Hi,
I am making some modifications to a discrete isolated DC/DC converter that is part of a high volume project. Currently I have a 555 timer, feeding into a flip-flop with those outputs going to a break-before-make mosfet driver circuit then to the transformer.
I am trying to reduce the cost of this circuit and the two parts I plan on replacing are the 555 timer and the flip-flop.
I saw this app note from TI that contained a low cost circuit
http://focus.ti.com/lit/an/slyt371/slyt371.pdf
The one issue that I see here is how do I ensure a 50% duty cycle from the three-inverter oscillator. I have seen this oscillator before and it is usually attributed with that property but I don't see that happening unless the logic threshold is half of Vcc. Most of the datasheets I see on inverters give a wide range for the threshold.
So does anyone have any ideas for how to handle this issue?
Possibly either recommending an inverter that is better specified for this circuit or some modification to the circuit that makes it less sensitive to the logic threshold.
Thanks,
Dan
I am making some modifications to a discrete isolated DC/DC converter that is part of a high volume project. Currently I have a 555 timer, feeding into a flip-flop with those outputs going to a break-before-make mosfet driver circuit then to the transformer.
I am trying to reduce the cost of this circuit and the two parts I plan on replacing are the 555 timer and the flip-flop.
I saw this app note from TI that contained a low cost circuit
http://focus.ti.com/lit/an/slyt371/slyt371.pdf
The one issue that I see here is how do I ensure a 50% duty cycle from the three-inverter oscillator. I have seen this oscillator before and it is usually attributed with that property but I don't see that happening unless the logic threshold is half of Vcc. Most of the datasheets I see on inverters give a wide range for the threshold.
So does anyone have any ideas for how to handle this issue?
Possibly either recommending an inverter that is better specified for this circuit or some modification to the circuit that makes it less sensitive to the logic threshold.
Thanks,
Dan