EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: eneuro on November 07, 2024, 06:11:49 pm
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I did not find any specifications in the MC34063A documentation of maximum reverse voltage Vout->Vin ?
I modified the AZ34063A circuit so that the output is now 13V instead of the original 5V/500ma and connected to a 24Voc 150W photovoltaic panel but I plan to charge the gel battery to about 13Vmax, so it may happen that at night the input voltage will be very low, so on the plus side of the PV panel I have diodes protecting against current flow from the battery to the panel 8) I am thinking about adding an additional 1N4007 bypass diode in the dc-dc circuit from output to input, because there are BJT transistors in the MC34063A chip diagram in the documentation :-\ What do you think about this solution, can this bypass diode be useful there or is it necessary in this case? ::)
Warning: in attached photo of bottom PCB bypass diode was connected from output ground to input plus which is a mistake of course, but it's not a problem, it is corrected right now...
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Reverse voltage rating VEC is omitted on discrete transistor datasheets as well.
In practice, you can simply use the VCE figure, which for the MC34063A is 40V
That said, I would include the diode anyway to prevent the battery from discharging through anything else in the circuit (e.g. through the feedback resistor voltage divider). BUT, not as a bypass diode as you've described it. I would install it in series with the battery, as you would a polarity protection diode.
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In practice, you can simply use the VCE figure, which for the MC34063A is 40V
I am talking about the protection of internal BJT transistors Q1 and Q2 in the MC34063A, when the voltage at the Vin input will drop practically to 0V, because after some time the 100uF input capacitor will discharge, while on a charged battery the Vout 13V will still be supported by the battery, so looking at the diagram of a typical buck converter from the MC34063AB documentation, it seems that a better place to install the bypass diode may be between the Q1 emitter, the SWE2 pin to the connected DRC8 and SWC1 pins, because it should not disturb the normal operation of the MC34063A circuit in buck converter mode.
In addition, the input capacitor will be charged via the resistor Rsc and the inductor L1 ...
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In practice, you can simply use the VCE figure, which for the MC34063A is 40V
I am talking about the protection of internal BJT transistors Q1 and Q2 in the MC34063A,
So am I.
I am saying that in practice, the maximum reverse voltage of a BJT is the same as the maximum forward voltage of the BJT.
The maximum forward voltage of the MC34063A internal BJT is 40V.
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I am saying that in practice, the maximum reverse voltage of a BJT is the same as the maximum forward voltage of the BJT.
The maximum forward voltage of the MC34063A internal BJT is 40V.
What about reverse bias of BE junction then? It's usually very low, maybe 5-7V and then it starts to zener. So it sets the limit of how positive emitter can go relative to base (npn).
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What about reverse bias of BE junction then? It's usually very low, maybe 5-7V and then it starts to zener. So it sets the limit of how positive emitter can go relative to base (npn).
For a discrete BJT transistor, you're correct.
But here we're talking about the internal NPN switch transistor inside the MC34063A, whose base is connected to a flip flop (probably at least two more transistor junctions).
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What about reverse bias of BE junction then? It's usually very low, maybe 5-7V and then it starts to zener. So it sets the limit of how positive emitter can go relative to base (npn).
For a discrete BJT transistor, you're correct.
But here we're talking about the internal NPN switch transistor inside the MC34063A, whose base is connected to a flip flop (probably at least two more transistor junctions).
I understand that, but strictly speaking we don't know what exactly is there. There could be circuitry not shown in datasheet. I've never done these tests myself, nor I was particularly interested, but I remember reading that some BE junctions don't like zenering and may experience degradation. Although I occasionally zenered them by design, and they seem to hold.
Anyway, in this case I might try a high value series resistor like 100k and slowly increase voltage, observing with a multimeter if it starts to increasingly leak and clamp at some point. Then judge the margin of how far you are from leakage in normal intended operation, aka do the missing characterization yourself.
