MOSFET linear regulator circuit

[VEGETA]

Well, I have put a 100uF cap on the output and then connected the pre-regulator circuit to it in one circuit to test it as a whole (Although it is not yet completed)... and guess what, IT WORKED! perhaps it is not perfect enough but I tested CC  and there were no problems. I am kinda happy that we reached this state, now we can continue adjusting our mosfet circuit more!

Combined circuit is attached below, the current and voltage curves are just so beautiful xD 

Now I think we should take care of the following stuff:

1- current measurement (the previous post).
2- output caps. will 100uF alu smd + 0.1u ceramic work for linear stage?
3- op-amp choice. it is pretty much finished: LT6084 for CC and crappy stuff for CV, perhaps even LT1013 if we need the other op-amp to be accurate (30-0v rails diff-amp for current measurement).
4- final mosfet choice. although IRFP250N is perfect but 240 is chosen lately. Plus, I wouldn't ever mind an SMD one although performance and quality is essential here.
5- most importantly, parts consolidation! can we enhance our choices here?

I give the mike to you, klein.

[VEGETA]

I played around with the "combined" circuit, the pre-regulator always lowers its voltage to be near the linear output which is just wrong and so weird! I even put it to around 18v (R1=10k, R2=105k) but still gets near 10v as the linear stage does this.

I studied more, and realized that modifying the R_SENSE of the SEPIC converter to make it lower gets it to be stabilized! now it works nicely (make it 0.005R). Let's not open this door yet xD

[Kleinstein]

The current source I3 can be a really simple one. So something like 2 transistors and 2 resistors. The same is true for I2 (just the other polarity, thus using PNPs).

However there could be one more problem: how to get a kin dof output disable ? Just turnung I2 and I3 off will also remove power from the CC regulator!

For current measurement, I see two options:
1) have the display floating, e.g. an ICL7106 or similar powered like the CC OP.
2) use an OP as a difference amp to measure the 0-2 V from the second half of the LT6084. And than have an ADC and display driver (µc?) ground referenced. This could be the second halt for the LT1013/LM358 used for voltage regulation.

The current source I4 still need a little attention - I would use an OP (e.g. TLC271 )powered from -5 and +5 V.

For the choice of OPs, it depends on the accuracy one wants: the cheap version would be something like LM358/LMV358 (or MCP6002). The accurate version more like LT1013 and LT6084. Instead of the LT1013 an OPA2170 could be an intermediate - lower cost than LT1013 and better specs than the LM358. There might be alternatives to the LT6084 too - there are many modern OPs in this range (3-5 V Rail to Rail). We might find a way to use an MCP6002 for the I4 source to, but the 5.5 V supply limit can be tricky.

[VEGETA]

I would still need to use the other op-amp in LTC6084... as for current measurement, I would revert like I said before and you now: use the other LT1013 to get the I+ signal to make it /10v then feed it to the uC. Now the uC actually already has the I- voltage which now makes the values for the current.

However, I tried to make a traditional diff-amp for the current but it just didn't work. the amplification ratio was wrong although 4 similar resistors. Is this what you meant by your (2) option?

Well, I guess things will be better if we could get a single op-amp like ltc6084 to get rid of the idea of using the other op in the package. Is there any Linear.com part?

[Kleinstein]

The trick for the current measurement is to use the second half of the LT6084 and the second half of the LT013. The LT6084 first does amplification to 1 V/A (but still relative to I+). The LT1013 is configured as times 1 difference amplifier between I+ and the 1V/A signal., not the I- signal.

Without the extra amplification the precision required for the resistors would be very high.

Attached is a circuit version including this current sensing part.

[VEGETA]

Well, your idea is nice but the current sense is not accurate... there is 0.1v more and 0.2v on the 2A portion, perhaps it does amplify the voltage drop?!

I was thinking of using something like LT1797 which worked nice, but didn't work for your last circuit. It is the same price as LTC6084 but still better specs - taking into consideration the no need of the other op-amp in LTC6084 package.

EDIT: LT6000 (and 2,3,..) works for CC loop too. are they worth it? Also LTC6087/8.

EDIT2: I tried removing the 2A sink load and replaced it with a resistor 10R to draw 1A but there is still 0.1v more. I don't think this is due to the gain in differential amp but maybe due to the other LTC6085 or anything else I still do not know.

