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I have a 2 amp 12 volt regulated power supply and I want to use it to emulate a 9 volt battery for a breadboard. However, I need to protect the power source and the components used in my breadboard experiments: transistors, LEDs, etc. None of the components or circuits need more than a 9 volt battery could supply new.

I am asking this because I am concerned that the 2 amps of my 12 volt source is too much current for my breadboard and the parts that would normally be used only with a 9 volt battery.

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  • \$\begingroup\$ use a regulator DC to DC and control the voltage to 9V \$\endgroup\$ – Solar Mike Apr 18 at 6:27
  • \$\begingroup\$ Since you only need the equivalent of a \$9\:\text{V}\$ battery from your \$12\:\text{V}\$ supply (with very much higher current compliance), all you need to do is drop the voltage using a very simple linear voltage regulator. An LM7809 or LM78L09 should be fine for this. \$\endgroup\$ – jonk Apr 18 at 6:38
  • \$\begingroup\$ "i am concerned that the 2 amps of my 12 volt source is too much current" - Your circuit will only draw as much current as it needs. The issue here is the over-voltage that your components rated for 9V would break down irreversibly if 12V were applied. You also mention "protect the power source" which is not just reducing the voltage, for example do you need things like fuses, isolation etc? \$\endgroup\$ – theguitarfreq Apr 18 at 6:56
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If you want 9V to power the circuit, use a 9V regulator. Or drop the excess voltage using a 2.7 or 3.3V Zener diode (reverse biased), or even five silicon rectifier diodes in series.

If you want to simulate the limited current capacity of a 9V battery, add a resistor of about 1.5 ohms in series with your power supply. See this Stack Exchange question.

Any circuit that is broken by being connected by a power supply with a higher amps rating was probably a bad design in the first place.

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