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14th February 2018, 07:02 #1
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FlyBack design using Relfected Voltage VOR Method
Hi,
I need design steps for the design of a universal (85265VAC) input, 12v 30 WATT "Discontinuous Mode" Flyback converter using VOR method. Is there any comprehensive document available.
http://micro.rohm.com/en/techweb/kno...pwm01/940/#p01
i need explanation of this method. (web link). How can i compare it with the method used in the attached file.
Regards

14th February 2018, 07:02

14th February 2018, 12:35 #2
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Re: FlyBack design using Relfected Voltage VOR Method
All methods are the same because the theory is the same. Just apply standard circuit analysis for the Flyback converter in CCM and to see when it enters DCM, just use the usual way of saying Average current < ripple current.
If you need to implement this practically, just find a suitable Flyback IC and follow their design procedure.
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14th February 2018, 12:35

14th February 2018, 12:55 #3
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Re: FlyBack design using Relfected Voltage VOR Method
i have implemented a flyback using uc3845. Transformer is recovered from an old supply with air gap of 0.5mm. 10 turns gives 16uH @ 100KHz. The supply becomes unstable at high load and high input voltage 250AC (rms).
I also need help in dot convention.
Kindly explain "Average current < ripple current."
regards
   Updated   
I want to design the supply by setting the peak primary current at 1A. The sense resistor is 1 ohm.

14th February 2018, 12:55

14th February 2018, 13:00 #4
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Re: FlyBack design using Relfected Voltage VOR Method
I also need help in dot convention.
"Average current < ripple current."
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14th February 2018, 13:08 #5
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Re: FlyBack design using Relfected Voltage VOR Method
is there any difference in inductance and "magnetizing inductance" of a core ?
   Updated   
I need explanation of the equations. see attached files
   Updated   
First we decide turn ratio.
Second We calculate secondary side inductance. and then primary inductance is calculated.
Can i find derivation of these equations?

14th February 2018, 17:18 #6
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Re: FlyBack design using Relfected Voltage VOR Method
First we decide turn ratio.
Second We calculate secondary side inductance. and then primary inductance is calculated.
Iout=Average current of the secondary (i.e. area of a triangle)=1/2 * IsecondaryPeak*(1Dmax) => IsecondaryPeak=2*Iout/(1Dmax)
Insert the 2nd equation in the 1st and you have the boundary which is what they have in their equations. Make it be an inequality to fulfill the DCM condition.
is there any difference in inductance and "magnetizing inductance" of a core ?
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15th February 2018, 06:46 #7
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Re: FlyBack design using Relfected Voltage VOR Method
Thanks for reply
http://micro.rohm.com/en/techweb/kno...pwm01/940/#p01
"To provide for a margin, such as an overload protection point, the maximum load current should be 1.2 times the Iout. Since specifications for Iout are 3A, Iomax should be 3.6A. In terms of specifications, Vout should be equal to 12V, and the VF and Duty, values calculated in Step (1) should be used."
What does it mean?
How can i add this margin on primary side using current sense resistor? May be by allowing slightly large peak current through primary winding?
   Updated   
Thanks for reply
http://micro.rohm.com/en/techweb/kno...pwm01/940/#p01
"To provide for a margin, such as an overload protection point, the maximum load current should be 1.2 times the Iout. Since specifications for Iout are 3A, Iomax should be 3.6A. In terms of specifications, Vout should be equal to 12V, and the VF and Duty, values calculated in Step (1) should be used."
What does it mean?
How can i add this margin on primary side using current sense resistor? May be by allowing slightly large peak current through primary winding?

15th February 2018, 06:46

15th February 2018, 12:10 #8
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Re: FlyBack design using Relfected Voltage VOR Method
How can i add this margin on primary side using current sense resistor? May be by allowing slightly large peak current through primary winding?
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