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Newbie asking advice

W

west

Jan 1, 1970
0
I have a 12v deep cycle battery for my wheel chair and I would like to power
a 6v radio receiver from it. I kinda of know what a voltage divider is but
do not know what values to use. I also would like for it not to waste too
much power on the side of a divider that's not used. Don't know if a
regulator or a zener would be a good idea. What would be a good circuit for
my situation? Thank you very much.

bill
 
D

default

Jan 1, 1970
0
I have a 12v deep cycle battery for my wheel chair and I would like to power
a 6v radio receiver from it. I kinda of know what a voltage divider is but
do not know what values to use. I also would like for it not to waste too
much power on the side of a divider that's not used. Don't know if a
regulator or a zener would be a good idea. What would be a good circuit for
my situation? Thank you very much.

bill
I'm assuming you just want a portable transistor receiver for music?

Easiest/safest/best way would probably be a three terminal regulator
like the LM317 adjusted for 6 volts out.

It will waste half the power - but it is probably not a concern if the
radio is a portable that is designed to run on dry cell batteries,
since the battery in your chair would be several orders of magnitude
bigger/longer lasting than a dry cell - and it doesn't take much power
to work a radio.

Voltage divider isn't a good idea - the power a radio takes varies
considerably depending on the volume and type of program material it
is playing - the voltage would fluctuate a lot - and you need to know
the average current and high and low to calculate a resistance divider
(or even learn if it might work OK) - you might get away with it if
you just use earphones at moderate volume. You need to know current
drain of the radio for a calculation.

Zener is a possibility - you could put one six volt type or some
combination that equals 6V in series with it - their power dissipation
will be low (hard to find high power zeners these days).

A one watt zener would give you 166 milliamps for the radio without
burning out - plenty for a small transistor receiver. If it did
overheat and short it might take out the radio.

A really good albeit a lot more complicated solution is to use a
switcher regulator like the National series of "simple switchers."
That gives you a regulated output voltage with minimal waste power.

Unless you're using a high power ham radio transceiver or like a huge
amount of bass and lots of loudness - the three terminal is your best
and easiest option.
 
D

default

Jan 1, 1970
0
My databook is a little dated - National makes a three terminal 6 volt
regulator PN: LM7806T or LM340T6

No resistors to calculate or adjust - put 12 on one side and get a
regulated 6 on the output. The datasheet is on line, Jameco price is
thirty cents each - Radio Shack may also stock it.
 
W

west

Jan 1, 1970
0
default said:
I'm assuming you just want a portable transistor receiver for music?

Easiest/safest/best way would probably be a three terminal regulator
like the LM317 adjusted for 6 volts out.

It will waste half the power - but it is probably not a concern if the
radio is a portable that is designed to run on dry cell batteries,
since the battery in your chair would be several orders of magnitude
bigger/longer lasting than a dry cell - and it doesn't take much power
to work a radio.

Voltage divider isn't a good idea - the power a radio takes varies
considerably depending on the volume and type of program material it
is playing - the voltage would fluctuate a lot - and you need to know
the average current and high and low to calculate a resistance divider
(or even learn if it might work OK) - you might get away with it if
you just use earphones at moderate volume. You need to know current
drain of the radio for a calculation.

Zener is a possibility - you could put one six volt type or some
combination that equals 6V in series with it - their power dissipation
will be low (hard to find high power zeners these days).

A one watt zener would give you 166 milliamps for the radio without
burning out - plenty for a small transistor receiver. If it did
overheat and short it might take out the radio.

A really good albeit a lot more complicated solution is to use a
switcher regulator like the National series of "simple switchers."
That gives you a regulated output voltage with minimal waste power.

Unless you're using a high power ham radio transceiver or like a huge
amount of bass and lots of loudness - the three terminal is your best
and easiest option.
You are very wise because the radio is actually a small walkie talkie. I'm
sure the transmit and receive current drain would be very different. A
voltage divider would of been a bad idea. Thanks for the caveat.
bill
 
W

west

Jan 1, 1970
0
I seen a couple of data sheets for the LM7806 and they said that the input
voltage shouldn't exceed the output voltage by more than 2-3v. My
application needs a 12v (battery) input & a 6v output. Any ideas? Thanks.

west

default said:
My databook is a little dated - National makes a three terminal 6 volt
regulator PN: LM7806T or LM340T6

No resistors to calculate or adjust - put 12 on one side and get a
regulated 6 on the output. The datasheet is on line, Jameco price is
thirty cents each - Radio Shack may also stock it.

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J

Jamie

Jan 1, 1970
0
In said:
I seen a couple of data sheets for the LM7806 and they said that the input
voltage shouldn't exceed the output voltage by more than 2-3v. My
application needs a 12v (battery) input & a 6v output. Any ideas? Thanks.

You could probably use a 7805 instead of a 7806, they're very very common
and you've probably already got several of them in most any old broken
piece of equipment. (a common spot to look for them is near a heatsink)

They give a little bit over 5 volts instead of 6, but, that's probably close
enough considering the radio was meant for batteries (which would eventually
degrade anyway) I've run those off of 12 volt before, they do produce 5 volts.

I suppose the other option is one of those ciggarette lighter adapters, you
might already have one of those too. Advantage there is the radio plug is
probably already included. :)

Jamie
 
D

default

Jan 1, 1970
0
I seen a couple of data sheets for the LM7806 and they said that the input
voltage shouldn't exceed the output voltage by more than 2-3v. My
application needs a 12v (battery) input & a 6v output. Any ideas? Thanks.

west

You are misinterpreting what you are reading. The 7800 series of
regulator has an absolute maximum input of 30 volts for 5 volts output
and 35 volts in for 12-15 volts out. The 24 volt output part allows
an input of 36 volts.

There's usually a requirement to have the input a MINIMUM of 3-4 volts
higher than the output for it to stay in regulation - perhaps that is
where you got the 2-3V . . .

Check the absolute maximum ratings on the data sheet that you have -
that is the what you have to respect for the part to survive. A
regulator that only allows a 2-3 volt differential between input and
output wouldn't be very useful.
 
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