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These are NPNs so they will likely break down near 7V as a few people pointed out. Then BC junctions will forward bias and supply power to Vin, possibly causing the chip to start operating and draw some not entirely negligible current through those output transistors.
A diode from pin 2 to 6 should protect the transistors effectively. A diode between pin 2 and the load would protect them too, and also prevent pointless power consumption.
Hard to tell more because I have no idea what larger circuit this converter is part of...
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I did not find any specifications in the MC34063A documentation of maximum reverse voltage Vout->Vin ?
Because you are talking about a working system, you are best to measure the actual current levels, day/night, to decide what the actual issues are.
You may be better off with an ideal diode
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But here we're talking about the internal NPN switch transistor inside the MC34063A, whose base is connected to a flip flop (probably at least two more transistor junctions).
You are right, it looks like the base of one of the internal BJTs Q2 in the diagram from ST's MC34063AB is connected to the flip flop, but ... :o Is it possible to supply voltage to the Collector-Emitter in reverse? https://www.rohm.com/products/faq-search/faqId/232 (https://www.rohm.com/products/faq-search/faqId/232)
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Hard to tell more because I have no idea what larger circuit this converter is part of...
As in the photos from the first post, a typical buck converter on a noname AZ34063A chip, reused from a 12V-24V car converter to 5V/500mA, mostly compatible with most of the documentation for MC34603A, and I am now designing my own converter but on the MC34603AB chip from ST ;)
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A diode from pin 2 to 6 should protect the transistors effectively.
Yep, I soldered a FR107G diode between the Switch Emitter of the output BJT Q1 pin 2 to the Drive collector pin 8, in practice this also protects the BJT Q1 because in a typical buck converter topology the Switch Collector pin 1 is shorted to pin 8.
Tomorrow the moment of truth when the sun comes out 8)
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By the way, I assume you're only using the MC34063A because you obtained it for zero cost from salvaged recycled e-waste?
Otherwise I'd recommend looking for a more efficient buck controller to conserve every watt from your solar panel.
What is the size of your gel battery?
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By the way, I assume you're only using the MC34063A because you obtained it for zero cost from salvaged recycled e-waste?
No, I am using a noname AZ34603A 5V500mA based car converter PCB modified by myself to 13V500mA because Dave from EVblog encouraged me to do so :o EEVblog #110 - Let's Design a DC to DC Switchmode Converter https://www.youtube.com/watch?v=qGp82xhybs4 (https://www.youtube.com/watch?v=qGp82xhybs4)
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You may be better off with an ideal diode
Nope, diode FR107G 1kV 1A DO41 1.3Vmax is sufficient as a bypass between pin 2 SWE and pin 8 DRC of MC34603A in this project, modifying the purchased car converter to 13V instead of 5V500mA 8) Fits perfectly on the bottom of the PCB :popcorn:
(https://www.eevblog.com/forum/projects/maximum-reverse-voltage-of-az34063a-step-down-from-24v-solar-pv-to-13v-battery/?action=dlattach;attach=2428685)
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No, I am using a noname AZ34603A 5V500mA based car converter PCB modified by myself to 13V500mA because Dave from EVblog encouraged me to do so :o
Have you performed the efficiency calculations that Dave shows in the video?
How big is your gel cell? If you have a small battery, then maybe you can afford to waste efficiency.
But even a LM2596 module from eBay is more efficient than all the 34063A variants.
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This still has the potential problem that if you use this module to charge a battery, it will be discharging it while not charging.
To prevent that, you would need a diode or some sort of switch between the charger and the battery.
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I already suggested a series diode in the opening reply of this thread.
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This still has the potential problem that if you use this module to charge a battery, it will be discharging it while not charging.
After storing the PV panel in the garage, the current consumption from the 12.2V battery was, as expected, only about 5mA, 1mA voltage divider, 1mA green output diode and the AZ34063A chip itself has a quiescent current of 2.5mA according to MC34063A datasheet 8)
I already suggested a series diode ...
