Guidelines for using 3.3V output in the AMS1117 and LM1117 series and low-cost alternative products

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product description

AMS1117-3.3 and LM1117MPX-3.3 are three-terminal output low dropout linear regulators with an output current of 1A. When the current is 1A, its maximum voltage drop is only 1.3V. Because of its excellent performance, it is widely used.

main feature

The voltage drop is only 1.2V at 1A output current, with current limiting function, overheating protection function, output voltage accuracy can reach 1.5%.

Usage Guidelines

Since its maximum input voltage cannot exceed 18V, I try to keep it below 14V in a battery-powered scenario. If we connect it to the back end of the switching power supply, it is usually recommended that the output voltage of the switching power supply be controlled at about 12V. The following is the most typical application circuit diagram. It is not recommended to omit the capacitors at both ends of the picture. The author has done a test, in a very stable DC input environment, the capacitor at the input end can be omitted, but it is recommended to keep it for the overall stability. In addition, the capacitance value of the capacitor can be adjusted according to the actual use scenario, but it cannot be lower than 10μF.

Special problem

When connected to the back end of some switching power supplies, occasionally the work will be unstable. If there is no error in the circuit of the switching power supply itself at the front end, then we need to insert a resistance of about 20Ω between the output end of the switching power supply and the input end of AMS1117-3.3. After being connected, the whole circuit can basically work normally.

Low-cost alternative

Because this product is used in China is very large, so Chinese brands have also developed products with the same parameters and packaging. Because Chinese manufacturing has many cost advantages, the price of Chinese brand products is much lower. The price as of the writing date of this article, LM1117MPX-3.3NOPB1000Pcs, is $0.15624 at www.digikey.com and $0.468 at www.mouser.com. The price of the Chinese brand is $0.08. If you need to know more about other products in the same series, please contact favkb@outlook.com.