LM2917 PDF

versions (LM, LM) and its output swings. Solenoids, Meters, or LEDs to ground for a zero frequency input. • Frequency Doubling For Low Ripple. Texas Instruments LMN Series Voltage to Frequency & Frequency to Voltage are available at Mouser Electronics. Mouser offers inventory, pricing. LM LM – Frequency to Voltage Converter, Package: Soic Narrow, Pin Nb= The LM, LM series are monolithic frequency to voltage.

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Far-seeker on Aug 23, Read towards the bottom of page 8 on the data sheet.

I’m trying to make a frequency-to-voltage converter by using LM If you look at the series diode capacitor connection and think about it carefully you will see that at some input condition pulses in the cathode of the lm917 must go positive as the diode prevents the capacitor from discharging and at some point the diode is biased off I once tore a circuit up and re-built it C40 is being charged by dumping charge into it at each zero crossing or perhaps at one edge only of the AC input.

This is the capacitor the charge pump is charging. Did you look at the data sheet I included? This is confusing too.

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I need a circuit which generates 1mV voltage per 1Hz frequency. I’ve checked the current that the circuit takes and it’s about 65mA.

You want it to keep the measurements stable. Page 1 of the data sheet says it all. C41 is a filter capacitor to reduce the ripple from the charge pump. What is the function of the second opamp? But how does this charge pump do this?

This is with the input signal frequency and the output voltage disconnected. A quick look at the datasheet suggests the diode on the input isn’t necessary, it seems desined to have the tach ac input, no experience with the ic tho. The lm291 indicates a typical use case for the chip being to light a warning light when input frequency exceeds a threshold, in which case having an output transistor capable of sourcing or sinking more current makes sense.


I think Know you will find a negative voltage present on pin 1 when the chip gets hot At some input condition the diode becomes reverse biased and cut off except for the diode and capacitor leakage and the load resistance which is the reason it ‘sorta’ works above 2 – 2. It is drawn to be a comparator rather than a buffer. L2m917 have made use of a frequency to voltage converter LM, 8pin version to convert the frequency from my car’s RPM tach signal wire to voltage to then read it with my Arduino and make a digital RPM readout.

Thanks again for the replies.

LM Frequency to Voltage Converter

The charge pump is charging a capacitor which one? It’s supposed to take less than 5mA.

Did you try all of these ics in the l2917 circuit? Perhaps you have burned them all. The resistor, capacitor and the diode connected to the tach signal wire is to get rid of the DC offset. There are 2 problems at the moment: The data sheet provides the detailed arithmetic, but the telling point is that the relationship between input frequency and output voltage only depends on C40 and R Since the chip was originally built to post-process a magnetic pickup for tachometer applications, the lm297 crossing would be easy to arrange for by directly wiring the pickup coil across pins 1 and 8.

As you’ve wired it, the feedback acts to keep the voltage on pin 4 equal to the voltage on pin 3, with far better drive aka lower output impedance than offered by the output of the charge pump tachometer stage alone.


Another thing I’ve found is that the reason why at higher RPMs it lows lower, is that, since the chip was getting hot the accuracy was dropping, so it seemed it was reading incorrectly. R46 is acting as a load for the charged signal. It just gives several example circuits and a formula for the output voltage. Has anyone got l2917 experience with this chip at all? How do I choose value of C41 I put a random one for now? Although not the high current issue, The reason for the discrepancy in the speed is due to that series capacitor and diode My Employer walked up behind me and asked me why did I have an output grounded Post Your Answer Discard By clicking “Post Your Answer”, you acknowledge that you have read our updated terms of serviceprivacy policy and cookie policyand that your continued use of the website is subject to these policies.

Andy aka k 10 I guessed the roles of the capacitors completely wrong initially. Post as a guest Name. As much as I ln2917 to say it I still make similar mistakes and I have to stop and think about what I had By clicking “Post Your Answer”, you acknowledge that you have read our updated terms of serviceprivacy policy and cookie policyand that your continued use of the website is subject to these policies.

Sign up using Email and Password. Docedison Faraday Member Posts: RBerteig 6 What happens is that the diode is cut off by the dc generated from the input pulses.