Transisor serie ?

Thread Starter

FroceMaster

Joined Jan 28, 2012
556
Hi.
In my Construction i need to know if this is the way to do it or ?
When IC4 goes high the output should activate all 3 transistors, and the LED's
When IC3 goes high the output should only activate the T2 and T3 and the LED's
and When IC2 goes high output should only activate T3 and LED's
Question is now,
How many diodes do i need ?
D1+D2 ?
D1+D2+D5+D6+D7 ?
D3+D4+D5+D6+D7 ?
D3+D4 ?
 

crutschow

Joined Mar 14, 2008
24,045
The diode gating won't work because of the 0.7V drop across each diode when conducting.
I suggest using OR gates to do the logic as shown below.
You can also use 74HCT4075 OR gates if you like. All I had in my library were CD4000 types.

LED Logic.PNG
 

ScottWang

Joined Aug 23, 2012
6,859
Are you sure that you want to used the 74HC154 and npn bjt?
Normally when the 74HC154 has been selected then the output will be low, so the bjt driver should be using pnp.
 
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