Hey guys,
I started reflecting about PWM duty cycle and the RMS dump load value...
In Chris Greacen's design, the 555 is operated in monostable mode. Everytime the input is triggered LOW, there's a pulse of a fixed width coming out of the ouput. If a the end of the timing sequence the input is still LOW, the pulse still goes on, as long as the input doesn't go high. It is operated in inverse logic.
This makes it perfect for our shunt loads, because the whole dump load is being used during the time period, which could be compared to 100% duty cycle.
But, in my desire to reduce the number of parts, I decided to try a TL494 PWM shunt controller. I used OperaHouse's design. The problem so far is, the maximum duty cycle seems to be 50%. When it's operated in push-pull fashion, the maximum DC goes down to 25%. Suppose you have a 500W genny and a 500W dump load. If your genny is producing full power, your controller will only dump 25% of 500W if it's operated in push-pull mode, and your batteries will burst.
So I am starting to reconsider the 555 design, which can produce a 100% duty cycle, over other PWM IC's that simply can't.
Any comments, or additionnal reflections???
Thanks
Vincent