Full wave Rectification Problem!

Discussion in 'Homework Help' started by big_tobacco, Oct 25, 2009.

  1. big_tobacco

    Thread Starter New Member

    Mar 9, 2009
    2
    0
    Hello,

    I'm currently revising some past papers for an up and coming phase test. Basically the question reads:

    "A full wave rectifier using ideal diodes is fed from a 50 (Hz) supply and has a smoothing capacitor of 1000 (microfarads). The rectifier should have an average DC output voltage of VL = 12 (V) when connected to a load of 3 (KiloOhms). Calculate the following....

    A) The value of Vmax
    B) The ripple voltage Vr
    C) The percentage regulation

    I can probabaly B & C (as I have obvious equations for both) but it's the first question I'm trying to solve.....fortunately I had my hair cut this morning otherwise I would have pulled it all out!!!!!!

    Please help me and point me in the right direction (no pun intended)
     
  2. Thav

    Member

    Oct 13, 2009
    82
    0
    If you can calculate Vr, I would imagine Vmax would be simply  V_{\mathrm{Max}} = \langle V \rangle  + \frac{V_r}{2} with \langle V \rangle representing the average value (12V) you're shooting for.
     
  3. big_tobacco

    Thread Starter New Member

    Mar 9, 2009
    2
    0
    Hello, thanks for your response

    To be honest I haven't seen that equation, plus this answer is prior to knowing what Vr is.

    I initially thought of rearranging

    VL = Vm ℮ -T/CR


    i.e. giving Vm = VL / ℮ -T/CR
     
  4. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    One approach might be:

    AT 50 Hz the full wave rectified component is 100Hz - corresponding to a 10ms interval.

    Assume the capacitor discharges over this 10ms interval at 12V into the 3kΩ resistor at a constant rate - not quite true but near enough. The capacitor charging time is considered negligibly small - not quite true but near enough.

    So the assumed constant capacitor discharge current is 12V/3k = 3mA

    Using I=3mA=CdV/dt = CVr/dt where C=1000uF and dt=10ms

    re-arrange to find the ripple Vr
     
  5. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    Sorry 12V/3k=4mA not 3mA!
     
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