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Confused about the LM334

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m12lrpv:
In Dave's power supply he has used the LM334 as a minimum load for the regulator.

I would have to go back and look but I think he did that based on it providing a constant current across the voltage adjustment range.

I have also noticed LTspice simulates it as providing a constant current regardless of the input voltage.

While working through the datasheet I have noticed that the formula for determining the set resistor is voltage dependant so the current must vary with voltage. Yet the general understanding seems to be that this is not the case.


So i'm confused as to what the real performance of this part is. From the datasheet it would seem that for varying voltages you may as well just dispense with the LM334 and just keep the set resistor (with the value increased a bit) to set a minimum load.


I would experiment with it but the only one I have is soldered into a circuit :)

amspire:

--- Quote from: m12lrpv on April 23, 2012, 11:01:43 pm ---
While working through the datasheet I have noticed that the formula for determining the set resistor is voltage dependant so the current must vary with voltage. Yet the general understanding seems to be that this is not the case.


--- End quote ---

No it is not. The equation for the current out of the LM334 is

ISET  = (227 uV/deg K)/RSET

So the current is temperature dependant, but not voltage dependant.

Richard.

m12lrpv:
My bad. I was reading Vr as Vin   :-[

Sometimes you just need someone else to take a look for you to pick whatever obvious thing it is that you're missing.

Thanks.

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