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I have one trigger which is a 200 ns pulse and a clock with 12.5 ns width and 50% duty cycle.

I have made 8 pulse each 5 V and 12.5 ns width.

I need to turn each LED for each of my pulse so when first pulse comes the first LED turns on and the second LED will turn on when the second pulse comes but the first LED will remain on.

I want to use some transistor but I cant make it works. i can use FF but not IC.

edit: i need to turn on the leds each at time and make them stay on until at any time i get new trigger and then they will turn off and will turn on each at time again. i just need take my 8 pulses and every pulse will turn on one led at time and keep them works until next trigger. in the question they said transistor can help. i know FF can be usefull here. Timing diagram.

 _ _ _ _ _ _ _ _ _ _ _ Pulse ___| |_| |_| |_| |_| |_| |_| |_| |_____.....__| |_| |_| |... __________________________________________ ________ LED 0 ___| |_| ... ______________________________________ ____... LED 1 _______| |_____| __________________________________ ... LED 2 ___________| |__________|
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    \$\begingroup\$ A timing diagram is better than a lot of words. Please check my edits. How do you want to turn off your LEDs? \$\endgroup\$ Commented Mar 14, 2020 at 21:02
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    \$\begingroup\$ actually i dont must to turn them off but if you have any easy idea i can use it will help. \$\endgroup\$ Commented Mar 14, 2020 at 21:11
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    \$\begingroup\$ why do you need to turn on the LEDs sequentially? \$\endgroup\$ Commented Mar 14, 2020 at 22:04
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    \$\begingroup\$ Unless you’ve special LEDS or aggressive drive and wiring, the LED on time is going to be around 50 ns. electronics.stackexchange.com/questions/86717/…. It would help your question if you said a few words about why you want this circuit to really do. \$\endgroup\$ Commented Mar 15, 2020 at 13:42
  • \$\begingroup\$ Is it possible that ns should be ms? If this is to be seen by humans then ms is a million times more likely. \$\endgroup\$ Commented Mar 15, 2020 at 17:41

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schematic

simulate this circuit – Schematic created using CircuitLab

Figure 1. A shift-register made with 'D' flip-flops.

How it works:

  • Every time the clock goes high (V+) the data on the 'D' input appears on 'Q'.
  • All the clocks read at the same moment so REG2 won't see the change on REG1 until the next cycle.
  • When SW1 is switched to ground the LEDs will turn off one by one starting at D1.

Timing diagram.

 _ _ _ _ _ _ _ _ Pulse ___| |_| |_| |_| |_| |_| |_| |_| |___ _________________________________ LED 1 ___| _____________________________ LED 2 _______| _________________________ LED 3 ___________|
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  • \$\begingroup\$ actually i cant use clock or counter. \$\endgroup\$ Commented Mar 15, 2020 at 5:24
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    \$\begingroup\$ Why not? The first line in your question says you have a clock. I did not use a counter. I used D flip-flops. \$\endgroup\$ Commented Mar 15, 2020 at 9:09
  • \$\begingroup\$ Well I have one trigger and I made eight pulses with the clock. Now I can use only the 8 pulses and 5v source. Also i need a solution which is using transistors \$\endgroup\$ Commented Mar 15, 2020 at 10:44
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    \$\begingroup\$ Why do you need a solution which uses transistors? Is this a homework question? \$\endgroup\$ Commented Mar 15, 2020 at 12:52
  • \$\begingroup\$ @IdanAra_18 You can make a flip-flop from transistors. \$\endgroup\$ Commented Mar 15, 2020 at 14:44
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You can do that with a shift register (for example 74HC595) or a decade counter (?). Search also for other models than those mentioned as example, and chose the one you prefer. If it's just an indicator led (max 8mA) you can drive them directly form these ICs. If they are power leds, consider adding a transistor mosfet to increase current and voltage.

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  • \$\begingroup\$ If you mean the CD4017 then that isn't suitable. It only turns on one LED at a time. (It's a Johnson counter, not a shift register.) \$\endgroup\$ Commented Mar 14, 2020 at 22:08
  • \$\begingroup\$ Please let us know where we can get a 74HC595 that will run at 80MHz. Where can we find a CD4017 that will operate at 8MHz, much less at 80MHz? Who makes a CD4017 or 74HC595 that can provide 20mA to an LED? Links to the datasheets would be much appreciated. \$\endgroup\$ Commented Mar 14, 2020 at 22:09
  • \$\begingroup\$ Where does the 20mA come from? Anyway LED's don't need 20mA these days. A high efficiency LED can work perfectly from 1mA. \$\endgroup\$ Commented Mar 14, 2020 at 22:13
  • \$\begingroup\$ Transistor. I didn't remember exactly. You must be right. Maybe there are simple counters with increment instead of one at a time? Does have to be a sophisticated shift register but it depends what you want to do. \$\endgroup\$ Commented Mar 14, 2020 at 22:19
  • \$\begingroup\$ Eillot Alderson Where does the OP speaks about such frequency. At such speed he can turn everything on at the same time as well. Doesn't make any sens. Most IC's (not all) provides up to 20 mA, that why I wrote "max". As Oldfart said, SMD leds can be lit with 1 or 2 mA. \$\endgroup\$ Commented Mar 14, 2020 at 22:22

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