IC Output Current Increase Circuits- General Purpose

Discussion in 'The Projects Forum' started by lhaw, Jun 21, 2010.

  1. lhaw

    Thread Starter New Member

    Jun 21, 2010
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    Hi! I'm a newbee to your forum, so please forgive any transgressions- I'll try to get it right. And thanks for being here! Here's my question:

    Is there a general purpose *circuit* for increasing the current, voltage & general ruggedness, of *outputs* from clock chips, op-amps, micro-controlers, etc.? I'm thinking of increasing outputs to around 9-20 volts with around 4 or 5 amps, but those are just ballpark ranges.

    I want to apply these integrated components in all sorts of electro-mechanical applications with solenoids, magnetic actuators/transducers, etc., & was hoping there was a general purpose *circuit* that could take, say the output from an op-amp or clock chip (like a 555 for example) & have it increased in current &/or voltage, so it can then be used to drive all sorts of other things. I don't have a specific situation in mind, but am seeking something that can take such outputs & make them more powerful & robust *across the board* so I can then concentrate on figuring out what to *DO* with them rather than having to worry about *HOW* to make things happen electronically.

    A sort of "one size fits all" power increasing interface that can be deployed with all sorts of IC outputs is one way to put it.

    Any comments or recomendations of books, web sites, etc., would be greatly appreciated!

    Thanks much!
    Lawrence (lhaw)
     
  2. retched

    AAC Fanatic!

    Dec 5, 2009
    5,201
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    They are called transistors. MOSFETs and power MOSFETS are more what you may be looking for.

    Logic level components.

    If you have a little 5v 10ma signal coming from your IC, you can have that small signal trigger a MOSFET to allow a different supply through.

    There is no circuit or device that alone will increase voltage and current.

    So you would need you 9-20v 4 or 5amp supply going to your MOSFET source pin.

    Connect the device you want to power to the drain pin of the MOSFET

    Your smaller device signal line will be connected to the MOSFET gate.

    Once your small signal hits the gate, it will allow the 9-20v through to the device you want to power.

    You
     
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  3. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
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    Usually it is called power amplifier. And there is no such thing as one-size-fits-all, especially when you want it to be cheap, fast up to several tens of MHz, with variable voltage AND with current as high as 5amp :eek:

    For example for current amplification you COULD MAYBE use the typical complementary output buffer
    Voltage amplifier? use an opamp

    What about the vast difference betwen a single supply 555´s digital output versus symmetrical supply opamp´s analog output? How could you possibly make something that works for all?
     
  4. Markd77

    Senior Member

    Sep 7, 2009
    2,803
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    The ULN2803 comes in pretty handy sometimes if you want somewhat lower but still pretty useful power. 8 darlingtons in a chip.
     
  5. lhaw

    Thread Starter New Member

    Jun 21, 2010
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    Thanks a lot guys! Transistor I suspected, but what *kind* was another thing entirely! High frequency isn't really an issue. I can't even imagine ever having any need for anything over 20khz. I'll look into MOSFETs & the other goodies you've all suggested. You are all very much appreciated!

    LHaw
     
  6. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Enhancement-mode MOSFETs are very handy for turning DC power on and off. They are typically used as a voltage controlled switch.

    MOSFETs have some basic similarities to regular transistors (bjt's, or bipolar junction transistors) in that they both control current flow from one terminal to another via a third terminal. However, bjt's control current on the collector using a smaller current on the base, and enh MOSFETs control the current flow from the drain to the source via a voltage level on the gate. If the voltage on the gate with respect to the source terminal, aka Vgs=0, the MOSFET is turned off. With standard N-channel MOSFETs, if Vgs=10, the MOSFET is fully turned ON and is conducting with low resistance from the drain to the source, normally referred to as Rds(on)

    If you are going to control them using logic ICs or microcontrollers, the N-channel enhanced logic level power MOSFETs are what you want to look at.

    There is a bewildering array of power MOSFETs on the market, and the specifications are really confusing for a n00b.

    The most important items are:
    Vdss - the maximum voltage rating to not exceed from the drain terminal with respect to the source terminal. You usually want to choose a Vdss that is not much higher than the voltage it will be exposed to.
    Rds(on) - lower is better.
    Qg - or Total Gate Charge; lower is better. It's specified in nano Colulombs. Google Wiki's Coulomb entry.

    This certainly isn't an exhaustive list, but three things at once is a lot.
    For a given Rds(on), if the Vdss requirement decreases, Qg decreases.
    For a given Vdss requirement, as Rds(on) requirements go lower, Qg increases.

    You might think that a MOSFET rated for 1000 volts and a low Rds(on) would be the greatest thing since sliced bread, until you looked at how long it would take to charge or discharge the gate

    A very handy N-ch logic-level power MOSFET to have is the IRLD024; which comes in a 4-pin DIP package. It's rated for up to Id=2.5A at Vdss=60v; and is great for breadboarding small low-power projects.

    It's a question of choosing the right tool for the job to be done. If the only tool you have in your toolbox is a hammer, everything starts looking more or less like a nail. Sure, you can install screws with a hammer - but the results would have been so much better if you'd used a drill and a screwdriver instead.
     
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  7. lhaw

    Thread Starter New Member

    Jun 21, 2010
    3
    0
    Thanks Sarge! Definitely something for me to chew on for a bit.
    If you have any suggestions for further study, they'd be appreciated,
    but otherwise, great info!

    LHaw
     
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