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I am making a project which works on 3.3v. Here I am also using 6 digits 7-segment display so I need large current with 3.3V input.

I am using 6v of a battery which it needs to regulate and generate 3.3v. I have ld1117v33 and its max input voltage range is 15v. I also got some information about to give Vr = 1.25v.

Here I am confused how can I give Vr at which pin of ld1117v33. Please help me an understanding of Vr here and how it is different from Vin. Do I need to give separate voltage to Vr?

Datasheet

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  • \$\begingroup\$ Where is your link to the datasheet? Add the info into your question. Please capitalise the part numbers correctly for legibility. \$\endgroup\$
    – Transistor
    Jul 5, 2017 at 7:28
  • \$\begingroup\$ here is datasheet link sparkfun.com/datasheets/Components/LD1117V33.pdf \$\endgroup\$
    – Aarav Soni
    Jul 5, 2017 at 7:43
  • \$\begingroup\$ Hyperlink it in the question. Make it easy for your readers. \$\endgroup\$
    – Transistor
    Jul 5, 2017 at 8:02
  • \$\begingroup\$ There is no Vr in the datasheet, only Vref and Vripple. \$\endgroup\$ Jul 5, 2017 at 8:51
  • \$\begingroup\$ I need large current??????? \$\endgroup\$
    – Andy aka
    Jul 5, 2017 at 10:08

2 Answers 2

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Vref, reference voltage only matters when using the adjustable version of the LDO in question. For LD1117v33 it is irrelevant. By the way if you check the datasheet, then you can see what Vref is on figure 2.

enter image description here

Vref = 1.25 V and Vref is the voltage across R1. The LDO adjusts its output until the voltage across R1 is Vref, thus you can set the output voltage to a desired value with an appropriate voltage divider.

Now, in case of the LD1117v33 the output voltage is fixed 3.3 V. There is no ADJ pin, just GND and you do not have to care about the feedback externally. You only need the input and output capacitors.

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I believe what you mean by Vr is actually Vref. I had a look at the DATASHEET and it shows that there are only 3 pins. Vin, Vout and GND, like most standard linear regulators. Now, your 6V input is going to be fine. Looking through the datasheet, you can see that the dropout voltage is a max of 1.2V if you have a load consuming 800mA (which is the max current). This means the regulator will work untill your Vin falls below approx 4.5V. enter image description here

Now, the Vref you mentioned is just an reference voltage which is used on the adjustable version. As you are using the set 3.3V regulator, you do not need to worry about this.

I hope this helps!

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