LM2907-N: Creating A Simple Frequency to Voltage Converter Circuit

Hi Gopi,

can you show us your schematic?

Kai

Hi Gopi,

Do you still need assistance with this LM2907-N inquiry? We will need the schematic, supply voltage, input signal and output load information to be able to best assist you.

Regards, Thomas
Precision Amplifiers Applications Engineering

Hello Gopi,

Do you have a DSO image or drawing of your tach input signal to the LM2907-N? Please confirm you are using the 8-pin package option.

Regards, Thomas
Precision Amplifiers Applications Engineering

   

        the above pictures are for 100 rpm with input wave form and output voltage of the Lm2907N

        

              

 the above pictures are for 1000 rpm with input wave form and output voltage of the Lm2907N .

    

     the above pictures are for 3000 rpm with input wave form and output voltage of the Lm2907N . 

for all the rpm frequency input was varying and output voltage was same as attached .please suggest .I am using 8 pin only .                                                  

Hi Gopi,

when using the 8pin LM2907 your input signal must toggle arround GND. But your input signal is always positive. So, you must AC couple your signal to the input pin of LM2907 like shown in figure 5b or 5c of this appnote:

www.ti.com/.../snaa088

Kai

Hi Gopi,

Be sure to include the resistor from the LM2907-N pin 1, to ground, as shown in figures Kai referenced. The TACH+ input (pin 1) requires a dc path to ground through which the PNP input transistor's base current can flow. A few kiloms should work.

Regards, Thomas
Precision Amplifiers Applications Engineering

Hi Kai,

Thank you for your suggestion.

Still i didn't get complete solution. As per your information i have done ,it worked really well.In out put the voltage level getting saturated after 1.7Khz             (Say 10.7V after which it remains same for all frequency). Still i am working on it.

Hi Gopi,

then you should try to adjust the scaling. This is explained in section 9.3.2 of datasheet.

Kai

Hi Gopi,

Additionally, if you haven't already seen it you may want to take a look at the LM2907-N Application note 162. Its provides more in-depth information regarding the selection of R1, R2 and C1.

Regards, Thomas

Precision Amplifiers Applicaitons Engineering