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I plan to use a MSP430 microcontroller to drive three different DC-DC solid-state relays. The thing is that the MSP430 provides a digital output of only 3 VDC @ 15 mA. (Vol: low-level output voltage).

The solid-state relay needs at least 3.5 VDC and max. up to 32 VDC as turn ON voltage @ 15 mA.

So after researching I plan on using a ULN2003A as a driver IC for high voltage and high current (50 V/500 mA).

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If the above circuit connection is right, where do I get Vcc from? I reason I ask this is because the MSP430 is powered by a 12 V battery, but the MSP430 has a supply voltage of 1.8-3.6 VDC. So I have used a DC-DC buck converter(TPS565242) to bring down the voltage from 12 V to 3.6 V. Is it okay to power the Vcc directly from the battery?

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  • \$\begingroup\$ "Is it okay to power the Vcc directly from the battery?" Yes, no, maybe. What is the context, is this a vehicle, a machine, what? Is there an alternator and/or starter? Are the SSR designed to handle things like surges and transients? Are they controlling any critical functions, are there machine safety aspects? \$\endgroup\$
    – Lundin
    Commented Feb 9, 2023 at 9:07

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You can power the VCC directly from the battery.

Even if the type of 12V battery is disregarded, the voltage at fully charged/discharged state would be well within the boundaries of ULN2003A (50V max) and your SSRs (3.5-32V) to power them correctly.

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