please for help with choice of a diode

[musaraza86]

electronic circuits 7805 supply with diode

I want to switch between two power supplies. the scheme is I want to give a 12 V supply to my circuit and a 9 V supply as a stand by. for any reason if the 12 v supply is disconnected the circuit is fed by 9V supply. for this i am using two diodes. one is forward biased when 12V is supplying power and the other remains reverse biased. as soon the 12V is disconnected the diode with 9V is forward biased. Now the question is how should i choose the diode ?

 

[dipnirvana]

why to choose 1n4007

Chose ur diode so that have low leakage current when reverse bias and in forward direction has low voltage drop across it at the currrent u draw

 

[hamdard]

diode choice

choose the 1n4007 diode. It will work.

 

[musaraza86]

low leakage current diode

i have not calculated the total system current. will it have any effect on the diode u told me. actually i am down converting from 12 V to 5 V usin LM 7805.

 

[barry]

choice of a diode?

If you use a Schottky diode, you'll get minimum voltage drop across the diode, but if you're just going into a voltage regulator, then just about any diode will work (as long it can handle the current).

 

[baysidebecca]

Re: choice of a diode?

A couple 1N4001 (50PIV, 1A) diodes is the cheapest solution if your current requirement is less than 1 amp, however the 7805 can briefly output peak currents of 2.2A, so consider the 1N5400 (50PIV, 3A) instead.
Since you're operating a linear regulator, there's no gain in efficiency with Schottky diodes, though they will run a bit cooler due to the lower voltage drop. Part #30BQ040 (40PIV, 3A) comes to mind.
You can also obtain dual AKA diodes mounted in a TO220 package, such as the 12CTQ035, which makes heat sinking (if needed) and mounting easy.

 

[Thanhlongbin]

Re: choice of a diode?

I want to switch between two power supplies. the scheme is I want to give a 12 V supply to my circuit and a 9 V supply as a stand by. for any reason if the 12 v supply is disconnected the circuit is fed by 9V supply. for this i am using two diodes. one is forward biased when 12V is supplying power and the other remains reverse biased. as soon the 12V is disconnected the diode with 9V is forward biased. Now the question is how should i choose the diode ?

1N4001 is OK.
Do not forget an alumilum capacitor (100uF-220uF) in the 7805 input!

 

[musaraza86]

Re: choice of a diode?

I am sorry guys for not replying. i was busy in mid semester. first of all thank u all for ur kind suggestions. i will be working upon the project from today again and i will update.