# A Dual Stage Low Power Converter Driving for Piezoelectric Actuator Applied in Micro Mobile Robot
## 5 Experiment Realization  
### Fabrication Specifications  
The circuit topology described in Figure 4 is soldered onto a well-designed printed circuit board using discrete components. Table 3 lists the specifications of the discrete components, which include a power MOSFET, a rectifier diode, a flyback transformer, and a filtering capacitor. The flyback step-up stage is responsible for increasing the input DC voltage. The basis of the selection is to ensure that the components can handle the predicted voltage and current without breakdown and failure. As mentioned earlier, if the input voltage varies within the range of 3.0-4.5 V, then the maximum average current can reach 200 mA. Therefore, when the output is approximately 100 V, the average output current should be less than 10 mA. In accordance with package specifications, the N-channel enhancement MOSFET (SI2304, Vishay Intertechnology Inc., Shelton, CT, USA) with the small outline transistor (SOT) package is used as the primary side switch, because of its high voltage stress, low on-state resistance, and sufficient compactness.  
The flyback secondary diode is an SOD-123 packaged Schottky barrier rectifier diode, i.e., SMD1200 PL (Micro Commercial Components Inc., Simi Valley, CA, USA), which can withstand more than 1 A average forward current and up to 200 V reverse voltage. Compared with a conventional diode with a turn-on voltage of 0.7 V, SMD1200 PL has a voltage of only 0.4 V at a forward current of 20 mA. Therefore, conduction loss is low, which is a key factor in selecting this diode.  
The flyback transformer LPR4012 (Coilcraft Inc., Cary, IL, USA) with a weight of 64 mg and made of ferrite material produced by Coilcraft has an excellent coupling coefficient (>0.95) and good electromagnetic interference (EMI) performance. Its primary inductance is 2 uH and the turn ratio is 1:10, which can withstand a peak current of 1.7 A under an unsaturated condition. The 1 uF/200 V output filter capacitor (Vishay Intertechnology Inc., Shelton, CT, USA) with a 0603 package is selected to diminish voltage ripple on the actuator outputs.  
Figure 10: Simulation waveforms of the drive stage.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Device Name** & **Chip Number** & **Weight (mg)** & **Size (mm)** \\ \hline Flyback transformer & lpr4012 (\(L_{m}\) = 2 uH) & 64 & 4 \(\times\) 4 \\ Power MOSFET (power stage) & SI2304 & 8 & 2.8 \(\times\) 2.1 \\ Rectifier diode & SMD1200 PL & 8 & 2.8 \(\times\) 2.1 \\ Capacitor (power stage) & 1 uF/200 V & 1.2 & 1.6 \(\times\) 0.8 \\ Power MOSFET (drive stage) & TN2404K & 8 & 2.8 \(\times\) 2.1 \\ Inductor (drive stage) & 15 uH/40 mA & 1.2 & 1.6 \(\times\) 0.8 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Specifications of the discrete components.  
For the half-bridge drive circuit, two N-channel enhancement MOSFETs TN2404K (Vishay Intertechnology Inc., Shelton, CT, USA) with an SOT-23 package are adopted as high-side and low-side switches, because of their high capability to withstand voltage and low on-state resistance. A 0603 package passive inductor (Vishay Intertechnology Inc., Shelton, CT, USA) with a high quality factor and good EMI characteristic is used to obtain excellent output signals. The image of the fabricated converter is shown in Figure 11.  
Using the above components, a prototype weighing 108 mg was fabricated. The length, width, and thickness of the circuit are 13, 13, and 4 mm, respectively. The converter realizes miniaturization at the gram level, thereby enabling it to meet the requirement of compactness for MMRs in harsh applications.