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Feb 03, 2013, 10:50 AM
Who let the dogs out?
phil_g's Avatar
Remember that the 2940 is an LDO, the combination of a 2940 and an external pnp is no longer LDO.
Cheers
Phil
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Feb 03, 2013, 11:00 AM
Stuart
srnet's Avatar
Quote:
Originally Posted by phil_g
Remember that the 2940 is an LDO, the combination of a 2940 and an external pnp is no longer LDO.
Cheers
Phil
Quite so.

And 2W dissipation for a LM2940 with no heat sink is not 'fine' the device would be on the point of its thermal limit, it will get very hot, 140C or so.
Feb 03, 2013, 01:59 PM
Registered User
It will be used with LiPO 3s so LDO + pass should be still stable.
Btw Do you know what is the thermal resistance of aluminium plate over TO220?
What's difference between pure plate and heatsinks like this http://www.digikey.com/product-detai...1023-ND/340321
Maybe I'll stay with single heatsinked IC.
Feb 04, 2013, 04:13 AM
Registered User
My opinion is that there are many applications which are not specifically outlined in manufacturer data sheets that have been in service and operating reliably for years. The fact that so many ESC's contain parallel regulators leads me to believe this is one of those applications that the manufacturers did not cover. This does not mean it doesn't operate properly.
If a regulator starts cutting back it's voltage for reasons of overcurrent or temperature, the paralleled regulators will start taking load. I see no reason that a regulator run at current or temperature limit will fail. The regulator protection circuits are usually very well designed. Does it really matter if one regulator takes all the load until it reaches it's operating limits?
Feb 04, 2013, 09:16 PM
Registered User
dave1993, you sir, should go here: http://bit.ly/YyWfQ9
Feb 05, 2013, 01:16 AM
"MAYONNAISE"
Acetronics's Avatar
MIC 29750 could be a number to consider ... if looking for a linear regulator.

btw. I got nice switching boards here ... but not LDO.
http://dx.com/p/mini-dc-dc-voltage-s...ule-red-126106

amazing , no ???

Alain
Feb 06, 2013, 09:48 AM
Registered User
switching bec 3a



Feb 07, 2013, 12:28 AM
Registered User
R1 and R2 would need changing to up the output voltage from 3.3V to 5 or 6V. Depending on the MP2365, the inductor may need changing or the efficiency may not be very good.

These kinds of buck converters are a dime a dozen on dx.com
Feb 07, 2013, 01:24 AM
Registered User
Quote:
Originally Posted by viperidae
.

These kinds of buck converters are a dime a dozen on dx.com
yes, but Mp2365 very small, integrated FET .
3A is enough for RC
Feb 07, 2013, 02:03 AM
Registered User
Quote:
3A is enough for RC
Correction, 3 amps is enough for your rc. I doubt anyone would run a 3 amp BEC on anything that uses high end digital servos.
Feb 07, 2013, 02:30 AM
Registered User
Quote:
Originally Posted by spog
Correction, 3 amps is enough for your rc. I doubt anyone would run a 3 amp BEC on anything that uses high end digital servos.
if your servo use currents 5-10a, you should use the battery separate
use BEC for ampe large is not feasible
Sep 01, 2013, 02:28 PM
Andres Lu
joker24458's Avatar
Hi, I know this thread is a bit old but I would like to make one of these and I have a question. I will be using a LM2904 with two 47uH capacitors. However, I have no idea which voltage of capacitors to get, I looked up "47uH capacitor" on eBay but there are 47uH capacitors ranging from 16V up to 450V. Which ones should I get? Thanks.

-Andres

PS I am new to this stuff so forgive me for the noob questions I ask.....thanks.
Sep 01, 2013, 04:11 PM
Who let the dogs out?
phil_g's Avatar
16v will be fine. Its a 'maximum rated voltage' spec, its a measure of how much voltage the cap will withstand before breaking down. Your input and output voltages are both well below 16v so those will be fine. Note that you absolutely must get the polarity right - tantalums smoke and can even burst into flames when reversed. The dot or bar and the longer leg mark the positive. Dave will be along soon to say that this is tosh, and that you should only use yellow ones.
Cheers
Phil
PS the unit is uF (microfarad) rather than uH (microhenry). uH is a measure of inductance and is used for coils, chokes, relays, etc.
Last edited by phil_g; Sep 01, 2013 at 04:35 PM.
Sep 01, 2013, 06:02 PM
Andres Lu
joker24458's Avatar
Quote:
Originally Posted by phil_g
16v will be fine. Its a 'maximum rated voltage' spec, its a measure of how much voltage the cap will withstand before breaking down. Your input and output voltages are both well below 16v so those will be fine. Note that you absolutely must get the polarity right - tantalums smoke and can even burst into flames when reversed. The dot or bar and the longer leg mark the positive. Dave will be along soon to say that this is tosh, and that you should only use yellow ones.
Cheers
Phil
PS the unit is uF (microfarad) rather than uH (microhenry). uH is a measure of inductance and is used for coils, chokes, relays, etc.
Ok, thanks I'll go with the 16V ones then. I wont worry too much about the polarity, my dad (yep, my dad, I am 12 ) works with this stuff all the time at work and he taught be a bunch of stuff (including how to solder - correctly ) and I will ask him for some assistance when making this. What's the difference between the black/grey circular ones and the small yellow ones anyways?

Thanks,

-Andres

Also I knew that but I got messed up while typing it...it's either too much or too little going on up there.
Sep 01, 2013, 06:29 PM
Who let the dogs out?
phil_g's Avatar
Quote:
Originally Posted by joker24458
...What's the difference between the black/grey circular ones and the small yellow ones anyways?
sorry that was just a little joke between me & Dave1993


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