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LM317: Review of the LM317 circuit construction.

Nam SangHoon
Prodigy 30 points
Part Number: LM317

Hello team,

I want to get feedback on the circuit I designed.
First of all, the Spec. is as follows.
1. Input voltage: 9 to 24V
2. Output voltage: 2 to 5 V
3. Output current: 200 to 700 mA

In the attached circuit
1. Input capacitor (Cin): C6 (1uF/50V/2012) Ceramic capacitor
2. Adj capacitor (CAdj): C7 (10uF/16V/2012) Ceramic capacitor
3. Output capacitor (Co): C8 (10uF/16V/2012) Ceramic capacitor
4. R8, R9 (60.4ohm/1 %/3216): Resistance will be changed according to output voltage based on 2.5V.
5. Protection Diode(D6, D7) : MURS140-13-F/ Diodes Incorporated

[Question]
1. Is the designed circuit reasonable?
2. I want to use a low-cost protection diode, do you have any parts to recommend?
3. We need to proceed with the design in a low-cost way, is there any way to lower the unit price of the parts by lowering Spec. among the above parts?

I would appreciate it if you could reply if you need any additional information.

Thanks.

Regards,

Nam

  • 0
    TI__Guru 50025 points

    Hi Nam,

    Your circuit design looks generally good. 

    What is the 2012 spec for the capacitors and 3216 spec for the resistors? They don't seem like normal sizes. 

    The diodes should be low-Vf Schottky diodes such as CUS10S30,H3F. 

    As for the cost, you could get away with less CIN and COUT. 100nF for CIN and 1uF for COUT would be fine. The datasheet says that COUT is not required, but transient performance would be very bad without any output capacitance. You could also remove CADJ altogether if you are not concerned with noise performance and PSRR. 

    Regards,

    Nick