power distribution problem

[ACTR]

hi every one

i have many circuits that require different amount Amp and voltage i want to supply all the circuits from one battery

the battery have 12V with 2.2 A

circuit 1 >>>> 3V with 500mA

circuit 2 >>>> 5V with 300mA

circuit 3 >>> 9V with 30mA

and two circuit(circuit 4) >>>>>> with 6.5V with 250mA for each ( this two circuit are servo driver and they may require more than 250 amp if they got more load but in normal state they need 100mA only....)

so i already try to design one circuit for supplying like this picture

[img][img]http://up09.s-oman.net/cvqDrAY.jpg[/img][/img]

after each resistance i can place the right regulator for each circuit to get the right voltage but the amount of current passing through each resistance will definitely burn them out because of high wattage ......


so what i should do to give the right current and right voltage for each circuit??????????? ....... i know about resistances with high wattage but haven't use them befor.......... any help will be appreciated


thank

zak

[pebe]

Two questions:
1. How stable is the voltage of your 12V battery?
2. Will the 3V and 5V supplies always take that amount of current?

[ACTR]

it is stable enough to provide constant 12V

yes they will take that amount of current only and always

[pebe]

You can drop the 12V battery voltage to 9V at 30mA with a 100ohm ¼W resistor.
The current drawn from your 6.5V supply varies, so you cannot use a fixed resistor - you will need a voltage regulator. I have not seen one advertised for 6.5V but you can use a 7806 with a diode inserted in the common terminal to jack up its voltage to about 6.6V. You can the cater for your 3V and 5V needs by taking feeds from that, rather than from the 12V battery, because the resistors will a lower wattage rating (1.7W instead of 4.5W for the 3V feed).

Even so, the 7805 will be dropping 6V at 1A = 6W, so it will need a heat sink. A much better way of getting 6.5V would be to use a buck converter like this:
http://www.ebay.co.uk/itm/1-DC-DC-Buck- ... 51b1086acb
They are very efficient and the power loss is much less than a 7806 regulator.

To drop to 5V at 30mA from 6.5V needs a 50ohm ¼W resistor.
To drop to 3V at 500mA from 6.5V needs a 7.2ohm 1.7W resistor.

Hope that helps.

[ACTR]

thanks alot ...... it works

after finishing my project i will upload the circuit for power distribution

it may help someone else


thank you again


Zaka