The simplistic Salas low voltage shunt regulator

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AndrewT

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Yes, and after that Press "download now" then wait and the next webpage "done" but nothing is on screen.
Minimise and there is nothing hiding behind.
Go back to the maximise screen and click "back" and it tells you you have used up your 30 minute allowance.
That's why I gave up previously and again and again.

Yesterday I persisted and after two one hour waiting periods I eventually got a successful download by using "open in a new window".
 
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njepitt

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Hi Salas,

Salas said:
... Break BF-C's IDSS with a source degeneration resistor down to ~4mA.
Click to expand...

Can you confirm I understood this? In the schematic in post #3200 this means a resistor between drain of Q4 and source of Q5, right? (I can find the value for the resistor by trial and error, sticking resistors on the source and testing Idss, I presume).

Cheers

Nigel
 
Salas

Salas

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You should put resistors or better a trimmer in line with source leg on a test board. You should connect the resistor's free end to gate. You should use a 9V battery feeding (+) to drain via a DMM in DCmA mode in series. You should connect battery (-) to gate. You must home in to about 4mA. You must transfer the particular FET and resistor value to your regulator. A resistor will be added in series with source leg in that position in the reg schematic is the final picture.
 
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njepitt

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Thanks Salas,

Salas said:
You should put resistors or better a trimmer in line with source leg on a test board. You should connect the resistor's free end to gate. You should use a 9V battery feeding (+) to drain via a DMM in DCmA mode in series. You should connect battery (-) to gate. You must home in to about 4mA. You must transfer the particular FET and resistor value to your regulator. A resistor will be added in series with source leg in that position in the reg schematic is the final picture.
Click to expand...

OK, I misunderstood the resistor connection, and am glad for the correction.

Also, I measure IDSS using a schematic I picked up somewhere here which uses a resistor in series with drain, and measures voltage across it instead of measuring current directly, but that amounts to the same thing, I guess.

I hadn't thought of using a trimmer though - pretty obvious once pointed out, I guess!

Thanks again

Nigel
 
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njepitt

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Hi there,

I tried the source degeneration; with no resistance I measured IDSS at 12mA, and a resistance of 480R brought this down to 4mA. This seems a little higher than I was expecting, but there you are...

However, I looked at the datasheet, and IDSS for C grade is 12-25 mA, for B grade is 6-15 mA, and A grade is 2-6.5mA. So it looks like I misread something, and its really BF245A that's wanted, not B??? (I looked everywhere for B, and couldn't find it, but I may know where to get A...)

Cheers,

Nigel
 
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njepitt

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Hi,

Another parts question, I'm afraid... As usual, I am restricted to components I can source locally here in Brasilia until I have enough to make an order to Mouser or somewhere else up north worthwhile. The latest problem is that I can't find IRF610 for the -15v and -5v regs mentioned above. (I've found IRF9610 for the +5 reg without any trouble). I have IRF620, 630 and 530 and IRFP240 on hand - would any of these substitute for IRF610 in the -15v reg (which is v1.2R from post #3200) or the -5 reg (which is planned to be the BiB schematic - mosfet version)? Or anything else relatively common?

Also, I am presuming that 2SK170 can be used in place of 2SK117 in the BiB schematics?

Cheers,

Nigel
 
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njepitt

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Salas said:
IRF620 is rather OK. K170 in K117 place it changes its behavior enough from intended but its the only one you can readily substitute in need.
Click to expand...

Thanks, Salas. I looked again at the BiB guide to see why 2SK117 is preferred, and it cites IDSS of 3-5 mA. Since the 2SK170 I have are all BL grade, with IDSS of 6-12 mA, if I select to be near the bottom end (6-7MA) will that be OK? Or use source degeneration like you suggested for the BF245? (Incidentally, a friend in the Elec. Eng. department let me have a couple of BF245A...)

The v1.2R schematic doesn't say anything about grade for the 2SK170, so I hope BL is OK tere, since I already used them!

Cheers

Nigel
 
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