Hello,
We are trying to measure the energy delivered to the 820uF capacitor connected to the output of our Offline Flyback SMPS when it charges this capacitor back up to 300V from 62V.
The capacitor is charged up to 300V, then the SMPS is turned OFF, then the xenon tube is flashed, then the capacitor (which discharges to 62V during the flash) is charged back up to 300V by the SMPS after the SMPS is turned back ON again. The flash rate is 1 Hertz.
Anyway, we first tried to measure the energy by capturing the capacitor voltage and the charge current on the scope over an entire charge interval from 62V to 300V. We then set up the math facility on the Wavesurfer MXs104 oscilloscope and took the integral of the instantaneous volt.current products from the start to the finish of a single recharge interval, then divided this by the recharge interval time (900ms) to get the average power over the recharge interval. The scope does this for you. We then divided this power reading by the recharge interval time in order to get the energy delivered to the capacitor in the recharge.
The problem is that this figure did not agree with the calculation which is done by simply subtracting the energy in the capacitor at 62V (0.5*C*62^2) from the energy in the capacitor at 300V (0.5*C*300^2).
In fact, the above two ways of doing the calculation differed by 6.5 Joules. The first method gave 49.5 Joules, and the second method gave 43 Joules.
The scope capture involved 16 Megasamples over the 900ms recharge interval…so that’s one sample every 56ns. However, the output current is very pulsey as it’s a high duty cycle flyback, and as such the flyback diode current is very low duty cycle……as such , I don’t feel there are enough samples being taken. However, our scope offers no more than 16 Megasamples.
We cannot afford a scope with more data memory so we wish to repeat the test with a 820uF film capacitor instead of an electrolytic just in case there was some “ESR situation” with the electrolytic one being recharged at such a low frequency (1Hz).
Do you know of vendors who cheaply sell such big film capacitors 350V and 820uF?
(incidentally the attached LTspice simulation shows how the circuit operates though doesnt have the same component values etc)
Electrolytic capacitor datasheet also attached
We are trying to measure the energy delivered to the 820uF capacitor connected to the output of our Offline Flyback SMPS when it charges this capacitor back up to 300V from 62V.
The capacitor is charged up to 300V, then the SMPS is turned OFF, then the xenon tube is flashed, then the capacitor (which discharges to 62V during the flash) is charged back up to 300V by the SMPS after the SMPS is turned back ON again. The flash rate is 1 Hertz.
Anyway, we first tried to measure the energy by capturing the capacitor voltage and the charge current on the scope over an entire charge interval from 62V to 300V. We then set up the math facility on the Wavesurfer MXs104 oscilloscope and took the integral of the instantaneous volt.current products from the start to the finish of a single recharge interval, then divided this by the recharge interval time (900ms) to get the average power over the recharge interval. The scope does this for you. We then divided this power reading by the recharge interval time in order to get the energy delivered to the capacitor in the recharge.
The problem is that this figure did not agree with the calculation which is done by simply subtracting the energy in the capacitor at 62V (0.5*C*62^2) from the energy in the capacitor at 300V (0.5*C*300^2).
In fact, the above two ways of doing the calculation differed by 6.5 Joules. The first method gave 49.5 Joules, and the second method gave 43 Joules.
The scope capture involved 16 Megasamples over the 900ms recharge interval…so that’s one sample every 56ns. However, the output current is very pulsey as it’s a high duty cycle flyback, and as such the flyback diode current is very low duty cycle……as such , I don’t feel there are enough samples being taken. However, our scope offers no more than 16 Megasamples.
We cannot afford a scope with more data memory so we wish to repeat the test with a 820uF film capacitor instead of an electrolytic just in case there was some “ESR situation” with the electrolytic one being recharged at such a low frequency (1Hz).
Do you know of vendors who cheaply sell such big film capacitors 350V and 820uF?
(incidentally the attached LTspice simulation shows how the circuit operates though doesnt have the same component values etc)
Electrolytic capacitor datasheet also attached
Attachments
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