EDIT3: I adjusted R8 to be 9k instead of 10k which adjusted the gain... I noticed this detail in the last moment: it is the same as my resistor divider ratio, not like op-amp resistor gain. 1k in series of 9k = 10k which means V_out= V_in*(10/1)... if R8 will be 10 this will be V_out = V_in*(11/1). I guess this is correct.

Since it is the exact same result, I guess your idea is 2-sided: 1- use the other LTC6084. 2-no need for precision resistors.

xD

[Kleinstein]

For the CC loop OP, there are many types to choose from as here. A low supply current is not an advantage here as current is needed for the MOSFET anyway. So it comes down to availability, price and offset as the main properties. Much of the offset could be adjusted in software and with an additional resistor.
The LT1797 would work. The LT600x might be a little on the slow side, but can still work too.

There might be very well need for the second OP, to get the current reading back to the µC.
The easier way is amplify first and than the difference amplifier. The more accurate (better CMR) way would be something like a current sense circuit and amplifier at the -5V side.

There is one more weak point of this type of circuit to solve, and this output enable and the behavior during turn on. The OP for CC regulation only gets power via the bias current, so it would not be powered when the bias is disabled. So far I have not found a really good solution - this could turn out to be a real show stopper. Mains powered I would consider a relay, and keep the regulator active.

[VEGETA]

OK, the LTC6084 is the final choice. It is cheap and really good. LT1797 didn't work for the last circuit while it did well on the one before it (without measurement). And thus keeping the slightly pricey LT1013 since we use both op-amps in it. paying a little more here is reasonable enough since it is the main circuit... surely the quad LM324 will have a place somewhere else xD.

What do you mean by output enable? is it turning on or off the load or regulation? As for the behavior during power on, it gives a spike of 20A or something but then it regulates properly.

Your idea is that the problem is getting the supply from the output stage assuming it has a load, which you said it is the bias voltage. Now, can we really use a separate supply for this? I tried +5 and -5 for the CC and measurement OPs but no use.

I also tried making the CV op-amp output 0v for 1mA (regulator is off) then 1v for 10v output or so while having a resistor load... and everything worked nicely.

can you identify the problem more so I can search more and more on the topic. quitting is not an option at this stage xD lol... if you quit, I will find you... and I will kill you, then kill myself with you. :D:D:D:D:D

[Kleinstein]

The output enable / disable function is there to temporarily turn of the supply output and allow to turn it on in a well behaved way. This can be important during turn on of the instrument. Ideally the output would be separated, like with a switch / relay.

The usual way is to turn off the output stage, only, as an relay would add contact resistance and would thus still need feedback from behind the contacts.

I have not found a really good solution so far. One option would be old style with a relay, but this needs extra power and switching the voltage sensing line is also not attractive.
Turning off the ouput drive might work too. This would be turning off the current sources I2,I3 and I4 together. This still leaves the problem to start the regulator, especially the CC mode part. Here a JFET or depletion mode MOSFET could be used to enable the MOSFET output only if there is sufficient supply for the OP  (D/S from base of Q4 to I+ and gate to a fraction of the OPs supply). This would prevent an excessive positive current, but would still allow a slight negative current (from the I3 source). So one would also need some good protection against an overall negative output voltage. For a good solution one might have to consider an really independent supply for the CC OP - but this is quite an extra effort.

Though this is certainly disappointing, my conclusion would be that this type of regulation circuit is not such a good idea. It works very good in some respects (CV-CC transition), but the startup and the disable function is really making it tough, complicated and likely not so well performing in this respect. Much of the effort was on learning - so keep what we learned and use it on a more conventional circuit.

At least for me the effort is smaller to go back and more or less start from scratch than to fix the on/off problems with this circuit type. It also gets quite complicated compared to the more conventional floating regulator. My first choice for a MOSFET output stage and low power consumption would be a floating regulator with a isolated supply for the regulator circuitry - this is more or less the second standard circuit, like used in the HP and many of the cheap Chinese supplies. The advantage is, we only need that one extra supply, but no more +30 V or -5 V. Also gate drive is directly from the auxiliary supply - this saves on the overall power consumption.

[VEGETA]

Well, I searched other threads and found the talk about "floating regulator", now what is the advantage of using it? I still don't know about it except that it is not referenced to the circuit ground. Hence it can be something like 10v-to-5v but where to use this in our circuit?

I am ready to modify the circuit to a more traditional one following your suggestion of floating regulator, but how to do that? I understood of your talk is that our problem lies in CC mode especially in starting the regulator and having output enable and disable feature. I suggested having the CV mode at 0v as a start and the same for CC mode I4 but you seem to dislike it for some reason. How can we see your problem in ltspice?