Such a 1Vf @ 500mA diode would be a 0.5W heater and -1V voltage drop, which in practice would make it impossible to charge this 12V battery to 13V :-DMM
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I already suggested a series diode ...
Such a 1Vf @ 500mA diode would be a 0.5W heater and -1V voltage drop, which in practice would make it impossible to charge this 12V battery to 13V :-DMM
You can compensate by increasing the output voltage of your converter to 15V
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You can compensate by increasing the output voltage of your converter to 15V
I don't have to, I want 13V, because such a 12V car or motorcycle battery with a capacity of tens of Ah usually loses about 10 times more mA than -5mA when using this 24V->13V converter :popcorn:
Protecting a battery from discharging has nothing to do with the topic \$\Omega\$
I guess you were wrong about the reverse voltage VEC of the BJT Q1 transistor, but I think I solved the problem by soldering a diode between pin 2 -> pin 8 of the AZ34063A circuit, because after putting the PV panel away in the garage, nothing burned out, the current consumption from the car battery -5mA is 10x smaller than the typical -50mA in this type of automotive applications :-//
Is it possible to supply voltage to the Collector-Emitter in reverse? https://www.rohm.com/products/faq-search/faqId/232 (https://www.rohm.com/products/faq-search/faqId/232)
(https://www.eevblog.com/forum/projects/maximum-reverse-voltage-of-az34063a-step-down-from-24v-solar-pv-to-13v-battery/?action=dlattach;attach=2428589)
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Protecting a battery from discharging has nothing to do with the topic \$\Omega\$
If battery discharge has nothing to do with the topic, then go ahead and remove the solar panel diode as well.
I guess you were wrong about the reverse voltage VEC of the BJT Q1 transistor
Well, I have heaps of 34063A chips that I’ve obtained from heaps of car chargers that people have disposed of in e-waste. I can perform a reverse voltage test on a bunch of them and let you know when they breakdown.
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Protecting a battery from discharging has nothing to do with the topic \$\Omega\$
If battery discharge has nothing to do with the topic, then go ahead and remove the solar panel diode as well.
Yes, your answers resemble AI prompts, while the topic of this thread is reverse voltage protection of the MC34063A family ICs. :palm:
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Why wasn't there any mention that the solar panel is 150W while a 34063A might realistically do 15W at most? I would go with a 555 switching a MOSFET buck converter at a duty cycle that approximates the MPPT curve, plus a voltage sensing circuit that simply stops the 555 to limit the output voltage.
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I noticed that the input power source for MC34063A is a voltage source. Let us recall that a solar panel is a current source.
I can't go on since I am not sure about the exact circuit which is of interest here.
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Protecting a battery from discharging has nothing to do with the topic \$\Omega\$
If battery discharge has nothing to do with the topic, then go ahead and remove the solar panel diode as well.
Yes, your answers resemble AI prompts, while the topic of this thread is reverse voltage protection of the MC34063A family ICs. :palm:
How rude of you to make such unfounded accusations!
Anyway here's my reverse voltage experiment.
As you can see, I have a whole bunch of 34063's to choose from
[attachimg=1]
And this is my breadboard setup
[attachimg=2]
The test schematic is straightforward.
pin 1 - GND
pin 2 - +V
pin 3 - open
pin 4 - GND
pin 5 - +V
pin 6 - GND
pin 7 - GND
pin 8 - GND
I have included a LED and 430 ohm resistor in series with +V, to act as a current limiter and visual indication. In addition, the bench supply has the current limit set to 200mA.
So starting with the power supply at minimum, I slowly increased voltage.
The LED started glowing faintly at 2.2V. Increasing the voltage up to 40V, the LED was bright.
I repeated the test with different chips with the same results.
So I guess that's conclusive.... ensure your 34063 circuit is protected against reverse voltage!
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Why wasn't there any mention that the solar panel is 150W while a 34063A might realistically do 15W at most?
