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Electronics => Projects, Designs, and Technical Stuff => Topic started by: 22 on June 13, 2017, 02:01:56 pm

Title: HV9910C duty cycle
Post by: 22 on June 13, 2017, 02:01:56 pm

Here is a datasheet for HV9910C http://ww1.microchip.com/downloads/en/DeviceDoc/20005323A.pdf (http://ww1.microchip.com/downloads/en/DeviceDoc/20005323A.pdf).
Can anyone tell if that IC is capable of 100% duty cycle without any hidden limitations ? The ic will be working in constant off-time operation. I know there are similar IC from the same manufacturer, but they all have limit to 80-93% duty cycle. Thanks.

Title: Re: HV9910C duty cycle
Post by: RobK_NL on June 13, 2017, 07:34:06 pm

At least the original Supertex datasheet (from 2004!) states 100% as maximum dutycycle.

Title: Re: HV9910C duty cycle
Post by: MagicSmoker on June 13, 2017, 08:01:15 pm

Quote from: 22 on June 13, 2017, 02:01:56 pm

...
Can anyone tell if that IC is capable of 100% duty cycle without any hidden limitations ? The ic will be working in constant off-time operation.
...

I don't need to look at the datasheet to answer your question: no, you can't reach 100% duty cycle if there is a constant, non-zero off-time per switching cycle. That should be self-evident.

Title: Re: HV9910C duty cycle
Post by: RobK_NL on June 13, 2017, 08:16:25 pm

Quote from: MagicSmoker on June 13, 2017, 08:01:15 pm

you can't reach 100% duty cycle if there is a constant, non-zero off-time per switching cycle.

But if the current through the LED(s) does not reach the threshold value, there will be no switching cycle ...

Title: Re: HV9910C duty cycle
Post by: 22 on June 13, 2017, 10:55:57 pm

Quote from: RobK_NL on June 13, 2017, 07:34:06 pm

At least the original Supertex datasheet (from 2004!) states 100% as maximum dutycycle.

Thanks! :-+