I have made up a mintyboost v2 power supply on a breadboard using the same components they have on their website to run the Arduino from 2 x AA (LR6) batteries. However, despite me trying about 3 different schematics out I only ever get 3v out of it and not 5v. I have tried 3 seperste LT1302 IC's with the same result.
Can anyone help please?
Hi Mike,
Can you post a link to the schematics you have tried and I will take a look.
Cheers
Yes here it is :-
I haven't done the bit on the right as I am going to use it to power the Arduino not a USB device.
Just a long shot - you show D1 as a zener, but if you're using a 1N5817 it's not and it shouldn't be.
I'll take a closer look when I have time, but I have used this circuit on a PCB with the ATMega. If you do that, a tip, use a ground plane on the board.
I'm using a 1N 5818 - Is that no good?
That should be fine.
OK well it still doesn't work. I rebuilt it again using a different breadboard but only ever get 3 volts max.
It could be that the inductor core is becoming saturated, that would limit the boost voltage. What type of inductor are you using?
Bro - That diode symbol is for a Shockley diode not a zener. The bars curl back on themselves where as a zener is only sloping shoulders.
It is the same one listed in the parts list on the Ladyada website :-
10-22uH power inductor
The schematic is for a LT1302 but the parts list shows this OR a Max 756, however the two ICs have different pin outs. I know you are using the LT1302 as you stated this in your earlier post.
The data sheet shows a 0.1uF decoupling capacitor across the chip where as the schematic doesn't have one. C2 should be a low ESR capacitor not just a general electrolytic one.
The data sheet shows pin 2 being connected to a 20K resistor and then on to a 0.01uF cap where as the schematic just show this connecting to a 0.1uF cap.
It is the LT1302-5 part you have is it?
Finally I am not sure if bread board construction is good enough, these sorts of circuits are very layout critical and the data sheet has a recommended PCB layout. The main concern is to keep the earth loops very short and have a good ground plane.
Thanks for the info. I have also tried the schematics in the datasheet to no avail.
It is the LT1302 not the LT1392-5.
I am not sure what you mean by a good ground plane? I am connecting the - of the battery to a common rail on the breadboard and ground all GND connections to that.
If you look on page 11 of the data sheet you will see the recommended layout. You will see an earth (ground) going under the whole of the IC. This is a ground plane, I don't think you can do this with bread board. You could try an use copper foil to mimic this.
That diode symbol is for a Shockley diode not a zener
It's actually a Schottky diode, named after Walter Schottky. The Shockley diode was a four-layer semiconductor, named after William Shockley, one of the co-inventors of the transistor.
It's actually a Schottky diode
Yes sorry I am dyslexic and the spell checker didn't stand a chance.
named after William Shockley
Odd that I thought it was named after William Diode.
Thanks Mike. Maybe I will give it another go on some perfboard and if that doesn't work resort to something else.
I am basically trying to power an Atmega168 chip and a 16x2 LCD display from a battery and want the longest battery life with the smallest package size I can get. I was originally going to use a 9v battery but they usually only give about 600mAh from the rechargable ones compared to about 2500mAh from AA's.
I thought this mintyboost circuit might fit the bill but perhaps not.
Ok even with perf board I would use copper foil on the component side to try and mimic that ground plane. As well as electronics stockists, you can get it from craft shops, they usually use it to do stained glass work.
Alternately you can use perf board with a colander ground plane on one side, if you do this try and cut it into the shape recommender.
However, high frequency, high current switching is not an easy thing. If you can get hold of a PCB then it would be best.
Since I brought up the ground plane subject, I should probably give more detail.
But first - sorry about the red herring on the diode - I thought I was looking at your schematic.
My experience is with the MAX756 chip. I had a PCB made with the boost circuit and the ATMega with external osc. on the same board. Not trusting my Eagle skills, I didn't use a ground plane. When I assembled the board, it appeared like the osc. would not start. I got another set of PCBs made with a ground plane, and the combination works perfectly. (So now I take the ground plane idea more seriously.)
However, while I was breadboarding I did not have this problem - probably because of the distance between parts - not sure.
The points in all this background are:
I think Mikes probably on to something re the difference between the two circuits. Also note that when I had the ground plane problem I still got 5V from the switcher.
I've used a mintyboost variant on a breadboard to give 12V from 4 AAs. It works fine when plugged into the DC input on an Arduino. I think it's likely there's some problem with your implementation rather than the circuit. Take a few pictures from several angles and post them, maybe someone can see what's wrong.
I have been thinking about this and what I would try is to put a potential divider (two resistors) in the feedback loop to see if the voltage is increased. My money's on that.
Ladyada do the PCB for £5 US so it might be easier if I just order that instead of trying to do it the hard way!!
Thanks for the help guys.