Heh guys,
Please consult the attached file for my question. Will my circuit work or will it blow up? I know the 7805 needs two capacitors but I didn't include them because my question doesn't really concern them. Anyway any help you guys could give me on this issue would be much appreciated. Thanks again guys!!! This site rocks.

 

Heh guys,
Please consult the attached file for my question. Will my circuit work or will it blow up? I know the 7805 needs two capacitors but I didn't include them because my question doesn't really concern them. Anyway any help you guys could give me on this issue would be much appreciated. Thanks again guys!!! This site rocks.

It should work fine. I am assuming that the 9 volt batteries are alkaline and don't need charging, and that the wall adapter is a standby supply.

 

Normally the battery will be the backup power for the device, what is purpose of the batteries and what is the load (V/I)?

 

Circuit in question:


What is the typical load? Will the batteries be connected in series or parallel? Are they "transistor radio" batteries?

 

The batteries are connected in parallel. The load is 450 milliamps at 5 volts. The batteries are alkaline. The purpose of the batteries is to power the circuit if the wall adapter is removed. (backup power) Would you guys recommend the diodes I used (1n5817) or perhaps another type and why? Anyway thanks for your help.

 

The batteries are connected in parallel. The load is 450 milliamps at 5 volts. The batteries are alkaline. The purpose of the batteries is to power the circuit if the wall adapter is removed. (backup power) Would you guys recommend the diodes I used (1n5817) or perhaps another type and why? Anyway thanks for your help.

The 1N5817 diodes are a bit of an overkill for such a simple circuit. You really don't need fast switching diodes. 1N4001 general purpose 50V, 1A rectifiers will do the job.

 

The batteries are connected in parallel. The load is 450 milliamps at 5 volts. The batteries are alkaline. The purpose of the batteries is to power the circuit if the wall adapter is removed. (backup power) Would you guys recommend the diodes I used (1n5817) or perhaps another type and why?

Runtime won't be long with a 450mA load.

Data for Energizer 9V alkaline battery:

You should use a schottky diode for the diode in series with the batteries. You're going to need every tenth of a volt you can get because the regulator will stop regulating when battery voltage drops to around 8V.

 

Use an LDO regulator, or a buck regulator for even more efficiency, greater battery lifetime.

Regards, Dana.

 

you DO NEED the two capacitors at the regulator. Those 0.1Mfd capacitors are to keep the regulator from oscillating. Also, at 450Ma the regulator should have a heat sink. Dana is correct that other regulator types will be more efficient, but if you have the listed parts on hand they will certainly work.