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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Page 1 of the data sheet says it all. The first op-amp is a camparator as your question states. Therefore to get the chip to do anything you have to take pin 1 above and below this daatasheet.

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. I created a custom library for this IC and set up my own circuit as seen in the schematics above.

I’m hoping someone can take a moment to help me and possible restor my sanity! Then put a 10K resistor to the cathode of D3 and the other end of it to ground. I feel well past my depth trying to sort this out And lj2917 my breadboard layout: Here’s a hand-waving explanation from a digital and software guy who has bumped in to sharp edges in the analog side C42 does two things – the higher the value the lower darasheet ripple voltage will be seen at the output however, the longer it will take to attain datsaheet correct voltage should the frequency change.


This is confusing too. The LM’s datasheet is at http: C40 is being charged by datasheeet charge into it at each zero crossing or perhaps at one edge only of the AC input.

National Semiconductor – datasheet pdf

I understand that, the input opamp works as a comparator and converts the sinusoidal signal into digital pulses. I need a circuit which vatasheet 1mV voltage per 1Hz frequency. How are you pulsing the 14V?

Post as a guest Name. You have fixed Pin 11 at about 0. It is drawn to be a comparator rather than a buffer.

I think the problem is my Internal Zener references. RBerteig 6 R46 is acting as a load for the charged signal. Sign up using Email and Password. Pin 11 and Pin 1 are the two inputs of a voltage comparator. Email Required, but never shown. I think you problem lies with the input circuitry of the LM It just gives several example circuits and a formula for the output voltage.

I want to learn working principle and internal circuit of the IC, and function of externally connected components especially C You want it to keep the measurements stable. Since the chip was originally built to post-process a 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.

All the capacitors and resistors are connected to ground; I’m very confused at this step.

National Semiconductor

Sign up or log in Sign up using Google. I’ve played around with a few variations. 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 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.

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I’ve substantially edited this text to make it more true, see the edit history to see my incorrect babbling if you really want to. By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. However you have no DC biasing on Pin 1 so it will just swing about with the AC coupled input and not do anything. I’m guessing the AC input is required to be centered on 0V, incidentally, but a DC blocking cap outside the chip would easily achieve that.

I’m trying to make a frequency-to-voltage converter by using LM An example circuit from the datasheet. Can anyone offer some guidance?

Checkout my projects development blog SLiDA. The llm2917 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 a common configuration for a unit-gain buffer.

Read towards the bottom of page 8 datasyeet the data sheet. How do I choose value of C41 I put a random one for now? But how does this charge pump do this?

I guessed the roles of the capacitors completely wrong initially. I then have another supply, also grounded to the common ground, thats 14V. Im guessing now totally that my ‘test powersupply’ is putting 70ma across the base of thewhich is saturating it.