Using Suppression Circuits; Protecting Dc Transistors; Protecting Relays Controlling Dc Power - Siemens Simatic S7-200 CPU 210 System Manual

Installing the S7-200 CPU 210
1.5

Using Suppression Circuits

Install or equip inductive loads with suppression circuits that limit voltage rise on loss of
power. Use the following guidelines to design adequate suppression. The effectiveness of a
given design is dependent on the application, and you must verify it for a particular use. Be
sure all components are rated for use in the application.

Protecting DC Transistors

The DC transistor outputs of the CPU 210 contain zener diodes that are adequate for many
installations. Use external suppression diodes for either large or frequently switched
inductive loads to prevent overpowering the internal diodes. Figure 1-12 shows typical
applications for DC transistor outputs.
Diode
Suppression
Zener Diode
Suppression
Figure 1-12 Diode Suppression and Zener Diode Suppression

Protecting Relays Controlling DC Power

Resistor/capacitor networks, as shown in Figure 1-13, can be used for low voltage (30 V) DC
relay applications. Connect the network across the load. You can also use diode
suppression, as shown in Figure 1-12, for DC relay applications. A threshold voltage of up to
36 V is allowed if you use a reverse zener diode.
Figure 1-13 Resistor/Capacitor Network on Relay-Driven DC Load
1-12
(1)
+VDC
Inductor
(1) (2)
+VDC
Inductor
R C
+VDC
Inductor
I
L
S7-200 Programmable Controller, CPU 210
(1) IN4001 diode or
equivalent
(1) IN4001 diode or
equivalent
(2) 8.2 V zener, 5 W
V
DC
R
I
L
where minimum R = 12Ω
C I K
L
where K is 0.5 to 1 µ F/A
C79000-G7076-C235-01