Pulse Transformer for Rectifier Circuit

Discussion in 'The Projects Forum' started by ZaaRz, Dec 31, 2009.

  1. ZaaRz

    Thread Starter New Member

    Dec 31, 2009
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    0
    Hello all,

    Im doing my final project entitled Single Phase Controlled Rectifier hardware design. So, before i build the hardware, i simulate the circuit using MULTISIM first, but... the problem arise when it comes to the pulse transformer (PT), which is none of PT is appeared in the Multisim. Does anyone know how to model PT using MultiSim ?

    And,

    What is different between Pulse Transformer (1:1:1), PT 1:1+1, and PT (1:1). Which are most suitable and economical for my circuit as attached below ?
    [​IMG]
    and which of these PT is recommended for the circuit ? Sorry, i know nothing about PT. Anyway, thanks in advance.. :)

    Farnell : Pulse Transformer List
     
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    In your Farnell listing click on the data sheet icon (pdf symbol) to download the PT details. It's in the Tech Info column.

    At 4kHz gate drive oscillator frequency (your circuit) the pulses are high for 125uS. If you need around 3V gate drive then your PT needs about 375 Vus capacity although you could probably get away with a lower value and still get reliable SCR turn on. Check your SCR specs and circuit load conditions.

    Look for something with say at least 200Vus capacity or better. For instance, the Vigortronix VTX shown in your listing has a 200Vus capacity. You may want to go higher for greater reliability - it's your call but the price will be commensurate with this figure of merit.
     
  3. ZaaRz

    Thread Starter New Member

    Dec 31, 2009
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    0
    Sorry, forgot to mention, actually i use 555 Timer (NE555P) as a astable oscillator with resistor, 2k and capacitance 100nF. The frequency for the astable oscillator is 1/1.4*R*C (there is diode across the 2k resistor) thus will generate between 3.5-3.6kHz. So, the time where the pulse is high is 140uS. I use 2N5061 SCR which is it need 200uA max current to trigger the gate.

    And perhaps, i intend to use two PT with ratio (1:1:1) as it need 2 SCR (2N5061) to be turned on during positive cycle pulse, and 2 more SCR during negative cycle pulse. I dont know much about Vigortronix PT (1:1+1), is it possible for Vigortronix to create 2 secondary windings in the secondary side ? Means, to be just like PT (1:1:1) and on two of the SCR simultaneously with only one PT used?

    Attached : 2N5061 Datasheet
     
  4. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    Yes with a 1:1:1 PT you can drive a pair of SCR's - one gate drive per isolated secondary. You might need to add a secondary resistance in series to each gate to offset any imbalance in the individual gate drive requirements due to SCR parameter variations.

    Presumably you have a single phase bridge arrangement in mind. If that's the case you could use a semi-controlled bridge with a pair of SCR's and a pair of diodes, rather than four SCR's.

    Given your chosen SCR requires such a minuscule gate drive current and gate turn-on voltage, I would probably choose the cheapest PT. With a bit of careful design you may even be able to drive the PT direct (in series with a limiting resistor - & don't forget the back emf diode) from the logic circuit and eliminate the [SL-100] pulse driver transistor. CMOS gates don't have a lot of drive capability but it could work OK. After all you are driving the [SL-100] transistor base from the CD4073 gate - albeit with a 680Ω series resistor.
     
  5. ZaaRz

    Thread Starter New Member

    Dec 31, 2009
    3
    0
    I dont understand why we need to put resistor in series with the gate of secondary PT. Is it to limit the current flow to the SCR?

    Erk, should i installed 2 SCR instead of using four SCR ? If that so, the rectifier will act as semi-controlled (cause only 1 SCR operating in each cycle). But the project given is to build fully controlled rectifier, i scared if this will run out from the project's objective.

    The cheapest PT in the farnell-list is PT6 & PT6E manufactured by OEP (due to availability in my country, near SG) which is having (1:1+1) ratio. I think this PT will work as 1:1:1 because after i refer the datasheet given, this PT able to generate 1 primary with two secondary winding if all of the pin is connected according to the datasheet (as i understand by looking the PT schematic).

    Anyway, correct me if im wrong. :) Thanks!
     
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