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"Burning off" 9V at 6A

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truenoteno

New Member
I have a 312 watt switchmode power supply that i would like to make use of.

It supplies upto 48V at 6amps.
I would lke to use an LM338 voltage regulator but the max input voltage is 40v. How could I chew up about 9V at 6amps ?
I could only think of having about 13 6A rectifiers but that is too expensive, takes up room and leaves more room for error.

thanks
 

stevez

Active Member
Do the power regulation in steps - take the 48 to 40 volts or so then go from there. My recollection is that the 338 is limited to 5 amps max - as long as you don't exceed power dissapation ratings. It would seem that you could "wrap" a power transistor or two around an LM317 - see datasheet for ideas on that.
 

bogdanfirst

New Member
how about using a 2n3055 transistor hooked with a zenner diode and another transistor. since the regulation is done with the LM then you dont need to have 40V regulated.
i guess that another solution is to buy 13 diodes rated at 6 amps, or 7 bridge rectifiers.....wich might be cheaper than the diodes.....
i think that the first solution is the best.....
what do you think?
 

Mosfet

New Member
Pre-regulator
Transistor Q1 can be any power NPN similar to a 2N3055 or MJE3055.
Transistors Q2 & Q3 could be TIP31C's, I happen to have a lot of them.
Or Q1 & Q2 could be a power Darlington instead.
Resistor R1 should be a 2 watt package.
Zener diode D1 sets the output voltage and could be lower.
Mount the transistors close by on the same heatsink as your LM338 [electrically insulated].
That way the thermal overload circuit in the LM338 will protect them also.
 

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