AND8116 Datasheet, PDF (2/8 Pages) ON Semiconductor – Integrated Relay/Inductive Load Drivers for Industrial and Automotive Applications

AND8116/D
Standard Discrete RELAY DRIVERS
For both type of applications industrial and automotive,
the most traditional and popular relay drivers are the ones
formed discretely with a bipolar transistor, two bias resistors
and a free−wheeling diode. In some cases, it is required to
add extra components such as MOVs (metal oxide varistors)
and extra diodes to ensure proper protection. Figure 1 shows
a typical discrete relay driver with the extra protection
devices. Diode D1 provides reverse supply protection and
diode D2 provides a clamp function to suppress the voltage
spike generated by the relay’s coil during the turn−off
interactions (V = Ldi/dt). A power MOV device is used to
limit positive transients to within the bipolar transistor’s
breakdown voltage. The saturation voltage of the bipolar
transistor (typically over 1.0 V) causes high power
dissipation which in some cases eliminates the option to use
inexpensive surface mount package devices such as
SOT−23 or smaller, therefore the need for bigger packages
such as TO220 is always present. The resulting discrete
circuit is expensive because it takes several components and
a big space in the PC board.
+12 V
ON Semiconductor’s RELAY DRIVERS
The ON Semiconductor’s relay drivers portfolio is
divided in two main categories:
• Industrial version (devices NUD3105, NUD3112)
• Automotive version (device NUD3124)
Industrial Version
Figure 2 describes the industrial relay driver version
(devices NUD3105, NUD3112). This device integrates
several discrete components in a single SOT−23 three
leaded surface mount package to achieve a simpler and more
efficient solution than the conventional discrete relay
drivers. The characteristics of the integrated devices are
listed below:
• N−channel FET 40 V, 500 mA
• ESD protection Zener diodes (7.0 V)
• Bias resistors (1.0 K W in the gate and 300 K W
between gate and source)
• Clamping protection Zener diodes (7.0 V for 5.0 V
relay’s coils, and 14 V for 12 V coils)
Drain (3)
D1
+5 V/3.3 V
D2
RELAY
R1
LOGIC
Q1
R2
VARISTOR
0
Figure 1. Typical Discrete Relay Driver
Gate (1)
ESD
Zener
7V
ESD
Zener
7V
1.0 k
300 k
Clamp Zener
7 V or 14 V
Clamp Zener
7 V or 14 V
Source (2)
Figure 2. Industrial Relay Driver Description
(NUD3105 and NUD3112 Devices)
http://onsemi.com
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