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Old 11th April 2012, 01:57 AM   #41
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Richard Murdey
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Default Mosfet voltage regulator circuit

This is the "suggested" voltage regulator to use with the J-Mo mk ii. It's a sister board to the main circuit, same size and mounting, same basic layout for the IRF510.

The Zeners are all 10 V. The output is 16 V DC, with a 1s soft start. The LED isn't needed, but since there should be some loading to allow the output to bleed quickly to 0 V on shut down, I figured might as well have an indicator light.

The IRF510 gate is protected from overvoltage by Zeners, and R1 gives some measure of overcurrent protection, worse case it acts as a sacrificial fuse.

The output ripple depends on the current draw of course, but it's quite low: about 0.25 mV at 200 mA output.

As configured, it drives one J-Mo channel. For stereo, R1 should be reduced to 5 ohms.
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File Type: png pcb-mreg-10c-sch.png (15.0 KB, 469 views)
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File Type: zip J-Mo2 power supply 10c LTSPICE.zip (1.2 KB, 32 views)
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Last edited by rjm; 11th April 2012 at 02:20 AM.
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Old 17th April 2012, 06:35 AM   #42
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Default Boards!

In "cheapskate green".
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Old 17th April 2012, 01:35 PM   #43
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A better photo, more accurate white balance. I'm really pleased how well these came out.
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Old 18th April 2012, 01:08 AM   #44
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Default Production model 001

Ready for testing...
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Old 19th April 2012, 04:17 AM   #45
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Default Thermals

Powered up and running as simulated. Excellent control of the bias current via the trimmer resistor.

With 16-20 V V++ and 180 mA bias current the MOSFET will dissipate 1.9-2.7 W.

I tried using Aavid 507302B00000G heatsink with the IRF510. It's rated at 24 C/W. For an ambient of 30 C, the MOSFET is expected to reach 75-95 C. I measured it at a couple of operating points and verified that this was indeed the case. (see photo)

The IRF510 is fine up to 150 C, so it's operating well within spec, but nevertheless the heatsink is a bit marginal... once the boards are in an small enclosure, and if people start running at over the rated bias current, things will rapidly get unpleasant.

The Aavid 504222B00000G (shown below) should substitute just fine on the PCB, and has a thermal resistance of only 6 C/W. MOSFET temperatures should, with this heatsink, stay under 50 C. I'll order a few and try them out.
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File Type: jpg 504222B00000G.jpg (66.5 KB, 144 views)
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Last edited by rjm; 19th April 2012 at 04:23 AM.
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Old 24th April 2012, 01:41 AM   #46
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The addition of the new heatsink reduced the temperatures down to the 50-75 C range, MOSFET case temp is 55 C at the standard operating point V+ = 16 V, Vs = 5.5 V, Rs = 30 ohms.

The temperature of the MOSFET case are a somewhat higher than anticipated based on the heatsink thermal conductivity. The specification is 6 C/W (which struck me as optimistic), while the actual temperatures suggest 15 C/W. No big deal, but just a memo that specifications vs. reality for heatsinks seems to be a bit hit-or-miss.
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File Type: jpg DSC_3918 1280.jpg (334.8 KB, 101 views)
File Type: jpg DSC_3934 1280.jpg (310.3 KB, 98 views)
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Old 24th April 2012, 07:39 PM   #47
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Do they specify the orientation and the mounting position of the heatsinks they used for their measurements? I think the thermal conductivity could be much higher when the sink is positioned vertically in the free air and not mounted to the pcb.

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Flo
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Old 25th April 2012, 12:45 AM   #48
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Mount Orientation: Horizontal

Nice thought though.
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Old 25th April 2012, 07:53 AM   #49
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O.k. then there is a lack of reality. Or they measured at a really well vented place.
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Old 9th July 2012, 03:52 AM   #50
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This looks like a pretty good simple amp to try. How did you make the connections on your prototype. Did you wirewrap it or just solder directly?
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