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Bottleneck 555's 0.2A Stuck project

Discussion in 'General Electronics Discussion' started by 123244, Apr 25, 2013.

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  1. 123244

    123244

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    Apr 25, 2013
    Hello

    I made this: (555 pwm, but it has a bottleneck because I can't use higher load than 0.2A)
    http://www.easterngeek.com/2008/06/simple-and-dirty-pulse-width-modulation.html

    How to easily mod it to accept more current ?
    1.) list what components to add.
    2.) a drawing how and where to solder these extra components.

    I hope it could handle:
    Voltage input: U=6-12V (I use different battery packs)
    Current draw: I=10A (max.could be less for geared motor 12V)

    Suggestions
    and easy to understand guides so I can solder the "add-ons" myself.
     
  2. GreenGiant

    GreenGiant

    842
    6
    Feb 9, 2012
    your best bet would be to use a transistor or mosfet, depending on how fast your PWM will be cycling and how accurate you need it this should work fine.

    This one is rated at 10A, and has a total time loss of 90ns (nanoseconds) for a full period (turn on delay, rise time, turn off delay, fall time) so unless youre running faster than 5MHz PWM frequency (half the total delay approx) you wont notice much of a loss, after that you start messing up and missing things.
     
  3. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Your lower voltage limit may be an issue. I don't think I've seen any logic level FETs that can handle 10A. This doesn't mean they don't exist though.

    Chris
     
  4. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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  5. 123244

    123244

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    Apr 25, 2013
    PWM frequenzy= 144Hz.
    OK. I buy one power heatsink MOSFET(I=10A; like IRFZ14)
    and works in the input range 6-12V and also I'm able to use many different ampere DC-motors small 0.05A toys up to the max.10A ?

    How to connect(where to solder) it: (for example 12V power supply)
    [​IMG]
     
    Last edited: Apr 26, 2013
  6. Rleo6965

    Rleo6965

    585
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    Jan 22, 2012
    You can swap the connection of pin 7 and pin 3 and use pin 3 to drive the dc motor for higher current.
     
  7. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Ain't that the truth! I saved those in my FET folder.

    Chris[/quote]
     
  8. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Good catch! That's a rather odd arrangement he has there. After all, the Discharge pin can only sink current. ;)

    Chris
     
  9. 123244

    123244

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    Apr 25, 2013
  10. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    The 555 can source or sink up to 200 mA (for a standard NE555, LM555, MC1455 etc).
    1. You need a pullup resistor, e.g. 1k, from pin 7 of the 555 to the positive supply rail (pin 8 of the 555).
    2. Drive the MOSFET gate from pin 3 of the 555.
    3. Connect the MOSFET source (which is internally connected to the substrate, shown as a separate connection marked "Su" in your diagram) to the 0V rail (pin 1 of the 555).
    4. Connect the drain of the MOSFET to the negative terminal of the load.
    5. Connect the positive terminal of the load to the positive supply rail (pin 8 of the 555).
    6. If the load is inductive (relay coil, solenoid, motor etc), connect a diode e.g. 1N4001 across the load with its cathode to the positive supply rail.
     
  11. 123244

    123244

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    Apr 25, 2013
    About that MOSFET. What kind... is IRFZ14 ok ? (So that it doesn't heat much and waste energy.)
    In what ampere MOSFET starts to show alarming temperature rise ?
    - In what ampere range can I use MOSFET without heat sink ?
    - When(amperes) do I absolutely need to use heatsink and when fan ?

    What power(wattage) rating on 1KΩ resistor ?

    I would like to use DPDT(15A rating) switch to reverse motor
    (No diode in motor is then possible... I'm right ? Diode breaks ?)
    http://www.robotroom.com/DPDT-Bidirectional-Motor-Switch.html

    [​IMG]
     
    Last edited: Apr 27, 2013
  12. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    The important MOSFET specification is Rds(on). This is the effective resistance between drain and source when the MOSFET is turned ON by positive gate voltage. It is usually specified at one or more values of Vgs (gate-source voltage). In your case the gate-source voltage will be somewhat less than the 555's supply voltage; assume about 9.5~10V. This is enough to saturate any MOSFET and produce a low Rds resistance.

    The IRFZ14 is specified with an Rds(on) of 0.2 ohms at Vgs=10V. You can calculate its power dissipation from P = I^2 R, where:
    P is power dissipation, in watts;
    I is load current, in amps;
    R is Rds(on), in ohms.

    In your case, I=10 so I^2 is 100, and R is 0.2 ohms. Therefore P = 20 watts. The MOSFET will definitely require a heatsink. If you want to avoid a heatsink you need to use a MOSFET with a much lower Rds(on). You need to keep the power dissipation less than about 1W.

    Calculating in reverse for an Rds(on) value to give 1W dissipation:
    R = P / I^2
    = 1 / 100
    = 10 milliohms.

    So you need a MOSFET that's rated for at least 10A drain current, and Rds(on) of 10 milliohms or less.

    Here's a suitable MOSFET:
    http://www.digikey.com/product-detail/en/IPS075N03L G/IPS075N03L G-ND/2081218
    Infineon IPS075N03L, 30V, 50A, Rds(on)(max) = 7.5 milliohms, USD 0.73 for 1-up.

