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Old 24th January 2012, 01:15 AM   #1
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Default Maida Regulator PCB

A while back I had some Maida regulator PCBs made and mounted the power parts on a large heatsink and ran wires to the PCB. I didn't like it. It was difficult to work on. I learned my lesson.

I whipped this one up with the idea that I could mount the LM317 and pass device on the heatsink and bend the leads upward to go through the board which greatly simplifies assembly.

There are provisions to stuff an LM337 and make a negative Maida. Board dimensions are 1.325" x 3".

Does anyone have any suggestions for improvement? I'm thinking I might get this fab'd soon, are there others that are interested in a group buy?

Last edited by SpreadSpectrum; 24th January 2012 at 01:21 AM.
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Old 24th January 2012, 01:20 AM   #2
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Sorry, I screwed up the attachments on that one. Here are the correct files.
Attached Files
File Type: pdf Power_Maida_REVB_board.pdf (37.7 KB, 586 views)
File Type: pdf Power_Maida_REVB_sch.pdf (16.1 KB, 632 views)
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Old 24th January 2012, 01:55 AM   #3
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Quote:
Originally Posted by SpreadSpectrum View Post

Does anyone have any suggestions for improvement? I'm thinking I might get this fab'd soon, are there others that are interested in a group buy?
Provisions for PS caps & Resistors (or choke connection)?

I'm interested in a couple if you do a group buy.
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Old 24th January 2012, 04:12 AM   #4
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I guess I should explain a bit more behind the purpose of this thing. I wanted to make something that would make it easy to have a bunch of different regulated voltages in an amp. I got a few fairly large heatsinks out of burned up motor drivers and designed this board so that they could all be lined up and make like five regulated voltages using one heatsink. One board is mounted over the pass device/lm317 of another and they can all be tightly packed. I don't want to make the board any bigger, because I need five of them to fit in a pretty small area and I have already drilled and tapped the holes by hand (30 of them).

I put the rectifiers and filter caps right under the power transformer on a terminal strip, point to point wired. I don't need a large capacitance or a choke for the filtering since the regulator is going to take on the job of ripple reduction. Basically, the board is acts as a three-terminal high voltage regulator. You build the raw supply with whatever filtering you want. In my experience you don't need to worry about low frequency stuff with Maida regs, but you don't want high frequency stuff like diode switching noise in there since the LM317 is not as effective at high frequencies. It is very effective at 100-120Hz.

Oh, and I guess I should mention that I used a few surface mount parts because it made routing easier and made the board much smaller. There are four SOD80 diodes and two 0805 resistors.

I was thinking of trying MYRO PCB for this board. Has anyone ever used them? Their prices are unbelievably cheap and I have read only good things about them so I figured they might be worth a shot. If their online quote is correct they should be under a few bucks per board. I'm thinking there has to be something wrong with them, it seems too cheap to be true.

Last edited by SpreadSpectrum; 24th January 2012 at 04:15 AM.
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Old 25th January 2012, 02:55 AM   #5
tomchr is offline tomchr  United States
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As the voltage across the cascode is limited to the drop across D6+D8, you'll likely poof the LM317/337 if you start up into a capacitive load. If you take the diodes out, you're likely to poof the cascode instead due to SOA overstress.... But if the load isn't (very) capacitive, no problem.

~Tom
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Old 26th January 2012, 12:44 AM   #6
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Thanks for the feedback, Tom. It is true that this regulator should not be used with a capacitive load.

I put the two diodes in there for a negative supply. A while back, I made a -450V supply from a -560V raw supply. I was afraid of damaging the pass device (there were only -500V p-channel fets at the time) even though I knew it should never see the complete voltage across it. I built it with the diodes and never had a problem, but they probably aren't needed and actually seem kind of dumb since they will just kill the 317/337 instead. Maybe I should get rid of them.

I would have just ordered your regulator since that is already done and would be much easier, but the amp I am working on has five supply voltages. I don't want to have to deal with that many LV windings for all of the error amps. Plus, two of the voltages are negative. Maida seems like the right medicine for this one.

It doesn't seem like there are that many interested in a group buy, but I'm going to order a bunch anyway since it hardly adds to the cost. I'll post here when I've successfully tested them and if any are interested they can get in touch with me then.
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Old 28th January 2012, 12:18 AM   #7
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I changed the diode protection so that it goes from input to output, limiting voltage across everything. Looking at the data sheet for the 200V zeners, I don't think that they will survive much capacitance on the other end and aren't a very good form of protection but I am going to leave them since the alternative will be empty space. I also added additional holes for C4 so that it would be easier to fit radial electrolytics should I ever want to. I'm probably looking at submitting these some time next week.
Attached Files
File Type: pdf Power_Maida_REVB_board.pdf (39.0 KB, 168 views)
File Type: pdf Power_Maida_REVB_sch.pdf (16.5 KB, 235 views)
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Old 28th January 2012, 12:41 AM   #8
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I've not double checked your design (so I assume it's OK), but was going to make up some of these for myself for a couple of tube projects. My plan was to vero them, but if you have some PCBs made, the few $ for them increases convenience a lot so I'd buy a few.
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Old 28th January 2012, 02:57 PM   #9
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The design is pretty much an exact copy of the circuit in the Maida app note except that I use a mosfet. I added the option of making it negative using an LM337 which would mean you would have to reverse the polarity of a bunch of the diodes as well. I also added some zener diodes to help protect in case of an over-voltage of marginally rated parts but I don't think it would work that well. I just left it in since I had the space.

What I'm going to do is order these, build and test some, post pictures/results here and then if they work well sell some to spread the cost. I'm not really looking to make any money, I just have like five boards I want to do for the current amp project so sharing the cost with others is nice for me. The next board I have to make is an automatic fixed bias board for push-pull amps based on a John Broskie circuit.
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Old 28th January 2012, 08:30 PM   #10
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I'd be interested in a few boards. Let us know if they work and how much capacitance they can handle on the output.
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