I have not only a car but also a motorbike in my garage, and I am also working on a 2A version, because the commercial charger did not work at all with such a current today, the voltage on the motorbike battery suddenly jumped to over 15V with the panel facing the sun, the available current was slightly over 4A when I tested it by directly connecting the PV to the battery without this system :palm:
However, this simple dc-dc based on the mentioned AZ3406A worked great, at the beginning it was almost 500mA, then at a voltage of 12.7V on the battery the current dropped to 300mA, probably because I used the original cable from this converter 12v-14v to 5v@500ma, but I have MC3406AB systems from ST, better 100uH inductors and the current will be around 0.666A at a frequency of about 69Hz, because in this Chinese converter a Ct of probably 1nF was used 8)
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I noticed that the input power source for MC34063A is a voltage source. Let us recall that a solar panel is a current source.
Even this noname AZ34063A based circuit converted from 5V@500mA to 13V@500mA works better than the purchased commercial charger set to charge a 12V motorbike battery, because it could not maintain a voltage of 13V, and the specification of this motorbike includes a 13V alternator, so it looks much better when using a 150W 24Voc -> 13V PV panel as a power source than what is available in stores.
The PV panel has a large potential, the maximum short circuit current is 5A, as I connected it today for testing without any regulators at 1:00 p.m. in Europe with a beautiful sun, cloudless sky, even set at a certain angle, it gave a charging current of around 4A.
It is always possible to connect several 500mA dc-dc in parallel, or design your own 2Amax dc-dc converter, because this is enough to charge small motorcycle batteries without removing :-/O
(https://www.eevblog.com/forum/projects/maximum-reverse-voltage-of-az34063a-step-down-from-24v-solar-pv-to-13v-battery/?action=dlattach;attach=2430831)
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And this is my breadboard setup
In my free time I will connect the VEC of the BJT NPN BC547 transistor to a 12V car battery, let's see what happens, because breadboard tests are good for YT influencers, it's not a real circuit :-DD
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What about have a single MPPT controller charging a 12V lead acid or LiFePO4 battery, then have the smaller 12V batteries connected in parallel with PTCs to limit the current?
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So starting with the power supply at minimum, I slowly increased voltage.
I repeated the test with different chips with the same results.
How long was the MC34063A family IC exposed to this reverse power supply >=13V in your tests ? :palm:
This is a typical example of tests being done without understanding the subject :o
Leave the reverse power supply connected MC34063A not for a moment, but for 12 hours, 30 days a week, 365 days a year, then it will make sense :-BROKE
These cheap systems as DC-DC 12V-24V to 5V can work great precisely because the output voltage is 5V, not 13V which is what I am interested in, so I soldered a bypass diode and that closes the topic. :popcorn:
(https://www.eevblog.com/forum/projects/maximum-reverse-voltage-of-az34063a-step-down-from-24v-solar-pv-to-13v-battery/?action=dlattach;attach=2428685)
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So starting with the power supply at minimum, I slowly increased voltage.
I repeated the test with different chips with the same results.
How long was the MC34063A family IC exposed to this reverse power supply >=13V in your tests ? :palm:
This is a typical example of tests being done without understanding the subject :o
Leave the reverse power supply connected MC34063A not for a moment, but for 12 hours, 30 days a week, 365 days a year, then it will make sense :-BROKE
It broke instantly as soon as power was applied, so what's the point of leaving it for longer?
Maybe you didn't understand how the test works?
If the chip could withstand reverse voltage, then the LED should have stayed off from 0V up to 40V. But the LED turned on immediately with 2V. Therefore the chip CANNOT withstand reverse voltage.
And in case you still don't understand, it failed reverse voltage immediately!
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I have included a LED and 430 ohm resistor in series with +V, to act as a current limiter and visual indication. In addition, the bench supply has the current limit set to 200mA.
So starting with the power supply at minimum, I slowly increased voltage.
The LED started glowing faintly at 2.2V. Increasing the voltage up to 40V, the LED was bright.
I repeated the test with different chips with the same results.
