This is another excellent IC series which can be used for a multitude of different circuit applications. Basically it's a frequency to voltage converter (tachometer) IC with many interesting features. Let's learn more.
Main Electrical Specifications
The main features of the IC LM2907 ad LM2917 are underlined as follows:
- Input tachometer pin which is referenced to ground can be directly made compatible with all kinds of magnetic pick ups having a varying reluctance.
- The output pin is linked with an internally set common collector transistor which is able to sink upto 50mA. This can operate even a relay or a solenoid directly without external buffer transistors, LEDs and lamps can also be integrated with the output including, and of course can be sourced to CMOS inputs.
- The chip can double low ripple frequencies.
- The tachometer inputs has built-in hysteresis.
- Ground referenced tachometer input is fully protected against input frequency swings exceeding the supply voltage of the IC or negative potential below zero.
The pinouts details of the various available packages of the IC LM2907 and LM2917 can be witnessed in the below given images:
The main application areas of this IC are:
- Speed Sensing: It can used for sensing a rotational speed or the rate of a moving element
- Frequency Converters: For converting frequency into linearly varying potential difference
- Vibration based touch switch sensors
The chip becomes specially useful in the automotive field, as given under:
- Speedometers: In vehicles for measuring speeds
- Breaker Point Dwell Meters: Also a vehicle engine related measuring instrument application.
- Handy Tachometer: The chip can be used for making handheld tachometers.
- Speed Controllers: The device can be applied in speed control or speed governing instruments
- Other interesting applications of LM2907/LM2917 IC incude: cruise control, automotive door lock control, clutch control, horn control.
Absolute maximum ratings
(meaning the ratings which mustn't exceeded, of the IC are)
- Supply voltage = 28V
- Supply current = 25mA
- Internal transistor collector voltage = 28V
- Differential tachomter input voltage = 28V
- Input voltage range = +/-28V
- Power dissipation = 1200 to 1500 mW
Other electrical Parameters
Voltage gain = 200V/mV
Output Sink current = 40 to 50mA
Striking features and advantages of this IC
- The output does not respond to zero frequencies, and produces zero voltage at the output as well.
- The output volatge can be simply calculated using the formula:VOUT = fIN × VCC × Rx × Cx
- A simple RC network decides the frequency doubling feature of the IC.
- An on-chip zener clamp produces a regulated and stabilized frequency to voltage or current conversion (only in LM2917s)
A typical connection diagram of the IC LM2907/LM2917 is shown below:
For more info, you can refer to this article