High Current LED flasher

[jalbers@bsu.edu]

Could someone please walk through how this circuit works breaking it
down into bite size pieces? https://ilocker.bsu.edu/users/jalbers/WORLD_SHARED/Electronics/LED
Pulser.PDF

I doubt that I will be able to find the germanium transistors so I am
assuming that it can be tweaked to work with silicon transistors.

I have been using a free java simulator at http://www.falstad.com/circuit/
to simulate this circuit but I cannot get it to work. Cut and paste
the following into the import window:

Any help would be greatly appreciated. Thanks

$ 1 5.0E-6 0.551975421667673 71 5.0 50
t 848 320 896 320 0 -1 2.005660611605064 -2.9014557175467566 100.0
w 608 320 608 416 0
w 896 304 896 176 0
w 896 176 736 176 0
w 736 176 448 176 1
w 448 432 448 336 0
w 448 176 448 240 0
w 448 432 448 624 0
w 448 624 736 624 1
w 768 624 896 624 0
w 896 624 896 496 0
w 896 496 832 496 0
w 608 496 608 448 0
r 448 336 448 240 0 100000.0
162 832 496 768 496 1 2.1024259 1.0 0.0 0.0
c 768 624 736 624 0 4.7E-8 3.4052934640812653
R 736 176 736 128 0 0 40.0 9.0 0.0 0.0 0.5
w 608 496 688 496 0
w 688 496 768 496 0
w 688 496 688 528 0
g 688 528 688 560 0
w 608 320 704 320 0
w 848 320 768 320 1
w 896 496 896 432 0
w 896 336 896 368 0
w 560 432 448 432 0
s 704 320 768 320 0 0 false
s 896 368 896 432 0 0 false
t 560 432 608 432 0 1 -5.4109540756863295 0.6875902067669138 100.0

 

[petrus bitbyter]

<jalbers@bsu.edu> schreef in bericht
news:7e22e1c5-1a74-41f6-9a04-0f1cc12f9b3d@34g2000hsh.googlegroups.com...

Could someone please walk through how this circuit works breaking it
down into bite size pieces?
https://ilocker.bsu.edu/users/jalbers/WORLD_SHARED/Electronics/LED
Pulser.PDF

I doubt that I will be able to find the germanium transistors so I am
assuming that it can be tweaked to work with silicon transistors.

I have been using a free java simulator at http://www.falstad.com/circuit/
to simulate this circuit but I cannot get it to work. Cut and paste
the following into the import window:

Any help would be greatly appreciated. Thanks

$ 1 5.0E-6 0.551975421667673 71 5.0 50
t 848 320 896 320 0 -1 2.005660611605064 -2.9014557175467566 100.0
w 608 320 608 416 0
w 896 304 896 176 0
w 896 176 736 176 0
w 736 176 448 176 1
w 448 432 448 336 0
w 448 176 448 240 0
w 448 432 448 624 0
w 448 624 736 624 1
w 768 624 896 624 0
w 896 624 896 496 0
w 896 496 832 496 0
w 608 496 608 448 0
r 448 336 448 240 0 100000.0
162 832 496 768 496 1 2.1024259 1.0 0.0 0.0
c 768 624 736 624 0 4.7E-8 3.4052934640812653
R 736 176 736 128 0 0 40.0 9.0 0.0 0.0 0.5
w 608 496 688 496 0
w 688 496 768 496 0
w 688 496 688 528 0
g 688 528 688 560 0
w 608 320 704 320 0
w 848 320 768 320 1
w 896 496 896 432 0
w 896 336 896 368 0
w 560 432 448 432 0
s 704 320 768 320 0 0 false
s 896 368 896 432 0 0 false
t 560 432 608 432 0 1 -5.4109540756863295 0.6875902067669138 100.0

I'm not astonished. It's a tricky circuit not dimensioned to work with even
mediocre modern Si-transistors. Nobody can guarantee it to work with the
original transistors either. You can try to raise the 100k to 1M or higher
but even then the performance - if any - will be poor. You'd better Google
for "LED flasher" to find a better design.

petrus bitbyter

 

[Hammy]

On Thu, 30 Oct 2008 12:57:00 -0700 (PDT), "jalbers@bsu.edu"
<jalbers@bsu.edu> wrote:

Could someone please walk through how this circuit works breaking it
down into bite size pieces? https://ilocker.bsu.edu/users/jalbers/WORLD_SHARED/Electronics/LED
Pulser.PDF

I doubt that I will be able to find the germanium transistors so I am
assuming that it can be tweaked to work with silicon transistors.

