High side discrete mosfet driver

Discussion in 'The Projects Forum' started by MatheusLPS, Jan 10, 2014.

  1. MatheusLPS

    Thread Starter Member

    Jul 16, 2011
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  2. MatheusLPS

    Thread Starter Member

    Jul 16, 2011
    34
    0
    OK, reading page 24 on this: http://www.ti.com/lit/ml/slup169/slup169.pdf

    I see that negative signal is expected.

    Another problem:

    A am only getting a maximum of 7.7V on the output (10% of duty cicle = inverted to 90%). Is there a way the increase this?

    bye
     
  3. crutschow

    Expert

    Mar 14, 2008
    13,006
    3,232
    You should be getting about 10V. Post the waveforms as you did for the 50% duty-cycle case.

    P.S. Why are you using the large, slow TIP122 darlington for the driver transistor? Much better to use a faster small switch such as the 2N3904 as shown in Audio Guru's circuit.

    Also the IRFP460 has a rather high ON resistance of 0.27Ω. A device with a lower ON resistance would be more efficient and give a higher output voltage for a given duty-cycle and load.
     
  4. MatheusLPS

    Thread Starter Member

    Jul 16, 2011
    34
    0
    You are right. On the simulation, I am getting ~ 10V. The problem is with the circuit on the protoboard. Look:

    [​IMG]

    The problem is that I do not have so many transistor with me and since it is weekend, I can not buy anything now. :D

    Searching my on my box, I found a BD135, some BC's... a lot of TIPs

    EDITED:

    Just found a 2N3904 laying on the last box of components..... wow... Changing the TIP122....

    Same thing as said before. Most of my FETs are found on old power supplies....

    I have others and will check for a lower RDs ON.

    EDIT:

    Forgot to mention that on the simulation i am using a 220uH inductor. But on the protoboard, I am using a inductor took from a power supply. Do not know the value. Ferrite core.

    thanks
     
    Last edited: Jan 11, 2014
  5. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,797
    1,103
    The inductor properties are critical in switch-mode circuits. The wrong inductance or core properties can lead to core saturation, which is a no-no.
     
  6. MatheusLPS

    Thread Starter Member

    Jul 16, 2011
    34
    0
    Thanks for the info. This one is just a prototype. With the final circuit, I will buy the right inductor.

    So. Changed the TIP122 with the 2N3904 and replaced the IRFP460 with the CEP51A3: http://pdf1.alldatasheet.net/datasheet-pdf/view/176714/CET/CEP51A3.html

    Improved. Getting now 9.3V at output. I using a potentiometer to change the duty cicle. Can change from 0V to 9.3V.

    Now, I need to check the waveforms with a oscilloscope. But, only next week.

    bye
     
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