Hello Moez,

The 7.5 V Zener diode is brought out to pin 6 in the LM2917N-8, and pin 9 for the LM2917N as seen in the right hand images shown below. The Zener provides a voltage regulator function internal to these version of the device. A supply voltage higher than 7.5 V and a series dropping resistor would be required just as with an Zener regulator circuit. Section 10.2.1.2.2 in the datasheet explains, "As an example, if the raw supply varies from 9 V to 16 V, a resistance of 470 Ω minimizes the Zener voltage variation to 160 mV." This provides an example of the typical performance had from the Zener under the stated conditions.

The other two versions of the product, LM2907N-8 and LM2907N do not connect the Zener internally and the internal circuitry operates at whatever voltage level is applied to the V+ pin. If that supply voltage varies the electrical performances are likely to vary more so compared to when the V+ pin is regulated.

Regards, Thomas

Precision Amplifiers Applications Engineering