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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Therefore to get the datsaheet to do anything you have to take pin 1 above and below this point. I think the problem is my Internal Zener references.

I datashest you problem lies with the input circuitry of the LM Sign up or log in Sign up using Google. Read towards the bottom of page 8 on the data sheet. I have then used the datasheet as well as this schematic to convert to 14 pin How do I choose value of C41 I put a random one for now?

However you have no DC biasing on Pin 1 so it will just swing about with the AC coupled input and not do anything. C41 is a filter capacitor to reduce the ripple from the charge pump. That chip is made to detect RPM, most engines Idle rpm-ish, so you’re going to need a bunch of pulses or it’s going to measure 0. What is the function of the second opamp? RBerteig 6 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.


An example circuit from the datasheet.

To help save hands, I hooked an LED up to the output signal. 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 a common configuration for a unit-gain buffer.

The output transistor is provided with open emitter and collector to permit its use in a variety of configurations. Ideally, you’re going to need 8 pulses per second minimum, would be better for test purposes.

National Semiconductor – datasheet pdf

And heres my breadboard layout: This is the capacitor the charge pump is charging. C42 does two things – the higher the value the lower the ripple voltage will lm217 seen at the output however, the longer it will take to attain the correct voltage should the frequency change.

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. Then put a 10K resistor to the cathode of D3 and the other end of it to ground. The charge pump is charging a capacitor which one? By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service.


You have fixed Pin 11 at about 0. C40 is being charged by dumping charge into it at each zero crossing or perhaps at one edge only of the AC input.

Problem with LM Tach Circuit – 14 Pin version

Its datasheet is very old and it doesn’t explain function of the IC well. You want it to keep the measurements stable. 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. Checkout my projects development blog SLiDA. 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.

National Semiconductor

The first op-amp is a camparator as your question states. Pin 11 and Pin 1 are the two inputs of a voltage comparator. 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