10 Stage Sequential Latch Switch Circuit

In this post we learn how to make a 10 step sequentially switching latch circuit which is used for switching ON 10 high power amplifiers sequentially. The idea was requested by Mr. Jerry B. Williams
The Request

GREETINGS!!! My circuit question will be more detailed than you really care to know about, but it is my wish for you to understand my entire application. Hopefully, you will be able to assist me here in my endeavor!!!
First…..I am – NOT – a circuit designer!!! I am a – BUILDER – of electronic equipment. You give me a schematic and I can design the PCB – and – the mechanical chassis the PCB will go into. However, I do have an understanding about all of the electronic components.
My circuit application — will be used to sequentially power-on the high-power audio power amplifiers used in sound-reinforcement systems for concerts in arenas and stadiums.
The amplifiers are mounted in 19″ racks and when AC-power is applied to the racks, instead of ALL of the amplifiers turning on simultaneously at the same time, I would like for the amplifiers to be turned-on sequentially with a time-delay. The amplifiers themselves will be controlled by a high-current solid-state relay (i.e. LED).
So, here is what I would like to obtain…..
A schematic of a sequential power-on circuit capable of driving 10 LED’s. Upon the circuit being powered-up with its DC voltage, there would be a 3 – 5 second delay for the circuit to stabilize and then the first “ON” pulse would be initiated to turn-on the first LED (which is actually inside the solid-state relay). – ALL – of the LED’s are to remain “ON” until eventually powered “OFF”!!!
After a 3-second delay, the second “ON” pulse is initiated and then it also remains “ON”.
After another 3-second delay, the third “ON” pulse is initiated and it also remains “ON” and the sequence continues until all 10 LED’s (solid-state relays) are turned-on and remain “ON” until eventually powered “OFF” after the concert is over and the audio racks are powered down to be loaded into their trucks.
As I mentioned earlier, the driven LED’s are actually the LED’s inside of a 25-Amp solid-state relay. The AC-load side of these solid-state relays will be wired to U.S. standard “wall-outlet plugs” on the rear panel of a rack-mount chassis which will be mounted to the rear of the amplifier racks.
I do understand already that the circuit will need its own DC power-supply and I am planning on designing a PCB for this circuitry and a small AC/DC power-supply module. Should you respond back to me directly with an e-mail, I could respond back to you with a photograph showing some of these audio racks. Each rack outputs 10,000 Watts of audio power!!!
I use either Altium or CADENCE/OrCAD for my schematics and PCB designs.
If you are unable to provide me with a circuit schematic designed to fulfill the requirement as I detailed above, then perhaps you can provide me the name of someone who can. However, as I read through your article above, you do seem to be quite capable in the design of timing circuits. THANKS!!!
One final comment…..this circuit – MUST – be ultra-reliable and – NOT – fail, as any type of “OFF” failure could very easily bring to an end a major concert by a world-famous artist, band and/or musician!!!
Jerry B. Williams

The Design

Circuit Description:

The requested design for a 10 step sequential latch switch circuit with adjustable delay is presented in the below shown diagram,  and can be understood with the help of the following explanation:

The circuit design employed here is basically a standard IC 4017 and IC 555 based chaser, wherein the IC 555 sends the clocks to pin#14 of the IC 4017 enabling its output to generate a sequential chasing output across its pin#3 to pin#11.
However as per the internal specification of the IC 4017 which is a 10 stage Johnson decade counter, register IC, the sequencing logic highs across its output pinouts shut-off sequentially as the logic jumps from one pinout to the other.
In order to ensure that the sequencing logic get latched across the pinouts, we introduce SCRs for triggering the external load.
SCRs as we know have the property of getting latched to DC switching in response to a single trigger to their gates, and we take the advantage of this characteristic of this device for acquiring the latched sequencing outputs from the 4017 pinouts.
As per the request the sequencing must freeze when all the 10 outputs are switched ON, we achieve this by linking pin#11 of the IC with pin#13, which ensures that the IC simply locks down itself as soon as the logic reaches the last pinout in the order: pin#11.
The delay time for the sequencing shifts can be set by adjusting the 100k pot associated with the IC 555.
This circuit fulfills the intended 10 step sequential switching latch circuit which is applied for amplifiers, nevertheless the design being too flexible can be customized for any other similar application need.

Parts List

All SCR gate resistors: 1K, 1/4 watt
All other resistors can also be 1/4 watt rated
All SCRs can be BT169, the mentioned C106 is not appropriate and must be ignored.
The SSR modules can be as per the user presfrence.

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  1. Swagatam:

    GREETINGS!!! I just came across your design for a "10-Step Latched Sequential Time-Delay Circuit" I have needed. THANK YOU SO MUCH for designing this circuit for me!!! You have > NO IDEA < on how much I sincerely appreciate your consideration and effort in designing this circuit!!! It really means a lot to me!!!

    I have read through your circuit description and with my limited knowledge of actual circuit design and functionality, I do have a basic understanding of what you have come up with schematically. As I had mentioned before, I can easily build your circuit into my application, I just cannot design it myself. THANKS!!!

