Impact of rise time driving signal and mismatch threshold voltage MOSFET’s in parallel connection of PushPull Power Inverter MYZAFERE LIMANI 1 , QAMIL KABASHI 2 , NEBI CAKA 1 , MILAIM ZABELI 2 1 Faculty of Electrical and Computer Engineering Prishtina 2 Faculty of Applied Technical Sciences Mitrovica University of PrishtinaKOSOVA myzafere.limani@fiek.unipr.edu , qamil.kabashi70@gmail.com , nebi.caka@fiek.unipr.edu , milaim.zabeli@gmail.com , —Analysis of the dynamic sharing currents at turnon process in power PWM inverter system with switching MetalOxide SemiconductorFieldEffectTransistors (MOSFET’s) connected in parallel is presented. The inverter circuit presented in this paper is low power inverter which can be used as a charger too. The influence of the diferent rise time driving signals and parameters mismatch between parallel MOSFET branches, over wide operating ranges is analyzed, resulting in dynamic currents, transition energy unbalance, time delay on switching process of parallel MOSFET’s, and time delay at output voltage of inverter. One of many potential causes of mismatch parameters is the threshold voltage V th . Results are presented for the time delays during On switching of the parallel branches in inverter with five power MOSFET’s in each of two legs, selecting same threshold voltage initially, for various rise time driving signals of the two legs of inverter when only one MOSFET in particular leg has lower threshold voltage than others. —Dynamic current, Mismatch parameters, PWM Pulse Width Modulation, Rise time, Switching, Threshold voltage, Time delay.  NTRODUCTION WM inverters are widely used in industrial applications such as: induction heating, frequency converter, standby power supplies, uninterruptible supplies and the induction machine speed control. For each inverter many technical and economic parameters are important, such as: DC input voltage (V i ), AC output voltage (effective value V o ), input current I i , output current I 0 , frequency of oscillator, power of the inverter, speed of transition from DC to AC and vice versa, power dissipation of inverter and cost etc. Block diagram of single phase of power inverter is presented in Fig.1 Fig.1 Block diagram of Power Inverter The inverter circuit presented in this paper is low power inverter (about 1kW). Most inverters operate performing two main functions: first they convert the DC from battery into AC, and then they step up the resulting AC to main voltage level using a transformer. The Push Pull PWM inverters use a basic circuit scheme as shown in Fig. 2. Fig.2 Single Phase PushPull Inverter (12V/220V) DC voltage from the battery is converted into AC by using a pair of N parallel power MOSFET’s on each leg. The positive 12V DC from the battery is connected to the centre tap of the transformer primary, whereas each parallel group of MOSFET’s is connected between the edge of the primary transformer and the ground. When 5 x Q t (top leg), are turned On, the battery current flow through the upper half of the primary transformer and to ground via 5 x Q t . By switching on 5 x Q b instead, the current will flow in the opposite direction through the lower half of the primary transformer and to ground. Therefore by switching On the two MOSFET’s legs alternatively, the current is made to flow first in one half of the primary transformer and then in the second one, producing an alternating magnetic flux in the transformers core. As a result, according to the principles of transformer we have on the secondary winding a rectangular wave AC voltage of around 650V peak to peak. The output voltage regulation is achieved by varying the width of the driving pulses of MOSFET’s, and hence the RMS value of the output voltage. It is usually done by having a P INTERNATIONAL JOURNAL OF CIRCUITS, SYSTEMS AND SIGNAL PROCESSING Issue 1, Volume 5, 2011 78