E-design
Advanced Member level 5
In his EEVblog, Dave designed a soft on/off switching circuit using a few discrete transistors.
It can be viewed via the link below.
https://www.youtube.com/watch?feature=player_embedded&v=Foc9R0dC2iI
While watching the video last night I wondered if it can be made even simpler.
After some thought I came up with the circuit in the attachment, using two transistors instead of 3.
This uses only 2 transistors and the state is off at the moment power is applied.
I also include the Multisim file if you want to experiment and play with the design values.
For some or other reason the circuit won't simulate well in Proteus.
I found it actually works the best with R1 = 100k when tested with a real circuit.
The design needs some minimum load (1-10k) to work reliably. You also need to wait about 1 sec between key presses to change states.
My breadboard circuit used a IRFI9634G that I had handy. Not sure if it will work with all other P types.
Circuit tested down to around 4V. Might need some tweaking to work below 4V.
**After I made my circuit I stumbled onto another design later on Dave's blog very similar to mine using another MOS device instead of the bipolar in my design.
**broken link removed**
It can be viewed via the link below.
https://www.youtube.com/watch?feature=player_embedded&v=Foc9R0dC2iI
While watching the video last night I wondered if it can be made even simpler.
After some thought I came up with the circuit in the attachment, using two transistors instead of 3.
This uses only 2 transistors and the state is off at the moment power is applied.
I also include the Multisim file if you want to experiment and play with the design values.
For some or other reason the circuit won't simulate well in Proteus.
I found it actually works the best with R1 = 100k when tested with a real circuit.
The design needs some minimum load (1-10k) to work reliably. You also need to wait about 1 sec between key presses to change states.
My breadboard circuit used a IRFI9634G that I had handy. Not sure if it will work with all other P types.
Circuit tested down to around 4V. Might need some tweaking to work below 4V.
**After I made my circuit I stumbled onto another design later on Dave's blog very similar to mine using another MOS device instead of the bipolar in my design.
**broken link removed**
Attachments
Last edited:
