Automotive 6 Volt Generator Transistor Voltage Regulator

Feb 6 UpDate! I had been running the LM393 Version here LM393 6 Volt Voltage Regulator in the car ever since the LM311 Prototype-1 failed due to the New 1K ohm 10 turn potentiometer used for current adjusting.
1st. I installed the LT-6700 with the B+ modification Voltage only prototype and it charges hower it oscillates about every 1 or 2 seconds completely dropping out then over shooting up to 7.6 volts or higher if the voltage is set higher.
So I went back to the Repaired LM311 Prototype 1-A with with a similar B+ Modification which samples charge at B+ rather then D+ and it's working well however I need a better Voltage adjust Pot as the last ones I ordered are a little flaky! It's working as it should with about 7.2 Volts up front lights off and 6.8 volts headlights on which is an improvement. Also I can adjust current limit now with the new old style current pot.
Not sure why the LT-6700 is oscillating it could be due to using the TL-431 or perhaps there is some kind of built in delay with the LT-6700 comparators.

Did you install bypass caps?

On the LT-6700? There was a .1 mfd on the VCC I have cleaned it up a bit and will try it again.

Just finished up the ADCMP350 4 pin Comparator Prototype and it works on the bench. This is by far the most simple design. Kind of a breakthrough in thinking as I realized a cool way around battery drain on a Voltage Control Only Design. The 4.7K Pull Up resistor on the output gets connected to B+ Everything everything else runs off of D+ so there is no Battery Drain and it will turn on the MOSFET from the start using B+ Voltage. I am hoping for more voltage stability by not having any Voltage or Current Potentiometers. This design gets its voltage adjusted via changing Vin zener diodes and there is no current limit circuit. If current overload is experienced the 80 amp cutout diode should handle it. Note (The LT-6700 should be able to be configured like this too.)

Just Finished up an Additional 350 Prototype This one in a slightly different old regulator housing. These are bench testing nicely. They leave no room for Potentiometer error by eliminating Pots. Voltage is adjusted by changing the Zener Diode in the Green Terminal Block. There is a Default 7.5 Volt Zener on the circuit board which caps the output voltage at about 8 Volts.
I am really looking forward to mounting this one in the car.

Got. a chance between rain showers today to install and drive with the 350 Model in the car. Saw the same erratic voltage as with the Last LM311 Comparator Design above. So I lifted the back seat and securely fastened the Fluke Voltmeter leads to the Optima 6 Volt AGM battery where it turns out the voltage is actually quite stable. The fluctuations I am seeing on the el cheapo digital display and hearing on the overvoltage alarm are clearly something behind the dash with the cars or my cludge wiring there.
The Model 350 delivered 8 volts steady at the battery with the 7.5 volt zener No HeadLights .2 less with the Headlights. And with the 6.8 Volt Zener it's 7.4 volts and 7.2 volts respectively with Headlights.
The 80 Amp Diode seems a little better too than the 40 Amp diode was. With only .2 volts difference between Headlights off and on.
There is a bit of battery drain from reverse current leakage through the 80 Amp diode (when its hot) after I shut off the engine when the car was driven a with headlights. It only last a couple of minutes. The 80 amp diode is able to cool down enough to no longer lower the battery voltage which is coming back up to about 6.4 volts rest voltage. This Model 350 Design is definitely a nice simple design. I will leave it on the car to see how it is over time. Thanks Everyone for your interest.

i thought you would go with a current limit as well.

Yes I would love to figure out current limit but it's a bit complicated and until I can get a test engine again or perhaps an Electric Motor Powered generator set-up it's a bit sketchy! I was hoping to use the LT-6700 and the Hall Effect ACS 773 for that.

Danwvw said:

I was hoping to use the LT-6700 and the Hall Effect ACS 773 for that.

Click to expand...

me too.

