Hi guys,
I'm trying to maximize the usage of energy stored in a capacitor that is to be discharged over a string of LEDs connected in series. Because the cap's output voltage drops rapidly during discharge, as soon as it falls below the combined forward voltage of the LEDs, current stops flowing and the LEDs turn off, even though there's still a significant amount of energy remaining in the capacitor.
Rather than try and hook up some sort of boost converter, I think I need to take advantage of the fact that any number of LEDs may be on at any one time (all that matters is total overall light output). I would like to implement some sort of cascading LED bypass circuitry. That is, as soon as the cap voltage drops below the necessary forward voltage and current stops flowing, the last LED on the string could be bypassed, reducing the necessary forward voltage and squeezing a little more energy (and hence, light output) out of the capacitor; as the cap voltage continued to drop, this would continue in a cascading fashion, until there was only one LED left in operation.
I've attached a diagram to try and illustrate this concept. The real circuit would have a lot more LEDs, with a possible need to bypass two or three at a time, however at this point I'm just trying to get help with general ideas on how it could be implemented.
Looking at it from a high-level, it should be able to be achieved through some sort of switching functionality, i.e. cap voltage drops too far, current stops flowing through LED string, causing bypass1 to switch on, and also enables bypass2 circuit ---> cap voltage continues to drop, current then stops flowing through LED string again, switches on bypass2, and enables bypass3 ---> and so on.
With that in mind, perhaps it could be implemented with BJTs? I also found an STMicro part, LBP01, that is a bypass switch for when an LED fails to open-circuit -- maybe that could be used, in conjunction with BJTs for the cascading/enable circuitry.
Any comments/suggestions greatly appreciated!
I'm trying to maximize the usage of energy stored in a capacitor that is to be discharged over a string of LEDs connected in series. Because the cap's output voltage drops rapidly during discharge, as soon as it falls below the combined forward voltage of the LEDs, current stops flowing and the LEDs turn off, even though there's still a significant amount of energy remaining in the capacitor.
Rather than try and hook up some sort of boost converter, I think I need to take advantage of the fact that any number of LEDs may be on at any one time (all that matters is total overall light output). I would like to implement some sort of cascading LED bypass circuitry. That is, as soon as the cap voltage drops below the necessary forward voltage and current stops flowing, the last LED on the string could be bypassed, reducing the necessary forward voltage and squeezing a little more energy (and hence, light output) out of the capacitor; as the cap voltage continued to drop, this would continue in a cascading fashion, until there was only one LED left in operation.
I've attached a diagram to try and illustrate this concept. The real circuit would have a lot more LEDs, with a possible need to bypass two or three at a time, however at this point I'm just trying to get help with general ideas on how it could be implemented.
Looking at it from a high-level, it should be able to be achieved through some sort of switching functionality, i.e. cap voltage drops too far, current stops flowing through LED string, causing bypass1 to switch on, and also enables bypass2 circuit ---> cap voltage continues to drop, current then stops flowing through LED string again, switches on bypass2, and enables bypass3 ---> and so on.
With that in mind, perhaps it could be implemented with BJTs? I also found an STMicro part, LBP01, that is a bypass switch for when an LED fails to open-circuit -- maybe that could be used, in conjunction with BJTs for the cascading/enable circuitry.
Any comments/suggestions greatly appreciated!
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