5-2 Relay Control
Overview
The power supply can be used to control an external relay. The control circuit is made up of
an open-collector transistor that functions as a switch for the external relay, a +5VDC source
(100mADC maximum), and a chassis ground return. The drive for the relay may be provided by
the supplied +5VDC source or an external DC voltage source.
Figure 5-1 shows the simplified control circuit in the power supply and shows a typical con-
figuration to control an external relay. As shown in the illustration, voltage applied to the power
supply must not exceed 15VDC and current for the relay circuit must not exceed 150mADC. If
the supplied +5VDC source is used to drive the external relay, the relay circuit must not exceed
100mADC.
Also note that a protection diode is required for the relay circuit. The protection diode pro-
vides a current dissipation path for fly-back voltage from the relay coil that occurs when the con-
trol circuit is opened. Without the diode, the high fly-back voltage could damage the power
supply.
CAUTION To prevent damage to the power supply that is not covered by the warranty,
adhere to the following precautions:
• ALWAYS use a protection diode for the relay circuit as shown in
Figure 5-1.
• Do not exceed the voltage and current limits of the RELAY CONTROL
port of the power supply (15VDC and 150mADC).
• Connect and disconnect relay drive circuits with the power supply
power OFF.
NOTE The current limit can also be used to control the external relay. Refer to “Current
limit modes” in Section 2.
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