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Return to Blog1.2 - 12V / 1A Low Voltage LED Indicator Power Supply by LM317
Posted Feb 08, 2012 at 2:01 pm
Figure 1
This is a 1.2 – 12 V, max 1A power supply with a low voltage indicator LED. The indicator part includes three diodes and one LED. For example you are charging a battery, you can observe the charge status at that moment. Another advantage of this circuit, when the drawn current exceeds 1A (practically 0.85A), the current protector in LM317 intervenes and LED indicator warns you about the very low output voltage.
Be careful while choosing the transformer. Most of the products are specified as 10VA but their outputs are not as said.
Another good property of this circuit is the mains noise does not pass to the DC part.
Comments on this post:
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3 years ago: I need a status LED for a project I have. It takes 12v DC 3500mAH from a battery, but there is no indicator as to when the battery is low. This would be more than ideal for the project, but I lack the time and patience to build one myself. How much to build one for me as soon as possible, shipping to the UK? I need it to be as small as possible. Email me and let me know, I might need more in the future.
3 years ago: original circuit on site http://www.belza.cz/pwrsply/ 317zdroj.htm
2 years ago: I'm just curious, at what voltage level will it give the "low voltage" indication? Is it less than 1.2V or less than what has been set?
2 years ago: hi dolphy, you can see that when the current gets below 1A like 0.85A, as stated in the explanation, the voltage will also drop due to this low current...