The topic is not the reverse voltage of the LED supply, but the IC MC34063A :palm:
The LED can be easily protected by soldering a second, reversely polarized diode in parallel.
If the LED diode fails, it doesn't matter in my case, because of course I added two 4.7k resistors to 560R which limited the current in the case of the original circuit at 5Vout, so now I have a green 3mm LED diode and 2x4.7k+560R, i.e. at a voltage of 13Vout, a current of about 1mA flows and there is no question of any reverse power supply, because the charged battery has the same polarity at the output. :o
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What the hell is the argument about? Andy clearly wrote that MC34063 sinks current into it's output while unpowered.
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I have included a LED and 430 ohm resistor in series with +V, to act as a current limiter and visual indication. In addition, the bench supply has the current limit set to 200mA.
So starting with the power supply at minimum, I slowly increased voltage.
The LED started glowing faintly at 2.2V. Increasing the voltage up to 40V, the LED was bright.
I repeated the test with different chips with the same results.
The topic is not the reverse voltage of the LED supply, but the IC MC34063A :palm:
Clearly you still don't understand the test.
Here is the test setup:
[attachimg=1]
If the LED lights up, that means the 34063A failed reverse voltage.
I don't know how else to explain it to you.
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Andy, do you still have that setup? Out of curiosity, have you tried pin 2 and 5 separately? Does pin 2 sinks too?
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Just tested again with pin 5 connected to GND instead.
Same result, the LED lights up.
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But the LED turned on immediately with 2V
This is really weird! It seems that the breakdown voltage of Q2 EB junction is close to zero unless a resistor, on Q2 BE, was omitted on the schematic.
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Do you mean that the hand-drawn schematic above lights up the LED with 2V instead of 40V?
I suppose it might be the 100Ω resistor, if it's made of a P diffusion into N silicon biased to Vcc. Basically, it's a diode to VCC in such case.
I have that Zeptobars image somewhere but I'm too lazy now to look at it to confirm if that's the case.
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There is also BC junction of Q1 in series with 100Ω, which you externally short with VCC.
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Do you mean that the hand-drawn schematic above lights up the LED with 2V instead of 40V?
With the schematic shown above, I slowly increased voltage from 0V. The LED began slightly glowing at 2.2V and only got brighter from there, until I maxxed out at 40V.
And yes, I was also interested in examining the die, to suss out what's going on. But I'm pretty much a n00b when it comes to reverse engineering dies.
https://zeptobars.com/en/read/MC34063
edit
There is also BC junction of Q1 in series with 100Ω, which you externally short with VCC.
you're onto something there! the BC junction is just a diode PN junction which allows current to flow like this:
[attachimg=1]
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Let us not forget the forward voltage of an LED. Even for a very small current it is not less than 1 V.
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This makes sense. And Q1 may even operate in reverse, so only some fraction of LED current has to pass through 100Ω.
So I suppose small currents should be relatively harmless to this chip and one might get away without a reverse diode.
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Clearly you still don't understand the test.
...
I don't know how else to explain it to you.
Create your own thread for these tests, because they are useless to me, I've 13vout and IC MC34063A protected with diode FR107G 1000V 1A :popcorn:
(https://www.eevblog.com/forum/projects/maximum-reverse-voltage-of-az34063a-step-down-from-24v-solar-pv-to-13v-battery/?action=dlattach;attach=2428685)
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So I suppose small currents should be relatively harmless to this chip and one might get away without a reverse diode.
Not necessarily, because it may be a matter of time before the reversely connected power supply damages the emitter of the NPN transistor even though a small current flows through it.
These tests are pointless because they do not test a real circuit I have, secured with this cheap fast diode, it charged my motorcycle battery to 12.9V connected to a PV panel, so the only thing I am doing now is my own version with a larger 100uH inductor for a slightly higher current operating at higher frequencies around 70kHz. 8)
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But the LED turned on immediately with 2V
This is really weird!