I have been using a free java simulator at http://www.falstad.com/circuit/
to simulate this circuit but I cannot get it to work. Cut and paste
the following into the import window:

Any help would be greatly appreciated. Thanks

$ 1 5.0E-6 0.551975421667673 71 5.0 50
t 848 320 896 320 0 -1 2.005660611605064 -2.9014557175467566 100.0
w 608 320 608 416 0
w 896 304 896 176 0
w 896 176 736 176 0
w 736 176 448 176 1
w 448 432 448 336 0
w 448 176 448 240 0
w 448 432 448 624 0
w 448 624 736 624 1
w 768 624 896 624 0
w 896 624 896 496 0
w 896 496 832 496 0
w 608 496 608 448 0
r 448 336 448 240 0 100000.0
162 832 496 768 496 1 2.1024259 1.0 0.0 0.0
c 768 624 736 624 0 4.7E-8 3.4052934640812653
R 736 176 736 128 0 0 40.0 9.0 0.0 0.0 0.5
w 608 496 688 496 0
w 688 496 768 496 0
w 688 496 688 528 0
g 688 528 688 560 0
w 608 320 704 320 0
w 848 320 768 320 1
w 896 496 896 432 0
w 896 336 896 368 0
w 560 432 448 432 0
s 704 320 768 320 0 0 false
s 896 368 896 432 0 0 false
t 560 432 608 432 0 1 -5.4109540756863295 0.6875902067669138 100.0


I cant see The site you link to.

https://ilocker.bsu.edu/users/jalbers/WORLD_SHARED/Electronics/LED

So I dont know what frequency or current your talking about but you
might try something like this.

http://i37.tinypic.com/1zq3iie.png

I built a similiar one with an inexpensive low power LMV116,using a
NDS351AN FET. I get about 120nS rise/fall times good enough for me.If
you use a better opamp with more drive ability you could improve that.
This was for 1 Amp pulses at 2.6uS 10% Duty .

I dont know why they are using an NPN as a highside switch. I placed
my LED's between Vcc and the FET drain (low side switch).The
schematic is from the LT1800 DATA sheet.

You can also buy LED drivers ( SMPS controllers) constant current that
have a strobe or pulse function. I found these too expensive as well
as the pulse frequency was limited typically to 10kHz.

 

[Jasen Betts]

On 2008-10-30, jalbers@bsu.edu <jalbers@bsu.edu> wrote:

Could someone please walk through how this circuit works breaking it
down into bite size pieces? https://ilocker.bsu.edu/users/jalbers/WORLD_SHARED/Electronics/LED
Pulser.PDF

I doubt that I will be able to find the germanium transistors so I am
assuming that it can be tweaked to work with silicon transistors.

I have been using a free java simulator at http://www.falstad.com/circuit/
to simulate this circuit but I cannot get it to work. Cut and paste
the following into the import window:

the circuit shown relies on the LED having resistance of about 10 ohms
try putting a 10 ohm resistor in series with the LED.

current flows through the 100K resistor charging the capacitor
when ther voltage reaches 0.6v the NPN begins to turn on,
this begins to turn the PNP on which increases the voltage on the
other end of the capacitor turning both transistors fully on

as the capacitor discharges the current through the base of the NPN
decreases and that transistor begins to turn off again
this begins to turn off the PNP and the voltage on the LED end of the
capacitor reduces this causes the voltage at the NPN end of the
capacitor to fall to turning it off.

the circuit is highly dependant on the performance of the transistors
and will probably be grossly effected by temperature etc...

I must admit I couldn't get the circuit to perform in that java
simulator, but in LT-Spice (Switchercad, free download from linear.com)
I got it working using 2n2907 for the PNP and 2n2222 for the NPN
and 10 ohms in series with the led.

you don't get the pretty moving dots in switchercad, but you do get
nice zoom-able oscilloscope (like) traces.


