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Author Topic: Lasersaber strikes again. A joule thief king ?  (Read 412370 times)

Vortex1

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Re: Lasesaber strikes again. A joule thief king ?
« Reply #90 on: May 15, 2014, 07:39:36 PM »
No goals are set for the design, but I can supply working circuits if you like, first just give me the design constraints i.e. what do you want the circuit to do?

Regards,
No idle talker



conradelektro

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Re: Lasesaber strikes again. A joule thief king ?
« Reply #91 on: May 15, 2014, 08:07:52 PM »
No goals are set for the design, but I can supply working circuits if you like, first just give me the design constraints i.e. what do you want the circuit to do?

1) The MAX931 multivibrator delivers a nice square wave whose frequency and duty cycle can be defined in a certain range, lets say 100 Hz to 5 KHz and duty cycles from 1 % to 50 %.

2) In addition the circuit can source up to 40 mA continuously from its output, lets say 20 mA would be enough to drive the gate or base of a very high current MOSFET.

3) The square wave from the MAX931 circuit can have a peak to peak Voltage of 2.5 V to 11 V (depending on the supply Voltage).

Now do that with less than 5 µA at 3 Volt or less than 14 µA at 11 Volt.

(One or two µA could still be saved by carefully selecting resistor values, at 11 Volt even more. The MAX931 circuit should be able to do it at around 3 µA at all Voltages from 3 V to 11 V if designed carefully. I think this is hard to beat with the same number of components.)

Attached please find a circuit diagram which you could redesign if you have time and ideas.

Greetings, Conrad

Vortex1

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Re: Lasesaber strikes again. A joule thief king ?
« Reply #92 on: May 15, 2014, 08:50:40 PM »
Greetings Conrad

Agreed, your original circuit is hard to beat if driving a single LED and your source voltage is limited to 2.5 Volts.

If you like nice clean rectangular pulses this is definitely a good way to go. You could substitute a cheap high gain low power op-amp for the Max931, a comparator is not absolutely required.

If you desire to drive many series LED's from a low voltage such as 2.5 volts, then the second circuit with the addition of the boost inductor is a good way to fly.

If 2.5 volts is not a constraint and you wish to drive many series LED's and only use the Max931 without the boost inductor, then you are limited to how many you can drive by the input voltage.

Since you can control duty cycle and frequency, there is no need to worry about inductor saturation, so no pre-emptive switch-off of the inductor is required. The second half of your circuit will work well "as is" provided the inductance is properly sized for the expected duty cycle and frequency.

I'm still uncertain what is the design goal? To run an LED for the longest time with barely visible light output while drawing the minimum amount of current from a given source voltage?

Unknowns are: peak led current required and duty cycle, type of LED required.

You could also use a simple relaxation oscillator based upon a unijunction transistor or PUT or even a simple two transistor multivibrator if the voltage is allowed to be up to 11 Volts.

I'll try to find some circuits in my archives and post them.

Kind Regards, Vortex1



conradelektro

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Re: Lasesaber strikes again. A joule thief king ?
« Reply #93 on: May 15, 2014, 09:30:01 PM »

I'm still uncertain what is the design goal? To run an LED for the longest time with barely visible light output while drawing the minimum amount of current from a given source voltage?

Unknowns are: peak led current required and duty cycle, type of LED required.


@Vortex1: thank you for taking the time to analyse the circuit.

Well, what are the requirements? Let's say it like a layman:

Drive a white LED at a "nice brightness" with as little power as possible. It would be desirable to do it with a single 1.5 V AAA battery. (This excludes the MAX931, so I decided to use two AAA batteries, the MAX931 still works with 2 Volt, so the circuit would work with two fresh batteries in series at 3 V and run down to 2 Volt eventually depleting the two batteries.)

"nice brightness": the LED is visibly shining in day light but far from nominal brightness. In darkness one would see the LED well but it would not really give useful light. (So, it is a pretty useless exercise.)

LaserSaber seems to be able to do it with 9 Volt and less than 10 µA (two red LEDs). I would like to beat that. Visibly blinking the LED is not allowed (that is why I used 120 Hz).

The trick obviously is to hit the white LED with very short pulses at more than 3 Volt, e.g. with 10 Volt spikes, because the LED would look brighter than with 3 V pulses.


