Most electromechanical shutters are driven with low voltage power supplies, typically in the range 3.3 – 24 VDC. Some are direct DC drive at constant voltage and some use more power efficient two level drives, with a higher voltage impulse to open, then a lower voltage to hold long term. More complex waveforms can be generated to provide de-acceleration at the open and closed stop positions, known as damping. Depending on switching speeds required, the damping can be partial (faster switching) or complete critical damping (slower, low noise/shock).