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I am interested in making an LED blink fast with a low duty cycle. To make the LED bright again (despite the low duty cycle), I thought I'd try to use some sort of charge pump to overdrive the LED. I'm hoping I can charge the capacitor while the LED is off, and place it in series with my voltage source when the LED is on.

Here's an example that doesn't work at all:

schematic

simulate this circuit – Schematic created using CircuitLab

(ignore the LED model, ignore the capacitor rating)

The circuit correctly charges the capacitor when the LED is off. However the capacitor needs to be reversed during the "on" part. Is there some way to accomplish this with minimal additional transistors/diodes? One way I can guess is to have a sort-of H-bridge around the capacitor, but I'm hoping for something simpler.

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As soon as Q3 becomes active C1 will charge such that the junction with Q3 collector and the lead will be close to 0V. Your circuit is not working as drawn because C1 has no discharge path. You do not state V+ volts but it is likely that you will zap your LED without any voltage boost. If look at the LED data sheet you will find the Peak Forward Current permitted is 90mA for 100uS at a duty cycle 1/10. Whilst the normal maximum running current is 30mA.

Now controlled 100nS pulses add to the complexity and maybe it will be more expedient to retain C1 to hold a controlled energy charge for pulsing the LED.

schematic

simulate this circuit – Schematic created using CircuitLab

This is only to give a guide of what mods your circuit needs need and as it is the first time I have used the schematic editor the semiconductors are what came up - whilst the C's and R's are about right for the LED shown. A usful formulae for capacitor stored energy is

P = CV^2/ 2T where P=watts; C=Farads; T=secs; V=volts

WARNING: strobe lights can induce Epilepsy. I was working with really high power oil cooled strobe lamps way back and at that time the danger range was 9 to 15 Hz. The main problem is that many people have latent epilepsy and once triggered it can more easily reoccur. See: http://www.windworksdesign.com/blog/strobe-light-induced-epilepsy/

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