need to give constiant voltage from battery, buck - boost converter?

[Gazz]

i have a LCD television that runs on 12 volts, it's sold to be used at home,
via the supplied switched mode psu, this gives out 12.33 volts at upto 4
amps,

i bought this tv to be used in a motorhome, where main will not be an option
very often, but the main power source is a few 12 volt lead acid batteries,
no problems you'd say.. just connect the tv directly to them,

someone i know did just this with his tv.. exact same one as mine, and it
was fine when on battery power alone, it even worked right down to 10.5
volts when he stopped dishcarging the battery bank to protect them.. no CRT
12 volt tv will do that,

However when he plugged into the mains to bring the battery charger on line,
hi TV got smoked, litterly, after having it on for 20 minutes smoke poured
out of it, and it died,

his charger gives out 13.8 volts max, and it seems these TV's are designed
to only take the 12.33 volts their mains psu gives them, they werent
designed to run in an automotive enviroment it seems, where the voltage can
range from 14.8 volts down to 10 volts,

i still want to use my tv in my van, and my mains charger is a higher output
version than his.. mine will be set to give out 14.4 volts for 2 hours to
equalize the battery bank,
also the engines alternator will bring the terminal voltage upto 14.4 volts
when it's running, so anytime i'm on shore power, or have the engine
running, i risk blowing an expensive TV,

I've been searching for a voltage regulator that will keep the voltage the
TV see's to no more than 12.33 volts..ever, but obviousely this is fine when
the engine or charger is on line and i have higher voltage than a battery on
it's own, but once off charge, the terminal voltage of the batteries will be
12.8 volts and will drop as they get discharged, so i was looking for a
regulator that would drop out of the circuit when it couldent keep the
voltage at the set level, seemed hard to do without having it drop out at a
higher than 12.33 volts.. as the regulator needed to have an input of at
least half volt above the output voltage,

I've just found out a little about buck - boost converters tho, would one of
these do the job for me?
http://www.linear.com/ezone/1625.html is the page showing a circuit that's
more than a basic buck - boost converter apparantly, this one can handle 3.3
amps max, i really need one to handle 4 amps max.. idealy 5 amps so i can
run the 12 volt DVD player off the same unit.. just to be safe,

my knowlage is limited of electronics, simple voltage regulator circuits i
have built, led arays using pcb's i make my self no probs, but like the
mosfet switch i was asking about in my last post, i seem to be getting out
of my depth here,

can someone tell me if a buck - boost converter is what i need, will it
consume a lot of power when in use.. i guess this is one place where i'd
rather use power to save the TV from getting dammaged, than save a few
milliamps of drain so i can get another few minutes out of my battery bank

Anyone point me to a better circuit diagram for one that will give me 12.33
volts out from 10 to 15 volts in, and at 5 amps idealy, oh and have a clean
output that won't affect the TV or it's tuner.

Cheers,

Gazz

 

[AG]

Try a 7812 regulator which gives you 12 volts quite accurately. Do a google
search and see where you can buy one!

AG

 

[Ian Stirling]

Try a 7812 regulator which gives you 12 volts quite accurately. Do a google
search and see where you can buy one!

<snip quoted message incorrectly placed at bottom>
Not reliably from an automotive 12V system.

 

[Ian Stirling]

i have a LCD television that runs on 12 volts, it's sold to be used at home,
via the supplied switched mode psu, this gives out 12.33 volts at upto 4
amps,

i bought this tv to be used in a motorhome, where main will not be an option
very often, but the main power source is a few 12 volt lead acid batteries,
no problems you'd say.. just connect the tv directly to them,

someone i know did just this with his tv.. exact same one as mine, and it
was fine when on battery power alone, it even worked right down to 10.5
volts when he stopped dishcarging the battery bank to protect them.. no CRT
12 volt tv will do that,

However when he plugged into the mains to bring the battery charger on line,
hi TV got smoked, litterly, after having it on for 20 minutes smoke poured
out of it, and it died,

my knowlage is limited of electronics, simple voltage regulator circuits i
have built, led arays using pcb's i make my self no probs, but like the
mosfet switch i was asking about in my last post, i seem to be getting out
of my depth here,

Honestly, I'd say the vastly, vastly simpler approach is simply an
inverter and the existing power supply.