    I do have 2 questions, however. First, is it possible for me to obtain a more visually clear image of your schematic? The image I see here on your website looks like it was drawn with a Crayon and I cannot determine what some items really are. Secondly, I understand that the 100K pot is used to set the time-delay period but, since I am only needing a 3-second delay with each output, can you provide me with a fixed resistor value to set that delay?

    And, finally.....since I cannot clearly see your schematic image, where is C106 in this schematic so I can eliminate it per your circuit description comment? And, I am assuming that I could use a 1K resistor-network on the 4017 outputs instead of individual resistors, right? THANKS!!!


    Jerry B. Williams


    1. You are most welcome Jerry, actually my site had moved to another platform a month ago, and quite a few articles along with the above were published during that time, but soon I had to return back to this blogger platform due to some technical difficulty....however in the process I lost all those articles which were published there.

      I had to retrieve each one from Google cache, but the images that I could get were small and therefore became blurry when zoomed in to their original level.

      The original diagram was actually perfectly clear, anyway I have tried to make the present one as distinct as I could, please check it out and see if you still have any concerning doubts.

      I have erased the C106 print from the diagram that's why you can't see it now.....C106 are meant for bigger loads, therefore BT169 look more appropriate here since these will be only used to trigger the low current LEDs of the SSR.

      You can use 1K resistors in any form as long as they are in series with each of the SCR gates.

      And i forgot to put resistors in series with the SSR LEDs, which is very important otherwise it could get damaged easily. you can use 1K for this.

      determining fixed resistors could be a bit time consuming, if possible please try the following software, and work with the second section of the article, with some trial and error you would be able to find the appropriate values for the the resistors.

      If you still have problems let me know I'll try to help you out

    2. OK I tried the software, and according to it for approximate 3 sec ON/OFF the upper 100K resistor needs to be 2k2, the 100K could be replaced with a 44K and the capacitor could be a 100uF/25V

  2. Swagatam:

    Once again I sincerely "THANK YOU!!" so much for your effort, time and consideration in assisting me with my timing circuit assistance. I do appreciate your help so very much!!!

    To show you my appreciation, if you use the following link, you can download a FREE version of the "OrCAD Capture" schematics program that was given to me by CADENCE/OrCAD themselves and they had both asked me and allowed me to share this software with others who could use this software to their benefit. And, I very strongly believe that - YOU - are one person that could benefit from using this software very much!!! Here is the link:

    Now....back to your circuit....first off, commercially available SSR's do NOT need an external current-limiting resistor in order to safely operate. The SSR's themselves have this resistor built into the device as standard. All the end-user needs to do is hook up the DC-voltage and you're "Good to go"!!! I have been using SSR's for over 30-years and have YET to ever have to use an external resistor on the DC-input side of one of these devices. But, I do appreciate your thought and concern!!!

    I "THANK YOU!!" for the updated resistor and capacitor values in setting the circuit for a 3-second delay. That's great!!! But, I do wish there was some manner in which I could upload a PDF file of my re-creating your schematic to confirm that what I have done is correct or not. All I can think of doing is to upload it to a storage site that I have and then again provide you with a link so you can download it. Is there some other way to do this?

    In addition, I "might" decide to use 40-Amp Triacs instead of the SSR's and I would like to send you the datasheet of the triac I am contemplating to use so you can determine if the BT169's or any of the other circuitry needs to be changed to accommodate the use of the triacs. Again, is there any way to send you datasheet PDF files? Or, do I just upload my information to a folder on my online storage site and provide you with a link so you can download these files? Let me know, OK?

    In case it is not showing up to you here in these replies, my e-mail address is:

    I have a PDF file of your schematic that I have recreated using my schematic software and a PDF file of the triac device I would like to "maybe" use instead of the SSR's. The triacs cost about half of what the SSR's cost. And, with my project using 10 of these "high-current AC switches", that ends up being a lot of money potentially saved!!! But, maybe you know of a reason on why using triacs would NOT be a good idea and you can tell me that.

    "THANK YOU!!" again for your kind assistance!!! THANKS!!!

    Jerry B. Williams


    1. Thank you Jerry, and I very much appreciate the free orcad link that you have provided here, I am sure the folks visiting this page will be hugely benefited by this.

      Although I use CorelDraw for all my schematic drawings and I find it extremely comfortable, I would surely want to try this orcad software as an alternative platform.

      Yes, SSRs are self contained and do not require external limiting resistor, since I am more used to with opto couplers which depend on external resistor (as far as I know), I seem to have mistakenly confused the two counterparts while commenting above.

      Yes, the best way to send the files is by storing them in some external site or possibly in your Google drive account and provide the link here. If you send a Google drive link then please make sure to toggle the "share" option so that I have the permission to open it.

      I have alredy discussed the datasheet of a 40 amp triac in this website, you can refer to it in the following link:

      This triac can be used in the above circuit, however you will need to add a current amplifier BJT stage to trigger them since they require a good 50mA to switch ON, which the IC alone would be incapable of supplying.

      Instead of a BJT driver stage, I would recommend using an opto coupler stage which would additionally facilitate a complete isolation of the DC circuit from the triac AC stage, to be more precise an opto triac driver would ideally suit this application. For more info you can refer to its datasheet here

      In the meantime if you wish you can send the schematic pdf file through any preferred option, I will check it out and let you know if there are any issues in it.

      Thanks for posting, and Keep up the good work.


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