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I have a +/-30V and +5V signal. I would like to rout this two signal by using the CPC1106N and CPC1006N solid state relay. According to the Absolute Maximum Ratings of the Input Control Current 50mA, but according the characteristic the Input Control Current to Activate is 0.5mA. So is it safe to control the solid state relay from the MCU?

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ You have confused one potential responder by drawing a magnetically actuated relay in your diagram, despite calling out a solid state relay in your text. \$\endgroup\$ – Chris Stratton Jul 27 '13 at 19:11
  • \$\begingroup\$ In the circuitlab I didn't find a SSR, this is the reason why I attached the links of the SSR. \$\endgroup\$ – OHLÁLÁ Jul 27 '13 at 19:14
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50 mA is the maximum absolute current the part can withstand. Yes it is safe to forward bias the diode using MCU, I suggest cross-checking the current source capacity of the MCU pin which you are connecting to the optocoupler.

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  • \$\begingroup\$ This is a solid state relay, which controlled by an optocupler \$\endgroup\$ – OHLÁLÁ Jul 27 '13 at 18:52
  • \$\begingroup\$ Hi run, sorry to ask but where is the opto coupler you talking about? \$\endgroup\$ – AKR Jul 27 '13 at 19:00
  • \$\begingroup\$ Controlled by a LED diode. Isn't it an optocoupler? \$\endgroup\$ – OHLÁLÁ Jul 27 '13 at 19:03
  • \$\begingroup\$ Got confused with the circuit you shown in circuit lab. I will edit the answer. Usually when it is relays, we use transistors. \$\endgroup\$ – AKR Jul 27 '13 at 19:05
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Like you said, the relays need maximum 0.5 mA to operate. A microcontroller can typically supply 20 mA. What AKR failed to mention (and it's a reason why it shouldn't be the accepted anser!) is that you need to place a series resistor. At 3.3 V supply a 430 ohm resistor gives you 5 mA, which is safe for the microcontroller, and makes sure the relay triggers under all circumstances. For a 5 V microcontroller you need a 820 ohm resistor.

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