# Design of the Converter Prototype for Powering the Hydrogen Electrolyzer
## 2 Constant Current Source
\begin{table}
\begin{tabular}{l c c c c} \hline
**Properties** & **Test Conditions** & **Value** & **Unit** & **Tolerance** \\ \hline Inductance & \(L\) & 100 kHz/10 mA & 10 & \(\mathrm{\mu H}\) & \(\pm\)20\% \\ Rated inductance & \(L_{R}\) & 100 kHz/10 mA/21 A & 7.8 & \(\mathrm{\mu H}\) & Typ. \\ Rated current & \(I_{R}\) & \(\Delta\)T = 50 K & 21 & A & Max. \\ Saturation current 10\% & \(I_{SAT,10\%}\) & I\(\mathrm{\Lambda L}\)/LI \textless{}10\% & 8 & A & Typ. \\ Saturation current 30\% & \(I_{SAT,30\%}\) & I\(\mathrm{\Lambda L}\)/LI \textless{}30\% & 26 & A & Typ. \\ DC resistance & \(R_{DC}\) & 20 \({}^{\circ}\)C & 3.4 & m\(\Omega\) & \(\pm\)10\% \\ Self-resonant frequency & \(f_{res}\) & & 15 & MHz & Typ. \\ \hline \end{tabular}
\end{table} 
Table 1: Inductor parameters. was determined by Equation (5), where Vref is the ADC reference voltage 2.048 V, A is the amplification factor of differential amplifier 6.8, and R15 and R16 are values of shunt resistors. The converter circuit diagram is shown in Figure 3.  
\[f_{df}=\frac{1}{2\pi RC_{D}}=\frac{1}{2\pi\cdot 33\ \Omega\cdot 180\ \text{pF}}=27\ \text{MHz} \tag{4}\]  
\[K_{CCS}=\frac{V_{ref}}{A\cdot R15||R16\cdot 4095}=0.00367736 \tag{5}\]  
Power MOSFET transistors are power switches designed explicitly for half-bridge topologies and packaged as dual devices within a single housing. After recalculating the power losses of various MOSFETs [20], the most suitable type was the \"OptiMOS--6\" dual-power N-channel IAUC60N04S6L045H transistors. The power loss was determined by Equations (6)-(11) for both transistors in a synchronous buck converter [21; 22]. \[P_{con}=R_{\text{DS}\_on}\cdot I_{L}^{2}=520\ \text{mW} \tag{6}\]  
\[P_{out}=V_{out}^{2}\cdot\text{C}_{oss}\cdot f_{sw}=8\ \text{mW} \tag{7}\]  
\[P_{in}=V_{\text{GS}}^{2}\cdot\text{C}_{iss}\cdot f_{sw}=48\ \text{mW} \tag{8}\]  
\[P_{on}=V_{\text{GS}}\cdot I_{L}\cdot t_{r}\cdot f_{sw}=48\ \text{mW} \tag{9}\]  
\[P_{off}=V_{GS}\cdot I_{L}\cdot t_{f}\cdot f_{sw}=192\ \text{mW} \tag{10}\]  
\[P_{t}=P_{con}+P_{out}+P_{in}+P_{on}+P_{off}=816\ \text{mW} \tag{11}\]  
The effect of applying a heat source to the component-mounting locations was simulated on a simplified PCB model (Figure 4). According to Equation (12), the transistor junction temperature was derived from the surface temperature of the mounting loca  
Figure 3.0 Scheme of one branch of the buck converter. tion, and the shunt temperature was derived similarly according to Equation (13) with an ambient temperature of 25 \({}^{\circ}\)C [23; 24]. Figure 3.1  
Figure 3.2  
The interleaved buck converter's input of each branch contains a capacitor bank. According to the requested parameters, the ripple current \(I_{RC\_RMS}\) was determined to be 5 A. The selected capacitor was EEE-FT1H331 AP, with a capacitance of 330 \(\upmu\)F and a maximum ripple current \(I_{RC}\) of 900 mA. The bank of six capacitors was connected in parallel to meet the requirements [13]. According to the simulated values under worst-case operating conditions, the I ripple on the capacitor bank is 5 A. When using six pcs of \(C=330\ \upmu\)F capacitors, the current is distributed to I\({}_{\mathrm{C}}\) 833 mA on each capacitor. Then, the power loss of each capacitor P\({}_{\mathrm{C}}\) can be calculated according to Equation (14), where tan\(\delta\) is the dissipation factor--the total is 500 \(\upmu\)W.  
Figure 3.3  
Power MOSFETs are driven using the isolated dual-channel MOSFET driver UCC21521 DW, configured according to datasheet specifications, as shown in Figure 3.4 Powering the upper branch of the driver was provided by an isolated DC/DC converter TBA1212, which is powered from the same voltage supply as a lower branch of the driver. Figure 3.5 PCB surface temperature simulation of the constant current source.