Bye.
Jasen

 

[petrus bitbyter]

"Jasen Betts" <jasen@xnet.co.nz> schreef in bericht
news:geejj0$j25$1@reversiblemaps.ath.cx...

On 2008-10-30, jalbers@bsu.edu <jalbers@bsu.edu> wrote:
Could someone please walk through how this circuit works breaking it
down into bite size pieces?
https://ilocker.bsu.edu/users/jalbers/WORLD_SHARED/Electronics/LED
Pulser.PDF

I doubt that I will be able to find the germanium transistors so I am
assuming that it can be tweaked to work with silicon transistors.

I have been using a free java simulator at
http://www.falstad.com/circuit/
to simulate this circuit but I cannot get it to work. Cut and paste
the following into the import window:

the circuit shown relies on the LED having resistance of about 10 ohms
try putting a 10 ohm resistor in series with the LED.

current flows through the 100K resistor charging the capacitor
when ther voltage reaches 0.6v the NPN begins to turn on,
this begins to turn the PNP on which increases the voltage on the
other end of the capacitor turning both transistors fully on

as the capacitor discharges the current through the base of the NPN
decreases and that transistor begins to turn off again
this begins to turn off the PNP and the voltage on the LED end of the
capacitor reduces this causes the voltage at the NPN end of the
capacitor to fall to turning it off.

the circuit is highly dependant on the performance of the transistors
and will probably be grossly effected by temperature etc...

I must admit I couldn't get the circuit to perform in that java
simulator, but in LT-Spice (Switchercad, free download from linear.com)
I got it working using 2n2907 for the PNP and 2n2222 for the NPN
and 10 ohms in series with the led.

you don't get the pretty moving dots in switchercad, but you do get
nice zoom-able oscilloscope (like) traces.


Bye.
Jasen

You're right. But that 10R resistor neglects the main objective of the
circuit which is to push as much current as possible through the LED. One
may try two or more LEDs in series to obtain the same effect producing more
light for the buck.

Another point not mentioned in the article is the influence of the internal
resistance of the power source. It's about the only current limiting factor
when both transistors are open. One of the reasons a similation may work and
the implemented circuit may not or vice versa.

BTW. It is not the basic circuit that is tricky. The principle is well known
and can be found in (older) textbooks and with no doubt you can find it on
the internet as well. Replace the LED by a lamp (or one or more LEDs and a
series resistor like you did), put some current limiting resistor between
the base of the PNP and the collector of the NPN and raise the 100k resistor
to something like 1M for modern Si transistors. That last thing was
mentioned in the original article already. Though neither rocket science nor
state of the art, the circuit will work as advertised. Including being
sensitive for temperature - and supply voltage variations.

Nevertheless, if you want some blinking light you can find a lot of more
effective and reliable solutions on the internet.

petrus bitbyter

 

[Robert Monsen]

On Thu, 30 Oct 2008 12:57:00 -0700 (PDT), "jalbers@bsu.edu"
<jalbers@bsu.edu> wrote:

Could someone please walk through how this circuit works breaking it
down into bite size pieces?
https://ilocker.bsu.edu/users/jalbers/WORLD_SHARED/Electronics/LED Pulser.PDF

I was just looking through my new GE transistor manual (7th edition,
copyright 1964) that I got for $1.50 on amazon.com, and they have a
very similar circuit, using the same transistors. It is a 1.5V ham
radio code practice oscillator. Figure 15.6. Fun stuff.

The resistor/capacitor pair charges up until the transistor pair is
triggered. This resets the junction voltage at the RC node to a lower
voltage, where it starts to climb up again. I was playing with the
circuit, and found that it is much more reliable with a small resistor
from the node connecting the two transistors to Vcc. There is leakage
otherwise which can cause the transistors to not turn off when the rc
node resets.

The code practice oscillator works from 1.5V, but Forrest needs more
voltage, since the LED will use 1.4V or so, so he bumps it up to 3V+

I always wondered where Forrest Mims got his circuits. Now I know, he
got them from the GE transistor manual...

