step up DC/DC and start up

[merco]

In my last project i did this step up

http://i43.tinypic.com/30su9tw.jpg

Ok IC8 isn't needed, but can't change the Jpg now...

I put an on/off button before SL1.
The positive rail (from batteries) is connected directly to the
positive SL1 (+) , and the negative rail is connected to the button
and then to the (-) batteries.

I see that often (always) is difficult to let the circuit start (my 90
led's bingo with internal speaker :lol: )

After a lot of on/off swithces , randomly, the circuit start working.

I notice that if i detach and reattach the SL1 connector from the
batteries, the circuit starts better.

Why ?
Must I use a different button ?
Something wrong in the design ?
Too much current request at startup ?

Thank you

 

[tomrei]

In my last project i did this step up

http://i43.tinypic.com/30su9tw.jpg

Ok IC8 isn't needed, but can't change the Jpg now...

I put an on/off button before SL1.
The positive rail (from batteries) is connected directly to the
positive SL1 (+) , and the negative rail is connected to the button
and then to the (-) batteries.

I see that often (always) is difficult to let the circuit start (my 90
led's bingo with internal speaker :lol: )

After a lot of on/off swithces , randomly, the circuit start working.

I notice that if i detach and reattach the SL1 connector from the
batteries, the circuit starts better.

Why ?
Must I use a different button ?
Something wrong in the design ?
Too much current request at startup ?

Thank you

A, why don't you use the shutdown pin on the Max756,
B, why did you connect the Feedback pin to ground???!!!

if you still need help,
tell me about the input voltage output voltage, and load current,
output ripple, load step (if you know them) and i may come up with a
solution for you.

yours Ren

 

[merco]

A, why don't you use the shutdown pin on the Max756,
B, why did you connect the Feedback pin to ground???!!!

if you still need help,
tell me about the input voltage output voltage, and load current,
output ripple, load step (if you know them)  and i may come up with a
solution for you.

yours Ren

A=> i don't know,How can i use It?
B=> i don't know, i have seen a lot of schematic like that on the net.

I had to use Max756, because i have a lot of it.
Input voltage are 3 Ni-Mh cells, current max (with all leds and
speaker on <=250mA),
output ripple very low (i use it to supply a PIC)

 

[merco]

If you're power leads are long and skinny then maybe too much inductance.
I've had PICs that didn't want to start with long power leads.  Connecta
cap across the power leads (near the switch) so that it is charged all the
time.

I'm sorry, but before (near batteries) or after the switch ?