Abstract: A deflection amplifier for driving a magnetic-deflection cathode-ray tube in a digital plotter has two switching circuits coupled to low- and high-voltage supplies respectively. An error amplifier compares the actual deflection-coil current, as indicated by the voltage developed across a resistor in series with the coil, with the command input voltage indicating the required current. As long as the difference between required and actual currents is less than a predetermined threshold value, only the low-voltage switching circuit operates, thereby limiting power dissipation. However, if the current difference exceeds the threshold value for at least 2.mu.s, the high-voltage switching circuit commences operation to supplement the drive provided by the low-voltage circuit. The high-voltage circuit is limited by logic circuitry to periods of operation 20.mu.s long with a 5.mu.s quiescent period between each. The low- and high-voltage supplies are bipolar, and corresponding bipolar threshold values are provided.