June 05, 2011

As I previously mentioned, I will be uploading an other schematic. So without further adieu, here it is.

I have shown the original work in progress version, that I posted in my previous post, to Chu Moy at Headwize, that created the CMoy, and was happy to see it and encouraged me to post in head-fi. I hope others will appreciate and like these variations too.

Now, I will explain a little bit the circuit. I researched for about a week for the most suitable diodes that would suit this design. The main objective was to have the lowest Vf @ 100 mA. Well, I thought it would be an easy task, it tourned out to be extremely time consuming.

I ended up with the SB220/240 (not the SB120/140) series in my original design. Now when you are on fire, and your design is not 100% finalised, ideas still tend to creep in to your head, ok even after 100%, there is always something you are not happy with. I had found the SR series by luck on the internet, until then I knew the Germanium diodes were better... for lower Vf. Well that is true, up to a point ;-) they are great in crystal radios for one reason., VERY LOW I or mA say, can someone say 1 mA and under?... yep! when I started viewing their datasheets, I was amazed at how low the Vf was, until I seen finally the charts for Vf against I. Then they did not seem nice!

Your best 'run of the mill' diode that you can find everywhere, is the 1n5817/8/9. Its Vf is: typical/maximum at 0.1A (100 mA) is ~0.28 / 0.34 for the 1N5819. I did start with the 1N5817, since I was looking at only one doubling stage with a '9v' Li-Ion 600mA battery. Then I added the other stages and safety margins and ended up with the 40v parts.

The SR and SB series are from Won-Top Electronics Co., Ltd., a Taiwanese manufacturer. Their products are available from Digi-Key and others, but I got some SR-140 from eBay due to the postage rates that Digi-Key charges on international orders. I w aould have loved to use the SB240, and yes I know they have free shipping at Digikey, but only for orders of $200 or more. Maybe another time.
As a side note, the SR sereies has been replaced by the SB series.

Now as to my comments previously about lasting at least 10 x as longer. It is simple, use 3000 mAh for NiMH batteries (AA size) or 1 x 18650 for Li-Ion at 3800 or 4000 mAh. The TC962 uses about 510µA-700µA. Lets say to make it easier, 1 mA x 4 = 4 mA, plus the LDO,

Now I do have a few other variations that include USB chaging of "Apple" devices as long as you have a USB cable to attach. A simple circuit would be the following:
Altoids Mint Tin Project - Minty Boost - USB Battery Charger. (and yes, there is also YouTube too).
This would be useful for many people. You can incorporate it in your own design and add a switch when you are to start charging.

I would recommend people to buy "Protected" Li-Ion batteries and chargers, as it will save them a lot of headache if they were unprotected and they deeply discharged.
What "protected" batteries are, is that they also contain a small circuit board inside the battery case.
It protects them from overcharge, discharge etc.
The only hard part for the 18650 is finding holders, of which are easy to find in the U.S. through Digi-Key etc. just search for 18650 battery holders. As an example here is a direct link.
Mouser has a similar policy with Digi-Key ;-)

Now, back to the design.

Capacitors, always use larger voltage ratings than what you are using.
If you are tight on space, in the 1st stage, you can use 16v, since it will not see that much, second stage, 25v and third 50v.
If you want it to look all the same, just use 50v versions. Try and find very low esr capacitors or use tantalum.
I do not have an osciloscope to check what is happening with the caps etc. I do recommend to ground pin 6 ALWAYS, so it is at 24 kHz, so it is out of the audio frequency.

Thank you for reading. I hope it has helped other people to get them thinking of designing the power section of their CMoy.

Btw, I recently came across a great page for a CMoy with Bass Boost. It can easily be altered to make an on-off switch for the BB. :-)

Here is the link to the page:


He also has schematics and all.

It is a very interesting design.

Until next time.

I will be posting a link to this blog on www.head-fi.org for more peoples opinions. Just go to the Forums section and from there to Misc.-Category Forums and then D.I.Y.

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