My first choice for a MOSFET output stage and low power consumption would be a floating regulator with a isolated supply for the regulator circuitry

Yup, so let's start from there. what is the isolated supply? I have a 30v aux supply stage to power the OPs and other stuff, I don't think you mean it.

Our regulator circuitry has CV and CC mode, I assume you speak about CC regulator here and you suggest to have an isolated supply for it. So we can assume that our CV part is ok?

The problem of CC part, according to my understanding, is that it gets power from the output stage itself - so it depends on it. You wanted to give it a separate "isolated" supply... is it the floating (ex. 10-5v) one? Since you mention that we won't need 30v and -5v this means CV needs to be adjusted. However, we still need around 30v to drive the gate.

Also gate drive is directly from the auxiliary supply - this saves on the overall power consumption.

what is the voltage of this supply? we need at least say 5v difference between mosfet gate to its output to turn on... so maximum output voltage is 20v this means 25v aux supply. we have 30v here.

and it is meant to be a floating one for the regulators (assuming CV also) so a zener diode of 4.7v makes it 30-to-25v or maybe making it 30-to-10v rails floating supply.

^ Is that what you meant?

Now what type of circuit should we use? we made 2 kinds: first one is my initial suggestion with ground based cv and cc loops with cc stage consisting of a transistor pulling the base to ground... this was messy and oscillated a lot. Second one was your (or someone else idr) initial idea of having 2 diodes to separate the cv and cc modes while having a bigger output voltage before the diode... so the active stage is the one with lower voltage. This 2nd one didn't oscillate but was slow in the cc mode.

Can you post a circuit in ltspice to demonstrate this? I tried to play around with our last one but no hope, still nothing. I am open to using other typologies that guarantee low dropout of 1v.   

I learned a lot surely but I don't understand the concept of floating regulators and why they will help, plus don't know why the traditional circuit oscillated in the first place.

[VEGETA]

I have nearly completed my ideas about the rest of the supply like switching supply stage and microcontroller stuff as well as display and protection... the only thing remaining is this linear post-regulator stage!

[ZeTeX]

I have nearly completed my ideas about the rest of the supply like switching supply stage and microcontroller stuff as well as display and protection... the only thing remaining is this linear post-regulator stage!

Have a look at this thread:
https://www.eevblog.com/forum/projects/anything-wrong-with-this-linear-psu-design/
this guy is doing a good job at designing fairly simple PSU.

[VEGETA]

I have nearly completed my ideas about the rest of the supply like switching supply stage and microcontroller stuff as well as display and protection... the only thing remaining is this linear post-regulator stage!

Have a look at this thread:
https://www.eevblog.com/forum/projects/anything-wrong-with-this-linear-psu-design/
this guy is doing a good job at designing fairly simple PSU.

Very nice, I went through and understood many parts of his design... very similar to our old one. Perhaps this is what klen meant by floating. gonna play around with this soon enough to do a re-cap of mine. Do you think 1v drop is achievable with that design? can I make it suite an N-mosfet one?

thx

[ZeTeX]

Probably yes but with a few modification, e.g protection for the MOSFET and maybe replacing the current source with a voltage source as MOSFETs are voltage driving devices, but I might be wrong.

[Kleinstein]

The floating supply circuit is something like the circuit in this post:
https://www.eevblog.com/forum/projects/anything-wrong-with-this-linear-psu-design/msg1104085/#msg1104085
(change the OPs to something more common and unity gain stable, like TLC27x - the LT1037 is a poor choice)

The point is that the OPs (and the controlling µC) from supply that is later relative to the positive output. So this would be something like an flyback SMPS, DCDC block or a royer converter. No more need for the 30 V and negative GND referenced supply. It is easy to change to a MOSFET output stange: just replace the NPN darlington by an N-MOSFET. One might need a slightly higher supply for the positive current (R6) too.
Even with the darlington the drop out is around 0.8 V.

Output disable/enable and a minimum current is relatively easy to add (the minimum current is a little unusual though, as it uses a transistor in base configuration and the positive OPs supply). In addition the circuit would need one more OP for the voltage control setpoint voltage, and likely one for the measurement - but these are not critical.