Possible useful application: one uses these new 220V (or 110V) LED lamps which give bright light at 6 Watt or 10 Watt. It seems to be possible to drive these LED lamps with short 220 V to 400 V pulses at a useful brightness (e.g. like a flash light) at very low Wattages. I could quite nicely light such LED lamps with 0.1 to 0.5 Watt (with a 3 Volt supply Voltage and a Joule Thief type circuit). This would be a battery driven emergency light which allows to wander through the house in case of a power outage.

I attach circuit and photos from a project I did some years ago. I want to do a similar project but with the MAX931 instead of the microprocessor and a LED lamp instead of a gutted CFL.

The microprocessor needed 50µA to 100µA at 2.5 Volt.  I used a fly back transformer salvaged from a black and white TV set. I could connect the miroprocessor to my PC and with a program I could flexibly change frequency and duty cycle. It was quite difficult to find efficient settings for various power demands.

Greetings, Conrad

Vortex1

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Re: Lasesaber strikes again. A joule thief king ?
« Reply #94 on: May 15, 2014, 09:56:05 PM »
Hello Conrad

Thank you for explaining in more detail what your desired specifications are and also for showing your fine work. I will be sketching up some circuits for you, but first I want to test them myself on the bench, so that will take some time.

I want to try a programmable unijunction transistor driving a NPN transistor. Thats only two active components and three or four resistors and a capacitor.

The other circuit will be a two transistor multivibrator, four resistors and one capacitor.

I like to squeeze as much out of a few common low cost discrete parts as I can. My circuits will be better than the ones attached from the web. The PUT circuit will drive a transistor with it's cathode inplace of LED. The LED will go in the collector.

Other variations of these circuits can be found on the web, but the frequency of operation is too low, they will have to be tweaked for higher pulse rate and low power operation.

Kind regards
Vortex1

MarkE

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Re: Lasesaber strikes again. A joule thief king ?
« Reply #95 on: May 15, 2014, 10:29:59 PM »
Conrad with 2V or more and very careful firmware design you should be able to get the MPS430 or similar low power uC down to 0.5uA or less average operating current.  The sacrifices that you have to make getting there may force a larger physical coil.


conradelektro

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Re: Lasesaber strikes again. A joule thief king ?
« Reply #96 on: May 16, 2014, 04:10:46 PM »
I worked a bit on my MAX931 circuit and could light a white LED a little bit brighter by help of a coil and a BC547C as switch.

Vortex1 was right, driving a LED with the back EMF spike of a coil makes it appear a bit brighter (for the same power consumption as feeding current directly through the LED).

MarkE was right, it needs a bigger coil.

One can now play endlessly with duty cycle and coil impedance to reach an optimum.

The lowest power consumption I could reach is 9 µA at 2.5 V, but the white LED is of course just shining, not really bright.

Note the 1N4148 diode in series with the white LED, it makes the LED a little bit brighter and lowers power consumption because the LED is a bad diode (high reverse current of LED consumes power, it helps most with a red LED).

Removing the Ferrite core from the coil reduced its inductance from 355mH to 48 mH. This makes the LED brighter but power consumption goes up to 30 µA at 2.5 V.

All measurements are stated on the circuit diagram. Note how clean the square wave on the output of the MAX931 is (although I use Mega Ohm resistors). Also interesting is the ringing (over collector emitter of the BC547C) which was also observed by LaserSaber in his 2N1304 circuit.

I found the low power OpAmp TLV2401 http://www.ti.com/product/tlv2401 which has the lowest power draw today. According to its data sheet from TI: "The TLV240x family of single-supply operational amplifiers has the lowest supply current available today at only 880 nA per channel." I might get some, looks interesting, but needs 2.7 Volt and the output is only 0.2 mA (enough to switch a little NPN transitor like a 2N2222, 2N3904 or BC547).

Concerning the leakage of electrolytic capacitors: my measurements showed that the leakage is low at 1V to 2V, around 1 µA, but then it goes up, at 10 Volt it easily is 10 µA to 20 µA.

Next week I try some fly back transformers to light a LED lamp. Keep the suggestions and ideas coming!

Greetings, Conrad

MarkE

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Re: Lasesaber strikes again. A joule thief king ?
« Reply #97 on: May 16, 2014, 05:07:11 PM »
I worked a bit on my MAX931 circuit and could light a white LED a little bit brighter by help of a coil and a BC547C as switch.

