# UJT firing circuits for SCR

Is it possible to replicate a random pattern of trigger and charge times to an UJT firing circuit for an SCR configuration?

What I mean is that, UJTs usually have a periodic sequence to them. Charging and discharging of the capacitor connected between its E and B1 terminals occurs in a periodic fashion. Now, say the power supply is about 5V and I assigned this the binary value 1 and the binary value 0 to 0V. Since charging and discharging happens in a regular periodic fashion say, 1001001001... Is there a way that a UJT firing circuit can be configured in order for the charging and discharging to occur in say an irregular un-smooth fashion like 0010110011110?

Here's a website that describes how a UJT firing scheme works: http://www.electronics-tutorials.ws/power/unijunction-transistor.html As you can see, the $$V_{R2}$$ waveform is regular and periodic. What I'm asking is if it's possible to redesign this circuit: so that it can produce an irregular waveform. Assuming that the high values of$$V_{R2}$$ and $$V_{ON}$$ are 1 and the low values $$V_{R2}=0$$ and $$V_{OFF}$$ are 0. Then can a circuit be designed to produce a firing scheme such as 0010110011110 that repeats itself instead of 1001001001 that repeats after every 100?? So that if you zoom the waveform out, then you can see that repeating pattern though it's not as smooth and nice as the regular 100100100 sequence.

• It is not clear what you are asking. Please provide a schematic (there's a button on the editor toolbar) and explain what you are trying to achieve. e.g., "I want to create a random interval lamp flasher using a random binary data stream of 13.7 bits per second. The power supply is xxx V, the load is an xxxx and the SCR would be something similar to XXyyy." – Transistor Aug 8 '16 at 19:44
• Hey i've changed it can you try to answer? – pkjag Aug 10 '16 at 9:14

No. Since there are no random components in that circuit and it is fed from a constant DC supply it should perform exactly the same on each cycle.

If you want random firing you need to introduce some further circuit elements. Given that you're probably looking for low frequencies you could use a small micro or a pseudo-random sequence generator. Figure 1. From Clabacchio's answer to https://electronics.stackexchange.com/questions/30521/random-bit-sequence-using-verilog.

• Remember to preload the circuit at start-up; all zeros is a state from which this circuit cannot recover. – Peter Smith Aug 10 '16 at 13:17
• Thanks for answering, but i don't want a truly random firing sequence, just a sequence that isn't truly periodic, can this digitial circuit be programmed to achieve this? – pkjag Aug 11 '16 at 12:30
• That's not what your question says. "... can a circuit be designed to produce a random un-periodic firing scheme ...". You need to edit your question and explain what you really want. – Transistor Aug 11 '16 at 12:52
• Basically what i'm asking is if you can program the circuit to fire in whatever order you want to. Can any sequence of this charging and discharging be replicated, that is with repeating pattern, say 1011 1011 1011 1011, or 011 011 011, instead of the regular clock like sequence 101010101? – pkjag Aug 11 '16 at 13:38
• Sure. Once you use a micro you can program it to do whatever you like. – Transistor Aug 11 '16 at 14:10