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I'm currently looking to buy a lab power supply. But there's something I wonder.

We can adjust the voltage and the current.

Let's say I have a circuit requiring 9V and draining 1A.

What if I setup my power supply to 9V 2A ? I think the circuit will only use 1A from the two available and the power supply will warm for nothing but the circuit will not be damaged. Can you confirm this ?

Emmanuel Istace
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2 Answers2

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The voltage and current adjustments work differently depending on the mode of operation (assuming the power supply supports both modes of operation).

(1) For constant voltage mode (power supply acts as a voltage source), the voltage adjustment sets the output voltage and the current adjustment sets the current limit.

This means that the power supply will output the set voltage as long as the connected circuit "draws" less than the current limit setting. When the output current reaches the limit, the power supply will reduce the output voltage to whatever is required to keep the output current at that limit.

(2) For constant current mode (the power supply acts as a current source, the current adjustment sets the output current and the voltage adjustment sets the voltage limit.

This means that the power supply will output the set current as long as the output voltage is less than voltage limit setting. When the output voltage reaches the limit, the power supply will reduce the output current to whatever is required to keep the output voltage at that limit.

Alfred Centauri
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  • If I get your answer correctly. (Sorry english is not my native language so I would like to avoid any misunderstanding ) I get the constant voltage mode but not sure about the current mode. In constant current mode I can set the power supply to 1V-1A and for example plug a 2V-1A device and he will adjust itself to output the 2V required but will lower the current (let's say 500mA) ? So he will "reconfigure" it self to 2V-"500mA" ? – Emmanuel Istace Nov 20 '13 at 17:10
  • @EmmanuelIstace, if the setting is 1A output current with 1V voltage limit, the power supply will not output 2V since that exceeds the 1V limit. – Alfred Centauri Nov 20 '13 at 17:18
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You are correct. Setting of the power supply to 2a, only sets its max limit.

Dale
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