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34 EE|Times EUROPE — Power Electronics
Miniature Current Transformers Keep Pace with GaN

EE5 EE4.4
749251050 749252050
Ls = 500 µH min. Ls = 205 µH min.
Measured Current Measured Current
Voltage across secondary winding Voltage across secondary winding

Figure 5: Comparison of two transformer sizes under the same operating conditions in a discontinuous-mode flyback circuit. The middle
trace is the measured current. The top trace is the voltage across the secondary winding, scaled (5 V/div) to show the reset pulse. The
bottom trace is the gate drive.

10 V
Figure 6: Reset response using various
0 V diodes. Fast and ultra-fast diodes
(black — 1N4934, t = 200 ns,
rr
-10 V V reset ≈ 12 V) provide smooth, timely
response. The Zener diode
Voltage -20 V (red — 1N5245B, t ≈ 600 ns,
rr
≈ 14 V) has a little more delay but
V
reset
-30 V controlled voltage. The signal diode
(grey — 1N4148, t = 4-8 ns, V reset ≈ 21 V) is
rr
-40 V fast and harsh and has a large voltage, all
* notscaled, only for reference of which will contribute to EMI noise.
-50 V
0 µs 1 µs 2 µs 3 µs 4 µs 5 µs 6 µs
Time

1N4934 1N5245B 1N4148 Gate drive *

FEBRUARY 2021 | www.eetimes.eu