Lm334

Orion

I need some guidance with the LM334.·
·
So far I have hooked up the LM as shown in NV #29 figure 29.3 http://www.parallax.com/dl/docs/cols/nv/vol1/col/nv29.pdf, I think at least.·
·
Here is the data sheet for the LM334 I am using http://www.st.com/stonline/books/pdf/docs/2157.pdf.
·
I am assuming the "TOP" of the chip means pins down.· With this setup, I'm reading around 4.02v across the 10k resistor.· If this were, .01v/deg then that would be 402K or 263.93F! I don't think so, this room is around 70F.·
·
So next I tried wiring it with "TOP" pins up.· This gave me around 2.88v or ~58F.· Still seems low but a lot closer to what I expect.
·
What am I doing wrong here?· Is my voltage => temp calculation wrong/wiring?
·

Beau Schwabe

Pins should be down.... It sounds like your LM334 might be rotated 180 deg.

1 o \/   8

2        7
 
3        6

4        5

For proper pin orientation you should see a dimple or notch near the "top" of the IC.

Note: The pinout of this chip is "keyed" so that 180 deg rotation should not dammage it.
However your description implies an upside-down connection which effectively swaps
V+ and ADJ. I'm not sure how this will impact the life of the chip.

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Beau Schwabe - Mask Designer III

National Semiconductor Corporation
(Communication Interface Division)
500 Pinnacle Court, Suite 525
Mail Stop GA1
Norcross,GA 30071

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Orion

Beau Schwabe said...

·I'm not sure how this will impact the life of the chip.

LOL!! Thats why I buy @ least·5 of any new IC.

BTW I'm using the TO-92 package.· Both readings where taken on different new·IC's.

Post Edited (Orion) : 3/11/2005 10:13:14 PM GMT

Beau Schwabe

In that case you have reversed V+ and V-, looking at the schematic I don't see any
current paths that should let the smoke out, but this could be a simplified schematic
in which damage may be likely.

The pins are a bit misleading, but judging from the schematic, Q2 might allow you
to do a DIODE check with a Digital Volt Meter to determine the proper pin out.
Q2's Base is connected to the ADJ or the ANODE of the B-E junction. Q2's Emitter
is connected to the V- or the Cathode of the B-E junction. I would expect to see a
value close to .6V on your meter across the ADJ and V- pins.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔

---

Beau Schwabe - Mask Designer III

National Semiconductor Corporation
(Communication Interface Division)
500 Pinnacle Court, Suite 525
Mail Stop GA1
Norcross,GA 30071

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Orion

I get .67 volts like you said, from what I assume is ADJ and V-. Which would seem to be backward from the data sheet, "TOP" being pins down? This is the only way I get any readings close to what they should be. Is this normal with a TO92, "Top" on the data sheet is pins looking up?

Thanks

upand_at_them

I use the LM335, which is the Celsius version.· And I use a 1K resistor with good results.· According to the datasheet you want less than 5mA bias current.· A 1K resistor will yield 2mA bias current at 25C.· I would think the LM334 behaves the same way.

I have my resistor at the sensor end, sealed with the leads in heat shrink tubing.· I've also cut off the adjustment lead; the offset is a constant, so any calibration I need I do in the software.

Here's where I got the images and information: http://web.mit.edu/rec/www/workshop/lm335.html

Mike





Post Edited (upand_at_them) : 3/12/2005 12:28:41 AM GMT