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24VAC to DC

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joeyjoejoe:
Would the transistors not need pulldowns?

mariush:
There are transistors with resistors built in, some even have diodes in the package.

Here's an example (first Digikey result, not saying it's cheapest or best): https://www.digikey.com/product-detail/en/diodes-incorporated/DRDNB16W-7/DRDNB16WDITR-ND/816539

Zero999:

--- Quote from: joeyjoejoe on January 26, 2020, 03:00:28 pm ---Would the transistors not need pulldowns?

--- End quote ---
No, especially with the LED. It's certainly less important, than with a MOSFET.

joeyjoejoe:
It would only shave a few cents off, but I do have two BC817's already for programming. And it means a bunch more questions

Sorted by price and still active components, I have

Currently,
DMN63D8LDW- N-channel mosfet (45 cents)

Options (sorted by price)
MBT3904DW1T3G - dual NPN (31 cents)
MUN5213DW1T1G- dual NPN, prebiased (33 cents)

I need 50mA for the coil. Will the MUN5213DW1T1G save me a pull-down resistor?

Resistors/diodes/led's are basically free, but the labor to place them isn't. I'd take fewer parts over a 10cent BOM increase anyday - the relays themselves from a legitimate supplier are just over 2$ a pop in small quantities, ESP32 5$ and coil for the switching regulator is 2$.



joeyjoejoe:
This might be useful as well.

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