I'm needing a voltage regulator or DC-DC converter or something
similar. I'm not too much of an electrical engineer so I need help
figuring out WHAT I need and WHERE to get it. If a part like this is
unavailable, I'll need some circuit design ideas to help me make one.
Here's the deal...

I'm needing to run a monster servo (Tone Seiko PS-050 if you've seen
it) off a 12V battery. I know, I know, just run it off the 12volts -
but I'm sticking to the manufacturer's recommendation of 8.4V max.
Max
current draw is expected in the 4 to 5 amps range.


So that's it. All I need is something to convert the 12V to 8.4V and
handle 5 amps. Something efficient would be nice (switching?) I
thought this would take about five minutes to find online but I'm
having a helluva time.


Any help appreciated!
Carsyn

On Aug 21, 3:37 pm, carsyng1...@aol.com wrote:
> I'm needing a voltage regulator or DC-DC converter or something
> similar. I'm not too much of an electrical engineer so I need help
> figuring out WHAT I need and WHERE to get it. If a part like this is
> unavailable, I'll need some circuit design ideas to help me make one.
> Here's the deal...
>
> I'm needing to run a monster servo (Tone Seiko PS-050 if you've seen
> it) off a 12V battery. I know, I know, just run it off the 12volts -
> but I'm sticking to the manufacturer's recommendation of 8.4V max.
> Max
> current draw is expected in the 4 to 5 amps range.
>
> So that's it. All I need is something to convert the 12V to 8.4V and
> handle 5 amps. Something efficient would be nice (switching?) I
> thought this would take about five minutes to find online but I'm
> having a helluva time.
>
> Any help appreciated!
> Carsyn
This link has a couple of circuits that will allow you to use a three-
terminal voltage regulator and use a few added components to increase
the current capability.
http://ourworld.compuserve.com/homepage ... page12.htm
The second and third entries of the webpage show a couple of ways to
do it. The circuit with a single pnp pass transistor is the simpler.
You can use a smaller resistor in the emitter of the pass transistor
than the one shown, for a higher current limit.

On Tue, 21 Aug 2007 22:37:11 -0000, carsyng1979@aol.com wrote:

>I'm needing a voltage regulator or DC-DC converter or something
>similar. I'm not too much of an electrical engineer so I need help
>figuring out WHAT I need and WHERE to get it. If a part like this is
>unavailable, I'll need some circuit design ideas to help me make one.
>Here's the deal...
>
>I'm needing to run a monster servo (Tone Seiko PS-050 if you've seen
>it) off a 12V battery. I know, I know, just run it off the 12volts -
>but I'm sticking to the manufacturer's recommendation of 8.4V max.
>Max
>current draw is expected in the 4 to 5 amps range.
>
>
>So that's it. All I need is something to convert the 12V to 8.4V and
>handle 5 amps. Something efficient would be nice (switching?) I
>thought this would take about five minutes to find online but I'm
>having a helluva time.
>
>
>Any help appreciated!
>Carsyn
This may be a good starting place.
http://www.national.com/appinfo/power/switcher.html
It doesn't get much simpler than the "Simple Switcher" if your goal is efficency.


Mike


"The scientist is possessed by the sense of universal
causation...His religious feeling takes the form of
rapturous amazement at the harmony of natural law,
which reveals the intelligence of such superiority
that, compared with it, systematic thinking and acting
of human beings is an utterly insignificant reflection."
Albert Einstein (theoretical physicist)

On Aug 21, 6:37 pm, carsyng1...@aol.com wrote:
> I'm needing a voltage regulator or DC-DC converter or something
> similar. I'm not too much of an electrical engineer so I need help
> figuring out WHAT I need and WHERE to get it. If a part like this is
> unavailable, I'll need some circuit design ideas to help me make one.
> Here's the deal...
>
> I'm needing to run a monster servo (Tone Seiko PS-050 if you've seen
> it) off a 12V battery. I know, I know, just run it off the 12volts -
> but I'm sticking to the manufacturer's recommendation of 8.4V max.
> Max
> current draw is expected in the 4 to 5 amps range.
>
> So that's it. All I need is something to convert the 12V to 8.4V and
> handle 5 amps. Something efficient would be nice (switching?) I
> thought this would take about five minutes to find online but I'm
> having a helluva time.
>
> Any help appreciated!
> Carsyn

When faced with something like this, I often just use several dropping
diodes in series sized to handle the current. This provides
unregulated voltage, but it's close enough for servos. Each diode
drops the voltage by about 0.7V, so you would would need five 5A
diodes in series for this. Note that diode drop voltage varies
between diode types, so you have to check the specs.

