Exam (elaborations) EAD 410 (EAD410)

EAD 410 Magnetic design tutorial 2019


A power processor is required to feed an application at a voltage of 48 VDC.
Galvanic isolation is required and it is decided to employ a half-bridge DC-DC
converter with transformer isolation to realise the interface. The switching
frequency is 150 kHz and a surface temperature of 1000C is to be assumed. Input
DC voltage is obtained by rectifying the available AC supply of 240±10% V, 50
Hz. The peak-peak ripple in the input DC voltage should not exceed 5% of the
peak DC voltage.

The secondary winding is centre-tapped and an LC filter is connected at the output
terminal of the high frequency rectifier. It keeps the peak-peak output current
ripple less than 15% of the nominal load current while the peak-peak output ripple
voltage is less than 2% of the nominal output voltage. Rated load power is 2000
W.

The high-frequency rectifier diodes have forward voltage drop of 1.5 V. The full-
bridge high-frequency inverter used to convert the input DC voltage into a high-
frequency AC waveform employs semiconductor devices with a voltage drop of 2
V when conducting. The output filter inductor has a series resistance of 10 m
and the semiconductor devices have rise- and fall-times of 250 ns with a tolerance
of 10%.

Data sheets for various core materials should be obtained and consulted where
necessary.

Stating any assumptions made, determine:

(i) Practical range of waveform duty ratio

 max  0.835
choose
 max  0.835

vˆ pri ,min  149.208V
I L,ave,min  41.667 A
vˆsec,min  59.78V
n  2.496




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, vˆ pri ,max  182.81V
vˆsec,max  73.241V
 Vs 264V  0.6815
Vo  48V
0.6815    0.835


(ii) Size of input low-frequency rectifier filter capacitor to meet
specifications

isw,nom,min  I pri ,nom,min  16.6935 A
Pin Vs  216V  2853.52W
Vo  48V

I dc Vs  216V  9.581A
Vo  48V

Cin Vs  216V  6.273mF
Vo  48V


Pin Vs  264V  3014.127W
Vo  48V

I dc Vs  264V  8.28 A
Vo  48V

Cin Vs  264V  4.435mF
Vo  48V

o Input power takes into account switching losses.

(iii) Capacitance and inductance of output filter components to meet
specifications

L Vs  216V  4.392 H
Vo  48V

L Vs  264V  8.478H
Vo  48V

C C Vs 216V  2.713F
Vo  48V

C Vs  264V  2.713F
Vo  48V
Choose
Lo  8.478H
Co  2.713F

(iv) Practical values of voltage and current ratings for high-frequency
rectifier and inverter semiconductor devices




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