Light LED with 4 nanoamps / High Voltage / Forums

Forums

4hv.org :: Forums :: High Voltage

« Previous topic | Next topic »

Light LED with 4 nanoamps

first previous 6 7 8 9 next last

Move Thread

LAN_403

mister_rf

Tue Apr 14 2015, 12:26AM

Registered Member #4465 Joined: Wed Apr 18 2012, 08:37AM
Location: Bucharest, Romania
Posts: 145

Yes, maybe thatâ€™s not so simple. Any LED is in fact a diode, and the ideal diode law gives an expression for the current through a diode as a function of voltage. But in practice at such very low currents, even that law itâ€™s not accurate any more.

For example, in my previous LEDs test, thereâ€™s a string of 5 LEDs in total.
For a very large current (5mA) the total voltage drop is around 12Vdc. If we reduce the current up to 100nA, the voltage drops to 7Vdc, and for 10nA up to 5Vdc. I have measured less than 0.05nA for a total voltage drop of 3.5V.
This means you canâ€™t charge the capacitor if the strings of diodes are permanently connected in parallel to the capacitor.

klugesmith

Tue Apr 14 2015, 07:58AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

mister_rf wrote ...
I have built a test circuit, controllable current source, connected to some various high efficient LEDs and cranked the dial down to observe the minimum threshold I could see the LEDs light.
It was as low as 10 nanoamps recorded by the camera, but in practice, in a complete dark room the light is quite visible with the naked eye down to 5 nanoamps.

Nice work there.
There was a 4hv thread about ultradim LED's a few years ago:

in which an old white LED with unknown credentials was visible at 12.5 nA.

You make me want to go back and try some newer LED's. The ones most efficient at 10's or 100's of mA might not be the most efficient at 10 nA (see Figure 3 in the report below). It's really a contest of luminance, not luminous intensity or flux. Nice trick, running multiple specimens in series so we know their currents are identical.

Ash Small

Tue Apr 14 2015, 01:29PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Sigurthr wrote ...

You'll get incredible leakage over a range below the Vf. It (any diode) isn't a perfect switch unfortunately.

So maybe if we can put a capacitor in the circuit before the switch, when it discharges it will provide more current?

Obviously, the capacitor will need to have virtually no losses.

As long as the capacitor charges to a higher voltage than the diode string, you'll get a 'flash'?

Obviously the 'flashes' won't be as frequent as without the capacitor.

Zamboni

Sun Apr 19 2015, 12:34PM

Registered Member #2836 Joined: Fri Apr 30 2010, 01:24PM
Location:
Posts: 41

I am having a hard time finding the OPTOSUPPLY OSW54L5111P white 75.000 mcd.
Any idea where I could get a very small order of 5-10 units?

Something on Ebay would be really handy.

Paul

mister_rf

Sun Apr 19 2015, 04:06PM

Registered Member #4465 Joined: Wed Apr 18 2012, 08:37AM
Location: Bucharest, Romania
Posts: 145

I have bought those LEDs from here:

Zamboni

Sun Apr 19 2015, 04:59PM

Registered Member #2836 Joined: Fri Apr 30 2010, 01:24PM
Location:
Posts: 41

I have ordered them today. I will let you know what happens once they get here.

Hopefully, I will post a picture of the "flash".

Paul

Newton Brawn

Tue Apr 21 2015, 04:03AM

Registered Member #3343 Joined: Thu Oct 21 2010, 04:06PM
Location: Toronto
Posts: 311

Hi Zamboni,

If you set the moving pendulum in a " neutral " position, the pendulum can start the oscillation movement by it self ?

Tony Matt

Tue Apr 21 2015, 04:42AM

Registered Member #3700 Joined: Sat Feb 19 2011, 12:59PM
Location:
Posts: 107

Zamboni,

You wrote:
"My thought was to try to use the battery to charge a capacitor, and have the capacitor light the LED intermittently. I could not figure out a way to charge a cap, and have the cap "switch on" to light the LED, and then automatically go back to charging the capacitor."

Your concept is ok.

The way to charge the cap could be keeping the cap connected with the battery all time. The primary cap will be 1nF.

The device to "switch" the capacitor current to the leds will be the spark gap, as you can see in the videos above. IN YOUR CIRCUIT, the spark gap switching action has better performance than other modern switching devices.

And to " amplify " the current from capacitor to the led you need a buck converter. The buck converter is the 1N4007 diode, 430uH coil, and a 0.5 mF cap circuity, as shown in the Antonio's videos

I hope you can deal with the machine arrangement to incorporate the leds

Cheers

Tony

Zamboni

Tue Apr 21 2015, 08:57PM

Registered Member #2836 Joined: Fri Apr 30 2010, 01:24PM
Location:
Posts: 41

If I understand your idea properly, you are suggesting using a spark gap as a switch.

With that in mind, do you think this would work?:
The Swinging pendulum will deliver the 400 volt (at 4 Nana-amp) â€œloadâ€ from the positive terminal to the negative terminal. The â€œloadâ€ would then flow through the high voltage diode to the capacitor. That should return the terminal voltage to zero. For the Device to function properly, the negative terminal must remain at or near zero (the voltage canâ€™t â€œbuild upâ€ on the negative terminal). Once the voltage reaches the capacitor, it will charge until it reaches a voltage that is sufficient to trigger the spark gap. When the gap is bridged, the LED panel (I will probably need to switch to a neon bulb array) should flash.

Is that what you had in mind?

I have never tried to use a high voltage diode with the Device. I know that an LED will function, (even though the â€œflashâ€ is almost invisible). I donâ€™t know if the â€œhigh voltageâ€ diode will even work at such low amperages. The leakage of the diode worries me.

Do you think it will work?

Paul

Antonio

Wed Apr 22 2015, 12:55AM

Registered Member #834 Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644

I don't think that the idea can work in this way. But your schematic shows something that was forgotten in the previous discussions. The swinging pendulum is not short-circuiting the battery, but just taking a small charge from one terminal of the battery and, after swinging, returning the charge to the other and taking a small opposite charge. A possible solution is then to increase the charge that goes to the pendulum by adding a capacitor connected to it (by a thin wire that can be its support), and make the charge pass through a "floating buck converter", as in the picture. Another capacitor is connected across the battery, that has the negative terminal grounded. The LED will flash when the pendulum touches the positive terminal.

first previous 6 7 8 9 next last

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob