The simplistic Salas low voltage shunt regulator - Page 140 - diyAudio
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Old 20th October 2009, 03:15 PM   #1391
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Quote:
Originally Posted by ikoflexer View Post
Logic level mosfets may work. For v1, something like this
NDP6020P Datasheet pdf - P-Channel Logic Level Enhancement Mode Field Effect Transistor - Fairchild Semiconductor

For v2, many choices of n-channel logic level mosfets.
Thanks for the input, and Salas too.

I think I will build a BJT version first as I have some BD140s on hand, then convert it to mosfet at a later date.
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Old 20th October 2009, 03:48 PM   #1392
iko is offline iko  Canada
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Quote:
Originally Posted by Telstar View Post
Checked it.

I'm evaluating shunt regulators circuits for a low-wattage class A amplifier dedicated to HF. The voltage requirement is 17V, amperage around 1A.

Which values would you suggest for my needs?
If you use 1N4738A for D1 and D2 you get around 16.7V output. You need to adjust R2 to get the current up to the value you want. That needs to be done experimentally. You can use a 10K trimmer for R2, and start at about 2K. If you're running 500uA through R2 then somewhere between 8k and 10k will give you the 1.xA current limit that you want.

It's not exactly a beginner's project, you need to be comfortable with applying Ohm's law left, right, and center. (I'm not kidding. )
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Old 20th October 2009, 03:50 PM   #1393
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Originally Posted by Spartacus View Post
Thanks for the input, and Salas too.

I think I will build a BJT version first as I have some BD140s on hand, then convert it to mosfet at a later date.
It'd be best to choose a target schematic, either v1, or v1.1, or v2. I'd recommend v1.1 or v1, to get your feet wet. Then choose your target voltage and current. Then, if you really want to use the BD140, someone needs to make sure it works in that schematic.
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Old 20th October 2009, 04:02 PM   #1394
Salas is offline Salas  Greece
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Spartacus will. Will work, or its smokie time.
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Old 20th October 2009, 05:24 PM   #1395
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Sure, I'm looking to build something close to V1, with up to 100mA total current. Load current is around 40mA. At worst it may oscillate, at which point I'll have to do something to decrease the gain of the circuit.

The trouble with getting a logic level mosfet is getting it in low quantities without paying ridiculous postage. I'll order some next time I need a batch of components from Farnell. Famous last words, but I can't see why the BD140 wouldn't work. There are plenty of shunt schematics out there, many of which use a PNP in a similar configuration. I'll report back.
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Old 20th October 2009, 05:33 PM   #1396
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The loop gain is much lower with the bd140, no need to worry about oscillation. This also translates directly into higher output impedance, if you care.

Otherwise, my sim shows it will work just fine. I used two LEDs of Vf=1.8V and two 1N4148 diodes as reference.
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Old 20th October 2009, 05:52 PM   #1397
Salas is offline Salas  Greece
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Just joking. There is a good chance it will work fine. Will just have different soncis. V1 is very limp for parts and substitutions. DIY friendly. The more you move up versions the same song gets harder to stay in tune.
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Old 20th October 2009, 06:34 PM   #1398
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Dear Salas, what should I change in V1 (or V1.1) schematics (zener aside) to get a "medium voltage" version of your shunt?
I mean a regulator that can deliver 50 to 60 V for a 80 mA load.
Is a 60 V AC toroid too much? I can eventually use a CRC to drop some voltage.
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Old 20th October 2009, 07:15 PM   #1399
Salas is offline Salas  Greece
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Put an 8.5mA Idss 2SK170 under the Vref and your Rx should roughly give you 50-60V between being 8k2-10k 2W.
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Old 20th October 2009, 07:40 PM   #1400
massimo is offline massimo  Italy
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Thank you for the dedicated schematics!
All resistors (R1 and Rx aside) can be 1/2W?
May I use a TO92 (ie MPSA42) for Q3? A TO5 heatsink will fit if required.
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