Film-Tech Forum ARCHIVE: How much ripple is acceptable from a switcher?

This is topic How much ripple is acceptable from a switcher? in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Eric Robinson (Member # 2966) on 08-08-2006, 05:25 PM:

Due to a complaint about short bulb life in a particular projector, I decided to measure the DC output of the switching power supply for any AC ripple.

The switcher is a Strong - 6280005 3000 to 5000 watt

When the bulb is running the DC power is 25VDC
Using a scope I measured the power out at 2.5 VAC peak to peak

This seems like an awfully high value for AC. Did I perform the measurement correctly by measuring the voltage output right at the switchers terminals while the bulb was running? Should I perhaps use a DVM set to AC to measure AC ripple?

Posted by Mark Gulbrandsen (Member # 72) on 08-08-2006, 07:58 PM:

quote: Eric Robinson
Using a scope I measured the power out at 2.5 VAC peak to peak

At what frequency was this ripple? Normally with any type of swtcher the ripple is so high of frequency >35khz as to be invisible to the lamp itself. This hf ripple is one of the main advantages of switchers. Your 2.5 volt level is ery low too. One can also control the inrush current alot better than on a brute force boat anchor type rectifier. In a strong switcher it is impossible to get any LF ripple through just by the nature of its design.

I would check for possible excessive inrush current(unlikley though) and for at least 1200 cfm exhaust at the stack with the doors shut and the dowser open assuming a 3kw lamp.

Mark

Posted by Eric Robinson (Member # 2966) on 08-09-2006, 12:51 AM:

I knew I should have measured the frequency. [Roll Eyes]

The cfms measure about 600 and I think it is a 3K bulb. I'll never get more cfms though, this is the nature of this business.

I am curious about the method for measuring inrush current though. Perhaps you could point me to some resources to learn about the inrush current spec for xenon bulbs and the measurement technique.

Posted by Monte L Fullmer (Member # 2797) on 08-09-2006, 01:07 AM:

Isn't the 628000 series the old black "large Suitcase" switcher?

Posted by Mark Gulbrandsen (Member # 72) on 08-09-2006, 08:17 AM:

Thats not enough air flow for a 3K... only about half enough. Check with your lamp manufacturer to find out his maximum allowable inrush spec. Note that you need a peak and hold DC amprobe or a storage oscilloscope and standard current shunt to measure it across...

Mark