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7. Product Specification
CNT24-2(USB)GY
63
Protection Circuit Introduction
Surge Voltage Countermeasures
When connecting a load that generates surge voltages and inrush currents, such as an
induction load (relay coil) or an incandescent light bulb, to the digital output,
appropriate protection must be provided in order to prevent damage to the output stage
or a malfunction due to noise. The rapid shutoff of a coil, such as a relay, generates a
sudden high-voltage pulse. If this voltage exceeds the voltage tolerance level of the
output transistor, it can cause the transistor to gradually deteriorate, or even completely
damage the transistor. Therefore, when driving an induction load, such as a relay
coil, you should always connect a surge-absorbing device. The following illustrates a
surge voltage countermeasure that can be employed:
Figure 7.6.
Surge Voltage Countermeasures
In order for a protection circuit to operate effectively, it must be connected within
50 cm of a load and a contact point.
*Examples of use of relay coil
Diode
Relay coil
Zener diode
External power voltage < Zener diode voltage
*Examples of use of lamp
Inrush current
prevention
resistance
Relay coil
Dark point-
lighting
bypass
CAUTION
Summary of Contents for CNT24-2GY
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