Hello,
i am having an issue with the LM2623A stepup converter. The aim is to drive a magnetiv valve from two AA Alkaline cells. The valve has 33Ohm a current of 200mA is necessary, therfore a voltage of 6,6V is necessary. The circuit is als following:
Q1,R9 and D4 are only used for polarity protection, and C9 is needed for ESD.
The plot below shows the voltage and current during the valve On-Pulse. I power supply with 3.5A and 2.4V was used. The Red line is the voltage at TP41 and the blue one is the input cuurrent, measured with an 0.1R shunt. I tested dfferent capcitors insted of the 10pF, but without succes. Even a series resistor in this path does not improved the problem.
At the beginning of the 250ms Pulse the voltage is stable, but it collapses after 20ms. Also the current rises to 700mA and drops afterwards to 500mA. The LM2623A has a switching capability of 2A, but why breaks down the current/voltage allready by 700mA and decreases to 500mA? Is there any suggestion for a suitable capacitor or any other wrong designed component?
Thanks for your help and best regards
Martin
