Joule Thief

[MarkE]

Excellent!  So, these are a very basic type of breakout board for smt devices then?  I will have to figure out which one I need for the 1402 but, after watching that video, I know I can solder to pads that are placed in the right area.  Thank you so much for your post...it really helps.

The one thing I can't figure out is why Sparkfun makes that nice board using the 1402 and other components (at a good price too) but their specs say it will take 1 volt and make it 3 volts.  That is good and all but the 1402 with the right components will take (once it begins to run at .8 volts) and keep running down to .3 volts and still output 3 volts.  I wonder why they did not use the optimum components on their nice little board?  Mark E. suggested a while ago that I should get those boards and swap in my components....this is still an option but why didn't they do that to begin with?  Different goals I suppose.

Thanks again,

Bill

The NCP1402's work fine on the SparkFun boards right down to 0.2V.  You can change the components if you have specific goals that the stock components don't realize but others will. 

[Pirate88179]

The NCP1402's work fine on the SparkFun boards right down to 0.2V.  You can change the components if you have specific goals that the stock components don't realize but others will.

Really?  I have read in many places that will only work down to 1 volt, including on their website and videos.  Are they just rounding up the starting voltage from the chip? (.8 volts) and not mentioning how low it will still run?

I will get one and test it for myself.  If what you say is correct, it will work better than what I am trying to build, and I will have a lot more than $6 in each board.

I must be getting old.

Thanks mark,

Bill

(Pasted from Sparkfun's site)

"Description: The NCP1402 is a 3.3V DC-DC converter. The breakout board will accept voltage inputs between 1 and 3 Volts (such as 1 or 2 AA batteries) and output a constant, low ripple 3.3V output capable of sourcing up to 200 mA."

I checked their data sheet but it is just a copy of the 1402's data sheet I already have.  I do not see where it says it will run below 1 volt.

ETA:  I just ordered one board and I will test to see how low it will go.  If this works, this is cheaper than I could get a blank board in 100 quantity from a supplier!  Plus, I won't have to solder those damn smd chips.  I will let you all know.

Bill

[Farmhand]

Well the NCP1400 I have works fine to output it's rated voltage and current down to 1 volt, but it struggles to hold the 3 volts on load
with under 1 volt, the output voltage does not remain rock solid at ie. 3 volts for a 3 volt output rated part, and they certainly
cannot maintain the full voltage and output current with voltages under 0.5 v.

The data sheet describes the best possible components, less than ideal can be used.

Also the frequency while it is fixed does vary over different input voltages as well. If the input voltage is stable the frequency is
stable but the frequency does change with varying input voltage. 

The input and output are current limited I think so once the voltage gets low enough and the output voltage and current
demands more input current than the part is rated for then something reduces as it must.

If anyone wants me to test something with the NCP1400 I will try to oblige.  I can try to max the output and input ect.
ans show it, or tell it, I've done some testing but don;t keep notes, only memory.

Cheers

So it seem that if the chip detects a peak current of 350 mA through the mosfet then it turns the mosfet off for the rest of
that cycle. What that means in practice is that the output voltage will droop if the input cannot keep up due to current limiting.

The NCP1402 part will have a higher peak current limit.

Current Limit
The NCP1400A series utilizes cycle−by−cycle current
limiting as a means of protecting the output switch
MOSFET from overstress and preventing the small value
inductor from saturation. Current limiting is implemented
by monitoring the output MOSFET current build−up during
conduction, and upon sensing an overcurrent conduction
immediately turning off the switch for the duration of the
oscillator cycle.
The voltage across the output MOSFET is monitored and
compared against a reference by the VLX limiter. When the
threshold is reached, a signal is sent to the PWM controller
block to terminate the output switch conduction. The current
limit threshold is typically set at 350 mA.

..

[Pirate88179]

Farmhand:

According to the 1402's data sheet, if you lower the inductance value you can increase the power output, but it also lowers the efficiency, if you increase the inductance value (above the advised 47 uh) it lowers the power output but increases the efficiency.  It also says the output cap  maintains the output voltage levels so, I wonder if playing with that might help at low v inputs?

I should have listened to Mark weeks ago and I would already have my board and could be experimenting with it.

Bill

PS You are doing some very nice work over on the Hopegirl topic.

[Pirate88179]

What that means in practice is that the output voltage will droop if the input cannot keep up due to current limiting.

The NCP1402 part will have a higher peak current limit.

..

Yes, but I believe it works the same way with the mosfet in the 1402.  I wonder if a much larger F output cap might maintain the output better when the voltage drops really low?  Possibly a supercap even?

Bill