BRW

On Tue, 21 Aug 2007 22:37:11 -0000, carsyng1979@aol.com wrote:

>So that's it. All I need is something to convert the 12V to 8.4V and
>handle 5 amps. Something efficient would be nice (switching?) I
>thought this would take about five minutes to find online but I'm
>having a helluva time.

If you sincerely want a switching supply for this, and I can
understand wanting that, you will probably need to use an IC. (You
can do it using discrete parts, too, but I don't have the time to try
that now.)

In case a linear, discrete design may help, I've this example below
which I simplified just a little bit from other existing designs
posted recently in the group. It might be useful to put a current
limit, but that would add a couple more parts and I'm assuming fewer
parts is better for now.

>: 12V
>: |
>: |
>: |
>: |
>: \
>: / R1 12V
>: \ 150 | 12V
>: / | |
>: | | |
>: | | |
>: | |/c Q2 |
>: +------| 2N2222 |
>: | |>e or |
>: | | 2N3904 |/c Q1
>: | '--------| 2N3055
>: | |>e
>: | |
>: | |
>: | |
>: | '+--------+--Vout
>: | | |
>: | | |
>: | \ |
>: | / R2 |
>: | \ 3.3k --- C1
>: | / --- 100u
>: | | | 25V
>: | | |
>: Q3 c\| | |
>: 2N2222 |----------------+ |
>: or e<| | |
>: 2N3904 | | |
>: | | gnd
>: | \
>: | / R3
>: | \ 680
>: +--------, /
>: | | |
>: | | |
>: --- --- C2 |
>: \ / D1 --- 100u |
>: --- 1N4148| 16V gnd
>: | |
>: | |
>: | |
>: gnd gnd

I haven't given C1 much thought, by the way. Also, I think Q2 is
going to need to dissipate close to a watt. Which probably too high
for a TO-92 or TO-18 device. Might be able to get away with it,
especially if you can place a heat sink around the TO-18, but I'm open
to suggestions as to alternatives. (I think there are heat sinks for
TO-92, too, but I've never used one.)

There also might be a better choice for Q1, that would have much
higher beta at high currents, can dissipate the heat, and won't need
Q2 to help boost things. That could save a part. Suggestions?

Jon

On Aug 22, 2:48?pm, ben...@bennetwilliams.com wrote:
> On Aug 21, 6:37 pm, carsyng1...@aol.com wrote:
>
>
>
>
>
> > I'm needing a voltage regulator or DC-DC converter or something
> > similar. I'm not too much of an electrical engineer so I need help
> > figuring out WHAT I need and WHERE to get it. If a part like this is
> > unavailable, I'll need some circuit design ideas to help me make one.
> > Here's the deal...
>
> > I'm needing to run a monster servo (Tone Seiko PS-050 if you've seen
> > it) off a 12V battery. I know, I know, just run it off the 12volts -
> > but I'm sticking to the manufacturer's recommendation of 8.4V max.
> > Max
> > current draw is expected in the 4 to 5 amps range.
>
> > So that's it. All I need is something to convert the 12V to 8.4V and
> > handle 5 amps. Something efficient would be nice (switching?) I
> > thought this would take about five minutes to find online but I'm
> > having a helluva time.
>
> > Any help appreciated!
> > Carsyn
>
> When faced with something like this, I often just use several dropping
> diodes in series sized to handle the current. This provides
> unregulated voltage, but it's close enough for servos. Each diode
> drops the voltage by about 0.7V, so you would would need five 5A
> diodes in series for this. Note that diode drop voltage varies
> between diode types, so you have to check the specs.
>
> BRW- Hide quoted text -
>
> - Show quoted text -

I was suggested this in another forum and it sounds like a simple and
cheap solution and I do love the KISS principle. A couple followup
questions...

1) Is there any heat concern? 17.5 watts max dissipation according to
my math, should I use a heatsink somehow? How would I accomplish that?

2) Do I just wire the three diodes in series inbetween the power
source and the component on the positive lead? A multimeter should
verify that its 8.4v alright?

3) I may also do this to run a 6v radio receiver off the 12v battery.
Same deal? 9 .7v diodes (of smaller current) will do the trick or some
similar configuration thereof?

Many thanks! I don't use Usenet often but it's where I go when I've
exhausted all my other options cuz I always know I'll get the answers
I'm looking for!

