Design Frequency to Voltage Circuit of LM2907N - Electronic Circuits Projects Diagrams Free

swear_swear · 2nd July 2003, 07:03 AM

I have followed the datasheet of LM2907N to design a frequency to voltage circuit. But I still cannot be sucessful to make a larger voltage output range. It only can be varying within 0-3V output for 40Hz input.
Can any professional give me a design which can achive a higher range of output, e.g: 0-50Hz to have an output range 0-12V. That range can give me a larger range to have a more accuracy signal to do speed control.
Also, the ripple of the output will affect the output range or not?
Thank you very much.

:roll: :roll: :roll: :roll: :roll: :roll:

Sebi · 2nd July 2003, 09:51 AM

Choose another type.As i read from d'sheet it can't do this.

swear_swear · 2nd July 2003, 10:06 AM

Sorry, can you give me any advice of which type can do such thing?
Or any other methods can achieve the task?
Really need help.
Thank you a lot.

Klaus · 3rd July 2003, 09:09 AM

Why not connect the output to a transistor (base). You can then drive the transistor to give you an output of up to Vcc.
Klaus

**mechie** · 3rd July 2003, 02:45 PM

I'm sure the LM2907 is capable of doing what you want,
it just needs some component changes to set the range.

The IC has three basic sections, a trip amp, a charge pump and an op amp,
if the charge pump (and following integrator) can't be set to the desired time constant then the op amp can give lots of gain.

As you don't mention any component values other than imply you are following some datasheet,
Try C1 (from pin 2 to ground) as 2uF
and R1 (from pin 3 to ground) as 10k

or
C1 = 1uF
R1 = 20k

with everything else as per the datasheet (I'm looking at http://www.national.com/ds/LM/LM2907.pdf )
Should give 50Hz as 12v out with a 12v supply ... BUT
As the circuit will lose some voltage it will stop short of 12v out.

To do better requires more info - supply voltage, rest of circuit components ?

swear_swear · 5th July 2003, 01:02 AM

Thank you for your reply.
As I want to know the attached circuit is correct as what you mention?
But i want to know the accuracy of this circuit?
because i use it to deteminate of the speed of the motor and by using this DC voltage to do control. So, can you give me any advice about the accuracy of the circuit?
Thank you very much~
:idea: :idea: :idea: :idea:

swear_swear · 9th July 2003, 04:38 AM

Sorry, can anybody give me advice or the circuit is correct or any incorrect place?
Thank you very much~
:!: :!: :!: :!:

**mechie** · 10th July 2003, 10:12 AM

As you show the 8 pin package circuit,
I assume this is what you have - there is a 14 pin version as well.

The 8 pin package has the op-amp input stage's inverting input connected to ground (via pin 8), the non-inverting input is on pin 1.
This op-amp works as a sort of 'trip amp', whenever the input on pin 1 exceeds the voltage on pin 8 (0v), the output to the charge pump will go high, being low at all other times.

This is important as the input signal MUST cross this zero volt threshold :!:
The input signal must therefore go positive AND negative for the circuit to work.

Other than that (you said the circuit worked, just gave the wrong range), the diagram you posted is correct, the vaues should be OK.

swear_swear · 10th July 2003, 05:08 PM

Thank for reply.
I have made the circuit but seem not work.
I don't know why. But I have used the 14 PINS version (LM2907N).
I am before use the below circuit and it work.
So, what can I do.
Please help~
:?: :?: :?: :?:

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2nd July 2003, 07:03 AM	(permalink)
swear_swear	Design Frequency to Voltage Circuit of LM2907N I have followed the datasheet of LM2907N to design a frequency to voltage circuit. But I still cannot be sucessful to make a larger voltage output range. It only can be varying within 0-3V output for 40Hz input. Can any professional give me a design which can achive a higher range of output, e.g: 0-50Hz to have an output range 0-12V. That range can give me a larger range to have a more accuracy signal to do speed control. Also, the ripple of the output will affect the output range or not? Thank you very much. :roll: :roll: :roll: :roll: :roll: :roll:

2nd July 2003, 09:51 AM	(permalink)
Sebi	Choose another type.As i read from d'sheet it can't do this.

2nd July 2003, 10:06 AM	(permalink)
swear_swear	Sorry, can you give me any advice of which type can do such thing? Or any other methods can achieve the task? Really need help. Thank you a lot.

3rd July 2003, 09:09 AM	(permalink)
Klaus	Why not connect the output to a transistor (base). You can then drive the transistor to give you an output of up to Vcc. Klaus

3rd July 2003, 02:45 PM	(permalink)
mechie	Stick with the LM2907 I'm sure the LM2907 is capable of doing what you want, it just needs some component changes to set the range. The IC has three basic sections, a trip amp, a charge pump and an op amp, if the charge pump (and following integrator) can't be set to the desired time constant then the op amp can give lots of gain. As you don't mention any component values other than imply you are following some datasheet, Try C1 (from pin 2 to ground) as 2uF and R1 (from pin 3 to ground) as 10k or C1 = 1uF R1 = 20k with everything else as per the datasheet (I'm looking at http://www.national.com/ds/LM/LM2907.pdf ) Should give 50Hz as 12v out with a 12v supply ... BUT As the circuit will lose some voltage it will stop short of 12v out. To do better requires more info - supply voltage, rest of circuit components ? __________________ I need a memory upgrade ... My head is full !

9th July 2003, 04:38 AM	(permalink)
swear_swear	Sorry, can anybody give me advice or the circuit is correct or any incorrect place? Thank you very much~ :!: :!: :!: :!:

10th July 2003, 10:12 AM	(permalink)
mechie	LM2907 - 8 pin package As you show the 8 pin package circuit, I assume this is what you have - there is a 14 pin version as well. The 8 pin package has the op-amp input stage's inverting input connected to ground (via pin 8), the non-inverting input is on pin 1. This op-amp works as a sort of 'trip amp', whenever the input on pin 1 exceeds the voltage on pin 8 (0v), the output to the charge pump will go high, being low at all other times. This is important as the input signal MUST cross this zero volt threshold :!: The input signal must therefore go positive AND negative for the circuit to work. Other than that (you said the circuit worked, just gave the wrong range), the diagram you posted is correct, the vaues should be OK. __________________ I need a memory upgrade ... My head is full !