User Manual

PD-1021 Hardware Manual (Rev. 1.00 / 2012-JUN-20) 11
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3.4 Power Supply
For proper operation care has to be taken with regard to power supply concept and design. Due to space
restrictions the PD-1021 includes just about 20µF/35V of supply filter capacitors. These are ceramic
capacitors which have been selected for high reliability and long life time. The module includes a 28V
suppressor diode for over-voltage protection. There is no reverse polarity protection. The module will
short any reversed supply voltage due to internal diodes of the driver transistors.
It is absolutely necessary that the power supply voltage is kept below the upper limit of 28V under all
circumstances (please see also chapter 6, operating values). Otherwise the driver electronics might be
seriously damaged! Especially, when the selected operating voltage is near the upper limit a regulated
power supply is highly recommended.
It is recommended to connect an electrolytic capacitor of significant size (e.g. 470µF/35V) to the power
supply lines next to the PD-1021!
Rule of thumb for size of electrolytic capacitor:   


 

In addition to power stabilization (buffer) and filtering this added capacitor will also reduce any voltage
spikes which might otherwise occur from a combination of high inductance power supply wires and the
ceramic capacitors. In addition it will limit slew-rate of power supply voltage at the module. The low ESR
of ceramic-only filter capacitors may cause stability problems with some switching power supplies.