cmos 4013 not working with load

[Sharagim]

Hi,
I have a cmos 4013 as schematic attached and trying turn on and off a lm2576 by enable pin.
When I use this circuit and test with voltmeter I see it is working properly but when I connect it to lm2576 I see nothing change.
Seems not working with load on out I tried to drive to use a pnp transistor but again same with voltmeter it is ok but with lm2576 enable pin nothing.

 

[E-design]

You have very long time constants on pin 3, which I am sure you don't need. Specs of the 4013 states clock should have rise-time of 5uS or faster for reliable operation. Put a 4093 schmitt trigger in to speed up the edges to pin 3.

 

[Sharagim]

By changing cap 1uf to 150nf problem seems to be solved but yet it is not clear for me why this circuit not working with load and was ok with voltmeter.

 

[FvM]

CD4013 has a maximum risetime specification for clock input which will be never achieved by this circuit. Thus reliable operation can't be guaranteed.

A special problem is capacitor discharge through pushbutton without series resistor. It will result in short button lifetime and oscillating waveforms.

 

[Sharagim]

Could you please let me know why it cant be guaranteed.
Is there any specific changes which help me?
do you know/have any other good schematic for using ?

 

[ftsolutions]

Look to the datasheet for part CD4013 - depending upon what Vcc voltage you are running it at, the clock edge must be less than 15microsecond rise time @5V Vcc, and less than 5 microsecond @15V Vcc. Observe the RC time constant of your switch debounce circuit and calculate the rise time/fall time. Is it well under 5 microseconds (and only 1 time-constant is still only 67% of the way)?
You can try to select different R, C values to provide some debounce but must meet the spec sheet timing or the output may not transition because the clocking edge is too slow to drive the circuit to output. Also, you should have at least some smaller R in series with the switch to limit the current from discharging the capacitor(s) - otherwise the charged caps are being shorted direct to ground through the switch and things won't last long, as FvM points out. Even ~100 ohms would be beneficial for that.