current regulator

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The block diagram shows this as a closed-loop regulator, not just some jfet sort of thing.

The high minimum voltage and unspecified capacitance/speed limits its use, but it is cute.

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John Larkin         Highland Technology, Inc 

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Fun. Might be a good safety feature for George's APD supply if it's quick enough. It's hard to get into much trouble with 10 mA, and that's way more than an APD needs. Mine uses LND150 depletion MOSFETs because I want a lower current limit.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
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Phil Hobbs

DN2530 with a source resistor is pretty good too. I have values.

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John Larkin         Highland Technology, Inc 
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Way too much current for the Spad. The spec sheet says ~200uA CW I've got an lnd150 and 10k ohm (G-S) for 100uA. (It's a few hundred volts, 100V @ 100 uA ~10 mW... it might take more than that but who wants to blow up a $250 part, I've been afraid to test the current limit until I make more measurements.)

George H.

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George Herold

I was talking about the safety current limit, not the device protection one. Unless I'm mistaken, UL wants the gizmo to be safe even when it's broken.

Cheers

Phil Hobbs

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I bought a bunch of depletion MOSFETs recently, including some of those. Useful gizmos.

The DN2530's specs are pretty loosey-goosey--Vdg_off is -1 to -3.5V, and there's only a minimum for transconductance and a maximum I_DSS.

Do you find that it's consistent enough in real life to make a good current limiter?

The On Semi 120V, 20 mA model has +-15% tolerance on I_DSS, and looks like about 35 ohms at room temperature, which wouldn't be bad for input protection of lowish-noise amps.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
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Oh right, something like 10 mA might be perfect for that. I haven't thought that far our yet. Heck at the moment I'm using a hunking linear HV supply, and haven't made the HV power supply.... Lot's to do.

George h.

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George Herold

I bought DN2540's -1.5 to -3.5V.. but that's no different than the lnd150's spread. Have you measured any?

Hmmm if I get a batch of lnd150's with closer to -3V than whatever I'm seeing now that could be a problem.

I'll have to measure some... I'm mostly machining today. I found this

2-56 gun tap in our drawer. It's really slick, shoots the chip out the far end of the hole, rather than having to work the tap in and out. (Wouldn't be so good for a blind tapped hole though.)

George H.

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George Herold

All the LND150s I've seen were right around 1.6 mA I_DSS. If the DN2530s are the same way, we can probably use them for our own products, but not in designs for licensing or work-for-hire.

The On Semi NSIC2020JB is 20 mA +- 15%, and has a small signal resistance of around 35 ohms at room temperature. For input protection on a high-Z input, it would contribute only about 0.76 nV 1-Hz noise at

300 K, and I could use low-capacitance Schottkys to the supply rails with no worries.

Fun.

Cheers

Phil Hobbs (doing Gerbers and proposals today--less fun)

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Yeah, I don't get to do it much these days, but I enjoy machining. (turning a hunk of metal into something useful.)

Sorry, there's always scut work, not sure how to classify proposals. Someone's gotta pay the bills.

George H.

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George Herold

I haven't tested enough of the DN2530s to get statistics. But all of the LND250s that I've tried had Idss close to 1.6 mA. The spec is 1 to

  1. What's that ON part number?

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John Larkin         Highland Technology, Inc 

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This one I think

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GH

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George Herold

NSI45030AZT1G is 30 mA +- 15%, 45V, and NSIC2020JBT3G is 20 mA +- 15%, 120V. They have lots of others.

Cheers

Phil Hobbs

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Phil Hobbs

Oh, the 2-terminal ones. I have some of those. Probably depletion mosfets. Ohmic near zero volts, with a reverse substrate diode.

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John Larkin         Highland Technology, Inc 
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Roight. The 3-terminal ones don't seem to be as good--at 0.5V D-S they're only up to 14% of max current, whereas the two-terminal ones are about 45%. So maybe they have resistors in both gate and source, and the external resistor is in parallel with the gate resistor.

S D

0-----*-RRRR-*----*-* ,---------0 | | | V | | R ------- | R ,----- | R | | | | `-RRRR-*---* | 0 Rx

Except that the current limit actually goes up when you put in the resistor, whereas in the circuit above it goes down.

Wonder what the actual circuit looks like.

Cheers

Phil Hobbs

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