Wanted an external BEC for 2s lipo
anyones got one?
Is this for the xt? If yes you should be looking for a lipo-cutoff :) if no please ignore this post .
If you want DIY,
An LM7805 do the trick. TO220 Package without heatsink can run 1.5A and can consume 1.9 watt. The device will looks like below, a 3 pin device like transistor cost about Rs 5-10/-.
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1 2 3
You can use series regulator
So, a for a 2S Battery, Input Voltage will be 2x3.7 = 7.4 volt and output voltage = 5 Volt.
and taking 30% duty cycle, power will be ((7.4-5) x 1.5) x .3 watt = 1.08 watt
means need no heatsink.
Now connect Pin 1 to Batt+ Positive and 2 is common negative for batt as well as output.
and PIN 3 is +5Volt +ve output.
But the most simplest circuit is Add 3 series and 3 parallel 1N 4007 diode, connect in series from bat+ to +ve terminal. 1.2-1.8 volt drop with 3A capacity will be available that will serve the perpose.
================================Added========================on Request
an zener regulator may be like this.
(http://upload.wikimedia.org/wikipedia/commons/e/ef/Voltage_stabiliser_transistor.png)
and if transistor is like Darlington pair with S8050 and C2233 transistor,
(Darling pair used to avoid continuously current drain in base resistance of Normal Power Transistor.)
Vbe = 1.2-1.4 Volt(Typ), 2.5 Volt (Sat)
hfe = 20 x 100 = 2000. hfe of c2233 = 20, hfe of d8050 = 100
Ic = 4A or less. So, Ib1 = 4/20 = 200mA (for c2233) and ib2 = 200mA/100 = 2mA.
Zener Calculation
therefore, this base current will pass through Rb resistance in excess of zener or at Iz=0.
Zener voltage = 5+1.4 = 6.4 Volt -Take 6.8 Volt.
And at zero load current, ib1=ib2=0, Zener current = 2mA.
.: Zener watt = .002 x 6.8 = 0.0124 watt = 12mW (any watt as min is .125 watt available)
Resistance Calculation
.: R = (7.4-6.4)V / 2mA = 500 Ohm.
Now as the current of BEC not go upto 4A, take next higher level resistance = 560 Ohm.
And Power = 1Vx1V/560 = 2mW, i. e. 1/4 watt or 1/8 watt will be enough (Crosscheck).
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And if u use only C2233, Ib = 4A/20 = 200mA.
Zener Spec
Vzener = Vout + Vbe drop = 5+1.2 = 6.2 Volt
IZener = 200mA, Pzener = 6.2 x 0.2 = 1.24 watt.
Resistance Spec
Resistance R = (Vin - Vzener)/Ib = (7.4 - 6.2)/ .2 = 6 Ohm
Rwatt = I x I x R = 0.2 x 0.2 x 6 = .24 watt
- Use 0.5 watt 6.2 Ohm or two 12Ohm 0.25 watt in parallel.
Advantage
You can get good regulation.
Disadvantage
You have constant current drain of 200mA.
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For switching regulator, google with "roman black SMPS"
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If you need Readymade BEC,
search
www.RCElectro.com
www.rcforall.co.in
www.rcbazaar.com
www.rcdhamaka.com
http://www.rcbazaar.com/products/807-avionic-sport-bec.aspx
Thanks
Thanks, Kalyan sir. it will hwlp me too.
Could you also give a DIY, circuit with Zener Diods.
Added to original post.
Thanks da.. :)
But now I guess IN 4007 diode method is the best. ;D
Abhay,
please don't mind, its 1N4007 Not IN4007.
1 Stands for No of junction = 1, i. e. 2 layer device N & P
Similarly 2N stands for transistor (3layer device, PNP or NPN)
3N Stands for 3 junction i.e. thyristor(SCR,UJT,SCS,GTO) with 4 layer.
4n Stands for 5 layer device with 4 junction like MOSFET(N-Ch,P Ch, Enhance/Deplation mode).
RCforall has them in stock
@ Kalyan Sir, i never mind it.. :)
We can also learn frm mistakes. ;D
I have used these diodes several times but I never went to buy these diodes, as i can get in most of the elctronic PCBs i have. And always read it IN4007 instead if 1N4007. So had a misconception of what seemed to be written on them. now i got it correct.. {:)} {:)}