Say 30 quid all-in, and maybe an extra battery draw of maybe 20%.
But, it's the difference between being able to watch TV for 5 or 4 hours
on a 30Ah battery safely.

The automotive enviroment is quite nasty, you can get spikes up to a
few dozen volts, nasty noise spikes, variation from 6-16V (car will
usually still sort-of work, though not well.)

 

[CampinGazz]

Honestly, I'd say the vastly, vastly simpler approach is simply an
inverter and the existing power supply.

Say 30 quid all-in, and maybe an extra battery draw of maybe 20%.
But, it's the difference between being able to watch TV for 5 or 4 hours
on a 30Ah battery safely.

The automotive enviroment is quite nasty, you can get spikes up to a
few dozen volts, nasty noise spikes, variation from 6-16V (car will
usually still sort-of work, though not well.)

Damn, i was hoping to avoid the use of the inverter, everythng else is 12
volts in this van, i have a dvd player by the same company that's fine on
voltages from 10 to 15 volts, it has a fag lighter adaptor, but it seems to
be more of a filter than a regulator, as the dvd player runs on 12 volts,
the battery supplies 12 volts, so it cant do much.. for it's size anyway.

idealy i'll need some sort of filtering anyway, as i'll have a lot of
electronic apliances in the van, even my light switches will be a touch
screen panel, which probably dosent expect the spikes and noise from the
alternator when it's online,

so maybe noise filtering is needed on the main supply wires? then a
buck-boost converter to keep the voltage at the TV to what it expects?

 

[Rolavine]

Subject: need to give constiant voltage from battery, buck - boost converter?

From: "Gazz" [email protected]
Date: 1/28/2004 2:53 PM Pacific Standard Time
Message-id: <[email protected]>

i have a LCD television that runs on 12 volts, it's sold to be used at home,
via the supplied switched mode psu, this gives out 12.33 volts at upto 4
amps,

i bought this tv to be used in a motorhome, where main will not be an option
very often, but the main power source is a few 12 volt lead acid batteries,
no problems you'd say.. just connect the tv directly to them,

someone i know did just this with his tv.. exact same one as mine, and it
was fine when on battery power alone, it even worked right down to 10.5
volts when he stopped dishcarging the battery bank to protect them.. no CRT
12 volt tv will do that,

However when he plugged into the mains to bring the battery charger on line,
hi TV got smoked, litterly, after having it on for 20 minutes smoke poured
out of it, and it died,

his charger gives out 13.8 volts max, and it seems these TV's are designed
to only take the 12.33 volts their mains psu gives them, they werent
designed to run in an automotive enviroment it seems, where the voltage can
range from 14.8 volts down to 10 volts,

i still want to use my tv in my van, and my mains charger is a higher output
version than his.. mine will be set to give out 14.4 volts for 2 hours to
equalize the battery bank,
also the engines alternator will bring the terminal voltage upto 14.4 volts
when it's running, so anytime i'm on shore power, or have the engine
running, i risk blowing an expensive TV,

I've been searching for a voltage regulator that will keep the voltage the
TV see's to no more than 12.33 volts..ever, but obviousely this is fine when
the engine or charger is on line and i have higher voltage than a battery on
it's own, but once off charge, the terminal voltage of the batteries will be
12.8 volts and will drop as they get discharged, so i was looking for a
regulator that would drop out of the circuit when it couldent keep the
voltage at the set level, seemed hard to do without having it drop out at a
higher than 12.33 volts.. as the regulator needed to have an input of at
least half volt above the output voltage,

I've just found out a little about buck - boost converters tho, would one of
these do the job for me?
http://www.linear.com/ezone/1625.html is the page showing a circuit that's
more than a basic buck - boost converter apparantly, this one can handle 3.3
amps max, i really need one to handle 4 amps max.. idealy 5 amps so i can
run the 12 volt DVD player off the same unit.. just to be safe,

my knowlage is limited of electronics, simple voltage regulator circuits i
have built, led arays using pcb's i make my self no probs, but like the
mosfet switch i was asking about in my last post, i seem to be getting out
of my depth here,

can someone tell me if a buck - boost converter is what i need, will it
consume a lot of power when in use.. i guess this is one place where i'd
rather use power to save the TV from getting dammaged, than save a few
milliamps of drain so i can get another few minutes out of my battery bank

Anyone point me to a better circuit diagram for one that will give me 12.33
volts out from 10 to 15 volts in, and at 5 amps idealy, oh and have a clean
output that won't affect the TV or it's tuner.

