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Salas SSLV1.3 UltraBiB shunt regulator
Salas SSLV1.3 UltraBiB shunt regulator
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Old 29th January 2019, 12:07 PM   #1081
Salas is offline Salas  Greece
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Salas SSLV1.3 UltraBiB shunt regulator
Quote:
Originally Posted by kurand View Post
Has anyone successfully built a +5V 2.2A version suitable for an RPi?

I have put one together using R1 with 0R27 7W, M1 IRF9640, M2 IRF640 and R9 with 1K5. It seems to work but M1, M2 and the rectifier diodes get very hot very quickly, and I seem to have smoked Rf (0R33 1W part supplied in the mini kit).

Should I have uprated Rf?

Also, what is the acceptable heat range for M1, M2 and the diodes? The spec sheet seems to say 150C but this seems quite high.

Any thoughts?
0.33R*2.2A=0.726V*2.2A=1.6W so Rf at 1W rightly smoked. Use a wire link instead of Rf or a 5W one. The bridge diodes need sinking help as they will be dissipating about 2W each.

IRF9640 IRF640 are not tested in this reg before and I don't know what stability margin they may achieve or not. They should at least present a flat DC line without specific waveforms riding at some high frequency as the scope is AC coupled to a probe while scanning with the horizontal knob through various time bases and the vertical knob is set in mostly mV ranges. If so, acceptable.

The quoted max C in semiconductors is core meltdown. Core is always hotter than tab or the plastic shell. Keep the tab below 100C in experiments. To make thermal calculations pay attention to the RθJC term and its listed value. Do a search, many thermal guides for sinking are floating on the web. This old Dave Jones video about thermal heatsink design will give an idea about the concept: YouTube
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Old 29th January 2019, 12:34 PM   #1082
Salas is offline Salas  Greece
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Salas SSLV1.3 UltraBiB shunt regulator
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Originally Posted by Malefoda View Post
M2 power at 5V should be low quite low, M1 depends on input voltage, let's say 12V: 7V drop *2.2=more than 15W! For a heatsink temp rise of 20°C above room temp you need something like that: SK58-100-SA | Heatsink, 1.3K/W, 100 x 150 x 27mm | RS Components. You want your UltraBiB reliable so you want good heatsink as other parts can't stand (think caps) the heat. Tiny heatsink on rectifiers' package are cheap.
I hope I'm right else I may fry next build!
Generally correct, 5V only helps, but the RPi is a computer and it will be at many times absorbing just 400mA or below but fully peaking only during boot or when too much USB power is used for external stuff. So M2 will have a wide range of possible dissipation states.
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Old 29th January 2019, 12:49 PM   #1083
Salas is offline Salas  Greece
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Salas SSLV1.3 UltraBiB shunt regulator
By the way, these days I was bread-boarding a possible linear solution for replacing SMPS bricks to such devices but without the high idling shunt heat. Based on the DCSTB series PSU of DCG3 fame but with a row of pins to can short and select how many Leds are lit for different voltage levels. Will 5V and 9V be enough or someone would need more levels up to near 18V? I don't know, for DACs with external bricks or Class D small amps maybe?

A TO-220 series transistor on a 50mm tall 25.4mm pitch board level sink would handle up to 5A peaks but the sink will be receiving low heat on average say 1.5W at 500-600mA Rpi consumption levels.
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Old 29th January 2019, 01:03 PM   #1084
Malefoda is offline Malefoda  France
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Well as you're asking 5V (RPi) to 15V (TA2020 Class D) is nice.
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Old 29th January 2019, 01:30 PM   #1085
Salas is offline Salas  Greece
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Thanks for opinion. If I used a ten Leds bar, only five of those are enough for 9V. So another five remain to reach up to 18V. A 2.54mm (0.1inch) pitch dual pins row next to the bar could be accepting a shorting plug to stop the lit Leds count at several voltage levels. Up to 15V eight energized reds are needed. Key for minimal sink saturation is to select a transformer that will not create much in-out DC drop for a given output level goal (2.5V drop is enough for this because BJT series type).
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Old 29th January 2019, 09:16 PM   #1086
derekr is offline derekr  Barbados
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Quote:
Originally Posted by Salas View Post
By the way, these days I was bread-boarding a possible linear solution for replacing SMPS bricks to such devices but without the high idling shunt heat. Based on the DCSTB series PSU of DCG3 fame but with a row of pins to can short and select how many Leds are lit for different voltage levels. Will 5V and 9V be enough or someone would need more levels up to near 18V? I don't know, for DACs with external bricks or Class D small amps maybe?

A TO-220 series transistor on a 50mm tall 25.4mm pitch board level sink would handle up to 5A peaks but the sink will be receiving low heat on average say 1.5W at 500-600mA Rpi consumption levels.
Yes, up to 18V, please. Even one that could do positive and negative on the same board
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Old 29th January 2019, 09:21 PM   #1087
Salas is offline Salas  Greece
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Salas SSLV1.3 UltraBiB shunt regulator
Why you would want a negative also to substitute an external SMPS adapter?
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Old 30th January 2019, 01:30 AM   #1088
derekr is offline derekr  Barbados
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So I could use it on, for example, a Soekris DAM1121 - which requires plus and minus 5VDC. After all, it’d be a Salas supply!!

The consumer Soekris units, 1321, 1541 etc are powered by Meanwell SMPS modules. The new 1921 and 1941 require an outboard supply...

I think you’re on to a good thing here, Salas - the ability to substitute factory SMPS supplies with a well-engineered linear supply that can be field altered to different supply voltages to power various devices (for example a NAS) has great potential. Go for it. But make it as universal as you can.

Also, again for example, the Allo Katana has a plus and minus requirement. They’re working on their own linear wallwart replacement to power the Katana.

A ‘universal’ Salas supply to replace SMPS wallwarts seems to me to have great appeal. Even if the implementation was somewhat compromised compared to the UBIB to achieve its universal appeal and price point.

Assuming the price was reasonable, I would jump at replacing the SMPS supplies on my modem, router, NAS etc (all in my audio chain) with a Salas-engineered linear solution that gets as close as possible to ‘one size fits all’. If it could be done such that all one had to do was set jumpers and source an adequately sized trafo the DIY world would thank you

Great concept, sir! Look forward to its realization
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Old 30th January 2019, 08:31 AM   #1089
Salas is offline Salas  Greece
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Salas SSLV1.3 UltraBiB shunt regulator
What lowish and near steady pulling dual polarity rail circuits you have in mind better serve with UBiB(s) for max subjective quality return. Series pass element linear substitution for external SMPS bricks I think is practical to be kept unipolar and simple.
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Old 31st January 2019, 03:54 AM   #1090
derekr is offline derekr  Barbados
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Fair point re using UBiB for 1121. Also had in mind powering a buffer but I’d be happy with unipolar, was just ‘wish listing’ with the bipolar option. Hope you bring it to market soon....
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