Alternate Circuits

Discussion in 'The Projects Forum' started by OmarAlMansoori, Oct 13, 2014.

1. OmarAlMansoori Thread Starter New Member

Oct 13, 2014
11
0
Hello!
I'm new to this forum and I'm fairly new to the world behind the world of electronics. I am at the most a beginner, I only have high-school based knowledge around creating circuits so bare with me.

I'll get to the point. My project revolves around two circuits, and I'm having some technical issues.
They are two circuits, one of which is a normal series circuit with a normal (single) load that looks like this (Child's play, I know).

I don't really know how to describe the second circuit, lets just say it looks something like this:

(BTW, I'm using iCircuit on mac, I have no idea how effective it is, the current amounts are always petty)

Here's My problem:
Let's call the first series circuit (Circuit A) and the second one -in the image- (Circuit B)
I want it to work so that as soon as circuit B is closed, that is the second part of it, (when the SCR is allowing current to flow from the Anode to the Cathode), Circuit A is cut and stops, and the load is no longer functioning. I thought about using a PNP transistor but I think that that won't work like I need it to.
I also wanted Circuit B to only work as long as circuit A is closed, I have considered using a NPN transistor, however I haven't a clue how to let the current reach it.
When I try putting the NPN on that activation part of circuit B around where the 300 resistor is, it just renders the whole circuit inoperable.
When I try putting a PNP transistor onto Circuit A it just ends up cutting the circuit.

Please help, I have limited knowledge beyond basic series and parallel circuits.
Keep in my mind that my circuit has to be DC as I intend on using a battery to power it.
Also, I'd rather not get into technicalities beyond connecting circuits like programming and such (if such a way exists) as that will create a ton more of complications for me.

Many Thanks!

Note: I'm not sure if "Alternate circuits" was a good name at all, I now realise that anyone can simply think I'm mistaking Alternating Current.

Last edited: Oct 13, 2014
2. Alec_t Expert

Sep 17, 2013
10,267
2,511
Those two requirements seem to conflict. I'm unsure what you are aiming at .

3. ScottWang Moderator

Aug 23, 2012
6,770
1,047
The SCR is a trigger component, the g is a trigger and only can be start(active) but it can't stop the SCR, unless you cutoff the A or K(cathode), so is this what you want?

Last edited: Oct 13, 2014
4. OmarAlMansoori Thread Starter New Member

Oct 13, 2014
11
0
They don't conflict as long as the part that circuit A is activating is the top part of circuit B and once enough current has the reached the gate, the circuit can continue as normal until it is stopped by the second switch from the left

5. OmarAlMansoori Thread Starter New Member

Oct 13, 2014
11
0
I guess that you can say that circuit A is like an activation circuit and once circuit B is active, Circuit A is no longer required

6. MrChips Moderator

Oct 2, 2009
19,132
6,148
You cannot hope to successfully assemble circuits using NPN, PNP transistors and SCRs without knowing the fundamentals of such devices.

SCRs will not turn off by themselves in DC circuits.

Read up on how transistors work:

http://www.allaboutcircuits.com/vol_3/chpt_4/1.html

7. OmarAlMansoori Thread Starter New Member

Oct 13, 2014
11
0
The SCR isn't what I'm trying to turn off, what I want is that as soon as the SCR is working circuit A should turn off as it is no longer required (because the SCR is working)

8. OmarAlMansoori Thread Starter New Member

Oct 13, 2014
11
0
I want it to be so that as long as the SCR is conducting from the anode to the cathode, circuit A doesn't work. Imagine as if circuit A is activating the top part of circuit B (giving the gate the required current) and as soon as that's done, circuit A is no longer required.

9. ScottWang Moderator

Aug 23, 2012
6,770
1,047
If every is match what you want, then the next are to calculate the value of Rg and Rk(resistor in series with cathode) for the Load if you need it.

So what you want as to turn on the key in K, and turn on the key in G, and the lamp or Load will be activated, and you turn off the key in G, if do so, why not just using a switch to turn off/on the load, any reason why not doing that?

10. OmarAlMansoori Thread Starter New Member

Oct 13, 2014
11
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So it is a more automated circuit, the less switches I have to manually toggle, the better.

11. Alec_t Expert

Sep 17, 2013
10,267
2,511
Something like this?

Last edited: Oct 14, 2014
OmarAlMansoori likes this.
12. OmarAlMansoori Thread Starter New Member

Oct 13, 2014
11
0
Thanks for your time!
This circuit is a real beauty! After looking at it and tracing it I thought that it should work, however iCircuit disagrees.
I think it's the software since this isn't the first time I've had issues with circuits using an SCR. (It could be that I don't know how to use the program.)
I really appreciate your time and response, I'd really appreciate a recommendation regarding simulation software (I'm using mac btw).
Many Thanks!

13. Alec_t Expert

Sep 17, 2013
10,267
2,511
In iCircuit you could try disabling one of CctA or CctB and check that the other works.
The simulation works fine in LTspice, a free download from Linear Technology. The SCR model I used is in one of the free libraries from the Yahoo LTspice User Group.
Here's the sim file

• AlternateCircuits.asc
File size:
1.5 KB
Views:
14
Last edited: Oct 14, 2014
14. OmarAlMansoori Thread Starter New Member

Oct 13, 2014
11
0
Sounds good, I'll check it out. However I do feel like I should have described my project a bit more in detail I'll see what I end up with and post an update.
Thanks!

15. OmarAlMansoori Thread Starter New Member

Oct 13, 2014
11
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I think I've completed it, this is almost exactly what I'm aiming for, Thanks!!
(note: the LED's are IR LED's and the switch after the buzzer is the receiver, I guess I should've mentioned that earlier)

Last edited: Oct 14, 2014