Data Sheet

www.id-innovations.com
12
ID-2/12/20 LA Series Datasheet X1
11.04.2013
12. Choice of Power Supply
The choice of power supply is very important. The ideal power supply will be a linear type such as
an LM7805 or a 3.3 volt equivalent. Batteries may also be used without a regulator, a suitable
arrangement can consist of a 3volt lithium cell or 3x 1.5v cells to give 4.5 volts. Note that
ID-Innovations will be introducing a low-range series of micro-power reader modules (current
<1mA) with the same pin out.
Switching power supplies are gaining increasing popularity, however switching supplies can present
several problems for 125 KHz readers. The switching frequency must not be close to a multiple of
125 KHz or severe interference can result which will reduce the read range. Another issue with
switching supplies is output voltage ripple. For good range the output ripple should be less than
3mV PKPK. This is very demanding on switching power supplies. Some recommended solutions are
shown below for use with working with switching power supplies.
The upper diagram shows a low pass filter which may help increase range if the output ripple from
the switching power supply is less than 10mV PKPK. The best solution, and the one which takes up
less space, uses an SOT23 linear LDO regulator. The circuit employs a Zetex device which may also
be powered down. Alternatively a Microchip MCP1702 could be considered, however the maximum
current is limited to 50mA and may not be suitable for the ID-2LA in some circumstances.