Fig. 5 (a) The maximum output voltage of the proposed resonant
converter, at an input of 3.7 V. (f) Input voltage and current. (g)
Output voltage and current. (h) Voltage amplitude before and after
adjustment under different loads (i) The percentage of each harmonic of
the output voltage. (j) The current decay curve as a function of battery
runtime.
Fig. 5a shows the output waveform of the LCLLC resonant tank with an
input voltage of 3.7 V. Using a 3.7 V DC battery and a transformer
inductance of 10 μH, the output voltage reaches 66.0 V, meeting the
requirements for tumor treatment. Generally, an output voltage of 50.0 V
is sufficient for this purpose, so it was set to ~50.0 V
with a DC-DC converter for further analysis.
Figs. 5b and 5c show the DC input voltage and current, as well as the
output voltage and current, respectively. The average input current
reaches 1350 mA, with a total input power of 5.1 W, closely matching the
simulation results. The output current can reach 960 mA, and the total
average output power can reach 27.2 W, demonstrating that an input power
of ~5 W is sufficient for TTFields treatment.
In simulation analysis, the capacitive impedances of 60, 75, 90 Ω for
TTFields treatment with 200 kHz. This study also chooses capacitor load
impedance of 60, 75, 90 Ω, respectively. Fig. 5d shows the voltage
outputs Vout with and without transformer
adjustment. For LCLLC structure with capacitive impedances of 75 Ω, the
output Vout is 51.3 V with the transformer
inductance (8 μ H). The output Vout could
reach to 50.0 V with the transformer inductance (5 μ H) for the
capacitive impedances of 60 Ω.
Fig. 5e shows the comparison of harmonics (1st–11th) of the
experimental waveform for proposed LCLLC resonant converter with
impedance of 90 Ω. High harmonic distortion (THD) is only 1.4% of the
output waveform, which is low enough for tumor treatment.
Fig. 5f shows the battery discharge current curve using four 18650 cells
(3200 mAh) as the DC power supply. As mentioned in the Introduction, the
output current of the clinical apparatus ranges from 400 mA to 1000 mA.
This study uses 700 mA as the standard to test the effective output
duration, ensuring that the output current does not fall below 630 mA
(10%). Fig. 5f indicates that this design maintains a voltage of 50 V
or more for 8.7 hours of continuous operation. For the Optune apparatus,
patients require an additional battery or power supply if they plan to
be away from home for more than one hour. The TTFields system requires a
battery power of approximately 50.0 W. As shown in Fig. 5b, the average
input power is only 5.1 W, which meets the requirements for both output
voltage and current. Fig. 5f demonstrates that the LCLLC structure
enables long-term outdoor TTFields treatment.