Full bridge circuit help

Discussion in 'The Projects Forum' started by Tahmid, Jul 19, 2008.

  1. Tahmid

    Thread Starter Active Member

    Jul 2, 2008
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    Hi,
    For full bridge circuit to convert from 300vdc to 220vac, if I use MOSFETs, I need isolated high side MOSFET gate drive. If I use MJE13009 NPN transistor instead, do I need high side isolated drive? Can I drive it directly from my SG3525 50Hz oscillator? :confused:
    Thank you in advance.
     
  2. Tahmid

    Thread Starter Active Member

    Jul 2, 2008
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    Hi,
    Will bootstrapping method work for frequencies such as 50Hz or 60Hz?
    I tried IR2110 at 50Hz. Unfortunately, the full bridge was delivering no output. But when I used it at 30kHz there was appropriate output.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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    The MJE13009 requires around 2A base current to get roughly 10A out. No, your SG3525 would not supply enough current; it's limited to 200mA.

    It wouldn't be able to directly drive high-side NPN transistors, either.
     
  4. Wendy

    Moderator

    Mar 24, 2008
    20,765
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    What about 2 H bridges inverted from each other?
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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    My best guess here is that you're attempting to run the bridge under no-load conditions. At 30kHz, there is enough parasitic LC in the bridge to get the high side caps charged, but not enough at low frequencies.

    Try using a 220K resistor as a load.

    Have a look at International Rectifier's Design Tip DT97-3
    http://www.irf.com/technical-info/designtp/dt97-3.pdf
     
  6. Tahmid

    Thread Starter Active Member

    Jul 2, 2008
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    I ran the bridge with a 25W lamp as load.
     
  7. Tahmid

    Thread Starter Active Member

    Jul 2, 2008
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    But if I'm taking only 0.3A (100W load at 300v), I would require less than 100mA. That is within the capability of the SG3525.
     
  8. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
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    If you are using the MJE13009 in the high side of a bridge, it will be functioning as an emitter follower. In order to have 300V on the emitter, you would need 300V on the base.
     
  9. Tahmid

    Thread Starter Active Member

    Jul 2, 2008
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    Hi,

    Thank you. Now I have gotten the answer to my question. Once again, thank you.

    Tahmid.
     
  10. Tahmid

    Thread Starter Active Member

    Jul 2, 2008
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    hi,

    I used full bridge circuit with 4 X MJE13009.The bridge works properly and the load lamp of 25W lights, but after a few seconds, 2 of the transistors get shorted and the circuit ceases to function. I have replaced the transistors twice, but same thing happens.
    The propagation delay time of MJE13009 is 1.6us. I have used SG3525 to drive the transistors with a driver transistor: MJE13001 for the high side. My guess is that the dead time set in the SG3525 is too narrow and the transistors are cross-conducting. That's why the upper and lower transistors are shorted. I have used 470 ohm resistor between the DISCHARGE and CT pin of SG3525 and this sets the dead time to the maximum possible.
    Is my assumption correct? If not, what can be the cause?
    What can be the remedy?


    Thanks.
     
  11. thingmaker3

    Retired Moderator

    May 16, 2005
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    The datasheet lists minimum frequency of the SG3525 as 120Hz. Perhaps it is unstable when operating at 50Hz and is unable to provide dead time?
     
  12. Tahmid

    Thread Starter Active Member

    Jul 2, 2008
    344
    25
    Hi,
    Thingmaker 3, you are correct. I checked the datasheet of SG3525 of ST Microelectronics. Then, if SG3525 is becoming unstable, what is my solution? What oscillator should I use?
     
  13. Tahmid

    Thread Starter Active Member

    Jul 2, 2008
    344
    25
    Hi,

    I have found out about SG3526 which can operate from 1 hz to 400khz. Should I use this?
    In the Microsemi datasheet, they have stated that at 40khz, if i use 22 ohm resistor as Rd, i get a dead time of 50%. If i use 10 ohm i get 25%.
    I want to know: if i will still get the same dead time at 50hz?

    Thanks.
     
  14. darla1

    New Member

    Jul 25, 2008
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    why dont you incerase dead time and see the operation
     
  15. Tahmid

    Thread Starter Active Member

    Jul 2, 2008
    344
    25
    Hi,
    For SG3525, i have set maximum deadtime and it is not working.
    I do not know how to set dead time in SG3526. That's why i require help. If you know, please let me know.

    Thanks.
     
  16. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
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    According to figure 6 of the SG3526 datasheet, dead time is proportional to the value of the resistor on pin 11.
     
  17. Tahmid

    Thread Starter Active Member

    Jul 2, 2008
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    Hi,
    I have seen the datasheet, but in the datasheet it specifies the dead time at 40khz. Will it be the same for 50hz?

    Thanks.
     
  18. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
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    I suggest experimenting with a resistor divider standing in for the transistors. You can then adjust the driver as needed without having to risk loosing more transistors.
     
  19. SgtWookie

    Expert

    Jul 17, 2007
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    The first thing I saw in the datasheet was a Vcc limit of 40V.

    I thought you were working with a few hundred volts?

    If so, and if you try this IC, you'll blow the lid right off of it.

    You must ensure that the driver IC meets all of your requirements before you connect it, unless you enjoy seeing bright flashes and large clouds of acrid smoke, accompanied by loud "BANGs".
     
  20. Pich

    Active Member

    Mar 11, 2008
    119
    4
    Can we see a drawing of the bridge?
    Have you tried driving the transistors with a pulse tranformer?
     
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