Cheers,

Gazz

Why don't you by an auto type inverter to make 110V AC out of your battery,
then use the AC adapter that came with the display?

This is not going to be as efficient, but designing some crazy gizmo power
supply for one stinkin' monitor is crazy, and you admitt you don't have the
know how anyway.

I think you can get an inverter for $40.

Rocky

 

[CampinGazz]

Why don't you by an auto type inverter to make 110V AC out of your battery,
then use the AC adapter that came with the display?

This is not going to be as efficient, but designing some crazy gizmo power
supply for one stinkin' monitor is crazy, and you admitt you don't have the
know how anyway.

I think you can get an inverter for $40.

I've got an inverter, but i dont want it powered up all the time just to run
the TV.. it's a 1200 watt unit (were on 230 volts here) and dosetn provide a
perfect sini wave, runs the microwave fine, but some switched mode psu's
i've tried get very hot with it.. due to the non pure siniwave.. a pure
siniwave inverter uses even more quinticential current than the modivied
quasiwave inverters,

i'd be running a monitor and a dvd player off the power supply, and at a
later date i'd want to build a few more to power the laptop, the on-board
computer for the gps unit, reversing monitors, engine monitoring system and
all that i'm building,
plus there are at least another 20 people i know of who want something
similar.. they have the same TV as me, or want to ensure they get a
constiant 12 volts from the battery, whether it's on charge or practicaly
dead, so the buck-boost converter sounded ideal.

i just need pointers on how to implement this, i've built a 50watt quasi
siniwave inverter before, but from a schematic that was already available,
to build the buck-boost converter i need a schematic tailored for the
voltage and current i need to extract, or at least some pointers on finding
out how to go about designing it.

 

[Ian Stirling]

Damn, i was hoping to avoid the use of the inverter, everythng else is 12

Why?
Just stick it in a box along with the existing power supply, and call it
a boost-buck converter
It's at most some 10-20% less efficiant than the best you could possibly
make, for lots less money than you would probably spend in making it.

volts in this van, i have a dvd player by the same company that's fine on
voltages from 10 to 15 volts, it has a fag lighter adaptor, but it seems to
be more of a filter than a regulator, as the dvd player runs on 12 volts,
the battery supplies 12 volts, so it cant do much.. for it's size anyway.

idealy i'll need some sort of filtering anyway, as i'll have a lot of
electronic apliances in the van, even my light switches will be a touch
screen panel, which probably dosent expect the spikes and noise from the

If you don't care about cost, you might look at something like the
DC/DC automotive converters shown in http://www.cpc.co.uk/ catalog, as
well as others.
(they don't seem to do a 12V-12V converter)
I'd also consider a big 12V deep-discharge battery, with a big high-current
inductor in series with it, and a big relay to take it out of circuit during
starting connected to the main battery, to provide a smoother supply.

You may want to look around for linear low-dropout regulators.

 

[Rolavine]

Subject: Re: need to give constiant voltage from battery, buck - boost

converter?
From: "CampinGazz" [email protected]
Date: 1/29/2004 4:00 AM Pacific Standard Time
Message-id: <[email protected]>




I've got an inverter, but i dont want it powered up all the time just to run
the TV.. it's a 1200 watt unit (were on 230 volts here) and dosetn provide a
perfect sini wave, runs the microwave fine, but some switched mode psu's
i've tried get very hot with it.. due to the non pure siniwave.. a pure
siniwave inverter uses even more quinticential current than the modivied
quasiwave inverters,

So put a switch on the inverter to shut it off when you don't need it? Test the
switching supply that came with the TV if it works, it works! If not find a DC
power supply that will work.

Other than that the simplist solution is to use a low dropout linear voltage
regulator, something like and LM1084, good for 5 amps with a big heat sink. Get
this in 12 volts and it will make 12 volts from an input above about 13 volts
at full rated current. When the battery drops below 13 volts the regulator will
put out about 1 volt less volt less than than the input. This has some
compromises but at over 90% efficiency is going to beat any but the most
optomized switching solutions. The LM1084 also has an on off pin, so if you
want to shut it off on low voltage situations, just use a comparator and some
reistors.

