hatch a latch

[timothyjackson]

hey guys n' gals.

Intro: Been studying more and more electronics, nearly getting to the stage of designing own circuit - still modifying other peoples.

Take a look at this:

https://www.electro-tech-online.com/custompdfs/2004/12/4013oneshotsPDF.pdf

with the "on/off latched function" - i wanna basically turn a set of leds on and off using the output of the 4013. I guess my question is, can i connect the leds direct (all in series, upto 20 leds), or, should the output pin feed a transistor, and thus a load of leds through the transistor function??

If a transistor is needed, im guessing it could be a 2n3904? ??

Many thanks for all your help so far.

Timbo

 

[jrz126]

What voltage are you going to run it at? for 20 LED's in series you'll need a pretty high voltage (if the leds have a 1v voltage drop, then they will have to be connected to 20V)

You will need to use a transistor as well, These logic IC's typically arent designed to handle high currents. Also, you can have 2 or 3 (or more) transistors connected to the latch, so you could run 2 sets of 10 led's.

Any general purpose transistor should work, like the 2n3904 or 2n3906.
Which one of the 2 to use depends on if you want the leds to turn on when the latch is low or high, you'll want a PNP for low and NPN for high.

Hope this makes sense, I gotta study for a diff eq :roll: test now so I cant get into more detail...

 

[k7elp60]

If you are using the one shot feature that is when you push the button the LED's come on for a period and then go off I suggest you use a driver transistor for the LED's because the 4013 will only supply about 10Ma of current. If you are using 12 volts I would recommend a 2N2222 transistor. Connect the emitter to ground, a 4.7k resistor from pin 13 of the 4013 to the base of the 2N2222 and connect the LED's in strings in series with a resistor and the strings in parallel between the collector and the 12V source. If you tell me the color of the LED's you want to use I can advise you better as the LED's have different forward voltage values for different colors.

If you are using the 4013 for the latch on or latch off, use an off/on switch instead.

 

[timothyjackson]

guys. thanks for your comments.


Im using the 4013 for a latch on and off. I'll be conneting an IR reciever as the switch, so, an IR transmitter can control the latched output state of the 4013 IC.

10Ma output. interesting.

I want to control a bank of (20 ish) LEDS all in parallel (drawing 20ma/ 3v in total) So, I will need a transistor then to open up power from the + to power up the LEDS.....I will do a drawing in a few days and ask u guys to confirm it will work or not.... or........well heck... i've ordered the ic... im going for it. ...


thanks for your time my friends.

timbo

 

[TheOne]

You can split say 21 leds in 7 banks, three leds in series per bank. Average voltage over a led is 2v, so the 3 leds will give you around 6 volt, leaving another 6 volts to drop over the current limiting resistor for each bank, if you operate from a 12v supply. The only drawback with this scheme is that if one led goes open, all three will be "silent". You can still use 1 transistor to switch the banks.