There would also be the option, to go back to the more original circuit in this thread, with the CC mode regulator and shunt low side. Inspired by the last circuit here, I found a relatively easy way to speed up the CC mode, so that there will be no more large current spike, even without super fast OPs or critical adjustments. The trick is just an transistor in base configuration instead of a diode.
So one could stay rather close to the classical circuit. So this would use the extra 30 V and -5 V supply levels. The circuit is still shown for a BJT power stange, but is not much different for a MOSFET.


The combination with a SMPS shown earlier in the thread is not yet that ready. One usually want's to adjust the SMPS part for a constant drop out in analog.

[VEGETA]

Thanks for the reply. the circuit is a big messy  so I couldn't figure much of it, even the one in the original post is not understandable, especially the ground in the circuit that is on the output. It didn't work properly too, I keep seeing odd values all the time. Can you post a proper one that demonstrate the idea better. EDIT: I changed the transistor to ZTX849 and it worked. only LT1037 works well, even if i change it to LTC6085 and then get it back won't work

Anyway, this last circuit is rather not accurate in current limiting as it shows 1.98 instead of 2 which was achievable in older circuits, there is always a drop. It also has odd voltage monitoring ration, I fixed it by having 9k and 1k so it is now /10 of the output. Perhaps the most odd thing is the 2 shunt resistors and the ground vs the output. I tried making it ground referenced but no use as current opamp stuff didn't work.

I somehow get the idea of making a negative rail after ground to take the Rshunt, which is the concept made by the original creator of that thread. However, what about sinking all that current into the negative regulator? this is not good for me as my design is battery powered (which is a must) and there is no transformer to take a center tap and make a negative rail that can absorb all that power... mine was a small 10mA charge pump xD. Not to mention that his design didn't work with a mosfet nor it can handle 1v dropout.

As for the switching stage, my idea is to adjust it via a digital potentiometer controlled by the same MCU. So when the user gives an order to adjust output voltage, the MCU sends the command so that the pot is adjusted accordingly. There is not other way of digitally controlling the sepic (or any other regulator). Analog ones are not known to me, like how to adjust a pot in analog? voltage control is not available for these types of converters.

for the CC op-amp with negative input, this can be done by feeding the control voltage from the mcu to an inverting opamp which in turns feeds it to the cc opamp. However, accuracy is what bothers me in this circuit as I tried to figure out why and I failed xD. Also the CV loop itself is not ground referenced so it is not going to be accurate if fed by a ground referenced mcu as the output voltage feedback itself is not (always some mV dropout due to the lowside shunt).

[ZeTeX]

Thanks for the reply. the circuit is a big messy  so I couldn't figure much of it, even the one in the original post is not understandable, especially the ground in the circuit that is on the output. It didn't work properly too, I keep seeing odd values all the time. Can you post a proper one that demonstrate the idea better. EDIT: I changed the transistor to ZTX849 and it worked. only LT1037 works well, even if i change it to LTC6085 and then get it back won't work

Anyway, this last circuit is rather not accurate in current limiting as it shows 1.98 instead of 2 which was achievable in older circuits, there is always a drop. It also has odd voltage monitoring ration, I fixed it by having 9k and 1k so it is now /10 of the output. Perhaps the most odd thing is the 2 shunt resistors and the ground vs the output. I tried making it ground referenced but no use as current opamp stuff didn't work.

I somehow get the idea of making a negative rail after ground to take the Rshunt, which is the concept made by the original creator of that thread. However, what about sinking all that current into the negative regulator? this is not good for me as my design is battery powered (which is a must) and there is no transformer to take a center tap and make a negative rail that can absorb all that power... mine was a small 10mA charge pump xD. Not to mention that his design didn't work with a mosfet nor it can handle 1v dropout.

As for the switching stage, my idea is to adjust it via a digital potentiometer controlled by the same MCU. So when the user gives an order to adjust output voltage, the MCU sends the command so that the pot is adjusted accordingly. There is not other way of digitally controlling the sepic (or any other regulator). Analog ones are not known to me, like how to adjust a pot in analog? voltage control is not available for these types of converters.

for the CC op-amp with negative input, this can be done by feeding the control voltage from the mcu to an inverting opamp which in turns feeds it to the cc opamp. However, accuracy is what bothers me in this circuit as I tried to figure out why and I failed xD. Also the CV loop itself is not ground referenced so it is not going to be accurate if fed by a ground referenced mcu as the output voltage feedback itself is not (always some mV dropout due to the lowside shunt).

No need for digital pot at all, watch this:

[VEGETA]

My switching regulator is a SEPIC one, it is LT3757. Will it work for it? this is not the main issue now, I just want the linear stage to be done then I can see what to do elsewhere.

