Interesting, so the functional diagram of the L293D from STMicroelectronics shows that an H-bridge with diode protection is basically two buffer circuits and a diode bridge.
20191111/https://www.digikey.com/product-detail/en/stmicroelectronics/L293D/497-2936-5-ND/634700
20191111/https://www.st.com/content/ccc/resource/technical/document/datasheet/04/ac/22/f9/20/5d/43/a1/CD00000059.pdf/files/CD00000059.pdf/jcr:content/translations/en.CD00000059.pdf
So, now the question to ask. If I can’t get the exact motor controller that I want, maybe I can build my own. First order of business. Can I get 3 V NAND logic in the through hole DIP form factor? Indeed I can!
20191111/https://www.digikey.com/products/en/integrated-circuits-ics/logic-gates-and-inverters/705?k=&pkeyword=&sv=0&pv16=294032&pv16=96863&pv16=107879&sf=1&FV=-8%7C705%2C247%7C378818%2C276%7C121108%2C276%7C121120%2C276%7C125356%2C276%7C128773%2C276%7C134904%2C276%7C168980%2C276%7C169006%2C276%7C169019%2C276%7C174218%2C276%7C202783%2C276%7C202787%2C276%7C202790%2C276%7C202794%2C276%7C202821%2C276%7C202873%2C276%7C34200%2C276%7C34201%2C276%7C36616%2C276%7C36636%2C276%7C38721%2C276%7C48870%2C276%7C48897%2C276%7C53178%2C276%7C53189%2C276%7C55776%2C276%7C56901%2C276%7C56916%2C276%7C57820%2C276%7C61308%2C276%7C61334&quantity=&ColumnSort=0&page=1&pageSize=25
20191111/https://www.digikey.com/product-detail/en/texas-instruments/SN74HC03N/296-8207-5-ND/376880
20191111/http://www.ti.com/lit/ds/symlink/sn74hc03.pdf
Okay, so that’s good and great, but really I only need some inverters to save myself one GPIO pin per motor. Can I get a package with just those at the 3 V logic level? Indeed I can!
20191111/https://www.digikey.com/products/en/integrated-circuits-ics/logic-gates-and-inverters/705?k=&pkeyword=&sv=0&pv16=96863&pv16=107879&pv16=142845&sf=1&FV=247%7C359778%2C-8%7C705%2C276%7C121108%2C276%7C121120%2C276%7C128773%2C276%7C134904%2C276%7C168980%2C276%7C169006%2C276%7C169019%2C276%7C202783%2C276%7C202787%2C276%7C202790%2C276%7C202794%2C276%7C202821%2C276%7C202873%2C276%7C34200%2C276%7C36616%2C276%7C36636%2C276%7C38721%2C276%7C48870%2C276%7C48897%2C276%7C53189%2C276%7C55776%2C276%7C56901%2C276%7C56916%2C276%7C57820%2C276%7C61334&quantity=&ColumnSort=0&page=1&pageSize=25
20191111/https://www.digikey.com/product-detail/en/texas-instruments/SN74HC04N/296-1566-5-ND/277212
20191111/http://www.ti.com/lit/ds/symlink/sn74hc04.pdf
Okay, this is going really good. Now let’s step it up a notch. Rather than using all my own MOSFETs, can I get an appropriate buffer IC that can work at 3 V? Almost. This has an operating range from 2 V to 6 V. And I plan on reusing some 9 V motors. Not bad for normal operation, it’s just that if the user turns the motor on their own, that could exceed the voltage range of the driver circuits and that would destroy them. So, although it works well most of the time, it’s not robust in exceptional circumstances. But if I bought a purpose-built 3 V or 5 V motor, that would not be an issue at all.
20191111/https://www.digikey.com/products/en/integrated-circuits-ics/logic-buffers-drivers-receivers-transceivers/704?k=&pkeyword=&sv=0&pv1291=96859&pv1291=97190&pv1291=107877&pv1291=108442&pv1291=142844&pv1291=143602&pv1291=154585&pv1291=154992&sf=1&FV=-8%7C704%2C276%7C121108%2C276%7C121120%2C276%7C128759%2C276%7C128773%2C276%7C128790%2C276%7C134895%2C276%7C134904%2C276%7C134909%2C276%7C134960%2C276%7C168980%2C276%7C169006%2C276%7C169019%2C276%7C171582%2C276%7C202783%2C276%7C202790%2C276%7C202794%2C276%7C202821%2C276%7C202873%2C276%7C34200%2C276%7C36616%2C276%7C36636%2C276%7C38721%2C276%7C45880%2C276%7C48870%2C276%7C48897%2C276%7C53178%2C276%7C53189%2C276%7C55776%2C276%7C56893%2C276%7C56901%2C276%7C56902%2C276%7C56916%2C276%7C57820%2C276%7C61308%2C276%7C61334&quantity=&ColumnSort=0&page=1&pageSize=25
20191111/https://www.digikey.com/product-detail/en/texas-instruments/SN74HC541N/296-1594-5-ND/277240
20191111/http://www.ti.com/lit/ds/symlink/sn74hc541.pdf
Finally, a diode bridge rectifier IC package. Yes indeed.
20191111/DuckDuckGo digikey diode bridge
20191111/https://www.digikey.com/products/en/discrete-semiconductor-products/diodes-bridge-rectifiers/299?k=&pkeyword=&sv=0&pv1291=227463&pv1291=227688&pv1291=228267&sf=1&FV=-8%7C299&quantity=&ColumnSort=0&page=1&pageSize=25
20191111/https://www.digikey.com/product-detail/en/on-semiconductor/DF04M/DF04M-ND/965265
20191111/https://www.onsemi.com/pub/Collateral/DF10M-D.pdf
UPDATE 2019-11-18 I did some more searching and found a broader range of buffer ICs that would work well.
20191118/https://www.digikey.com/products/en/integrated-circuits-ics/logic-buffers-drivers-receivers-transceivers/704?k=&pkeyword=&sv=0&pv16=96863&pv16=107879&pv16=142845&pv16=154586&pv16=154592&pv1291=96859&pv1291=97190&pv1291=107807&pv1291=107877&pv1291=108442&pv1291=142705&pv1291=142844&pv1291=143602&pv1291=154585&pv1291=154992&sf=1&FV=-8%7C704&quantity=&ColumnSort=0&page=1&pageSize=25
This one works from 3 V to 18 V. Maximum input current = 100 mA. Max 10 mA per input, maybe not exactly what I need. I probably want something that can handle 300 mA for a single motor, just to be on the safe side, though my actual motors will not be that big. Of course I am designing my entire system to not consume more than 1 A of current at 5 V, with the Raspberry Pi Zero + Camera able to consume a good 500 mA at 5 V. Maybe I really should invest in smaller motors then. And although a buffer IC would be smaller, power MOSFETs are safer simply due to their size for handling larger power and more cooling.
20191118/https://www.digikey.com/product-detail/en/texas-instruments/CD4010BE/296-2160-5-ND/67239
20191118/DuckDuckGo how much current does a 9 v dc motor draw
20191118/https://www.quora.com/How-much-current-can-a-12V-DC-motor-draw