This is a pretty trivial project!

Rocky
"have scope won't travel"

 

[CampinGazz]

So put a switch on the inverter to shut it off when you don't need it? Test the
switching supply that came with the TV if it works, it works! If not find a DC
power supply that will work.

The psu does work, but gets hotter than i would like, and i've only powered
it from my inverter for 20 minutes before i unplugged it, so i'd need
another inverter just for this TV, and then a cheap one prolly wont do the
job if an expensive one wont.

Other than that the simplist solution is to use a low dropout linear voltage
regulator, something like and LM1084, good for 5 amps with a big heat sink. Get
this in 12 volts and it will make 12 volts from an input above about 13 volts
at full rated current. When the battery drops below 13 volts the regulator will
put out about 1 volt less volt less than than the input. This has some
compromises but at over 90% efficiency is going to beat any but the most
optomized switching solutions. The LM1084 also has an on off pin, so if you
want to shut it off on low voltage situations, just use a comparator and some
reistors.

cheers, that's kind of what i was looking for origionaly, some way to limit
the voltage when the charger is on-line, and have it drop out of the circuit
when the charger is off line, and the battery voltage is 12.8 and dropping,

i'm going to be worried about spikes, ripples and all that kind of thing
from the alternator (the mains charger should be pretty well behaved, as it
is sold as a psu charger, and supposed to be used while your powering items
in the van,
the alternator on the other hand provides a dirty output,

would i just need a few big smoothing capacitors, or something a little more
complicated to prevent spikes and all that getting to the tv.

i guess i like things complicated, it's prolly be easier for me to use
something to boost the voltage to 24 volts, then use the LM1084 type
regulator, no problems with it ever having to drop out.. but i'm back to a
buck-boost regulator things again.

 

[Rolavine]

Subject: Re: need to give constiant voltage from battery, buck - boost

converter?
From: "CampinGazz" [email protected]
Date: 1/29/2004 1:28 PM Pacific Standard Time
Message-id: <[email protected]>




The psu does work, but gets hotter than i would like, and i've only powered
it from my inverter for 20 minutes before i unplugged it, so i'd need
another inverter just for this TV, and then a cheap one prolly wont do the
job if an expensive one wont.


cheers, that's kind of what i was looking for origionaly, some way to limit
the voltage when the charger is on-line, and have it drop out of the circuit
when the charger is off line, and the battery voltage is 12.8 and dropping,

i'm going to be worried about spikes, ripples and all that kind of thing
from the alternator (the mains charger should be pretty well behaved, as it
is sold as a psu charger, and supposed to be used while your powering items
in the van,
the alternator on the other hand provides a dirty output,

would i just need a few big smoothing capacitors, or something a little more
complicated to prevent spikes and all that getting to the tv.

i guess i like things complicated, it's prolly be easier for me to use
something to boost the voltage to 24 volts, then use the LM1084 type
regulator, no problems with it ever having to drop out.. but i'm back to a
buck-boost regulator things again.

Yes, large electrolytic caps will eat the noise from the alternator. Put them
on both the input and output of the Regulator. Linear regulators are pretty
damn great these days If you search National, Maxum, Linear Tech, and maybe
some others you might just find a regulator better than the one I suggested. I
picked the LM1084 ahh, this may be a 2nd sourced Linear Tech. part?) because it
was good for 5 amps. Boosting to 24V would be bad, and make the regulator
dissipate as much power as it supplies.

Rocky

 

[onestone]

A conventional linear regulator won't do this, so the 7812 suggestion is
out the window. Either get an inverter (but they are generally hellish
noise sources), porbably a sinusoidal one, or build the BUCK/Boost
circuit. I did a similar thing on a Mining Truck, using an LTC1370 in
SEPIC configuration. This can deliver the voltage and current
requirement. Linear Tech have a good app note on SEPIC on their website.
In the SEPIC configuration you have to make sure that your inductors can
carry the required current. BUt SMD 6A inductors are common place nowadays.