[Kleinstein]

The floating regulator circuit was a bit messy and needed extra models. There was also something funny hidden in the load - I had to remove is and add again.

With minimal higher supply (e.g. 6 V) and other OPs (here universal OPs with 1 MHz GBW used) it also work with a MOSFET, though I have not adjusted the compensation for this (compensation is still from using 2N2222+2N3055 before).  Even the BJT Version got down to 1 V dropout.

Looking at the result is a little more difficult, as one has to use differential probe: set positive (red probe) and drag mouse to negative (black probe).

There is a little overshoot in the current, but not much (way less than the current from the output capacitors).

Edit: Tracking Feedback is essentially the same as shown in Dave's video. It may need the the capacitor that Dave deleted in his video. Also keep the base resistor. It does not matter much what type of regulator. Only with a negative or insulated regulator you will need a different, but still similar circuit.

[VEGETA]

Thanks for all. Latest circuit is the best we've got so far, but I have these questions:

1- Why are we using the ground as + output and negative rail as - output?

won't it be better and easier to do it like traditional circuits?

2- I tried many op-amps and none of them worked! LT1007/1678/1037/6085/1013/...! the LT1797 seemed to work but bad result. I did that for both cv and cc together.

3- there is always 2mA or 1mA in the circuit that makes the output always less than required. Like having 999.74mA instead of 1A. I made the op supply -6 instead of -5 and it got a little better with 999.90 which is kinda good (still the 1.00 is awesome xD).

this opens the door for the question of what are these supplies? I can think of lm317 or similar for the positive one but the negative one is tricky with my battery pack being the source. I don't know if connecting them like you posted here will be ok or not.

4- I used the IRFP250N and it worked good without any problem, just a bigger spike (0.5A) before CC kicks in. Although I have removed the 0.2R totally and still no problem. Is there any other types of mosfets or similar stuff can be used to enhance the circuit? I am not insisting on a mosfet to be the absolute must, I just saw from my search that it allows better low dropout than bjts. I can go to an adventure of having a 0.5v dropout regulator!!! If it didn't work, then 1v is the choice... So I have to guarantee that 1v is always ok.

5- I will try switching regulator later, it is not a problem now. You way seems working nice which BTW will be better for me. Who wants extra parts (digital pot) and extra software stuff? ha?


6- this is similar to #1, will the user notice this flipped polarity? will it affect anything or will it work properly like other supplies? what if he wants to put it in series with other supply or say a channel 2 of this same design... will it work?

7- protection:

originally i thought of having a big diode on the output and another one reverse biased from the output of the mosfet to the input. Also a zener to protect the mosfet from exceeding its vds voltage, but this last one is not needed as we have our supply of maximum 6v or so.

THX

[Kleinstein]

The simulation might have a problem with many other OPs, as they are not coming close enough to the positive rail. So they might need a little more than the 6 V. It depends on the FET used.

The same circuit works with a darlington too - dropout would be around 0.8 V or so, depending on the current. There is not that much difference for this circuit - especially with a low threshold type, there is really not much difference in this circuit. So it is really to the personal choice or even later change.

You might need the 0.2 Ohms resistor (could be 0.1 Ohms or similar) to prevent too much gain for a MOSFET at high currents. This resistor does not to be stable or accurate, but low inductance could be an advantage.

The extra +6 and -5 V supply needs to galvanically insulated from the main power, so you would need something like an insulated flyback or royer converter. It would also need to power the µC. Depending on the OPs used and the MOSFET gate threshold, the needed voltage could be a little higher, like +8 v. The neagative side is essentially only for the OPs. So - 3 V, or maybe even without the negative side cold work. They do not need to be really stable, so just the switching regulator should be good enough, especially if R6 is replaced by a current source (could turn that off for disable and when supply is yet there).

If the gain is a little off, or a possible offset in measured current (e.g. some bias), this could be compensated in software. The shunt and ADC ref is usually not accurate anyway. So I would not care so much about this. The shown circuit uses rather low impedance sensing divider - one can easily go higher there by something like a factor of 10. R9 is effectively in parallel to the shunt and the current set-point also adds a little offset (e.g. 0.1 mA).

