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View Full Version : Optimization- HElp



rohan_bhatia
05-17-2008, 04:01 PM
hey guys, i was able to get my bot running, interface an lcd, solve grids and follow walls. Since there are not many competitions coming, i have started to fine tune somethings. First of all can u tell me if i remove the heat sink of 7805 will it save me power, since it says that with heat sink it can deliver 1 A but thats not needed, my ckt at max consumes <.5A. Another thing since i am using a 12v lead acid batt i had to limit current through uln2003 using high power res 2.5ohm. Any other alternatives to save power , my batt r good for running bot cont for 15-20 min then voltage drops to 10v.

docel
05-18-2008, 08:51 PM
PWM

MohitM
05-20-2008, 10:19 AM
If your 7805 is hot to touch, you are better off with a heatsink. And why would removing the heatsink save you power?

rohan_bhatia
05-21-2008, 10:24 AM
Hi MohitM, i have seen robot videos..i think they use 7805 without heatsink.probably they dont need. Anyway the 7805 operates, by varying resistance acc to junction temperature. Less temp less current==less power dissipated ,right?.I am not a 100% sure about this but i went through the graphs in the datasheet. The current delivered depends upon temp.

allbits
05-21-2008, 10:48 AM
its not the current which is dependent on the temperature, the temperature is Dependant on the current (and the voltage).

If you are taking up too much current (especially continuous current), more current will pass through 7805, and will heat it up. Heat generated is a function of power - if you are giving 12V at input, and you are using a 7805, approx 7V is dropped at the regulator, so that will heat it up, even if you are drawing less current.


heat sink has only one job to do - dissipate the heat into air, fast so that the IC remains cool, and at its recommended operating temperature.

To save power, i would recommend you find alternatives to your battery. removing the lead acid will reduce a lot of weight, and in turn, the power consumed. Using resistors to reduce current is not always good, as there will be power loss across the resistor. Ultimately, it converges to what doc said - PWM.

Redesign your circuit - turn off LCD backlight if not necessary - it drinks current. there aretoo many components, reducing the component count and using power save features in your controller - (or choosing one with less power cons.) will help. And yes, Good PCB, and good soldering saves a whole lot of power, believe me on THIS.