I am driving an IR LED (LED914 and LED907) in series at 4.5 A for 2.5% duty cycle, In the 28 V I connect a DC supply and set the current to 150 mA, the idea is to continuously charge the capacitor C17. Based on the calculation $$Irms= 4.5A(.025) = 112.5 mA$$ but I gave 150 mA from the DC power supply \$(\frac{28 V}{0.15 A})\$ just to make sure the capacitor will be replenish I tried up to 500mA just to get 30 pulses which is way away on the calculation.
Channel 3 is the Voltage across the capacitor and channel2 is the voltage across the current sense (R28). As you can see the last 9 pulse voltage across the current sense is less than 0.450 mV, The IR LED \$Vf=4.6 V\$ (during this pulse),I supply 28 V/0.15 A on the capacitor C17 continuesly to charge the capacitor while discharging.
On bench the charge on the capacitor is getting drained. I checked the leakage on C17 and I am getting in \$µA (120 µA)\$, I am wondering why I cannot replenish the charge on the capacitor with the DC supply?