Vortex1 was right, driving a LED with the back EMF spike of a coil makes it appear a bit brighter (for the same power consumption as feeding current directly through the LED).

MarkE was right, it needs a bigger coil.

One can now play endlessly with duty cycle and coil impedance to reach an optimum.

The lowest power consumption I could reach is 9 µA at 2.5 V, but the white LED is of course just shining, not really bright.

Note the 1N4148 diode in series with the white LED, it makes the LED a little bit brighter and lowers power consumption because the LED is a bad diode (high reverse current of LED consumes power, it helps most with a red LED).
Replace the 1N4148 with a small Schottky like a BAT54 or BAT46 and you will decrease the voltage drop while still blocking losses due to the LED's slow reverse recovery time.
Quote

Removing the Ferrite core from the coil reduced its inductance from 355mH to 48 mH. This makes the LED brighter but power consumption goes up to 30 µA at 2.5 V.

All measurements are stated on the circuit diagram. Note how clean the square wave on the output of the MAX931 is (although I use Mega Ohm resistors). Also interesting is the ringing (over collector emitter of the BC547C) which was also observed by LaserSaber in his 2N1304 circuit.
A low threshold voltage power MOSFET may do much better than the BC547 NPN.  They aren't that easy to find in leaded parts.  If you can deal with surface mount parts, a DMG1012 from Diodes Inc only needs about 1nC gate charge to fully turn on.  If you are pulsing at 100Hz or less that will be less than 0.1uA to turn the MOSFET on and off.
Quote

I found the low power OpAmp TLV2401 http://www.ti.com/product/tlv2401 which has the lowest power draw today. According to its data sheet from TI: "The TLV240x family of single-supply operational amplifiers has the lowest supply current available today at only 880 nA per channel." I might get some, looks interesting, but needs 2.7 Volt and the output is only 0.2 mA (enough to switch a little NPN transitor like a 2N2222, 2N3904 or BC547).
The DMG1012 might help you there.
Quote

Concerning the leakage of electrolytic capacitors: my measurements showed that the leakage is low at 1V to 2V, around 1 µA, but then it goes up, at 10 Volt it easily is 10 µA to 20 µA.

Next week I try some fly back transformers to light a LED lamp. Keep the suggestions and ideas coming!

Greetings, Conrad
At 1.8V, 100Hz and 10nF your timing circuit is using about 2uA by itself.  If you have a smaller capacitor like 1nF or 2nF and larger resistor values you could see some improvement there.

d3x0r

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Re: Lasesaber strikes again. A joule thief king ?
« Reply #98 on: May 16, 2014, 05:08:42 PM »

conradelektro

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Re: Lasesaber strikes again. A joule thief king ?
« Reply #99 on: May 16, 2014, 06:35:32 PM »
@MarkE: thank you for your input, the DMG1012 looks very interesting, just the right transistor to be driven by a TLV2401 multivibrator narrow square wave.

I will go in the direction of driving a 220V LED lamp with two AAA batteries and the multivibrator. The 2 V to 3 V from two 1.5 AAA or AA batteries seem to be just right.

What I have to do now is find or wind the right transformer, but I have a few sitting somewhere in my house. I think that a useful emergency light or flash light can be done with 0.1 Watt.

I found that a LED needs at least 1 mW to shine brightly, and there are plenty of Joule Thiefs doing that nicely.

I like what LaserSaber is doing, the 1 µA power draw is amazing, but I dread the winding of different pot core coils. I will wait to see where he goes before running in the same direction.

Greetings, Conrad

MarkE

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Re: Lasesaber strikes again. A joule thief king ?
« Reply #100 on: May 16, 2014, 06:42:43 PM »
@MarkE: thank you for your input, the DMG1012 looks very interesting, just the right transistor to be driven by a TLV2401 multivibrator narrow square wave.

I will go in the direction of driving a 220V LED lamp with two AAA batteries and the multivibrator. The 2 V to 3 V from two 1.5 AAA or AA batteries seem to be just right.

What I have to do now is find or wind the right transformer, but I have a few sitting somewhere in my house. I think that a useful emergency light or flash light can be done with 0.1 Watt.

