How to turn on/off a MC34063 dc/dc step-down converter

[guest2003]

mc34063-app-note.pdf

Hi all,

Any idea how to implement a control to turn on/off a MC34063 DC/DC converter ??

I want to do this without adding extra active parts...

thanks

 

[flatulent]

mc34063 dc/dc

The application note **broken link removed** shows that the nodes that would do this do not come to the outside world. Your next best thing is to make it think that the output voltage is too high by summing in another voltage at the comparator pin 5 through another resistor from a logic gate output.

Then you get rid of the other resistor to ground and have a voltage divider with the switcher output connected through a resistor to the pin 5 and the logic gate connected to a resistor to pin 5. Size them so that when the logic gate is low you get the right switcher output and when the logic gate is high, you will get more that 1.25V at pin 5 even if the supply output is zero.

You may have to have a resistor from pin 5 to ground so that the voltage at pin 5 is not high enough to damage the part. Two simultaneous equations and fixing the value of the resistor from output to pin 5 should yield the other two values.

 

[Nicholas Lindan]

Re: mc34063-app-note.pdf

Any idea how to implement a control to turn on/off a MC34063 DC/DC converter ??

Try using an NCP3064 instead. It replaces the DRV pin with an enable control.

You can also control the '63 by robbing/grounding the DRV pin - this would remove collector current from the darlington driver.