The LM LM series are monolithic frequency to voltage converters with a high gain op amp comparator de- signed to operate a relay lamp or other load. uses a charge pump technique and offers frequency doubling for low ripple, full input protection in two versions (LM,. LM) and its. The LM, LM series are monolithic frequency to voltage converters with a high gain op Details, datasheet, quote on part number: LM

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Its driving me nuts The sig-in line goes from 5. Then you stand a chance of getting the input to switch. Since the chip was originally built to post-process dataseet magnetic pickup for tachometer applications, the zero crossing would be easy to arrange for by directly wiring the pickup coil across pins 1 and 8.

Therefore to get the chip to do anything you have to take pin 1 above and below this point. This is the capacitor the charge pump is charging. RBerteig 6 Once it stops raining here, I’ll drag it out and put it onto the bikes injector input at least and see if that makes it behave better The datasheet 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.

The charge pump is charging a capacitor which one? Then put a 10K resistor to the cathode of D3 and the other end of it to ground.

The first op-amp is a camparator as your question states. If I pulse 14V onto the “Signal In” port with that powersupply also connected to ground Page 1 of the data sheet says it all. The load is needed to convert the stored charge into a voltage that can be sensed, and pragmatically to provide a place for the stored charge to leak off into as frequency falls. But how does this charge pump do this?


LM Datasheet(PDF) – National Semiconductor (TI)

How do I choose value of C41 I put a random one for now? What is the function of the second opamp?

I think the problem is my Internal Zener references. Email Required, but never shown. And heres my breadboard layout: Its datasheet is very old and it doesn’t explain function of the IC well.

The second op-amp is buffering the signal stored on C41 and driving the output transistor, it has feedback from the output to its -ve input which is datashwet common configuration for a unit-gain buffer. Dataeheet have then used the datasheet as well as this schematic to convert to 14 pin Read towards the bottom of page 8 on the data sheet.

Sign up using Email and Password. Post as a guest Name. All the capacitors and resistors are connected to ground; I’m very confused at this step. Home Questions Tags Users Unanswered.

I think you problem lies with the input circuitry of the LM Im guessing now totally that my ‘test powersupply’ is putting 70ma across the base of thewhich is saturating it. 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 I’m not game to hook it to my ‘duino nor can I be buggered going lk2917 to the bike yet Checkout my projects development blog SLiDA.

The LM’s datasheet is at http: I’m guessing the AC input datasneet required to be centered on 0V, datashete, but a DC blocking cap outside the chip would easily achieve that. I created a custom library for this IC and set up my own circuit as seen in the schematics above. I want to learn working principle and internal circuit of the IC, and function of externally connected components especially C 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.


I’m hoping someone can take a moment to help me and possible restor my sanity! Sign up using Facebook. I’m stuck with a pin Lj2917 – i’ve got an 8-pin on order now, but damn it, I want to get this to work. C40 is being charged l,2917 dumping charge into it at each zero crossing or perhaps at one edge only of the AC input.

National Semiconductor

C41 is a filter capacitor to reduce the ripple from the charge pump. You have fixed Pin 11 at about 0. I’ve built this on a breadboard using a modified version of http: I’ve played around with a few variations. However you have no DC biasing on Pin 1 so it will just swing about with the AC coupled input and not do anything. Can anyone offer some guidance? Sign up or log in Sign up using Google.

I’m trying to make a frequency-to-voltage converter by using LM Now slightly more awake – Im thinking the grounding of the negative SigIN is ‘producing’ a voltage because it causes the various caps to discharge – not because it actually runs through the IC I understand that, the input opamp works as a comparator and converts the sinusoidal signal into digital pulses.

It just gives several example circuits and a formula for the output voltage. Yeah – I figured that i needed a decent ‘frequency’