I found that a LED needs at least 1 mW to shine brightly, and there are plenty of Joule Thiefs doing that nicely.

Greetings, Conrad
If your goal isn't chasing the lowest power still visible LED but to have a useful long lasting light powered by one or a couple of AAA cells then there are some very good options out there.   I think that 10 lumens is kind of the low end of useful light.  With the right LED you can get that on 80mW to the LED and a little more than 100mW drawn from the batteries.  A pair of AAA batteries gets you more or less 2Wh.  So you could go for 200 hours on such a circuit.

conradelektro

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Re: Lasesaber strikes again. A joule thief king ?
« Reply #101 on: May 16, 2014, 09:37:32 PM »
I just saw a replication of LaserSaber's low power Joule Ringer on YouTube https://www.youtube.com/watch?v=h-_aWDt79fw (by itsusable)

Greetings, Conrad

 

conradelektro

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Re: Lasesaber strikes again. A joule thief king ?
« Reply #102 on: May 17, 2014, 11:35:17 PM »
Just wanted to try with a little fly back transformer. Could be optimised with a more suitable MOSFET (depends on power supply and LED lamp Wattage). The duty cycle has to be adjusted to the particular LED lamp.

I went for a two battery (2.5 V to 3 V) or three battery (3 V to 4.5 V) power supply and a low Wattage 220V LED lamp (0.7 Watt to 3 Watt).

At around 4 V and ~100 mA (about 0.4 Watt) one has a very useful low Wattage LED lamp (220V 0.7W to 3 Watt LED lamp). But also around 3 V and ~30 mA (about 0.1 Watt) the LED lamp starts to be useful.

May be the whole thing is not of much use. I wanted to show that an OpAmp astable multivibrator can be used to create a LED or LED lamp driver. I was surprised that it is today very easy to create an OpAmp based astable multivibrator which operates at a few µA. Of course, the real up to date design would be a microprocessor based circuit which would offer a very high flexibility. The modern 16 Bit microprocessors also operate at a few µA, there are even some which work down to 0.9 Volt (45 µA active mode).

http://www.ti.com/lsds/ti/microcontroller/16-bit_msp430/low_voltage/overview.page?paramCriteria=no

Once I get some 2N1304 germanium transistors, I will have one more go at a LaserSaber Super Joule Ringer replication.

Greetings, Conrad

Pirate88179

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Re: Lasesaber strikes again. A joule thief king ?
« Reply #103 on: May 18, 2014, 12:11:22 AM »
Has any one tried the Touchstone TS3002 chip with their demo board yet?  This has an amp draw of less than 1 micro amp.  I happen to have one of these demo boards and will dig it out and see what happens.  I also have about 6 spare chips for it.

This should be able to drive an led for a very, very long time.

Bill

d3x0r

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Re: Lasesaber strikes again. A joule thief king ?
« Reply #104 on: May 18, 2014, 12:18:20 AM »
Just wanted to try with a little fly back transformer. Could be optimised with a more suitable MOSFET (depends on power supply and LED lamp Wattage). The duty cycle has to be adjusted to the particular LED lamp.

I went for a two battery (2.5 V to 3 V) or three battery (3 V to 4.5 V) power supply and a low Wattage 220V LED lamp (0.7 Watt to 3 Watt).

At around 4 V and ~100 mA (about 0.4 Watt) one has a very useful low Wattage LED lamp (220V 0.7W to 3 Watt LED lamp). But also around 3 V and ~30 mA (about 0.1 Watt) the LED lamp starts to be useful.

May be the whole thing is not of much use. I wanted to show that an OpAmp astable multivibrator can be used to create a LED or LED lamp driver. I was surprised that it is today very easy to create an OpAmp based astable multivibrator which operates at a few µA. Of course, the real up to date design would be a microprocessor based circuit which would offer a very high flexibility. The modern 16 Bit microprocessors also operate at a few µA, there are even some which work down to 0.9 Volt (45 µA active mode).

http://www.ti.com/lsds/ti/microcontroller/16-bit_msp430/low_voltage/overview.page?paramCriteria=no

Once I get some 2N1304 germanium transistors, I will have one more go at a LaserSaber Super Joule Ringer replication.

Greetings, Conrad
the last model was built with mpsa16 which has low gate on voltage; NTE47 equivalent