6VDC Power Supply.....

[Janitor Tzap]

Does any one know of a good 6VDC power supply circuit?

I have a Casio 2.5" Color LCD Television that I use a 6VDC Power Supply with it.
But even after filtering the 6VDC, I still get the 60Hz hum bars.

I've been looking for a SMP type, but I'm not seeing anything in the 6VDC range.

The current Power Supply is: 6VDC at 500ma.


Signed: Janitor Tzap

[philba]

it's hard to be 100% certain what you should get from your description. I'm tempted to say get something like this (regulated 6V wall wart): http://jameco.com/webapp/wcs/stores/ser ... tId=684721

but your interference could be from anything.

You don't say if you want to plug it into 120VAC or something else (like 12V car outlet). Is your current power supply a wall wart? unregulated?

[haklesup]

Can you confirm the interference is not present when you use a battery. Are you using some sort of external antenna or AV input or an internal antenna and built in tuner.

Most small TV's are somewhat immune to 60Hz noise from the primary supply (You can assume there is another supply regulator and filter inside the TV). It could indicate a bad filter cap inside the TV. Did it ever work well?

I ask about the AV input since a signal from another device using a different P/S but same ground is similar to the ground loop problems you get in automotive setups. Isolation using a transformer (like in a standard video splitter) might be what you need if this is the case.

[Janitor Tzap]

I see I didn't supply you with enough information.

Ok....

1) The Current Power Supply I'm using is A 120Vac to 6VDC 500ma output Wallwart.
{Modified with extra filtering}

2) The hum bars show up when I use its built-in dipole antenna, or when connected to an external antenna.
{So, I'm fairly sure it isn't a ground loop problem}

3) The hum bars are not there when I use it on battery power.
{4 X 1.5V AA Alkaline Batteries}

4) Yes, I has been working fine on just batteries ever since I purchased it.

philba,
That Power Supply that Jameco has is rated for 2000ma.
That's abit too high of a current rating for this little set.


Signed: Janitor Tzap

[philba]

that's no problem. The tv will only draw what it needs. Maybe you can find cheaper but higher current capacity doesn't hurt.

I assume that your current wall wart isn't regulated. did it come with the set? did you ever run the set off of a WW without the interference? maybe a dumb question but does the set have a power input jack or are you hooking up to the battery terminals?

By the way, I'm a bit suspicious of the comment "modified with extra filtering". care to explain what you did there?

[Chris Smith]

Also,...often when the original batteries are dead, [or missing] they stop acting like a filter and pick up some hum. My old TV used to do that.

[Timothy Rasch]

Hi, open up the wallwart carefully and see if there is a full wave rectifier circuit [2 diodes or 4 diodes-bridge circuit ] .If there is, there could be a open diode or, 2 diodes open in the bridge circuit. They might test ok but are bad under load. Use an oscilloscope to check for 120 hz ripple with the added caps removed and plugged into the tv for load. Another way the hum bars were eliminated was to put .01 uf Z5U ceramic caps across each of the diodes. This practice was used by RCA in the CTC19 CTV chasis. To make a story short I have a[ 10watt lamp ,1 rectifier diode in series with the battery cells] brute force battery charger powered from 120vac , from the 1960's that would make hum bars on the ctv 10 feet away till I added a .047uf cap across the rectifier . You can vary the caps value a little amount.No more hum bars !!!!! I still use the charger and it works good. Tim Rasch [email protected]

[dyarker]

Caps across the diodes. It makes sense when you consider the current wave form through the diodes to the filter cap. The extra filtering added by Janitor Tzap may even have made the bars worse by increasing the amplitude of the current pulses and decreasing the rise time and duration.

Cheers,

[Robert Reed]

All quality high voltage power supplys will have capacitors directly across each diode. This becomes more critical as voltage is raised. The reason for this is to absorb transients at the moment each diode shuts off. These transients will produce short burst of wideband RF ringing at a 60 & 120 Hz rate. These will cause interference in the form of radiated RF. Usually an 0.005 Mf will solve this problem.

[MrAl]

Hi there,

You have to be careful when adding caps to a power supply that is
just a bridge rectifier and a small cap. This is because the average
DC voltage output goes *UP*. This is because the diodes supply
current in pulses which charge the caps near the peaks of the
sine wave, and adding more caps means having more energy
available to the output.
I would suggest that you try to regulate the output to 6vdc using
a LM317 or similar voltage regulator IC. You may need to add
more caps to the wall wart too though. Just make sure the
IC does not overheat or you will have to add a small heat sink.

