# Not getting 5V output

I am trying to build a 5V constant 3A DC circuit. As stated in this datasheet: http://www.ti.com/lit/ds/symlink/lm338.pdf on page no.15.

According to calculation R2= 1.28 ohms, but I don't have it I have 1.6 near to it.

I have created the circuit using R2=1.6 ohms resistor and placed a 1K resistor as load and checked the voltage across it, it is giving me 15.68V which is a problem.

How can I accomplish this?

As stated in this datasheet: ti.com/lit/ds/symlink/lm338.pdf on page no.12. I have created the circuit and it is giving me 5.1 V constant just want to ask for confirmation that current drawn through this ckt will depend on load right? and we can take out max 5A right?

• You can use a MOSFET's body diode. But may I ask why? Why not put a 1N4007 or equivalent? If your intention is power-related then it's not needed to use a high power diode. Commented May 6, 2019 at 8:01
• I added the circuit from page 15. Note that this is simply a voltage regulator. It will deliver a constant 5 V if you choose R2 correctly. It will not deliver a constant 3 A. The current depends on the load. This circuit can deliver up to 5 A (limit of the regulator) provided it is kept cool enough. Commented May 6, 2019 at 8:39
• I want to use IRFZ44N as a Diode and replace it in the above-mentioned circuit WHY? The IRFZ44N has a drain-body diode, do you want to use that or do you want to make a "more ideal" diode by switching on/off the MOSFET to make it behave as a diode? What would be the advantage of that? You need to explain better what you're trying to achieve and why the circuit with diodes is not usable for you. Commented May 6, 2019 at 8:43
• Sir, I have calculated as per formula on page15. I got R2=1.28 ohms. I am thinking of using 1.2 ohms or 1.5 ohms or say max 2Ohm resistor. I was not having the diodes so I wanted to switch to MOSFET but now the retailer said it will be delivered within 2 days. So I am gonna use 1N4007 Diodes. Commented May 6, 2019 at 9:50
• I have taken I(adj)= 3A Commented May 6, 2019 at 10:04