I can not find an smd version of lm331 voltage to frequency converter in farnell rs or avnetexpress. Anyone can recommend a cheap equivalent in smd package?. I need 0 to 10V input and 100Hz 10Khz output.
ad537 seems relative expensive (I have high cunsumption)
will lm331 be discontiniued or not anymore frequently used?
incal99
Not likely SMD. It is an OLD part and DigiKey only shows DIP.
It is now a TI part and their web site says "active", not "end of life". The spec sheet only shows DIP-8.
Jim
Would the AD7740 work in your app?
Would the AD7740 work in your app?
Interesting that for this Voltage to Frequency converter you have to supply it with a frequency source... 
(reminds me of dehydrated water, to use just add water) But will keep it in mind. Thanks.
And this voltage-to-PWM converter has an internal frequency source:
LTC6992 - TimerBlox: Voltage-Controlled Pulse Width Modulator (PWM)
(reminds me of dehydrated water, to use just add water)
"The process uses a liquid that allows the hydrogen to be locked up in a liquid-based inorganic fuel." - Lee Cronin (University of Glasgow, School of Chemistry)
Read more at: http://phys.org/news/2014-09-hydrogen-production-breakthrough-herald-cheap.html#jCp
Sorry for the delay but avrfreaks.net seems different and I dont receive emails notifying forum posts anymore.
AD7740 needs an external crystall. Overall cost is much higher. It has also a limitation of 32.7KHZ (minimum frequncy)
I would need 100HZ to 10Khz freqeuncy range because in that way i can use cheap optocouplers such as PC817 to isolate the output pulse.
Timerblox from LT is also more expensive and frequency lower limit is not suitable.
the old good lm331 is the best fit. But very interesting , though it is an active part it is only available in DIP8 ?!?!?
incal99
Sorry for the delay but avrfreaks.net seems different and I dont receive emails notifying forum posts anymore.
After many threats and promises, the NEW Atmel AVRFreaks web software has arrived... with some problems and some mysteries. Enjoy it.
Cheers,
Ross
Older version was really good with quick links on the left and right side. Need a long time to get used to the new format
hey Incal.
See this http://www.ebay.com/itm/1-pcs-LM...
I think you can ask for bigger quantities.
cheers
Nachus
(I have high cunsumption)
So this is an existing design, being re-laid-out?
I peeked at the datasheet; it is indeed a "precision" device. But tell more how it is used. If a re-design, my first thought would be to use an AVR if 10 bits are good enough.
331 has a linearity which is an order of magnitude higher than the AVR 10 bits worth. ( 0.01%)
Nachus and Incal,
The LM331 was originally a National Semiconductor product. NS was taken over by Texas Instruments. TI list the LM331 but only in a DIP8 package, so I would be wary of the eBay product being offered in a SMD package. It could be a Chinese clone, or... a piece of coal. Buyer beware.
Last century I used the AD537 but it isn't available in SMD either.
Of corrs yes Ross! I don't know what are that chips, if they are NS original leftovers or not.
I've bought some time ago some chips that were discontinued by their manufacturers, and they sold it to me as a regular off the shelf part.
I asked what were the maximum available quantity and they told me that there were no limits. It's possble to find many of those chips in Argentinian component suppliers too.
I dont know about the chip's quality nor it's operating life expectancy though
cheers
Nachus
I don't know what are that chips, if they are NS original leftovers or not.
My point is that they were NEVER available in SMD format... so they cannot be leftovers.
Cheers,
Ross
a CD4046 / 74HC4046 could perform the conversion equally well albeit over a narrower voltage range .
a CD4046 / 74HC4046 could perform the conversion equally well albeit over a narrower voltage range .
Hi Iggy,
Yeah, a PLL could be interesting. Have you tried it yourself? Performance?
Cheers,
Ross
The circuit is for an isolated current sense. The shunt resistor has 0..60mV range for ex: 0..30A 60mV will be amplified to the whole adc range using the cheapest low offset opamp (ex MC616 0.4€ 0.15mV offset voltage) . The output of opamp will be then converted to a frequency signal where this signal goes though a cheap optocoupler (ex: 12KHz bandwith PC817) . The other side of the optocoupler is an mcu counting and resetting every 5ms to evaluate the frequecy in order to calculate the shunt current on the isolated path.
In between I also thought abaout realizing through a cheap mcu like atmel or pic reading the amplified data and converting the amplitude to a pwm frequency to do the job , low cost mcus have 10 or 8 bit adc so it is a question if the linearity can be achieved using a micro?
total budget is 1€ , so 0.4€ for mcu 0.4€ for low offset opamp 0.05€ for opto and rest for passives.
LM331 should be replaced because it is an old part (not even available as smd) . I feel it is dangerous for future . (think that you solder every board by hand after all done by the Pick and place machine just for lm331)
Any ideas?
NOTE on admin: I checked the send email notification but I dont receive emails when a new post arrived, so i can not react quicker to forum posts.
LM331 is now available through rochester electronics who specialise in supporting discontinued product lines. According to Rochesters web site they have thousands of these buggers in various shades of gray ( temperature and tolerance specs ) in stock.
Exar also have a similar product in PDIP8. They do have various PLL products in SMD packaging.
The key question is.... what linearity and resolution do You need?
The afore mentioned cd4046 pll is capable of operating over the frequency range and will produce the result You are looking for with less than the stelar performance of lm331. It's voltage /frequency tends to become a bit ugly at low analog control voltages.
I would like to invite You to consider the CMOS variant of 555 timer as a viable solution ( in absence of a clearer deinition).The other option ofcourse is a relaxation oscilator of own design.
EDIT: https://www.rocelec.com/
Rather annoying that there's not a modern SMD replacement for this old, useful part.
The largest known prime number: 282589933-1
It's easy to stop breaking the 10th commandment! Break the 8th instead. 
Rather annoying that there's not a modern SMD replacement for this old, useful part.
Tom,
I was so curious about the eBay part that I ordered one (its on its way)... will let you know if it turns out to be a piece of coal.
Cheers,
Ross
While we wait in Ross' report... last night i was doing some reading andcame upon a mention of linear techs solution to a problem whihc incorporated V/F conversion.
So here is a link which covers many sins:
http://www.linear.com/solutions/...
EDIT: the reading was pointed to by Bruno's posting on toneohm like shorts locators
ignoramus: the ltc6990 is x8 - x10 more expensive than lm331 :((
In that case, and in order to save some money, reform the DIP8 pins into SMD format and place and solder in one pass with the rest of SMD components
Yes, I also thought abaout the possibility for the smd convertion. I also examine a low cost micro 0.5$ with adc and PWM (there are many from 12Fpic and atmel). The linearity issue may be corrected in the MCU.
I am still waiting for the delivery of my "piece of coal".
lets see
