Automotive 6 Volt Generator Transistor Voltage Regulator

[KeepItSimpleStupid]

Look here https://webee.technion.ac.il/Sites/People/gad/Papers_Gadi/146.pdf at figure 6 and figure 8. Hey, I worked characterizing semiconductor diodes (Solar cells). Activation energy, ideality factor, Calculated shunt resistance, calculated series resistance. At very low currents.

Look at the figure on the right (the I-V curve) before the magic number of 0.3-0.7 V. https://en.wikipedia.org/wiki/Shockley_diode_equation
If the LT6700 is basically being powered by a 1 meg resistor to power the LT6700 (the non-ideality of the diode, a guess0, your not supplying at least say 40 uA. It's approx 20 uA from the datasheet.

So, you need to parallel a resistance across the LT6700 supply pins to get your 0.3 V or whatever it's supposed to be across that diode. Don;t forget at these levels, your 10 M resistance of your meter may interfere with the measurement.

 

[Danwvw]

Oh? Maybe that is what was wrong with the 1st LT-6700 Prototype, I finally see. It may be happening to the the 350 prototype as it sometimes doesn't start charging. Interesting.

 

[KeepItSimpleStupid]

I'm still looking over your shoulder. Not too many people have the experience of setting up systems to measure a few pico amps (1e-12 amps). Wierd things start happening in that realm. Wiggling wires generate current. Physics tells us that a wire in a magnetic field generates current. Well, it was a wire, a fan was pushing it in an environmental chamber and it generated current. Squishing things like teflon generates current. I could put my probes on a piece of paper and I could measure a conductvity depending on the moisure level.
I could get a reading if methanol was placed on a glass slide and evaporated and not dried properly.

We changed from Acetone, methanol, tri-chlorethane, and forced dry with electronic grade argon for 1 of samples. We had to find substitute for trichlorethane. We had a vapor dryer that used the chemical.

Fingerprints were deadly. Ever hear of a vented screw? It has a hole down the center so air doesn't get trapped between the threads.

 

[Danwvw]

It. gets into the atomic physics a subject that I follow although I don't know how to calculate the threshold charge of a given semiconductor junction, That's cool.

 

[KeepItSimpleStupid]

I'm still looking over your shoulder. So, I guess what I;m saying is put a resistor across the LT6700 power pins so it draws like 10 mA and see what happens. Make sure there is a normal drop in voltage across the diode. Add a 10M resistor when your done if you have to, to simulate the addition of a 10M meter to measure it.

 

[Danwvw]

Ok, Progress UpDate. I was able to get the LT-6700 I prototype working and testing on the bench: One issue it may have is the current regulation may cause the regulator to shutdown completely during an over current situation. At least it does with my Bench setup which can't deliver enough current for the 3.3 volt Hall Effect Supply with any kind of current load beyond the LED 6 Volt Tail Lite and since it shuts down on Low ie.. below the .4 volt threshold on the LT-6700-1 comparator + input, it may stay shutdown after the .4 volt threshold is crossed (from above to below) as it should at 50 amps. And because the Hall Effect 3.3 volt supply needs to run from the generator D+ there may be no power to bring it back above .4 volts. Now it may work fine on the car because D+ is so strong directly off of the generator. Just need to try it. One concern is that the Current limit might keep it from starting up however it's OK on the bench the B+ pullup is active before the LT-6700 get's powered.

 

[KeepItSimpleStupid]

Your prototypes are looking "prettier".

 

[Danwvw]

Testing the LT-6700-I on the car today. It had the same issue as before with the voltage surging but not as bad. about 6.5V to 8 volts every second. I have stabilized it by adding an 220uf electrolytic and a .1uf across D+ to ground, something none of the other comparator designs needed.
Start charging is excellent, Voltage regulation good hower voltage output is climbing over time as the engine warms up, also this design needs more RPM on the Generator to Output 7 volts especially when cold. It has more voltage drop about 1/2 a volt when the headlights are on too. (The 350 design was just the .2 volts across the cutout diode! the LT-6700-I design is measuring .31 Volts drop from D+ to B+ with a voltmeter).
As far as current regulation goes the Hall Effect ACS-773 output is (2.4 Volts), too far above the LT-6700 + input threshold to work. I can measure the ACS-773 output drop of about 40mv by turning on the headlights but I think that's caused by poor 3.3 volt supply regulation. I have some 3.3V regulators on order that should be better. I have calculated at 26.4mv/Amp the ACS-773 should output 528mv less with the headlights on so it's got some problem. I have left the headlights on to run down the car battery to see if when I try it next any current can be measured with the ACS-773 Hall Effect IC.