    It may seem over-rated but it's one of the cheapest suitable through-hole parts available from Digikey.

    Just 1/4 watt is fine.

    In that case, connect the diode on the MOSFET side of the reversing switch. In other words, connect the diode with its anode to the drain of the MOSFET and its cathode to the positive supply. Connect the input wires of the reversing switch across that diode, and connect the output wires of the reversing switch to the motor.

    You can avoid having a large reversing switch if you drive the motor using an "H-bridge". This requires four MOSFETs instead of one. Search for H-bridge on Google or Wikipedia for more information.
     
  13. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    For those who are experiencing headaches after viewing 123244's schematics do the following. Save it and open it in the Picture-Fax Viewer and rotate it clockwise 90°. Viola!! The headaches magically disappear! :D

    Chris

    Edit: I think you need a small value resistor (~10R ) between pin 3 and the Gate. It's usually required to dampen ringing on the Gate.
     

    Attached Files:

    Last edited: Apr 27, 2013
  14. 123244

    123244

    21
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    Apr 25, 2013
    Only one problem:
    MOSFETs seem to be scarce to find and a bit expensive. :confused:
    Shipping to: EU
    Payment: PayPal

    What is the cheapest and easy to find MOSFET that fits but doesn't get terribly hot ?

    Infineon IPS075N03L (30V, 50A)
    - No listings on Ebay.com.
    - Not in www.uxcell.com.
    - Not in any other cheap china store, dx.com, buyincoins.com, dinodirect.com,...

    IRFZ14 (Closest ebay deal is in England: one piece £4,59=$7,00 :mad: )
    http://www.ebay.de/sch/i.html?_saca...p=15&_clu=2&_fcid=70&_localstpos&_stpos&gbr=1
     
  15. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    I'm afraid you will have to find that out for yourself.
    I understand the problem with Digikey. Their shipping charges to countries outside the U.S. are prohibitively high for hobbyists.
    I didn't know that you were outside the U.S. because you didn't say so, and you didn't fill in the "Location" field in your profile. It would help others to help you if you did fill in that field.
    I've explained the critical parameter Rds(on), and how to use it to calculate the power dissipation in the MOSFET. Now you need to look at the available devices and find one that's suitable.

    Edit: Chris is right, you should use a low-value resistor between pin 3 of the 555 and the MOSFET gate.
     
  16. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    What about Maplin? Isn't that where most of the UK shops for components or are they the UK's Radio Shack?

    Chris
     
  17. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    If you want to use eBay, try searching for "mosfet (20A,25A,30A,35A,40A,45A,50A)" and have a look at what you come up with.
     
  18. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    I just searched for MOSFET on eBay and found several suitable devices on the first page of the results, in quantities from 2 to 10 and prices from USD 4 to USD 15.
     
  19. 123244

    123244

    21
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    Apr 25, 2013
    N-type MOSFET (specifications: )
    • ID=10A (Load current max.possible)
    • RDS(on)= <10mΩ=; <0.01Ω
      [*]U(minimum working voltage)=6V (power supply ranging from 6-12V)
    Search on Ebay.com (only the cheap and common ones)
    1. IRF2804 (How many voltages do I need to operate this ? Operating voltage symbol on datasheet ?)
      VDSS= 40V (Do I need 40V min. power supply or is this the max. voltage it withstands ?)
      RDS(on)= 2.0mΩ (this seems really good)
      ID= 75A
      http://www.irf.com/product-info/datasheets/data/irf2804.pdf
      http://www.ebay.de/itm/5p-x-IRF2804...Electrical_Test_Equipment&hash=item20cdcf21e9
    2. STP55NF06
      VDSS= 60V
      RDS(on)= 18mΩ (too high)
      ID= 50 A
    3. RFP50N06
      VDSS= 60V
      RDS(on)= 22mΩ (too high)
      ID= 50A

    1. Can I order "the IRF2804" and have good results ?(no heating ?)
    2. Are there any added kickbacks\danger when using so low RDS(on) ?
      [*]From what point on do I need thicker wires(10A) ? Is that added 1A diode rating good ?
    [​IMG]
     
    Last edited: Apr 28, 2013
  20. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    The VDSS voltage specification is the maximum voltage it is specified to withstand.

    Thanks for the links. That makes it easier for me to help you.

    Yes, the IRF2804 is perfect for this project. It will dissipate almost no power at all, as long as it is switched ON and OFF quickly and fully.

    The Rds(on) resistance of the IRF2804 is only specified at Vgs=10V. Looking at Fig. 3 on page 3 of the data sheet, you can see that it will not saturate fully with only 5V on the gate. Therefore you can't run your circuit from 6V. It will need a power supply of at least 9V to ensure that Vgs will be high enough to saturate the IRF2804 and achieve the low ON-resistance. A 12V supply would be better.

    The diode from drain to positive needs to have a higher current rating. It needs to be rated for at least as much current as the motor draws. I would add a 50% safety margin. Probably your best bet will be a high-current Schottky diode rated for at least 20V. This one is suitable:
    http://www.ebay.de/itm/5-Dual-Schot.../360645183228?pt=Bauteile&hash=item53f820c6fc

    I assume you are in Germany. You should add your location to your profile. Your location shows up with your posts and knowing that information will help others to help you.
     
    Last edited: Apr 28, 2013
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