Chapter 7
Power Supply
A2400 modules may be powered with an unregulated +10 to +30Vdc. Power-supply ripple must be limited to 5V peak-to-peak, and the instanta- neous ripple voltage must be maintained between the 10 and 30 volt limits at all times. All power supply specifications are referred to the module connector; the effects of line voltage drops must be considered when the module is powered remotely.
The A2400 modules employ an on-board switching regulator to maintain good efficiency over the 10 to 30 volt input range; therefore the actual current draw is inversely proportional to the line voltage. The A2400 consume a maximum of .5 watts and this figure should be used in determining the power supply current requirement.
In some cases, the A2400 may be operated by “stealing” power from a host computer or terminal. Many computers provide a +15 volt output on the RS- 232C DB-25 connector.
Small systems may be powered by using wall-mounted calculator-type modular power supplies. These units are inexpensive and may be obtained from many retail electronics outlets.
A2400 modules may be locally powered. This eliminates the voltage drops on the Ground lead which may interfere with communications signals. In this case the V+ terminal is connected only to the local power supply. The Ground terminal must be connected back to the host to provide a ground return for the communications loop.
The A2400 modules are protected against power supply reversals.