Stacking CD4052 for higher voltage - Page 1
Forum section: electronics / projects

author: Confucij
author_rank: Newbie
timestamp: April 04, 2023, 07:20:18 am
content: Hello,I'm learning electronics and decide to design battery voltage monitor for 5-7S cells. For this I've thought of using MUX like CD4052 and connect each battery to OP AMP in differential configuration. It looks good for me with 4S batteries, but with 5S+ voltage across the batteries goes for more than MUX max voltage(20V).I've thought of using 4th battery '+' as GND connection for second MUX so it would not see more than 16.8V difference between VSS/VEE and VDD. At the output stage I'm going to use 36V OP AMP but I have strong feeling that I've messed up with it connection.Will this approach work as I expect or I've missed something crucial?

author: jfiresto
author_rank: Frequent Contributor
timestamp: April 04, 2023, 07:51:13 am
content: Perhaps an easy solution would be a DG409 dual 4:1 multiplexer that uses 44V CMOS.

author: Confucij
author_rank: Newbie
timestamp: April 04, 2023, 08:26:08 am
content: Yeah, I've thought about this part. This would also cut some transistors to control CD4052. MY thoughts against this is that *4052* mux is widely available and costs fraction of a cost of DG.

author: Kleinstein
author_rank: Super Contributor
timestamp: April 04, 2023, 11:37:08 am
content: The supply for the upper 4052 is still wrong. To have the 4052 floating for the high voltages the GND / VEE connections would also need to be high ( like Vbat4). This also needs extra effort for the control signals, not just the simple transistor to ground. The way the control signals are linked is wrong anyway.A point to keep in mind is that the supply must stay lifted up, even of the rest of the circuit is not powered.The resistors in the control signals are rather low - so quite some current flow there.The extra switching with the MOSFETs is not working: the modern MOSFETs usually have protective zener diodes to limit the gate voltage to some 20 V, rarely more. So the lower 4 channels would need a lower voltage. With anyway the CMOS switches, there is actually little needed for the extra MOSFETs.The level shift part with the 2 nd OP-amp looks odd and likely wrong with the zener / ref voltage. The ref / zener would likely need an extra resistor in the supply, otherwise it would limit the OP+ voltage.Normally one could get away with a single ref voltage.CMOS switch chips are a bit prone to latch-up and should have a current liming resistor in the supply path.

author: Confucij
author_rank: Newbie
timestamp: April 06, 2023, 07:17:27 am
content: Hi. I've got your points except zener in diodes. How they will obstruct switching?

author: Kleinstein
author_rank: Super Contributor
timestamp: April 06, 2023, 10:59:03 am
content: The zener diode would not onstruct switching, but there would be extra current flowing from the drive side to source, mainly with Q4. So curent would flow from OP+ to the 1st cell.Independent of the Q4 may not turn on of the voltate in Vbat1 is relatively low. A similar thing can happen with Q13, even more if the battery is out of balance and Vbat5 not much higher then OP+ / 2.