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Purpose of Diode D1

Suraj Prajapati
Intellectual 255 points

Hello,

One of my section uses a circuit shown in following figures. 

1) With V1 = 24V  and VCC = 5V, I am getting 5.49V at anode of D1 as shown below.

2) With V1 = 5V  and VCC = 24V, I am getting 4.5V at anode of D1 as shown below.

I ma not getting what's the purpose of D1? 

Please guide me for the same

Best Regards,

Suraj

  • 0
    TI__Genius 9147 points
    Hi Suraj,

    I'm not sure I completely understand the purpose of these 2 circuits, but I can tell you this:

    - The voltage at the anode of D1 will be equal to the voltage divider of V1 formed by R1 and R3, unless the voltage exceeds a diode drop above VCC

    - The 2N7002 has an absolute maximum Vgs rating of +/- 20V

    - In the first circuit, 24V x (10M / 1M + 10M) = 21.8V, which is why D1 is clamping your probe voltage to 5.49V; this protects the 2N7002 from exceeding its 20V Vgs rating

    - In the second circuit, 5V x (10M / 1M + 10M) = 4.55V (as your probe indicates); D1 is not being utilized in the second circuit

    Please let me know if this helps.


    While you're here, please check out our latest reference designs, our library continue to grow and many customers find these beneficial while designing their products: www.ti.com/.../index.html


    Thanks,
    Jim
  • 0 in reply to Jim Carrillo
    Intellectual 255 points
    Hello Jim,

    Greetings!!

    Thanks for your valuable feedback. This is really helpful.

    Regards,
    Suraj