Yes, absolute nonsense, there is no information about the color of this LED to estimate its Vf and current limiting resistance values in series, in addition, instead of a resistor ladder at the output, the output is connected to GND :-DD
Keep things simply as shown below 8)
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But the LED turned on immediately with 2V
This is really weird!
Yes, absolute nonsense, there is no information about the color of this LED to estimate its Vf and current limiting resistance values in series, in addition, instead of a resistor ladder at the output, the output is connected to GND :-DD
Keep things simply as shown below 8)
The colour of the LED is shown in the breadboard photo :palm:
The size of the limit resistor was specified in the post with the breadboard photo :palm:
Clearly you still fail to understand the purpose of the test setup, to investigate maximum reverse voltage of the 34063A.
Yes, your diode works to protect the chip, but you still have not answered the question.... what is the maximum reverse voltage?
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I have included a LED and 430 ohm resistor in series with +V, to act as a current limiter and visual indication. In addition, the bench supply has the current limit set to 200mA.
I have successfully tested the MC34063A protected by a diode by charging a car battery VARTA Silver Dynamic 12V 63Ah 610A with a 150W solar panel, where the short circuit current is limited only by battery internal resistance, it will definitely exceed 1000A >:D
Yes, your diode works to protect the chip, but you still have not answered the question.... what is the maximum reverse voltage?
This does not matter, because the IC MC34063A has been tested in real working conditions at a battery voltage of 13Vmax, even if I start a car or motorcycle during charging, nothing will happen because the car alternator can raise this voltage to 14.2Vmax or the documentation for the motorcycle alternator says 13V, that's why I charge to 13Vmax with this circuit. :phew:
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I have successfully tested the MC34063A protected by a diode by charging a car battery VARTA Silver Dynamic 12V 63Ah 610A with a 150W solar panel, where the short circuit current is limited only by battery internal resistance, it will definitely exceed 1000A >:D
I can also test reverse voltage with a car battery and NO PROTECTION DIODE, however my LED test predicts what will happen with the car battery.... fried 34063!
I can make a smoke video, but I am not a YouTuber. I do not make videos of things blowing up.
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This may be off topic.
I guess the circuit of interest here (which I am not sure of) uses an inductance after the output emitter (or source, if MOSFET). And the input collector (or drain) is connected to the positive output of the solar panel.
If this is the case, when the output transistor (or MOSFET) is off (while driven by PWM), it cuts the current of the solar panel. Naturally, this decreases the efficiency of the solar cells. In this application, the efficiency (speaking relatively) decreases from 100% (using the right topology) to 13V/24V (close to).
This may not be important here. But it has to be considered when designing a step-down converter in case one likes to get all energy provided by his PV. This is achieved by allowing the PV continuous/available current to enter the charger all the time.
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If this is the case, when the output transistor (or MOSFET) is off (while driven by PWM), it cuts the current of the solar panel. Naturally, this decreases the efficiency of the solar cells.
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 :-/O 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. ::)
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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 :-/O 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.
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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. :popcorn:
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 https://www.youtube.com/watch?v=_TOCRjF9WuE (https://www.youtube.com/watch?v=_TOCRjF9WuE)
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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. :popcorn:
You can use external BJT NPN e.g. 2SC4242 or KSE13007. These are NPN BJT used in older AT/ATX computer power supplies.
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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 :wtf:
Are these fakes or do they come from unknown ST subcontractor? :palm:
We'll find out, because I've designed a PCB for the MC34063ABN :-/O
(https://www.eevblog.com/forum/projects/maximum-reverse-voltage-of-az34063a-step-down-from-24v-solar-pv-to-13v-battery/?action=dlattach;attach=2458613)
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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...
:popcorn: :-BROKE
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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.
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FYI it was a month ago and the OP has already added a protection diode.
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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 :-/O
(https://www.eevblog.com/forum/projects/maximum-reverse-voltage-of-az34063a-step-down-from-24v-solar-pv-to-13v-battery/?action=dlattach;attach=2459381)