Regards,
bob monsen

 

On Nov 1, 3:39�pm, Robert Monsen <rcmon...@gmail.com> wrote:

On Thu, 30 Oct 2008 12:57:00 -0700 (PDT), "jalb...@bsu.edu"

jalb...@bsu.edu> wrote:
Could someone please walk through how this circuit works breaking it
down into bite size pieces? ďż˝
https://ilocker.bsu.edu/users/jalbers/WORLD_SHARED/Electronics/LEDPulser..PDF

I was just looking through my new GE transistor manual (7th edition,
copyright 1964) that I got for $1.50 on amazon.com, and they have a
very similar circuit, using the same transistors. It is a 1.5V ham
radio code practice oscillator. Figure 15.6. Fun stuff.

The resistor/capacitor pair charges up until the transistor pair is
triggered. This resets the junction voltage at the RC node to a lower
voltage, where it starts to climb up again. I was playing with the
circuit, and found that it is much more reliable with a small resistor
from the node connecting the two transistors to Vcc. There is leakage
otherwise which can cause the transistors to not turn off when the rc
node resets.

The code practice oscillator works from 1.5V, butForrestneeds more
voltage, since the LED will use 1.4V or so, so he bumps it up to 3V+

I always wondered whereForrestMimsgot his circuits. Now I know, he
got them from the GE transistor manual...

Regards,
�bob monsen

Hi Bob,

The circuit you described started my electronics career. I didn't find
it in the GE Transistor Manual (which I bought years later). Instead,
it was used in a single board code-practice oscillator that I bought
for $0.96. (I still have the receipt.)

I modified the circuit to make my first travel aid for the blind.
Later, I used the same circuit to make light flashers for model
rockets. This became the first product of MITS, Inc., the company that
introduced for Altair 8800 computer and provided Paul Allen and Bill
Gates a way to launch Microsoft.

Best regards,

Forrest

Forrest M. Mims III
www.forrestmims.org
www.sunandsky.org

 

[Bob Monsen]

<forrest.mims@gmail.com> wrote in message
news:2ff1fdb4-21d0-4c39-bb97-fdfdbef5e44f@o40g2000prn.googlegroups.com...
On Nov 1, 3:39�pm, Robert Monsen <rcmon...@gmail.com> wrote:

On Thu, 30 Oct 2008 12:57:00 -0700 (PDT), "jalb...@bsu.edu"

jalb...@bsu.edu> wrote:
Could someone please walk through how this circuit works breaking it
down into bite size pieces? ďż˝
https://ilocker.bsu.edu/users/jalbers/WORLD_SHARED/Electronics/LEDPulser.PDF

I was just looking through my new GE transistor manual (7th edition,
copyright 1964) that I got for $1.50 on amazon.com, and they have a
very similar circuit, using the same transistors. It is a 1.5V ham
radio code practice oscillator. Figure 15.6. Fun stuff.

The resistor/capacitor pair charges up until the transistor pair is
triggered. This resets the junction voltage at the RC node to a lower
voltage, where it starts to climb up again. I was playing with the
circuit, and found that it is much more reliable with a small resistor
from the node connecting the two transistors to Vcc. There is leakage
otherwise which can cause the transistors to not turn off when the rc
node resets.

The code practice oscillator works from 1.5V, butForrestneeds more
voltage, since the LED will use 1.4V or so, so he bumps it up to 3V+

I always wondered whereForrestMimsgot his circuits. Now I know, he
got them from the GE transistor manual...

Regards,
�bob monsen

Hi Bob,

The circuit you described started my electronics career. I didn't find
it in the GE Transistor Manual (which I bought years later). Instead,
it was used in a single board code-practice oscillator that I bought
for $0.96. (I still have the receipt.)

I modified the circuit to make my first travel aid for the blind.
Later, I used the same circuit to make light flashers for model
rockets. This became the first product of MITS, Inc., the company that
introduced for Altair 8800 computer and provided Paul Allen and Bill
Gates a way to launch Microsoft.

Best regards,

Forrest

Forrest M. Mims III
www.forrestmims.org
www.sunandsky.org

-----------------------------------------------------------------------
I have several of your 'cookbooks'. They always had lots of fun things to do
and try. I think it is so cool that you hang out (or at least listen in) on
sci.electronics.basics!

Regards,
Bob Monsen