DC-DC isolated Zeta converter

• DC-DC isolated Zeta converter
  Posted by GuilTy on 19 Dec, 2015 12:51
• Hello everybody,
  
  I want to construct a DC-DC isolated zeta converter with the following specification
  Input voltage:
  -min 8V
  -max 14V
  Output voltage:
  -constant 5V
  Output power:
  -min 5W
  -max 12W
  The ripple current throug the inductances(L2 and Lm) are set to 1/4*current throug them, the ripple through the first capacitor(C1) is chosen at 1/10*voltage through it, and the ripple through the output capacitor(C2) is set at 100mVpp.
  Case 1:
  -input voltage Vg=8V and output power P=5W
  -in this case the load(R1) is 5ohm, the duty cycle is 0.55, and the n parameter for the transformer is n=0.5. The M parameter for the converter is M=Vo/V1=0.625.
  -the output voltage is fixed around 4.2V, instead of 5V and I believe that the ripple from the output is too high.
  The other cases are:
  -V1=14V, P=5W
  -V1=8V, P=12W
  -V1=14V, P=12W
  I don't understant why the output voltage is fixed around 4.2V, and why the ripple is so high. The components in the other cases are different from this one and they depend on the input voltage and on the output power. Maybe I don't know how to read the results of the simulation or they are wrong.
  I've attached a few prinscreens with the schematic, output voltage and with the litteral expression of the currents through the inductances and with the voltages through capacitors.   
  Im=current through the magnetizing inductande
  Il2=current through the second inductance
  Vc1 and Vc1 are the voltages through the capacitors
  PS: this is the ideal case of the convertor.
  
  Thank you,
  GuilTy

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• #1 Reply
  Posted by bugs on 19 Dec, 2015 15:08
• Did you take the voltage drop over the diode into account?
• #2 Reply
  Posted by GuilTy on 19 Dec, 2015 15:59
• I didn't take it into consideration because in the ideal case the diode is considered as a short.
• #3 Reply
  Posted by Kalvin on 19 Dec, 2015 16:39
• Quote from: GuilTy on 19 Dec, 2015 15:59

  I didn't take it into consideration because in the ideal case the diode is considered as a short.
  

  Check the manual and you may notice that the diode threshold voltage is 0.6V by default. Check also other components' model default parameters, and you may find the remaining missing voltage.
• #4 Reply
  Posted by GuilTy on 19 Dec, 2015 21:35
• Quote from: Kalvin on 19 Dec, 2015 16:39

  Check the manual and you may notice that the diode threshold voltage is 0.6V by default. Check also other components' model default parameters, and you may find the remaining missing voltage.
  

  Thank you @Kalvin, I did what you said and the output voltage is around 4.8V~4.9V.
• #5 Reply
  Posted by GuilTy on 19 Dec, 2015 22:12
• I have another question. Why does this appear during the transient regime? I've put it into a red square.

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