## 4 Peripheral Circuits  
For feasible IGBT switching, the PWM signal from the microcontroller must be amplified and be able to supply enough current to the gate to ensure the transistor's smooth operation. Also, without proper isolation, the high voltages in the inverter will make their way into the electronic circuits. In this case, the possible damage will be irreparable. For this reason, the TLP250 chip [34] was used, as shown in Figure 5. The TLP250 chip is an opto-electronic power driver with internal isolation capabilities [35].  
In Figure 6 part 1, the voltages across the two ends of the coil and capacitor are reduced by a resistor pair and fed to the op-amp in part 2. Because the designed circuit is not functioning in feedback mode, the output of the op-amp (PULSE-DET) will also change along with the oscillation, as shown in Figure 7 (blue waveform). Therefore, by observing the PULSE-DET signal, it is possible to confirm the presence of the load on the coil.  
The LM324 chip has four operational amplifiers inside of it, which are used here to sample collector-emitter voltage fluctuations and the IGBT current and detect the critical temperature of the heatsink on which the IGBT is mounted. For the sake of simplicity, the design circuitry is divided into five sections in Figure 7. In the following, their utilization will be briefly discussed.  
Figure 4: Coil’s inductance measurement.  
Figure 5: IGBT driving circuit.  
Figure 6: Measurement circuits.  
During the excitation of the coil (transistor switching), the operation condition can be categorized into two types based on the oscillation that takes place. According to Figure 7, if there is a load present on the coil (a), the oscillation voltage (shown in orange) is damped out in the first few periods. However, if there is no load present (b), the oscillation continues. Therefore, this feature can be used to ensure the existence of the load on the coil.  
The resistors and capacitors in part 2 provide sufficient filtering for the VIN_DAMP and VC_DAMP voltages. For example, capacitor C8 and resistor R14 form a low-pass filter with a specific frequency cutoff of \(\mathrm{f}=\frac{1}{5\mathrm{Kc}}\approx 90\) kHz. This removes upper disturbing frequency harmonics from VC_DAMP. Zener diodes D6 and D7 protect the op-amp input in the case of an overvoltage surge [36]. In Figure 6 part 3, VC_DAMP (IGBT collector-emitter voltage) is an input signal for the op-amp, which in this case acts as a follower; then, the op-amp output (ADC_IGBT_VCE) is sent to the microcontroller for further processing. Also, an NTC resistor (Figure 8) is placed on the heatsink, which is used to secure the temperature of the transistor and protect it against overload.  
Measuring the system's current is necessary to calculate the output power. Therefore, a 150 m\(\Omega\) shunt resistor (wire-wound resistor in front of the IGBT in Figure 8) is introduced to the circuit. The derived voltage as a result of the current passing through it is filtered by a conjunction of C6 and R13 (Figure 6 part 4). Therefore, it can be assured that the  
Figure 8: IGBT heatsink and its NTC.  
Figure 7: Resonating voltage. (a) Load is present. (b) Without load.  
ADC_IGBT_CURRENT signal correlates with the average current of the system. This signal is also passed to the MCU for sampling.