Carsyn

On Aug 22, 4:48 pm, pornoofthemonthc...@gmail.com wrote:
> On Aug 22, 2:48?pm, ben...@bennetwilliams.com wrote:
>
>
>
>
>
> > On Aug 21, 6:37 pm, carsyng1...@aol.com wrote:
>
> > > I'm needing a voltage regulator or DC-DC converter or something
> > > similar. I'm not too much of an electrical engineer so I need help
> > > figuring out WHAT I need and WHERE to get it. If a part like this is
> > > unavailable, I'll need some circuit design ideas to help me make one.
> > > Here's the deal...
>
> > > I'm needing to run a monster servo (Tone Seiko PS-050 if you've seen
> > > it) off a 12V battery. I know, I know, just run it off the 12volts -
> > > but I'm sticking to the manufacturer's recommendation of 8.4V max.
> > > Max
> > > current draw is expected in the 4 to 5 amps range.
>
> > > So that's it. All I need is something to convert the 12V to 8.4V and
> > > handle 5 amps. Something efficient would be nice (switching?) I
> > > thought this would take about five minutes to find online but I'm
> > > having a helluva time.
>
> > > Any help appreciated!
> > > Carsyn
>
> > When faced with something like this, I often just use several dropping
> > diodes in series sized to handle the current. This provides
> > unregulated voltage, but it's close enough for servos. Each diode
> > drops the voltage by about 0.7V, so you would would need five 5A
> > diodes in series for this. Note that diode drop voltage varies
> > between diode types, so you have to check the specs.
>
> > BRW- Hide quoted text -
>
> > - Show quoted text -
>
> I was suggested this in another forum and it sounds like a simple and
> cheap solution and I do love the KISS principle. A couple followup
> questions...
>
> 1) Is there any heat concern? 17.5 watts max dissipation according to
> my math, should I use a heatsink somehow? How would I accomplish that?
>
> 2) Do I just wire the three diodes in series inbetween the power
> source and the component on the positive lead? A multimeter should
> verify that its 8.4v alright?
>
> 3) I may also do this to run a 6v radio receiver off the 12v battery.
> Same deal? 9 .7v diodes (of smaller current) will do the trick or some
> similar configuration thereof?
>
> Many thanks! I don't use Usenet often but it's where I go when I've
> exhausted all my other options cuz I always know I'll get the answers
> I'm looking for!
>
> Carsyn- Hide quoted text -
>
> - Show quoted text -

1) There's no heat concern if you use diodes that are rated for the
current you need. They are designed to dissipate the heat for their
rated current without heat sinks.

2) That's right, but you'll need about 5 diodes in series to get
approximately 8.4 volts from a 12 volt source.

3) That's right. But for a small load like a radio receiver, I just
use a 7806 voltage regulator. Much easier than 7 diodes. When
powering the radio from the same battery as the servo, it's a good
idea to add some filtering. For the servo load you mentioned, I would
run the battery through one diode, then the 7806. Put a 1000 uF cap
and 0.1 uF cap in parallel on the input side of the 7806 (between V+
and ground), and a 0.1 uF cap on the output side of the 7806 (between V
+ and ground). This will give your radio nice clean 6V power. The
diode / capacitor combination gives you good noise filtering. Without
the filtering, a big servo like you mentioned can hose your radio.

BRW

carsyng1979@aol.com wrote:
> I'm needing a voltage regulator or DC-DC converter or something
> similar. I'm not too much of an electrical engineer so I need help
> figuring out WHAT I need and WHERE to get it. If a part like this is
> unavailable, I'll need some circuit design ideas to help me make one.
> Here's the deal...
>
> I'm needing to run a monster servo (Tone Seiko PS-050 if you've seen
> it) off a 12V battery. I know, I know, just run it off the 12volts -
> but I'm sticking to the manufacturer's recommendation of 8.4V max.
> Max
> current draw is expected in the 4 to 5 amps range.
>
>
> So that's it. All I need is something to convert the 12V to 8.4V and
> handle 5 amps. Something efficient would be nice (switching?) I
> thought this would take about five minutes to find online but I'm
> having a helluva time.
>
>
> Any help appreciated!
> Carsyn
>

See page 17 of the datasheet at:
http://cache.national.com/ds/LM/LM117.pdf

It shows a 5A regulator that should work for you.
You can simplify it if you don't want adjustable
current, like this:

MJ4502
+12 ---+------- -------------+
| e\ /c |
| --- [.2R] 5Watt
| | |
+--[33R]--+---[LM317]-----+---> Vout 8.41V
| | |
| +-[240R]-+
|+ | |+
[1uF] [1375R] [10uF]
| | |
Gnd ---+----------------+--------+---> Gnd


You can make the 1375 ohms with resistors in series;
the 240 is a standard value. Put the IC & xsistor on
heat sinks.

Ed