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  1. #41
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    Re: Why Does The NTE5465 SCR In My Circuit Remain Closed, Even With No Current?

    Unfortunately the reported results aren't plausible unless there's a remaining load keeping the SCR in triggered state. I see little chance to debug the design from a distance.

    - - - Updated - - -

    I worked with flash bulbs as a school boy. If I remember right, the flash units often used a capacitor to store the ignition energy. Respectively the battery could be made much smaller. I presume you can design a capacitor based SCR ignitor that automatically releases the hold state by making the capacitor charge current low enough.



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    Re: Why Does The NTE5465 SCR In My Circuit Remain Closed, Even With No Current?

    Thanks FvM!

    This is what I have run into everywhere I turn with this issue. I have worked in my spare time for many months, on many different circuit designs, none successfully. I am just a photographer that is trying to achieve a goal. I even hired an actual electrical engineer. Paid him money. After many designs, even he gave up.

    I will study the capacitor based SCR trigger approach. I will also work on Barry's design with the 555 timer. Maybe something can be achieved there.

    Thinking as a non-engineer. I could actually place a couple of simple manual on/off switches into this circuit, as I know things do work as desired for one shot. It would just involve a long tedious process of steps between each photograph to accomplish.
    a) Install a bulb in flash & take first photograph
    b) Remove spent bulb (This breaks the flash circuit)
    c) Flip a switch to break the breadboard circuit between the trigger side battery and Pin 1 of the MOS
    d) Flip another switch to break the breadboard circuit between the flash side circuit resistor and Pin 6 of the MOS
    e) Reinstall a new flash bulb into the flash
    f) Flip both switches back on & ready for the next shot

    Thank you all for your help. I will likely still ask questions on specifics as I have them. Thanks again.



    •   Alt13th January 2018, 16:22

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  3. #43
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    Re: Why Does The NTE5465 SCR In My Circuit Remain Closed, Even With No Current?

    Quote Originally Posted by btvarner View Post
    Thanks FvM!

    This is what I have run into everywhere I turn with this issue. I have worked in my spare time for many months, on many different circuit designs, none successfully. I am just a photographer that is trying to achieve a goal. I even hired an actual electrical engineer. Paid him money. After many designs, even he gave up.

    I will study the capacitor based SCR trigger approach. I will also work on Barry's design with the 555 timer. Maybe something can be achieved there.

    Thinking as a non-engineer. I could actually place a couple of simple manual on/off switches into this circuit, as I know things do work as desired for one shot. It would just involve a long tedious process of steps between each photograph to accomplish.
    a) Install a bulb in flash & take first photograph
    b) Remove spent bulb (This breaks the flash circuit)
    c) Flip a switch to break the breadboard circuit between the trigger side battery and Pin 1 of the MOS
    d) Flip another switch to break the breadboard circuit between the flash side circuit resistor and Pin 6 of the MOS
    e) Reinstall a new flash bulb into the flash
    f) Flip both switches back on & ready for the next shot

    Thank you all for your help. I will likely still ask questions on specifics as I have them. Thanks again.
    Sounds like you hired a pretty poor EE.



  4. #44
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    Re: Why Does The NTE5465 SCR In My Circuit Remain Closed, Even With No Current?

    Is it possible battery contact exceeds 100V/us or 3V/30ns? Maybe a small cap across Gate-Cathode of SCR?
    A good design question lists your overall requirements™ The best question deserves a better answer. ™
    ... Tony Stewart EE since 1975



  5. #45
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    Re: Why Does The NTE5465 SCR In My Circuit Remain Closed, Even With No Current?

    OK - it is possible that leakage thru the isolated mos switch is responsible, you need a gate to source resistor (say 1k) and possibly a 100nF caps G-S also, to keep the gate below 2V for applied step voltages - unless you are trying to fire it - whereupon you provide a longer pulse.

    - - - Updated - - -

    As to the SCR, when you put a new one in you are putting a step voltage on the device and it is self triggering, this is not uncommon for sensitive gate SCR's, usual cure is again a resistor, 100 ohm in this case say, and a 470nF cap from gate to cathode(k) ,assuming cathode gate SCR which almost all are these days, this will stop the SCR turning on when the battery is applied, or a new bulb, and should give you the operation you initially desired.

    We use SCR's ( the TYN640 ) for firing large DC pulses for ignitor circuits for un-exploded munitions detonation, with a peak firing voltage of 420VDC and peak currents of 250A - all in a TO220 package
    Last edited by Easy peasy; 14th January 2018 at 02:22.



    •   Alt14th January 2018, 02:07

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  6. #46
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    Re: Why Does The NTE5465 SCR In My Circuit Remain Closed, Even With No Current?

    Hi All,
    I have given up on this effort for now. Sorry if this post is not appropriate. I would like to hire another electrical engineer but only locally this time. I live in the Kansas City Metro area. I think it is best to be someone that I can physically see and that can physically handle the flash. I have two other requirements that I am sure will eliminate almost, if not everyone. 1) I will not pay another dollar to anyone until a successful prototype is provided. 2) The finished product is for my personal use as an individual hobbyist, so I cannot just hire a firm to attempt a solution for large sums of money. Just hoping that somewhere out there, someone might find this task interesting.

    I can be contacted via my website: http://BruceVarner.com/ Thanks again for everyone's input and help!



    •   Alt18th January 2018, 21:42

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