 

[KeepItSimpleStupid]

Did you look at some ideal diode IC's. Would they help? e.g. https://www.analog.com/en/products/ltc4358.htm

or use an over the top OP amp to generate the power rail for the LT6700.

 

[Danwvw]

Help with what the Voltage Surging? What is a diode IC?

 

[KeepItSimpleStupid]

URL messed up: https://www.analog.com/en/products/ltc4358.html#

Won't work anyway.

Selector: https://www.analog.com/en/products/...ion/powerpath-ideal-diodes-load-switches.html

This https://www.analog.com/en/products/ltc4372.html might work:

Quote:

• Reduces Power Dissipation by Replacing a Power Schottky Diode
• Low Quiescent Current: 5μA Operating, 0.5μA Shutdown
• Wide Operating Voltage Range: 2.5V to 80V
• Reverse Supply Protection to –28V

• High Side External N-Channel MOSFET Drive
• Drives Back-to-Back MOSFETs for Inrush Control and Load Switching
• Fast Reverse Current Turn-Off within 1.5μs
• 8-Lead MSOP and 3mm × 3mm DFN Packages

This chip drives an EXTERNAL MOSFET. So, you get a voltage drop smaller than a Schotkey diode.

 

[KeepItSimpleStupid]

Or an OP amp like https://www.analog.com/en/products/lt6016.html

 

[Danwvw]

Just what are you saying? For current monitoring of the main generator D+ output?

 

[KeepItSimpleStupid]

I'm thinking of the source for V and a replacement for that diode nearby.

Could an OP amp at unity gain, and connected to D+ for the supply. Now have the output of the OP amp feed the LLT6700 power.

 

[Danwvw]

To what end the 6700 is working fine. Yes it was surging but that 220 mfd cap was the fix to that. The only problem with it now is the Hall Effect doesn't work. I am thinking I must have burned it out or it's wired wrong. It needs a good 3.3 volt supply and those are on order. I think I need to do some lab work with the Hall Effect 773's to see how they behave get my 12 volt lawn tractor battery and a bunch of old 12 volts headlights and power the ACS-773 up with the new 3.3 volt regulator STMicroelectronics 3.3V 950mA LD1117V33 Voltage Regulators
and test the ACS-773 at least to 10 or 20 amps..
So you think I should run the 6700 off the regulator too?

 

[Danwvw]

Looks like I have the ACS-773 wired wrong. I have the output and the supply Pins 1 and 3 switched. That would explain part of the current problem!

 

[KeepItSimpleStupid]

Did you make toast?

 

[Danwvw]

Maybe not, have to reverse the wires and see if it starts working. Still on the car! (3.3 volt supply) -.1V =3.2V and 3.2V2= 1.6V at Zero Amps and 1.6 V- 50*.0264Volts=1.32 delta volts so that would leave 1.6-1.32=.28Volts which is below the threshold, 44 Amps would be about 0.44 volts threshold ie where it should current limit.

 

[KeepItSimpleStupid]

I;m going to yell at you. Never write things like you did below:

-.1V

That should be written as -0.1V. the 0 is significant and the decimal point fades into the "paper".

 

[Danwvw]

Well, Ok! So I reversed the supply and installed a 3.3 Volt LD1117V33 Regulator. (much better!)
1. It won't start charging now unless I short the field to ground because the 6700 powers before the ACS-773 which holds the + input of the 6700 Low.
2. The ACS-773 apparently is wired backwards on current direction at Pin 4 and 5. I am getting 2.4 Volts out lights off and 2.9 out lights on.
3. The good news is that would be 0.5 volts ACS-773 output change with headlights 0.5/0.0264mv per amp = 19 amps "correct answer"

So now I need to pull it off the car again and switch ACS-773 pin 4 and figure out a solution to make the 6700 pin 3 high at start up.