The first semiconductor inverters functioned in this way, replaced the thyristors as switch elements and quickly proved itself robust and reliable. As a result of the further development of semiconductor technology much more is possible since then. Modern power transistors have a maximum switching frequency of more than 10,000 Hz, thus can switch much more quickly than would be necessary for the output frequency of 50 Hz. One takes advantage of exactly this with pulse width modulation technology: a considerably faster synchronized bridging circuit generates many short voltage pulses  of various durations (pulse width), which produce the desired output signal in the time average. The pulsed voltage is able to be modulated therefore to every desired signal form - naturally also to the desired sine wave [Fig.5]. An inductor smoothes out the signal (low-pass filter) composed of short pulses - the result is a clean, sinusoidal alternating voltage. In order to achieve the necessary magnitude of voltage (230, 400 or 20,000 Volts) a transformer is normally connected downstream of the inverter bridge. This additionally ensures a galvanic separation between DC and AC grid. There are however also inverters without transformers: The devices are smaller, respectively lighter and achieve a somewhat better efficiency. The desired magnitude of voltage is in this case achieved via a boost chopper  which is connected upstream of the inverter bridge.
Most solar inverters are voltage driven, since they feed into the electricity grid with their specified grid voltage. Here, the sinusoidal alternating voltage is correctly composed of short current impulses
 Electronic switching for the increase of direct voltages