[VEGETA]

Well, is galvanic isolation a must? the cheapest linear.com part for doing this is LT3573 which is 5$ and for +-12v it needs a 7$ transformer xD. or can it be just an isolated dc-dc converter module. If so then this module is kinda good enough:

http://www.digikey.com/product-detail/en/murata-power-solutions-inc/CMR0512S3C/811-2899-5-ND/4693727

but it is only 30mA for each rail. there are versions with +-9v which can give more current.

why would it be isolated in the first place? plus, won't it share the circuit ground?

___

I forgot to mention that output caps make it worse if they got bigger. slower transition.

___


I've made it +12/-12v but still no opamp working! I even replaced R6 with a current source model of 10mA and still nothing.

___

You still didn't answer me about why ground is top and negative rail is there.

[Kleinstein]

The circuit with the floating regulator needs the isolated supply. Usually this is just a separate transformer winding. A DCDC converter brick would work. As the positive side is always using more current than the negative side one can use single voltage type (e.g. 9 V or 12V) and get the negative side from a shunt regulation / diodes. The problem is more like the often relatively large minimum load of some 10 mA. It depends on the µC - as the µC will also be powered from the source, and one might want to add an minimum current (simple circuit, but tricky to find).

If you want low cost and don't mind winding your own transformer (no need for good insulation), one could use an old style royer converter.

The reason for the insulated supply is, that the GND point (and that of the controlling DAC) is at the positive supply - that is the whole trick with this circuit. However the need for the extra supply is also a big downside. So this type of circuit might not be the most attractive one - it usually is, if the output voltage is higher than about 25, as essentially the same circuit can be used from a few volts up to 1000 V or so.  For voltages below 25 V and with no need for a low dropout, the other type of circuit, more like from the very beginning can be easier.

I tested the simulation with LT1001 and a +12 V (AFAIR), and it worked - most others should work to, just not a de-compensated type like the LT1037. Just take care to get it in the right direction (use mirror,
not rotate).

If you don't want the insulated supply, there should in principle be a similar (from control theory side) version, with the shunt and MOSFET at the low side. However this would be a negative regulator and thus might need a different interface to the SMPS part. Also noise could be different than.

P.s. with the FET output stage, there is a way to get around the second small resistor and use R2 as the shunt. It even makes the part still missing slightly easier.

[ZeTeX]

http://www.ebay.com/itm/B0505S-1W-DC-DC-5V-Power-Supply-Module-4-Pin-Isolated-converter-NEW-Z3-/252029953042?hash=item3aae27e412:g:RzIAAOSw3ydVqPj7
1.32$ including shipping and your problem solved.
You might get it even cheaper if you search only the part number and add a "lot" to your search, I just bought 5 of those for less then 2$.

[VEGETA]

Ok so we can use a single output DC-DC module to output 12v and use a zener diode or something as a shunt regulator for the negative terminal (although I connected it to ground and showed no problem).. Here are the DC-DC converters suitable:

http://www.digikey.com/products/en/power-supplies-board-mount/dc-dc-converters/922?FV=15c0002%2C2dc1bff%2C1f140000%2Cffe0039a%2C17d4002c%2C17d40071%2C17d40096%2C17d400b6&mnonly=0&newproducts=0&ColumnSort=1000011&page=1&stock=1&pbfree=0&rohs=0&quantity=1&ptm=0&fid=0&pageSize=25

The parts I want are those who can be bought from digikey. The shown parts allow 5v input to 9/12v output, so I will get a linear regulator ic of 5v before the module.

___

well for mirror.... yes! I was rotating the damn thing and didn't notice it is not the same! LT1013 worked well so I guess this is a final decison.

__

I am not sure I fully understood the ground as positive output, but how will this affect other stuff? like other circuits like LCD, buttons, other ics, ...etc. which are usually connected to a 5v regulator and to the ground which is the battery - terminal, just like the switching supply itself. I am not sure how will all this mix?

for one part of the circuit the ground is positive rail and the other part it is the negative one. according to the schematic, the SMPS will be connected instead of V3 which means the + terminal of it is to the mosfet and the - terminal of it is to out- which is somehow became -v voltage... while the SMPS itself is + and - voltage by itself... let alone the other stuff connected to MCU and misc. stuff.


I say MCU because if we power it from this DC-DC converter, and it has LCD and stuff... dc-dc won't supply much current at all.. like 80mA or so.


___

If other circuits are functional like this one, do you think it is good to use them or just stick to this? I mean, what is the gain of this particular one? The guy (power..) of the other thread made a simpler circuit and I tested it with success... the only thing I hate it is the negative sensing thing. which one is better and what do you think we should follow?