Comparison of H-bridges

Discussion in 'General Electronics Chat' started by Dritech, Mar 26, 2012.

  1. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
    756
    5
    Hi,

    For my project i had to use an H-bridge to control a 12V 2A motor. I had a choice between H-bridge using TIP122, H-bridge using irfz44n MOSFET and the L298 IC. I decided to use the L298 IC.

    Now i have to say why i have chosen the L298 instead of the others. Can someone tell me some advantages of using this IC instead of an H-bridge using TIP122 and an H-bridge using irfz44n??

    Is it more efficient or does it consume less power?

    Thanks in advance.
     
  2. praondevou

    AAC Fanatic!

    Jul 9, 2011
    2,936
    488
    The advantage is that all components are contained in one package.
    Driver logic, interlock, and power transistors.
     
  3. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
    756
    5
    Thanks for the reply. Apart form that, are there any other advantages?
     
  4. strantor

    AAC Fanatic!

    Oct 3, 2010
    4,302
    1,988
    TIP122 is right out - old, inefficient, BJT technology
    Now you need to compare datasheet numbers between your L298 & your irfz44n. The L298 I believe is still using BJTs inside, so my money is on the irfz44n as far as efficiency & performance.
    So, yes, Probably the convenience of single package design is the only advantage, + price.,
     
  5. shortbus

    AAC Fanatic!

    Sep 30, 2009
    4,003
    1,517
    Convenience is the only advantage. The L298 is a very inefficient chip, look at the voltage drop from the data sheet.
     
  6. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
    756
    5
    Hi again,

    I am using a dual supply (5v and 12v) to control the L298. With the 5V supply i also have the PIC and LCD.
    The problem is that when the motor is active, the LCD is dimming and i noticed that the 5v is dropping to approx 4.6V. Is this normal? and how can i solve this?

    BTW the current limit of the supply is 3.2A so its suppose to handle current of the motor, PIC and LCD.
     
  7. shortbus

    AAC Fanatic!

    Sep 30, 2009
    4,003
    1,517
    Do you have "bypass capacitors" at each IC power connection?
     
  8. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    With a load of 2A, the L298 has a maximum saturation voltage loss of 5V!
    Then with a 12V supply, your 12V motor gets only 7V. Some L298 ICs might have a little less voltage loss.

    With good Mosfets, the motor gets close to 12V.
     
  9. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
    756
    5
    Hi, thanks for your replies.

    I have a problem with the L298 IC. When the H-bridge is active, the output pin 1 is reading 10.5V and output pin 2 is reading 1.2V. Shouldn't output 2 read 0V?? (Note that the readings were taken while the motor was connected and running).

    This 1.2V is causing the LCD do dim.
     
  10. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Haven't you seen the datasheet for the L298?
    It shows that the outputs do not get anywhere near 0V or the supply voltage. They have a high saturation voltage loss.
     
  11. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
    756
    5
    and is there a way to eliminate the 1.2V from going to ground and causing the LCD to dim?

    Thanks
     
  12. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Yes.
    Don't use an old L298. Instead use Mosfets.
     
  13. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
    756
    5
    I did an H-bridge using IRFZ44N but for some reason it was only outputting approx 9V from a 12V supply.
     
  14. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The IRFZ44 is N-channel. If it is the bottom one then the motor is connected to its drain that goes to 0V when its gate is +10V. Is its gate only 5V? Then it might be only barely turned on. Instead use "logic-level" Mosfets if driven from only 5V.

    If the IRFZ44 is the upper Mosfet then the motor is connected to its source pin. Then the gate must be +20V for it to completely turn on. I betcha it does not have 20V.
    Instead you can use a P-channel Mosfet with a transistor driving its gate or use a Mosfet driver IC.
     
  15. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
    756
    5
    Hi, i am using the circuit in the attached pic. All the transistors are IRFZ44N. So i have to supply the gate with more than 12V?

    If the gate voltage is equal to the collector voltage (eg. both 12V), will the transistor get fully saturated (i.e. outputs the full 12V) ??
     
    Last edited: Mar 28, 2012
  16. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
    756
    5
  17. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Mosfets have a drain terminal, not a collector.
    The gate-source voltage must be at least 10V for the IRFZ44 to be completely turned on. Some turn on with maybe 8V.

    Your lower Mosfets have a gate-source voltage of 12V so they turn on completely.
    You want the source pin of the upper Mosfets as high as possible (+12V) so their gate must be at least 12V + 10V= 22V for them to be completely turned on. But the gate gets only 12V so the output voltage is very low.
     
  18. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
    756
    5
    If i use the h-bridge in the link below (figure 8), do i need to supply 22V for them to be completely turned on?? the problem is that the maximum voltage the supply of this circuit can output is only 12v.

    http://www.bristolwatch.com/ele/h_bridge.htm
     
  19. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Their upper Mosfets are P-channel so they work properly if the gate voltage swing is the entire supply voltage.

    But your Upper Mosfets are N-channel which is a completely different circuit.
     
  20. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
    756
    5
    Thanks for the reply.

    In the description of figure 4, it says that :

    Are the transistors swapped?
     
Loading...