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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And heres my breadboard layout: I’m trying to make a frequency-to-voltage lmm2917 by using LM It just gives several example circuits and a formula for the output voltage. This is the capacitor the charge pump is charging. I understand that, the input opamp works as a comparator and converts the sinusoidal signal into digital pulses.
You have fixed Pin 11 at about 0. That chip is made to detect RPM, most dtasheet Idle rpm-ish, so you’re going to need a bunch of pulses or it’s going to measure 0. I think you problem lies with the input circuitry of the LM Its datasheet is very old and it doesn’t explain function of the IC well. Read towards the bottom of page 8 on the data sheet. Therefore to get the chip to do anything you have to take pin 1 above and below datashet point.
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 datashete alone. C41 is a filter capacitor to reduce the ripple from the charge pump.
An example circuit from the datasheet. Pin 11 and Pin 1 are the two inputs of a voltage comparator. Home Questions Tags Users Unanswered. 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 datahseet output transistor capable of sourcing or lm291 more current makes sense. I’m hoping someone can take a moment to help me and possible restor my sanity!
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.
Email Required, but never shown. All the capacitors and resistors are connected to ground; I’m very confused at this step. The sig-in line goes from 5. Can anyone offer some guidance? What is the function of the second opamp? C40 is being charged by dumping datashee into it at each zero crossing or perhaps at one edge only of the AC input.
LM Datasheet(PDF) – National Semiconductor (TI)
You want it to keep the measurements stable. Here’s a hand-waving explanation from a digital and software guy who has bumped in to sharp edges in the analog side But how does this charge pump do this?
This is confusing too. 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 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 Checkout my projects development blog SLiDA.
Then put a 10K resistor to the cathode of D3 and the other end of it to ground. I think the problem is my Internal Zener references. 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’m not game to hook it to my ‘duino nor can I be buggered going out to the bike yet The load is needed to convert the stored charge into a voltage that can be sensed, and pragmatically to provide a place for ddatasheet stored charge to leak off into as frequency falls.
Page 1 of the data sheet says it all. R46 is acting as a load for the charged signal. C42 does two things – the higher the value the lower the ripple voltage will be seen at the output however, the longer it datasneet take to attain the correct voltage should the frequency change.
I’ve played around with a few variations. Sign up or log in Sign up using Google.