the filter caps value to 50V if you go this route. I don't know what the availability is of cheap parts is "up North". I have visited some of Canadas supplier websites and found some good deals. One in particular was an obsolete Dallas chip I was looking for and at a good price, however they would not ship to the states. What I needed was a "go-between" stop for this order and did not know of anyone that could do this for me.
Robert Reed
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Post by Robert Reed »

For those interested
Well, I just received the Tex. Inst. isolated DC/DC converter chips(DCH0105xxx series) I had previously mentioned. I just finished running some quick initial tests on them and here are the results. No details on the internals in the data sheets, but from a quick once over,they appear to be a saturated 70 KHz 'LC' oscillator with the 'L' being toroid of construction with a secondary winding feeding a half wave or full wave bridge depending on model,with subsequent filtering. These chips come in 5V;12V;15V versions either single output or dual (+/com./-).
Now for the good,bad and ugly:
THE GOOD - they come in a compact SIP 7 package (easy to install or shoehorn anywhere). They operate from a 5VDC supply +/- 10%. They are WELL isolated and the dual output units have excellent balance. They can put out 1 watt of power max. without heat sinking.
THE BAD (or fair?)- they have a ripple content of about 40 mv p-p at 140KHz. Does not look like it would be easy to filter out to a much lower level. The input/output efficiency from half load to full load (full load being 1 watt) is 50% to 70 %. The voltage out put swings about 15% for the mid and upper potions of its load range. The dual units fared much better.
THE UGLY - At very light loads, the output voltage increases dramatically (up to 40% increase). The efficiency at a full load (70% )drops off rapidly with decreasing load current , to as low as 2% at 1 ma output and in fact draws 65 ma just sitting there unloaded (again the dual units were better in this respect). Digikey lists the per unit price at $8.
So there you have it.A simple way to get isolation and/or split supplys for analog circuits. Definately not a device for most battery applications and might have to tailor the circuit somewhat for specific application. If devices are used near their rated load current---a pretty sweet device. If used at very low load currents---well not so sweet. Looks like the designer will have to make descisions based on available primary power, neccessity of isolation , etc. and cost. As usual in electronic design, tradeoffs play a big role and are a fact of life.
Robert Reed
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Post by Robert Reed »

OOPS!
Craig
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Post by Craig »

That's interesting. To make sure I have this straight, what you are describing is an IC that will take a single 5V source and split it into two "individual" sources that are isolated from each other?

Can you tell I'm a newbie? lol.
Robert Reed
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Post by Robert Reed »

This chip comes in six different versions and all require 5VDC +/- 10% input. The versions are as follows:
5VDC single output
12VDC " "
15 VDC " "
5VDC dual output (+/com/-)
12VDC " " "
15 VDC " " "
All output voltages are highly isolated from input.
All chips are rated at one watt of output power.
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