Current limiting Help PLZ

[Hero999]

Thank you for explaining the circuit to me. At least now I have some understanding of the circuit. I figured that the best way for me to achieve 3A of current is to use 0.22 Ohm Rsc resistor because its available to me.

0.22hm: would be fine but would result in a power dissipation of 1.98W (check the resistor is rated to 2W). Alternatively you could parallel two to give 0.11hm: to reduce the power dissipation to 0.99W but you'd obviously need to double the gain.

So I calculated the following:

Gain of Ic2b = 1.87 because 1.237V \ 1.87 = 0.66V across Rsc

And 0.66V \ 0.22Ohm = 3A

Thus R6 needs to be 115K Ohm because (1 + 100k\115k) = 1.87G

R5 should therefore be 53.5K ohm

That would be fine but finding those resistor values could be difficult, although I suppose get them by connecting resistors in series and parrallel.

I am not very confident about the Vout.

Can you please explain

"Suppose you make both the resistors the same in the potential divider, so it will divide the output voltage by 2.The voltage across the bottom resistor will be 1.237V which is half the output voltage (remember the divider always divides the output by 2) so the output voltage will be double the reference or 2.474V. If you configure the potential divider so it divides the output voltage be 3 then the output voltage will be three times the reference voltage of 1.237V or 3.711V."

What resistors are you talking about in "Suppose you make both the resistors the same in the potential divider, so it will divide the output voltage by 2." ?

I found the formula in the datasheet:

Vout - Vref(1+R2\R1)

but not sure how to implement it into this circuit because I don't know what resistors serve as voltage devider in this circuit.

Thank you Hero999 !!!!

Don't worry about Vout, the whole point of this circuit is to regulate the current, not the voltage. I was providing a bit of background by explaining how the LM2576 works when it's configured as a constant voltage regulator. My intention was to provide a bit of background which would make it easier to understand. I'm sorry if it confused you but reading the datasheet and understanding how the LM2576 works as a voltage regulator will help a lot.

You appear to be missing the point?, using the IC regulator dissipates exactly the same heat inside your case - it's no different to using a resistor. Use a simple (LARGE) resistor, and mount it outside the case on a suitable heatsink. Or use an IC regulator, and mount that on a similar sized external heatsink.

You're missing the point.

If you use a switching regulator it dissipates much less power than a linear regulator; with switcher it's possible for the regulator to only burn a couple of Watts.

 

[Frosty_47]

Thank you Hero999

I contacted Electro sonic and they told me that they have resistor values as low as 0.05Ohm! Perhaps I will use something like 0.1 Ohm for Rsc since it only cost around 2 dollars vs. 8 dollars for 0.05 Ohm. Anyhow, thank you for all your help and suggestions!

Sincerely,

Andrew Frost

 

[Hero999]

$2 for 0.1hm: and $8 for 0.05hm:? If you really wanted 0.05hm: units it's cheaper to use two 0.1hm: resistors in parallel!

 

[Nigel Goodwin]

You're missing the point.

If you use a switching regulator it dissipates much less power than a linear regulator; with switcher it's possible for the regulator to only burn a couple of Watts.

Sorry, I missed the change to switch-mode! - but as he's struggling understanding a simple linear current source, the more complicated switch-mode type probably isn't too good an idea?.

 

[Sceadwian]

Dunno, with modern IC's switch modes are easier to understand than simple linear supplies. You just have to value the analog components more carefully, such as the primary inductor and capactive filtering elements.

 

[Blatman Bond]

What is peltier? A heater?
Just a though. Why not just create heat from power transistor? If the transistor has 12Volt at Vce and you limit the emitor current for only 3A, it will provide 36 watts of heat. But might be maximum temperature only 125 Celcius.

 

[Hero999]

A peltier is a cooler, not a heater. Why would he want to heat his overclocked processor up anymore?

 

[Nigel Goodwin]

A peltier is a cooler, not a heater. Why would he want to heat his overclocked processor up anymore?

Actually it's both, and neither, it's a heat transfer device, it transfers heat from one side to the other - so to cool a CPU you use it to transfer heat from the CPU to outside the case.

 

[Hero999]

Alright then, a peltier is a heat pump.

 

[Frosty_47]

Will such a low value ( 0.05 Ohm ) be ok ? I mean it will only have a potential of 150mV. Will this be ok for the regulator ?

Thanks again!

 

[Frosty_47]

Inductor Question

I forgot to ask bout inductor. The 100uH inductor must be able to handle a current of at least 3A right? If so, than I found one that can handle 7A and it costs $5 dollars (cheaper than the one that handles 4.25A ). Damn those ppl that make the pricing lol...

Thank

 

[blueroomelectronics]

Seriously I've never understood the effort and cost to get a few more MHz out of a CPU when all you have to do is wait a couple months for a new chip that blows your overclocked chip out of the water.

Just dump the whole thing in cooking oil.
**broken link removed**

 

[Frosty_47]

few MHZ ??

Seriously I've never understood the effort and cost to get a few more MHz out of a CPU when all you have to do is wait a couple months for a new chip that blows your overclocked chip out of the water.

Just dump the whole thing in cooking oil.
**broken link removed**

I achieved a 510 Mhz over clock already on Air Cooling alone. And can push it further with better cooling. I currently use AMD XP 2500+ Mobile (stock 1.832Ghz) Running at 2.342Ghz. And to tell you, this old bird pulls very nice. I haven't played a game yet that this CPU can't handle. I got 2 gigs of RAM and AbIt AN7 board so I am settled for at least another year lolz. Might as well get the most out of my system and most importantly I learn something doing it...