Hi I need Help on a Bridge Rectifier

Discussion in 'General Electronics Chat' started by prasanthebenezer, May 26, 2008.

  1. prasanthebenezer

    Thread Starter Member

    May 26, 2008
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    I designed a simple bridge rectifier with IN4007 diodes and connected the mains supply to it directly. The problem here is that the diodes continually get burnt out or the fuses blast. I can't figure out the problem. Should I provide a step down before the bridge.... Please help me. The design is for an SMPS and i prefer not including a transformer in the circuit. Kindly advice :(
     
  2. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
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    Did you put any of the diodes in backward?

    Also, you should be aware that working with anything over 48V is not a good idea for a beginner.
     
  3. prasanthebenezer

    Thread Starter Member

    May 26, 2008
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    No the diodes are connected as per the general bridge design. Is it any problem of the ratings of the IN4007 diodes should I use any other higher rated diodes. If so can you give me any recommendations...
     
  4. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
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    What was your load? Was it small enough to exceed the current rating of the diodes?
     
  5. prasanthebenezer

    Thread Starter Member

    May 26, 2008
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    i just put a 100K resistor as the load. to check it out.
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    I suggest in the kindest way that this experiment is not worth your life.

    Please do not continue with this project while you are running without a transformer from the mains, as you may not survive it. :eek:

    A transformer will help to ensure that the power level is low enough to be safe. It also provides isolation from the mains, so that you are much less likely to suffer a fatal shock.
     
  7. prasanthebenezer

    Thread Starter Member

    May 26, 2008
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    but sir that aint a fair enough answer. I just wanted to know if it is possible to connect the bridge directly to the mains. and if it is not possible how do they do it inside the mobile phone chargers. Please help me and advice me of alternative components or design that i may be able to use
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    BTW - 1N4007 rectifiers are rated for 1000V, 1A, 3W. They can take very brief (8.3mS) one-time pulses up to 30A.

    You are probably trying to charge up a capacitor on the output of your bridge. Had this charging worked, you would have wound up with an electrical bomb on your workbench in the form of a capacitor charged up to about 167v.
     
  9. prasanthebenezer

    Thread Starter Member

    May 26, 2008
    12
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    Thanks a lot for the information. Could you suggest any alternatives that I would be able to use for my full bridge rectifier design. I m designing a PIC based SMPS for my project.
     
  10. SgtWookie

    Expert

    Jul 17, 2007
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    OK, so how long have you been dabbling in electronics? I mean, seriously dabbling in electronics?

    I see you signed up here earlier today, and you've made 5 posts so far; all in this thread.

    You're talking about connecting up components to high voltage and are not sure why they are letting out smoke.

    You're brushing aside my genuine concern for your safety with apparent disregard.

    I can understand and appreciate enthusiasm for a project, but... as I see things at the moment, you're in over your head.

    You haven't even posted a schematic or picture of your project - or put in your profile your country, so we know where to send flowers when you go out in a blaze of glory.
     
  11. prasanthebenezer

    Thread Starter Member

    May 26, 2008
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    With all due respect to your concerns sir. i m just starting off for the first time in my life with high voltages and i m a bit weak in hardware level of design to be frank. I m into Embedded firmware. I am now into this project PIC based SMPS. i have done the microcontroller part and it is functioning pretty fine on the simulators and in the test circuit wherein a transformer was used. Now for the real time part I thought after seeing the ratings that it would not be of any harm connecting the diodes to the mains (Really I m not sure of this now). But when I did so the fuse blew out. I removed the whole microcontroller based and other parts of the circuit and only connected the bridge with a 100K resistor as load the result was pretty much the same. So, now I wanted to know where i flawed. The project is very important to me so please please help. Advice me on the design of the bridge. Also if you think I had to use other components instead. This full bridge rectifier is now the biggest hindrance to my project.
     
  12. pradeeba

    Active Member

    Feb 27, 2008
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    can you post the schematic of the bridge connection?
     
  13. SgtWookie

    Expert

    Jul 17, 2007
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    You don't have something connected up properly.

    However, since you have only mentioned 1N4007 diodes, a bridge scheme, and mains voltage, I cannot tell you anything other than to provide more documentation as to what you are doing.
     
  14. prasanthebenezer

    Thread Starter Member

    May 26, 2008
    12
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    i will surely post the schematic
     
  15. SgtWookie

    Expert

    Jul 17, 2007
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    You can't simply post something from your hard drive. I can't see either of those.

    You need to click the "Go Advanced" button below, and use the "Manage Attachments" dialog.
     
  16. prasanthebenezer

    Thread Starter Member

    May 26, 2008
    12
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  17. prasanthebenezer

    Thread Starter Member

    May 26, 2008
    12
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    sorry for that i ve uploaded the image please look into it. and help
     
  18. SgtWookie

    Expert

    Jul 17, 2007
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    What is the voltage rating of an IRFZ44?

    Your schematic is too fuzzy to make out many of the values. I don't really feel like workng that hard.
     
  19. SgtWookie

    Expert

    Jul 17, 2007
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    Never mind. Voltage rating of an IRFZ44 is 55 volts.

    Congratulations, you have completely fried your project, since you have subjected it to nearly 170V.

    You chose a high-current low-voltage power MOSFET when what you needed was a high-voltage low-current MOSFET.

    Had you started off using a transformer, you might not have a smoking pile of rubble in front of you. At least you are still breathing, and can recover from this debacle.

    Your design has very serious problems.

    How do you expect your uC to control it's own power supply when it needs to have power before it can be "alert enough" to perform it's duty?

    You can't control the gate of a big MOSFET like that from a microcontroller. You need a driver IC, or a driver built from discrete components.

    The capacitors you used after the rectifier bridge are tiny at 1nF. They are so small that they may as well not have been there. Just as well, I suppose - as you probably don't have any 200V rated electrolytic caps around anyway, which isn't enough for the kind of voltage you would've seen across them.
     
  20. prasanthebenezer

    Thread Starter Member

    May 26, 2008
    12
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    VDS Drain-source voltage - - 55 V
    VDGR Drain-gate voltage RGS = 20 kW - 55 V
    ±VGS Gate-source voltage - - 20 V
    ID Drain current (DC) Tmb = 25 °C - 49 A
    ID Drain current (DC) Tmb = 100 °C - 35 A
    IDM Drain current (pulse peak value) Tmb = 25 °C - 160 A
    Ptot Total power dissipation Tmb = 25 °C - 110 W
    Tstg, Tj Storage & operating temperature - - 55 175 °C

    IDR Continuous reverse drain - - 49 A
    current
    IDRM Pulsed reverse drain current - - 160 A
    VSD Diode forward voltage IF = 25 A; VGS = 0 V - 0.95 1.2 V
    IF = 40 A; VGS = 0 V - 1.0 -
    trr Reverse recovery time IF = 40 A; -dIF/dt = 100 A/ms; - 47 - ns
    Qrr Reverse recovery charge VGS = -10 V; VR = 30 V - 0.15 - mC

    WDSS Drain-source non-repetitive ID = 45 A; VDD £ 25 V; - - 110 mJ
    unclamped inductive turn-off VGS = 10 V; RGS = 50 W; Tmb = 25 °C
    energy
     
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