Series resistor affect on Voltage Regulator

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if resistor connected between power , linear voltage regulator, how circuit affected. math figure such thing out.
  • how voltage regulators' output affected
  • how voltage resistor drop , how regulator drop


my guess regulator acted diode , dropped constant voltage not result of tests.

here example circuit.
  • the resistor in question r1
  • please ignore diode , capacitor.
  • this not circuit tested on. mine simpler




thank you!

volt drop across series resistor depends on current through it.
an 7805 regulator needs @ least 2volt across maintain output voltage.
that leaves 12volt - 5volt output - 2volt regulator = 5volt max across resistor before things go haywire.
that's max possible current draw 100ohm series resistor of 5/100 = 0.05a = 50ma.
a regulator without resistor dissipates 12volt - 5volt output = 7volt across * 0.23amp estimated = 1.61watt.
should not problem small clip-on heatsink.
a better option 5volt buck converter. lower drain 12volt battery, , little or no heat.
leo..


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