**2.2 Large-scale prototype**

A large-scale prototype, depicted in **Figure 4**, was designed and implemented. This design was based on through-hole elements for purpose of verification of simulated circuits and selection of appropriate switching transistors.

Switching transistors, which were used during simulations (ZTX657/757), were not available in surface mount housing, therefore other complementary high-voltage bipolar transistors FMMT458/FMMT558 were tested. Better transistor-to-transistor matching and hence better DC offset control was achieved using PBHV9040/ PBHV8540 pair of transistors. A test setup, comprised of three Agilent 33120B arbitrary waveform generators and a Siglent SDS1102X oscilloscope was connected to initial prototype: First Agilent 33120B generated micropump operation frequency by supplying square-wave signal to the 40,257 multiplexer, while the other two generators provided square-wave PWM modulated frequencies for high switching frequency excitation of corresponding transistor Q3/Q4 (refer to **Figure 1**). Synthesized driving signal frequency was set from 100 Hz to 400 Hz in 100 Hz steps. At each micropump frequency setting, high-switching frequency and duty-cycle were altered with aim to determine output voltage peak-to-peak maximum, whilst maintaining the minimum of DC offset. After each completed micropump frequency sweep, power supply voltage was altered (5 V, 10 V and 12 V). Resulting excitation signal frequency scan vs. micropump amplitude is depicted in **Figure 5**. Amplitude values were very promising, especially in the upper-frequency range (i.e. 400 Hz), where amplitudes up to 240

**Figure 4.** *Large-scale driver prototype (mutually exclusive SMPS).*

**Figure 5.** *Frequency sweep of the initial prototype.*

Vpp were achieved with 12 V power supply voltage. In addition, **Figure 5** shows the boundaries of application range in terms of power supply voltage and high-switching frequency for micropumps, developed in our laboratory [7].

PWM duty cycles of Q3 and Q4 transistors, referred to as DQ4 and DQ3, which provide maximal micropump amplitude values in **Figure 5**, are summarized in **Tables 1** and **2**. The values are referring to an active part of duty cycle, where a certain transistor is open (i.e. NPN\_DRIVE set to VCC, PNP\_DRIVE set to GND).

Values, listed in **Tables 1** and **2**, were used in software as pre-programmed dutycycles, which yield symmetrical positive and negative amplitude of micropump driving signal.
