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I am supposed to simulate this circuit (regulated power supply 5V), however I am not understanding what's the point of the resistor R. Is it a load resistor? Cause i thought these needed to be before the regulator. circuit

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    \$\begingroup\$ yes. it's a load resistor. \$\endgroup\$ – Marko Buršič Apr 1 at 18:08
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    \$\begingroup\$ @KingDuken: I don't see anything to do with current regulation in the OP's schematic. \$\endgroup\$ – Peter Bennett Apr 1 at 19:06
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If you look at a typical 7805 datasheet you'll find a statement like

Note: Minimum load current for regulation is 5 mA

If the circuit is expected to maintain a 5V output with a load going right down to zero, the resistor R ensures that enough current is drawn from the 7805 to guarantee that the 5mA minimum is met. In this case a 1000 Ohm resistor would be needed.

It's often not seen in the real world because the 7805 will normally be built into a circuit that will always take at least the minimum load.

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As you adjust \$R\$ in your simulation, you should be able to see the input voltage (across \$C\$) go up or down, but the voltage across \$R\$ should remain relatively constant.

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