I’m looking for a specific LED driver or circuit…
Main requirements are:
7Vdc Input voltage max
1A LED current minimum
15Vdc Output Voltage minimum
IMPORTANT:
ON / OFF LED control by external pin with to limitations and fast response.
Need to be able to generate fast current pulses in the 10 us range.
Need to be able to have very small pulse time increments (in the nanoseconds range)
So all the LED Drivers with PWM pin that reshapes the PWM signal cannot be used.
I will use an external PWM designed in an FPGA to generate output pulses.
Thanks !
Greetings,
Making 10us pulses requires control bandwidths in 100 kHz territory, which is on the fast side for most LED drive ICs. Typically, people interested in such things resort to using some sort of linear method, in conjunction with a switch-mode converter to do any bulk voltage transformation necessary.
I’d suggest using a DC-DC converter of one’s choice to perform the boost from <7V to >15V, and an op amp driving a suitable NPN BJT as a low-side switch for modulation. Something along the lines of the below, for reference. Scale the DC-DC’s output to keep the BJT just out of saturation for minimal power dissipation and decent response, and pick an op amp that’s content with common-mode inputs and outputs near the negative rail; most of the newer single-supply types designed for low-voltage operation should fit the bill.
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Hi,
Thanks for the reply…
I have seen some articles with a similar approach.
However, the transistor was used to “short” the LED string.
I guess when you have a constant current source, it is not the best (or event possible) to open/close the loop at a fast pace.
The inconvenient is that there is more power consumption overall.
The “shorting” approach referenced is also a feasible and valid option; if a CC source is already available and arbitrary waveforms are not needed, there’s a lot to recommend it.