Al

 

[CampinGazz]

A conventional linear regulator won't do this, so the 7812 suggestion is
out the window. Either get an inverter (but they are generally hellish
noise sources), porbably a sinusoidal one, or build the BUCK/Boost
circuit. I did a similar thing on a Mining Truck, using an LTC1370 in
SEPIC configuration. This can deliver the voltage and current
requirement. Linear Tech have a good app note on SEPIC on their website.
In the SEPIC configuration you have to make sure that your inductors can
carry the required current. BUt SMD 6A inductors are common place nowadays.

Al

So basicaly this circuit http://dion.swamp.dk/carpower.html i found last
night is the best thing to go for, i just need to omit the 5 volts part of
the circuit.. as it's a car computers dc psu, i just need 12 volts for my
application,
i don't fancy winding the inductors my self.. even tho i have a blown
switched mode mains psu to hand with a few of them on, and somewhere i have
about 100 torrodial inductors.. bought them with other components years ago
and i didnt know what they were.. i was 12 at the time

So i'll have to find a place in the UK that sells inductors of the right
values.. RS components, Maplins, Farnell is all i can think of,

On the origional hand drawn circuit diagram on that site, he has a 18 volt
surge absorber, and a 6 amp polyswitch fuse, the geezer that made the eagle
circuit board layouts omitted those parts as he couldent get them, i kinda
see them as essential for my application, the polyswitch fuse i can prolly
locate, it's just a self re-setting fuse isnt it?

but the surge absorber, that i'm stumped on, anyone able to give me a part
number for one of these things so i can see if they are available in the UK
at the usual electronics shops i have access to.

Cheers,

Gazz

 

[Robert C Monsen]

i have a LCD television that runs on 12 volts, it's sold to be used at home,
via the supplied switched mode psu, this gives out 12.33 volts at upto 4
amps,

[SMPS advice]

Anyone point me to a better circuit diagram for one that will give me 12.33
volts out from 10 to 15 volts in, and at 5 amps idealy, oh and have a clean
output that won't affect the TV or it's tuner.

Cheers,

Gazz

It sounds like your real issue is that you don't want overvoltage, which
will destroy the TV. You can build a simple overvoltage cutout circuit from
a comparator, a zener, and a mosfet pretty simply. That saves the expense of
a converter circuit, at the cost of not being able to use the TV when you
are plugged in. (View with courier font)


+-------+------+---------------+----------+
| | | | | |
| | .-. | .-. |
| | | | | | | |
| | | | 1k | | |10k |
| | '-' | '-' |
| | | | | |
| | | | | |
| | | |\| | |
| | +-----|-\ | |
| .-. | | >------+-------||-+ P-MOSFET
--- | |<----------|+/ ||->
- | | | |/| ||-+
| '-' | | |
| | | |
| | - 6.2V | +
| | ^Zener | Your TV
| | | | -
| | | | |
| | | | |
--------+------+--------------------------+
|
===
GND
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

The comparator will try to ground the output as long as V- > V+. That will
cause the P-MOSFET to conduct.

So, adjust the pot such that its wiper is 6.2V when the battery input is
12.33V. Then, when the battery input gets bigger than 12.33V, the comparator
output will go high, and shut down the mosfet, turning off the TV power
input. Adjusting the pot will be a bit of a challenge without a variable
power supply. However, if you just use two 1k resistors instead of the pot,
then the voltage where the comparator will drop out will be around 12.4V.
Since there will be a small drop through the P-MOSFET equal to Ron * 4, you
should be safe.

Make sure the comparator will handle the maximum voltage as a power supply.

You might also want to put in a crowbar circuit, so when the comparator
fails in a few years, overvoltage doesn't destroy the TV. You can do that
with an active Zener as follows:


5A Fuse
____
12V -|_--_|------+---|---------------+
| | |
12V - | |
Zener ^ |
Diode | |/ Your TV
+-| 2N3055
|> |
| |
| |
Gnd -----------------|---------------+
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

When the zener starts to conduct, it'll shunt current from the load. The
zener will conduct at 12 V, and thus the 12V rail will have to be at 12V +
0.7V before it starts. When it conducts, it'll cause the 5A fuse to fail.

You can also build a crowbar from an SCR such as the 2N4441.

Regards,
Bob Monsen