Voltage Regulator ICs?

Question

i want to use a voltage regulator IC (7809) to give a circut a constant supply of 9 volts. if i was to use a 9 volt battery with a voltage that is constantly dropping would that work (even though the voltage is under 9 volts? thanks.

Answer 1

Yes as long that the voltage amount of your source is range from 8.0 - 9.0 V. But if it is below 7.9 >, Voltage regulator is useless already. You need transformer for that matter.

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Answer 2

No..   Linear regulators burn off excess power so that the applied voltage is reduced to the regulated value.   It does this by changing its resistance to cause a voltage drop. The current flowing through this varying resistance will generate heat.  

As you increase load on the power supply the output voltage starts to droop. THe 7809 regulator quickly adjusts its resistance so as to allow some of the extra applied power to be passed on to the load there by keeping the output voltage relatively constant.    

Inorder to provide the load with additional power upon demand the input to the regulator must be more than the regulated output voltage.   Any short fall in output voltage is boosted by passing additional voltage from the input.  

If you apply less voltage than 9 volts the regulator will not have any excess power to work with. Its resistance will drop to its minimum and you will have an unregulated output that is less than 9vdc

Answer 3

No. A voltage regulator requires a certain minimum output to sense voltage drop, with the lowest I've seen about 1.2v, so your supply would need to be at least 1.2v about the voltage that you wanted (since you want 9v, you would need to source 10.2v)

Answer 4

That type of voltage regulator only lowers voltage and dissipates excess as heat.  To keep 9 volts from a 9 volt battery you would want a boost converter.  Unfortunately they are more complex.