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bmcculla said:Protel is a PCB Layout tool. Its expensive but you can get a 30 day evaluation for free.
stevez said:Not necessarily better but possible- use 1 ohm resistor followed by LM338K set for 5 volts with proper heat sink.
1 ohm resistor at 5 amps will drop voltage by 5 volts so your input to the voltage regulator is somewhat tempered. At 16 volts the voltage drop across the regulator is slightly over the specs however it's supposed to be thermally limited internally. While system voltage could run that high it probably doesn't most of the time. 5 amps is at the limit of the 338 though it's supposed to handle brief overloads.
1 ohm resistor has to get rid of 25 watts. Rather than purchase one large resistor make it up by taking a number of resistors of same value in parallel.
This approach might be technically simpler though it has some risks (fully loading 338) and requires a way to get rid of the heat from the resistors and the 338 itself. Note also that a pass transistor or two can be wrapped around a voltage regulator. Note that getting rid of the heat is still a problem. The switching approach is less demanding in this respect.
Sebi said:L4970 from ST microelectronics.
Sebi said:If this tail-light not a ready-made device, You can connect seriel minimum 6 pieces red LEDs and one resistor for higher efficiency.
If really need all LED connect in parallel, i recommend to use lower voltage as 5V ( for red LEDs 2.5V so the serial resistor have low dissipation.)
theboss said:but voltage in car varies between 11.8 to 16 volts.. wouldnt it be a problem for led's... bcuz as far as i think it would frown up led's designed for a 12 circuit
Ldi Edt said:You could use a simple method such as burning off the excess voltage,
but as you can see, at 16Vin, 5v@5a out, you need to dissipate 55watts
of power. Not a good scenario. Your overall system efficiency will be 31%.
Save yourself time and money, and buy a point of load converter.
The synchronous buck topology is simple and very efficient. The entire supply will be about the size of a cigarette lighter. (volumetrically).
Plus, these run at typical efficiencies(%) in the low to mid 90s!
Look at Wall Industries, Datel, Tyco....just to name a few.
S.P.
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