TS78L00 series question ++

Discussion in 'General Electronics Chat' started by TheBellows, Dec 3, 2009.

  1. TheBellows

    Thread Starter Active Member

    Jan 18, 2009
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    I got some help with a tone sequencer circuit some days ago and it works so good i decided to make a cool boxed version with some tweaks.
    I also added a delay circuit with a PT2399 and a treble, bass and volume control i had laying around.

    It sounds very good and works like a charm. The only problem is that it drains too much power from the battery...
    I decided to use a 9V AC-DC adapter, but when i measured the voltage from the adapter with my multimeter it said 14V. Is this normal?

    So i tried the voltage regulator and i didn't read the datasheet so i added two 10uF elec caps because i remembered that from another VR.
    That didn't seem to work too well...i read the datasheet now and it says i should use an 0,33uF and an 0,1uF tantalum caps and here is the real question:
    Is it of any importance that it should be tantalum caps? All i have is two 0,1uF tantalums, could i use these or maybe use a polyester cap for the 0,33 one?

    All i care about is that the voltage doesn't fall much below 8V and not above 10V.
    I've seen people use voltage regulators without caps, how important are they?


    I attached a couple of pictures if you're curious. :)
     
  2. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    The AC-DC 9 Volts adapter is probably an unstabalized one.
    The 14 Volts you measure will be the unloaded voltage.

    The capacitors at the in and output of the 78XX series stabelizers are placed there for better stability and to prevent oscillation of the stabelizer.

    Greetings,
    Bertus
     
  3. TheBellows

    Thread Starter Active Member

    Jan 18, 2009
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    Ok, thanks, but what about the 0,33uF tantalum cap, could i replace it with a polyester one?
     
  4. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Yes, the capacitors may be electrolitic or foil.

    Keep in mind the stabelizers need at least 3 volts more at the input as the output voltage.

    There are low voltage drop stabelizers to.
    Those only need a voltage drop of about 1 Volt.

    Greetings,
    Bertus
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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    Nice job. Are you going to label the knobs and switches?

    "Wall warts" generally output within about 10% of their rated voltage when they are under their rated load. If their is no load, you will measure a good bit more output voltage. Yes, it's normal.

    Can you expound on that a bit? What do you mean by "that didn't seem to work too well"?
    Tantalum capacitors generally have a far lower ESR rating (equivalent series resistance) than electrolytic capacitors.
    You could use one in parallel with each of the 10uF electrolytic caps. They should have a voltage rating of at least twice the expected input voltage; so on the input, 14vx2=28v min, on the output 9v x2 = 18v min.

    The 78xx series regulators are a very old design. The "L" series has a maximum output of 100mA. There is a minimum voltage drop from the input to the output of the regulator of about 2v. As current increases, the voltage drop increases.
    The input capacitor(s) are important for regulator stability. I've had some 78xx series regulators that oscillated at frequencies in the MHz range if they did not have capacitors on the inputs.

    The output cap(s) are important for improving transient response. As your circuit is for audio, you want good filtering and very good transient response.
     
  6. TheBellows

    Thread Starter Active Member

    Jan 18, 2009
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    Datasheet says typically 2.0V drop, so i thought 14V to 9V should work, but is the unstabalized 14V actually not 14V as in a battery?

    Not shure if polyester caps goes as foil? Metalized?
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    Right. You measured 14v with no load on it. Once you have a load on the supply, it will drop down below 14v. How far down, I have no idea, as you have
    not given the wall wart's ratings, nor the current requirements of your circuit.

    It would be easiest to just measure the 78xx input voltage to the return line while you have the thing powered up - then you'll know.

    Metalized poly is one type. Good caps for audio. They should work OK.
     
  8. TheBellows

    Thread Starter Active Member

    Jan 18, 2009
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    Thanks. :)
    Yup, probably do a better paint job aswell, but now it's -10 degrees celsius outside and my spray cans are not popular inside the house.

    Aha, that makes sense.

    Well, the VR turned very hot and it seemed very unstable, the delay didn't always turn on like when battery falls below 7V or so.


    I only have 25V rated 10uF el. caps, but do i really need those when i use the tantalum caps?

    We still live in the middle age here in Norway. :p
    Could it be my circuitry drains more than 100mA?

    Thank you for detailed answers, i appreciate that. :)
     
  9. SgtWookie

    Expert

    Jul 17, 2007
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    Apparently, your circuit requires a good bit more than 100mA. Consider upgrading to another regulator with a higher power rating. A low-dropout regulator would be a good choice. You should consider using a heat sink on the regulator.

    You could get by with the 25v caps. The "rule of thumb" is 2x the input voltage; this is to ensure low leakage current and long life. If you used caps rated for 16v, you would be flirting with disaster.

    In reality, you should be able to get by with just the two 10uF electrolytic caps, one on the input, one on the output. However, you may need to use more bypass capacitors in your circuitry. We don't know what that consists of. If your sound quality isn't what it should be, consider adding more capacitance across the power supply leads of your various IC's, particularly in sections that may be producing amplified power output.

    Very likely that it does.
     
  10. TheBellows

    Thread Starter Active Member

    Jan 18, 2009
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    The adapter is rated 9V 500mA 4.5VA, but the circuit i have no idea.
    I'm an amateurish noob and i just use the try and fail method... :p
    I thought i was way under 100mA, but maybe i was wrong...

    Not shure if i understand, what is "return line"

    Good, they're way cheaper and better voltage rate than my elec caps too.

    Looks like we're writing in cross here, sorry about that. :p
     
  11. TheBellows

    Thread Starter Active Member

    Jan 18, 2009
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    You said earlier that i should place a 0.1uF cap on each IC, do you mean i should increase the capacitance further?
    Would i come better off with poly caps there too, instead of the ceramic ones i've used?
     
  12. SgtWookie

    Expert

    Jul 17, 2007
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    It's very easy to underestimate power requirements.

    Your "wall wart" supply has two wires; one is positive, one is negative.
    The negative lead would be the return line.
     
  13. SgtWookie

    Expert

    Jul 17, 2007
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    If you already have 0.1uF capacitors across your IC's, then you should be OK - unless they are higher power ICs. 555 timers in particular require large capacitors across their Vcc/GND supplies; 220uF + 0.1uF. If you are using audio amplifiers, they will also need larger capacitors. Opamps are generally OK with just the small caps.

    I like to use metalized poly film caps, but ceramic work fine.
     
  14. TheBellows

    Thread Starter Active Member

    Jan 18, 2009
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    Hehe, stupid me had to try the adapter without the VR, but that was a bit much for the 74hc4049 chip i think...
    I replaced it with a hef4049bp, but that didn't sound too good...i hope there is not more damage done...
     
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