Despite the improvements in high frequency switcher design, Linear regulation still offers the lowest output noise and the best transient response （recovery time from a sudden current step）.

It also offers the most benign stability characteristics when driving complex load conditions.

Most linear regulated power supplies offer low output noise with figures below 2mV rms being typical.

The QL series goes a stage further with an RMS noise figure of 0.35mV and tightly specified pk-pk noise.

Many higher power linear regulated designs include a line frequency switched pre-regulator.  Whereas this may not compromise differential output noise, it significantly increases common mode noise currents.

The QL Series uses true linear regulation without any line frequency switching regulation.  Consequently it offers exceptional common mode noise levels of <4uA rms at 20MHz bandwidth.

The QL series provides multiple ranges for increased current capability at lower voltages.

For the QL355, the main range offers 0 to 35 volts at up to 3 amps. The higher current range provides up to 5 amps for voltages up to 15V.

The QL564 has a main range of 0 to 56 volts at up to 2 amps. The higher current range provides up to 4 amps for voltages up to 25V

On both models, a further low current range provides an enhanced current setting and measurement resolution of 0.1mA.

Voltage and current are controlled using instrumentation quality 16 bit DACs enabling voltages to be set to 1mV resolution even at full output.

Indeed, the accuracy is sufficient for the QL to be used as a calibration source for some hand-held DMMs.

Every engineer needs to have confidence in their equipment. A power supply is one of the most fundamental of bench instruments.

You need certainty that the voltage you apply to a circuit is precisely what you want it to be.

You need certainty that the output of your power supply is clean and stable.

You need the ability to define a precise voltage at the load and maintain regulation independent of lead resistances.