Supply Current in relation to total current consumed by a circuit - Page 1
Forum section: electronics / beginners

author: firstoption
author_rank: Newbie
timestamp: March 08, 2014, 02:22:27 pm
content: Good day to all,Please I need your support and guide on how to get the required current to my circuit.The power supply I intend to use has a switching regulator (RT8289GSP ) with output voltage of 5V/5A(based on the current configuration of the switching regulator-application note from datasheet).However the total current consumed by my circuit is less than 1A(Attiny2313-1pc/tlc5971-4pcs/Max232-1pc/ftdichip2232).According to the datasheet,the switching regulator can output up to 5A which means that the output current can be adjusted just like the output voltage.But after going through the datasheet ,the only formular relating to current is this:Irms=I(out)max Vout/Vin?Vin/Vout-1.The idea of Irms coming into this equation is what actually confused me.i do not know how to figure it out so that I can get the desired output current.My knowledge of electronics is still very limited,i will really appreciate your guide on how I can solve this problem as I can not supply the 5A which the regulator outputs now (based on the current configuration) to the circuit.once again thank you for the support.best regards.

author: cyr
author_rank: Frequent Contributor
timestamp: March 08, 2014, 02:50:10 pm
content: 5A is the maximum the regulator can supply, it will not force that much current into your circuit (it can't, not without supplying a higher voltage).Unless you have a supply / regulator explicitly designed to drive a constant current (which means it will supply different voltages depending on the load) the current rating is always just a maximum or limit. The voltage will be constant, and the current will depend on the load.

author: Astroplio
author_rank: Regular Contributor
timestamp: March 08, 2014, 03:00:04 pm
content: The power supply you want to use has this chip but it is set to regulate for a certain output voltage.I assume it is already set for 5V. But don't worry the application circuit draws as much current as it needs.5A is just what is capable of.Also, just make sure the input voltage is always within range.

author: madires
author_rank: Super Contributor
timestamp: March 08, 2014, 04:28:24 pm
content: As the others already wrote, the voltage is regulated and the buck converter is able to deliver up to 5A. That doesn't mean that it has to :-) If your circuit draws just 0.1A, that's fine! But the buck converter is totaly oversized for that. With a small load of 0.1A the efficiency will be quite low. You have also to consider the external components like caps, diode and inductor (more Amps = more expensive). Check how much current your circuit needs at maximum and select a matching buck converter, maybe a 0.5A type.

author: firstoption
author_rank: Newbie
timestamp: March 08, 2014, 05:44:35 pm
content: Thank you for taking the time to explain in details what is actually going.i am really very grateful.i actually thought the 5A was cable of blowing up the components on the board,that was why I was looking for ways of adjusting it.Your explaination has given me the clear picture of what is going on behind the sceen.thank you once again for the guide. best regards