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For a cost sensitive application we need a 4V supply for a GSM module and a 3.3V supply for a STM32 MCU and couple of sensors. Would it be possible to use a diode like 1N4148 to drop from 4V to supply these parts?

We can make sure not to put the MCU or the sensors in sleep mode and keep the current draw constant. Or add another resistor to keep drawing a couple of mA to keep the drop. Any issue with such a design?

Thanks.

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    \$\begingroup\$ You should be able to get a voltage regulator for ~$0.05. Compared to the cost of a GSM module, is that really significantly different from the cost of a diode? \$\endgroup\$ – The Photon Dec 12 '20 at 5:05
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Its perfectly reasonable to do that BUT if you don't have some minimum current flowing through the diode, you won't get 0.7V drop. Check the datasheet. Sleep mode (if you have one) is where you'd have trouble.

We do this in our designs (battery operated) all the time.

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