Yes the circuit could be like the LT-6700 Schematic or something where a 2N2222 transistor is used as an inverting buffer. I would probably eliminate the TL-431 in favor of a Fixed Zener diode like the 350 design.

Came up with a way to test these 6 Volt Electronic Voltage Regulators that is like a Generator without needing a Generator. It uses an 2N2955 PNP transistor that connects to the Electronic Voltage Regulator Field Terminal and feeds a simulated voltage back to the D+ Terminal of the Electronic Regulator. Seems to work perfectly with the model 350 above.
Below a 6 Volt LED Tail Lamp Bulb is being powered between Field Terminals simulating the generator fields load. The Waveform on the scope is the signal at the PNP transistors Emitter and the fluke is measuring the 12 volt supply voltage. Scope Time/Div setting is 1 ms/1 cm


Comparator ADCMP350

The Model 350 is Oscillating at 25K hz @ 7.4 Volts while the LT6700 is up close to 30 Khz at it's test voltage here 7.27 Volts.
The LT6700 seems to work nicely with the gen simulator, it is very adjustable and the frequency drops as the voltage is lowered toward 5 volts where it's only 15 Khz and its frequency goes up as I adjust it above 7 and 8 volts output. The bottom photo below contains the physical prototype of the generator simulator which Measures 25mm X 50mm.
Comparator LT-6700:

Here the LT-6700 Comparator set to just barely charge. (Note! the Frequency drops down to 300 Hz before the oscillation drops.)

And Here the LT-6700 is Operating at 8 Volts and 20khz with the LED Tail lite and some batteries for a load:

Here are the test results on the Scope for the 393 Regulator, Note the High Frequency Oscillation which is affected by the load and Battery on B+ and the Voltage Output setting. (Note! Low in the waveform is full charge.)

Went out for a Drive today with the 350 did some testing of how hot it gets with headlights! It's good it's a solid design.
Now. The L:T-6700 is still one of the prospects I think might work out with a Hall Effect measurement of the current instead of using a Shunt.

A start on the Hall Effect Current Regulation.

There is something I donl;t like. The 1N5817 and the LT6700 and I can;t find what i need.

Temporarily make the diode conduct about 10 mA and see what happens. Resistor across the LT6700 power pins.
The source isn't stiff enough and your operating around Rds(on) which varies by current. R<=6V/10mA).

If it works or if it doesn't , you might try to stiffen up the power to the LT6700 with a low power unity gain buffer to the supply voltage/ or may be a divider to 1/100 of the supply voltage or whatever the output of the op-amp can sink too.
If it can output to 100 mV of the supply, then make the divider get to 200-300mV o f the supply.

The IN5817 is a good choice here as the link to the generators output ie.. "D+" it only drops about .3 volts or even less with such a small load as 10ma. It should deliver power of 1 amp continuous and more peak and the generator will be putting out about 7.5 volts the only drawback with the unregulated supply is it can deliver too much power, there is not anything to stop this. One solution is to put a 50 Ohm resistor in series with the 1N5817 which I have tried on previous regulators however that caused delays in starting charging. So the un-regulated supply is basically the full generator output and the fuse is the 1N5817 Diode. Remember this design does not need the LT6700 Operational to start charging because the MOSFET gate is now pulled up to B+ with the 50 ohm and 4.7K ohm resistors on the gate.
The Hall Effect ACS773 needs good stiff power and voltage to operate accurately and it does need a current limiting resistor to allow the zener to regulate voltage. It's on two 100 ohm resistors in parallel and the 3.3 Volt Zener is a 3 Watt Zener.
Thanks, let me know if I messed what your saying here.

You missed my point, I think. The diode might be a good choice, but the comparitor is "low power", so the diode is operating at the wierd part of the diode curve, Jut try drawing some significant current. Put the resistor ACROSS the pwer supply pins of the LT6700 so the diode is conducting fully and not in the 0-0.3V region where Rds plays a part. Trying to conduct 1uA through the diode to power the LT6700 I don;t think will work.