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Topic: few questions on opti isolator (Read 3833 times) previous topic - next topic


Take MarkT's advice to heart, learn how to properly draw schematics. Often, just redrawing it will cause the fault to jump out at you.


Your basic problem is that you are trying to switch the low side of the battery to select between sources that have a common ground (the 32V power supply). And PNP are absolutely the wrong transistors to use in a low side switch.

You have enough charger voltage headroom to simply connect the two CC and CV circuits in series. Put the constant current first, then constant voltage. Then you have a current limited, voltage limited charger. It will never put out more current than the setpoint, and never put out more voltage than the setpoint.

Oh look it's Mr grumpy. Dude in my other post u just said it wouldn't work, so now I try something else and now u say I must do it the other way again. All you do is give negative feedback. It's such a hassle for me to keep asking questions so someone can help me then u came along and give demotivating feedback. BY THE way I have not used PNP transistors for the low side switching. I have used NPN transistors for the low side switching. And I got my circuit to basically work. What pisses me off is you also always recommend your way instead of helping me understand what is wrong with my way. If I ask a question u completely ignore it as well. I am trying my best to read and learn all day but then guys like you just make as if I'm not trying at all. Sorry we not all as bright as you ok


What the heck are you talking about?

You have clearly drawn PNP transistors.

All that I've said is meant to be helpful.

Tell you what... you are a good boy who is doing everything exactly right. There, does that help?
Steve Greenfield AE7HD
Drawing Schematics: tinyurl.com/23mo9pf - tinyurl.com/o97ysyx - https://tinyurl.com/Technote8
Multitasking: forum.arduino.cc/index.php?topic=223286.0
gammon.com.au/blink - gammon.com.au/serial - gammon.com.au/interrupts



May 31, 2014, 07:03 pm Last Edit: May 31, 2014, 07:13 pm by wes000000 Reason: 1
I am still learning a lot of stuff, but this is a 12V sealed lead acid battery charge circuit I put together. I have yet to build or test it. But I am pretty sure in theory it should work. I figured it may help to just put it up hear since it accomplishes what you are trying to do. I am not saying you have to use it, but maybe it will help.

3/4 of the circuit it just power management, regulation, and a basic ATTINY setup.

The charging portion is simple I think. It is simply a 15V power source that goes through a high side P channel MOSFET, a current sensing resistor setup, and then through a diode and battery.

To control the high side MOSFET with the arduino I am using a PWM signal to control an NPN transistor. By varying my duty cycle I can control how much the transistor is On/Off In effect changing the voltage in between the pull up resistor and the transistor. Then I just put a low pass filter to turn the PWM into a pseudo analog signal to control voltage at MOSFET gate. Doing so allows me to turn MOSFET all the way on (voltage limited charging circuit) or turn MOSFET partially on (current limited circuit). I can also completely shut off transistor and MOSFET gate gets pulled up to 15V effectively shutting off charging.
"I have not failed. I've just found 10,000 ways that won't work." - Thomas A. Edison

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