pulse Transformer

Discussion in 'General Electronics Chat' started by Far, Jul 25, 2009.

  1. Far

    Thread Starter Member

    May 11, 2009
    20
    0
    I need some practical information about pulse transformer.
    I want to Isolate a LM555 timer (control circuit with 5V/50Hz pulse output) from the Thyristor in power circuit(a fully controlled half wave rectifier 12Vac to 5Vdc).
    is there any extra circuit to use beside the pulse transformer?
    thanks for your help?
     
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    Use an opto-isolator instead of a pulse transformer.
     
  3. Far

    Thread Starter Member

    May 11, 2009
    20
    0
    I need at least 1A output current. I have tested MOC3020 & TLP521 but their output current is very low(50-60mA) and may disturb easily. Is there any optocoupler which could tolerate a higher current at the output?
    thanks for your help;)
     
  4. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
    Hello,

    You could take a look at the CPC1979.
    It can drive 1.4 A without cooling, 3.5 A with cooling.
    See datasheet.

    Greetings,
    Bertus
     
  5. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    You can buffer its output with a transistor to increase its current capacity.
     
  6. Far

    Thread Starter Member

    May 11, 2009
    20
    0
    How should I buffer the output? what kind of transistor is appropriate for this use? I already have a TLP521 with 0-5V/50Hz pulse in output.
    Thanks Very much for your help:)
     
  7. Tahmid

    Active Member

    Jul 2, 2008
    344
    25
    Hi,
    I use MOC3021 and used it to drive BTA26 and BT139 Triacs and I used them for very high wattage circuits. Never had a problem with gate drive current.
    60mA should be enough if you use a triac with low enough gate current requirement, eg. BTA26 and BT139.
     
  8. Far

    Thread Starter Member

    May 11, 2009
    20
    0
    I already use a TLP521 to drive a thyristor Bt 151 with no problem.
    I just want to ensure that no damage will happen to my optocoupler.:)
    I tried to setup a simple rectifier with Bt151 but the gate pulses occurs in output load voltage.
    how does it happen? is there any solution?
    Regardes
     
  9. Far

    Thread Starter Member

    May 11, 2009
    20
    0
    I should isolate the driver circuit from the power side. Is it OK to use the same supply I used in micro controller, for the collector side of optocoupler?
     
  10. Ruptor

    Active Member

    Apr 26, 2009
    44
    0
    Hi Far
    It is common practice to turn on the thyristor at zero crossing point so that spikes are not generated. It will be more difficult to obtain an EMC pass otherwise. If you have to switch elsewhere then you need snubbers to quench the spike.
     
  11. Far

    Thread Starter Member

    May 11, 2009
    20
    0
    Hi
    I already detect the zero crossing point(synchronizing pulse with 220Vac source) and generate a pulse with adjustable firing angle with Atmega8 then by using a 555 change it to a pulse train. after that by using an optocoupler I made an isolation between driver and power stages. there is no spike so no snubber is needed. but the thyristor doesn't turn on. what's the problem?
     
  12. Far

    Thread Starter Member

    May 11, 2009
    20
    0
    please help me! what should I do?
     
  13. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
    Hello,

    Can you post a schematic of what you have upto now?
    With the schematic it is more easy to help.

    Greetings,
    Bertus
     
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