If you order a new wall wart, make sure it has a regulated output.

If using a regulated power supply doesnt work, you may be picking
up interference from the line just because of the capacitance in
the transformer used with the wall wart that tends to couple some
low level ac onto both (+) and (-) lines of the wall wart output.
To test for this, connect the tv to a 6v battery, then connect
ONE lead of the output of the wall wart to first the (-) terminal of
the battery (note only one lead) and then to the (+) terminal
See if the TV acts up again with this connection.

[Timothy Rasch]

Hi again MR. AL, small value capacitors like .01uf-.047uf won't change the dc voltage peak especially on low voltage power supplies . The Hum bars will be eliminated on the TV . Tim Rasch [email protected]

[Janitor Tzap]

I assume that your current wall wart isn't regulated. did it come with the set? did you ever run the set off of a WW without the interference? maybe a dumb question but does the set have a power input jack or are you hooking up to the battery terminals?

I purchased the wall wart separately.

I have yet to find a 6Vdc Wall Wart that doesn't produce the hum bars.
{A sales man at Radio Shack had suggested they're own Wall Wart.}
{Which was a Switch Mode Power Supply for $25}

The television has a power jack.

By the way, I'm a bit suspicious of the comment "modified with extra filtering". care to explain what you did there?

The original WallWart had two diode full wave rectifier with a single 1000uf
10Vdc electrolidic in it.

I replaced the two diodes with a full wave bridge rectifier.
Replaced the 1000uf cap with Two 10,000uf 16Vdc Caps plus added a choke coil then a 10uf 16uf Cap.

Hi, open up the wallwart carefully and see if there is a full wave rectifier circuit [2 diodes or 4 diodes-bridge circuit ] .If there is, there could be a open diode or, 2 diodes open in the bridge circuit. They might test ok but are bad under load. Use an oscilloscope to check for 120 hz ripple with the added caps removed and plugged into the tv for load. Another way the hum bars were eliminated was to put .01 uf Z5U ceramic caps across each of the diodes. This practice was used by RCA in the CTC19 CTV chasis. To make a story short I have a[ 10watt lamp ,1 rectifier diode in series with the battery cells] brute force battery charger powered from 120vac , from the 1960's that would make hum bars on the ctv 10 feet away till I added a .047uf cap across the rectifier . You can vary the caps value a little amount.No more hum bars !!!!! I still use the charger and it works good. Tim Rasch [email protected]

Yup, I remember that trick.....
But to get the best filtering of the AC ripple across the diode, you had to sometimes try different value caps.
I'll have too try that, and see if that solves the problem.

I worked on a power supply for an audio amplifier that was that way.
Only it also had a resistor across the diode as well.
{Strange}.


Signed:Janitor Tzap

[MrAl]

Hi again,

Did you try a regulated wall wart yet?

I didnt mean the small caps like 0.1uf i meant the big ones like
1000uf.

[jollyrgr]

Wall warts are so much fun. My guess is that you are drawing more current than the supply can handle. Using a 6VDC 2000mA (2Amp) power supply is "not too much current". This is a mistake I see many people perceive when dealing with power supplies. When I explain the principle that the device will only draw as much current as needed and that an underrated supply is much more of a problem than an over rated I get resistance (no pun intended). When I point out that an AC outlet that is able to supply 15 Amps of current does not "blow up" a 15uA EL nightlight people tend to understand the concept.

I know what you are seeing is likely due to not enough current being available from the 500mA supply. I picked up a couple Atari "Flashback" games from a flea market but the supplies that came with it turned out to be cell phone chargers and did not even fit correctly. The only supply I had on hand voltage and polarity wise (without rewiring) was from a small radio wall wart. Not nearly enough current for the game and I saw hum bars. After I got a big box of warts off eBay the problem was solved.

YAGOOLING CASIO TV POWER SUPPLY brought up the following part number: "Casio ADK-64 AC Adapter"

as a device for a number of sets in your general description. This supply is one pound shipping weight. My guess is this is a bit larger than 500mA.

[Janitor Tzap]

Thanks for your suggestions and help everyone.

I think I'm going to goto one of the local Electronic Surplus Stores and
look for a 9Vdc or 12Vdc WallWart that has an output Current of 800ma or
higher.
Next; I'll install a 6Vdc Regulator, and add extra filtering to it.

Hopefully this will end my ripple problem.


Signed: Janitor Tzap