Maximum reverse voltage of AZ34063A step-down from 24V solar PV to 13V battery ?

[KerimF]

I'd like to have 2A charging current, so I found an easy solution, connect three MC34063A circuits in parallel designed for 0.666A*3~1.998A current  The probability that at the same time none of these systems will draw current from the PV panel is very small, because the input capacitors will be charged even if one of them blocks the current, and the switching frequency will never be identical, because the CT IC MC34063A capacitor will never have the same capacity in each circuit. 

Your reasoning seems good.

[eneuro]

Your reasoning seems good.

I could put in an NPN MOSFET to get 2A at the output using one IC MC34063A, but I like BJT transistors, it's a reference to analog circuits, non-linearity compared to on/off and unnecessary digitization of simple processes.   
Advanced Semiconductor Materials Lithography ASML is such a complicated process now, this  can be done cheaper, simpler, but it does not mean that it will be a better solution, because it may be susceptible for example to the influence of cosmic radiation, because this pursuit of miniaturization may lead to the construction of IC transistors not based on BJT technology but MOSFETs more sensitive to chip war which currently dominates electronics: The race for semiconductor supremacy

[Andy Chee]

I could put in an NPN MOSFET to get 2A at the output using one IC MC34063A, but I like BJT transistors, it's a reference to analog circuits, non-linearity compared to on/off and unnecessary digitization of simple processes.   

You can use external BJT NPN e.g. 2SC4242 or KSE13007.  These are NPN BJT used in older AT/ATX computer power supplies.

[eneuro]

Hello,
I ordered a few DIP-8 MC34063ABN ICs, but today I took a closer look at the delivered ST CHN 063AB chips for which I can't find any datasheet anywhere   
Are these fakes or do they come from unknown ST subcontractor? 

We'll find out, because I've designed a PCB for the MC34063ABN 

[magic]

CHN is country of origin, 063AB is probably abbreviated marking of MC34063AB, although usually you are more likely to see such things on SO8 than DIP8.

If you bought it from AliBayZon it's very likely a Chinese clone with fraudulent markings.
Will it work and for how long? There is only one way to find out...

[schmitt trigger]

I did not find any specifications in the MC34063A documentation of maximum reverse voltage Vout->Vin ?

Bob Pease, the late analog guru, once said: “anything that is not fully specified on a data sheet, assume at your own peril.”
Or words to the effect.

[magic]

FYI it was a month ago and the OP has already added a protection diode.

[eneuro]

the OP has already added a protection diode.

The only change is that the cathode of the protection diode (D2) in this version is connected to the 6Vcc pin, to avoid current flowing to the input through the resistor (R3) used in this circuit to limit the output current