Just use a TL431 to light the LED
Right, but that's not really my priority tbh.
Hi,
It does not have to be that complicated. A LM317 with a few parts werks well too without that extra LM chip.
I can find the design if you need it but it's just a LM317 set up as voltage regulator with series resistor to get a taper charge.
Do you mean the current limited circuit in the LM3XX datasheets? with one resistor on the output and adjust connected after the resistor?
Hello info,
there are a few things that should be considered:
Now I have a couple of questions:
- Is a diode really necessary across the input & output from output towards input (dotted lines)
The diode is there to protect LM317 that may die if Vo is much higher than Vi.
- I copied the 0.7V virtual ground for the LM358 off some circuit I saw here on the forum. Is that a cheap and dirty way of allowing the OP-Amp to go down to zero?
With this schematic the LM358 will never go to 0V. Instead it will go to Vforward(D3) that is about .6V. Simply short D3 and it will go to 0volt.
- Perhaps a bit of critique on my schematic. I do want to improve overall, so please don't hesitate.
You modified the original schematic to obtain more current but D4 is just a 1A diode and probably it will die. Furthermore there is no current regulation and you will probably end with a much higher current than 2A when the battery is empty. The original design rely on the ability of the LM317 to limits its current and, since you added an external series pass transistor (Q1), you have lost the current limiting capability.
Note that this circuit is not protected if the battery is connected in reverse polarity since the supply of the LM358 is taken directly from the battery itself.
As others said there are many different and easier ways to accomplish a SLA charger but if you want to continue to this route you need a bit more refinement of your project.
Best,
0xfede
Gotcha. Will remove the diode D3 and D4 is an MBR1550CT, I didn't have a footprint of it so I just used the 1N4007 as placeholder. Otherwise, I could also use STPS2045C which I salvaged from a dead SMPS. Either should handle the 2A I was aiming for but then I am reconsidering adding a current limit to the circuit. Will update the schematic and post.
Here is a simpler schematic...
This was an Li-ion charger so you need to modify a few things. Not much though.
Of course you adjust the output to over 12v, like maybe 13.9v or a little higher.
Yes, I thought of going down that road but I wanted something that could fully charge and/or float in one circuit. I know I could set the LM317 to a voltage of 13.6V and leave the battery attached for a permanent float but that doesn't really charge up the battery to full capacity which is what I was aiming for.
I chose this route because:
a. I can charge the battery fully and
b. If it's fully charged, it can be *theoretically* floated indefinetly
I will change the circuit and post the newer version for feedback