# Finding duty cycle ratios in full-bridge DC-DC converter

Discussion in 'Homework Help' started by bwc, Feb 19, 2015.

1. ### bwc Thread Starter New Member

Feb 19, 2015
3
0
I am asked to find the duty cycle ratios, D1 and D2, and their ripple frequency in the following circuit:

Vo is controlled to provide an average output voltage of 200 V.

What i've tried doing is setting up this equation:

V0 = Va - Vb = D1 * Vd - D2 * Vd

Resulting in:

200 = D1 * 250 - D2 * 250

From the looks of it, I need another equation so I can find D1 and D2. Where do I go from here ?

Thank you.

2. ### Dodgydave AAC Fanatic!

Jun 22, 2012
5,154
770
Where are D1 and D2, i see Da+/- and Db ??

3. ### bwc Thread Starter New Member

Feb 19, 2015
3
0
I found these equations (here on slide 28):

Duty cycle of (TA+,TB-): D1 = ton/Ts =0.5(1+vcontrol/Vtri)
Duty cycle of (TB+,TA-): D2= (1- D1 )
Vo = VAN - VBN = D1 Vd – D2Vd

4. ### bwc Thread Starter New Member

Feb 19, 2015
3
0
Ok, so looking more closely at these equations, assuming Vtri = 250:
D1 = 0.5 (1+200/250) = 0.9 ; D2 = 0.1

Is this correct ? how do i find the ripple frequency for this setup ? i'm trying to look for equations, but can't seem to find something for a dc-dc converter.