Thank you for your great work gchart, I want to make a tint adjustable driver and I think I should go with those 1 series attiny. The 3 wires flashing, calibrated temp sensor, and fast higher resolution PWM all sound very good.
A bit late but here is the answer :
I’m a novice in EE too but I want to make an Anduril tint ramping driver and those 7135 wont do so I’m trying to learn.
To explain a bit, the signal from the MCU (attiny1634) is divided down to Rsense level (50mV for a 10mΩ Rsense and 5A) by R3-R4, and is filtered by R4-C3 and fed to the non inverting input of the Op Amp, output to the gate of the mosfet, and Vsense to the inverting input, creating a feedback loop which makes the op amp adjust Vgs of the mosfet to maintain both its input at the same voltage. Reducing the duty cycle on PB3 lowers the voltage at the op-amp’s Vin+, for example at 10% we get 5mV, thus the gate voltage is lowered to get Vsense at 5mV, so 0.5A.
C5 : I suppose it is a decoupling capacitor for the op amp VCC.
R6 : gate resistor.
R7 : gate-source resistor, I’m not sure it’s necessary here ? I thought it was needed to discharge the gate capacitance as fast as possible when switching. No switching here.
C4 : when I simulate the circuit without it there are massive current oscillations so I guess it’s to eliminate those, 100pF seems to be sufficient, the higher it is the slower the current is adjusted, especially at very low currents, I’m guessing this is why there is a turn ON delay at level 1 and 2 and maybe its value is too high and could be reduced to improve that (I just put some probable values for the capacitors on the schematic, I didn’t measure them)
R8 : looking for precision Op-Amp I came upon this page , the diagram mentions “resistor cancels out parasitic seebeck effect voltage”, so hmmm… probably that :nerd_face: .
There is a 2.8V LDO (MIC5205) powering the MCU and the aux LEDs, and a second mosfet for the direct drive channel.
In the led4power driver there is a direct drive option with just one mosfet onboard so I’m guessing there is simply another signal from the MCU going to the gate of the mosfet, pulling it to high for direct drive. I don’t know if it ramps down from DD to CC with PWM, but in simulation PWM on the gate seems to cause some problems and only seems to work at low frequencies, it seems that the op amp feedback loop is not fast enough to respond each time DD is OFF. Probably why on the Noctigon there is a dedicated mosfet for DD.
I tested the opposite thing in simulation to achieve very low output, instead of pulling the gate to high, pulling it to low (a small nFET between the gate of Q2 and GND, controlled by another pin) when dimmed analogically at low output, say 10mA, even just 8bit PWM would give extremely low outputs, but again it only works at low frequencies unfortunately.
So the other way mentioned in the thread is increasing the resolution, it would help a bit, if it works in practice in this case because the voltages compared by the op amp become extremely low, 12uV at 12bit, the offset voltage of the TLV333 is 2uV(typ) 15uV(max) so it’s just really close. It would do 1.2mA, which is sublumen if we assume 3mA/lm.
Probably another channel is preferable, maybe just a resistor would do but current varies with the cell’s voltage, a low current PWMable CC linear regulator would be preferable, I see the ones you mentioned in another post but smaller packages would be better.
It would be great to have a BLF reference linear driver based on this design(noctigon, convoy, led4power), it’s more efficient than FET+n*7135 drivers while still not being as complicated/large as switching converters.
Anyway I’m basing my tint adjustable driver on this Noctigon driver, basically by putting two linear CC channel on it.
One question that have is about Timer/Counter D, when it says that there is one, does it means that only one of the 2 pins which can use it at a time, or is that not what it means at all ?