• hshah8970

MemberSep 17, 2011

Hello everybody!

I'm working on a project and am facing a problem I simply cannot solve. I'm unable to design the electronic circuit that accomplishes the following task:

I want to couple 2 DC inputs in such a way that when Input 2 reaches certain voltage level (from zero), both inputs become connected in series. Before this threshold voltage level is reached by Input 2, we simply get Input 1 at the output. Check out #-Link-Snipped-# to see what I mean: #-Link-Snipped-#

For voltage values of DC Input 2 higher than the threshold voltage, the series combination is maintained.

I would highly appreciate it if somebody helped me out with this! Thanks! And an explanation to go along the circuit would be nice too. Again, thanks a lot to anybody who responds!
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Replies
• MemberSep 18, 2011

hshah8970
Hello everybody!

I want to couple 2 DC inputs in such a way that when Input 2 reaches certain voltage level (from zero), both inputs become connected in series. Before this threshold voltage level is reached by Input 2, we simply get Input 1 at the output. Check out #-Link-Snipped-# to see what I mean: #-Link-Snipped-#

For voltage values of DC Input 2 higher than the threshold voltage, the series combination is maintained.
Why not connect source 2 in series with source 1 isolating S2 from S1 by a relay using NC contacts. Using a Zener and a transistor switch the relay using S2 at the desired voltage. Wire the NO contacts of the relay to put S2 In series.
If S2 < set voltage, relay bypasses S2 and only S1 operates. When S2 reaches set voltage S2 switches on the relay and the NO contacts puts S2 in series.
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• MemberSep 18, 2011

I'm a student a quite weak in electronics! I haven't dealt with relays before but I'm getting an idea of what you're saying. A rough schematic though would be immensely appreciated! Also, could you elaborate on the zener and transistor connections as control for the relay?
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• MemberSep 18, 2011

hshah8970

I'm a student a quite weak in electronics! I haven't dealt with relays before but I'm getting an idea of what you're saying. A rough schematic though would be immensely appreciated! Also, could you elaborate on the zener and transistor connections as control for the relay?
What is the voltage at which you need to put Input 2 into circuit? The choice of the Zener depends on this value.
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• MemberSep 18, 2011

@bioramani: Let's say that Input 1 will be operating at 12V and Input 2 will be included when it reaches 5V.
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• MemberSep 19, 2011

Your circuit is the equivalent of: If V2<V(threshold), then Output = V1, Else Output = V1 + V2.

I feel that this circuit will do the job. You may have to add a 3V Zener in series with the base resistor if you want accuracy. The circuit here uses the base-emitter forward drop to adjust the potentiometer for switching the transistor.