Position of switching transistor

[debasisswan]

Hi friends,

As a novice in the field, I need your help.

I am preparing a timer to switch a load of around 24W/ 12V DC. My objective is to have a switching frequency of 1Hz with variable up/down ratio. I have got a suggested schematic that suits my need (Attached with this post).

May I change the position of TIP 122 in the manner I have drawn as alternative?

Actually I want the load to have a common negative for the ease of assembly.

Please suggest

Debasisswan

[debasisswan]

Hi,
It was my fault to configure TIP 122 (NPN transistor) in a way to have its collector attached to + v. After realizing that, I have solved the problem by using a PNP one, TIP127. The flasher is now working. Only difference is, instead of UP position of the output cycle of 555, the DOWN position of the 555 output cycle is being used to put the load to ON. But it is serving my purpose.
Thanks and regards to all-
Debasis

[I_Daniel]

The point to remember is a darlington transistor inverts the output. If you used an "ordinary" transistor the original position would have worked fine.