Shunt regulator TLV431

It really depends on why you want the "output resistance".

Normally, you will use this circuit to supply a range of output current to other circuitry. I would measure the output voltage when sourcing the min and max designed output current and derive the "output resistance" from that.

-- Sue

Correct!

The data sheet would imply it will act like a zener with < 0.4 Ohms impedance.

...Jim Thompson

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ymlink/tlv431.pdf

I need a low impedance voltage reference for the circuit linked below (the red arrow in the image). I need a +2V since the output of the AD629 has to be withing 2V of either rail. Do you know of a better way to achieve this? I'm rather unfamiliar with voltage references/ voltage regulators. Note: +Vs =3D 5V, -Vs =3D GND in the attached image. VREF would be the circuit referenced in my original post.

The datasheet for the AD629 can be found here:

Thanks! J

Is

symlink/tlv431.pdf

=A0 =A0 ...Jim Thompson

=A0 | =A0 =A0mens =A0 =A0 |

=A0 | =A0 =A0 et =A0 =A0 =A0|

=A0|

=A0 =A0 =A0 |

awesome! thanks Jim!

here:

At first glance, it looks like a less than an ohm source impedance with an over ten thousand ohm load impedance. So, I wouldn't be too worried about the impedance issues.

I think that you have misunderstood the significance of the "2v". This chip, with a 10v supply, is incapable of producing an output voltage lower than 2v or an output voltage higher than 8v. Without the application of a 2v Vref, if used as a unity gain device, you would get a constant 2v output for any input lower than 2v. Only after the input exceeded 2v would the output start to change.

With 2v Vref, the output is still 2v when a zero input is applied, but will start rising as soon as the input does - so, by the time the input is 2v, the output will be 4v.

Obviously, once the output reaches 8v (with a 10v supply) it will stop going up - no matter how much the input increases further.

So, it all looks fine. The only change I might make is to up the supply voltage a tad. 5v is the minimum. I'd probably go for a 10 or 12v supply, if one was available. I am always suspicious when manufacturers quote one voltage range for operation, but use a rather narrower one for important performance figures, like power supply rejection ratios.

-- Sue

I don't seem to be able to look at that image without signing up at Imageshack, which I have no desire to do. However, I assume it's the usual adjustable shunt regulator circuit, with a resistor Rs from supply to cathode, anode grounded, and a voltage divider between them to drive the feedback pin.

Output resistance is a small-signal parameter, so shorting the output (and so turning the TLV431 off completely) will give the wrong answer, because the output resistance is Rs when the regulator isn't running, but under an ohm when it is. (The datasheet says 0.25 ohm typical, 0.4 ohm max.)

If you have a good voltmeter, you can measure the change in the output voltage when you change Rs, and do the math.

Cheers

Phil Hobbs

Weird. The referenced post showed up as new in Thunderbird today--I just noticed the 2008 date. I hope the OP figured out the problem!

Cheers

Phil Hobbs

Phil, you're replying to a 10-year-old thread.

BTW, Imageshack was free then.

My guess(tm) is that your Thunderbirdie global messages database is mangled. Easy fix: For a while last year, Thunderbirdie was delivering indexing failures, searches returning blank messages, and tangled threading. Rebuilding global-messages-db.sqlite fixes the problem.

You may also want to rebuild some of the associated MSF message indexes: I'm not sure if this part is really necessary, but it doesn't hurt to rebuild everything.

You can watch the action by monitoring: Tools -> Activity Monitor

No, of course that's wrong. Shorting the 'output' means powering off the feedback amplifier in the TLV431, which is NOT normal operation. Testing for a linear property (like output impedance) makes sense only with small-signal perturbations of output current that do not exceed normal operating conditions.

From time to time my Agent mangles threads too. I always check the dates.

Cheers

Yep. I'm currently using Agent 5.00/32.1171 mostly because later versions seemed to make the problem worse. The usual symptom is a new thread of articles magically appear grafted into the middle of an old thread, usually many years old. Rebuilding the indexes doesn't fix the threading. At one time, I thought that some news readers were generating duplicate ID numbers, but upon checking, that was not the case. It only happens to me about 4 times per year, so I just ignore the problem. (I should probably try a later version).

I'm currently using Agent v7.20/32.1218 without issue.

Don't bother paying for any version later than that... "Support" still hasn't fixed the "expire after 10-days of inactivity" problem with filters when Win7 and Win10 munged them.

suckers for more and more useless "features" :-( ...Jim Thompson