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Picture of Adjustable Voltage Step-up (0.7-5.5V to 2.7-5.5V)
Introduction:
A voltage step-up is a circuit that increases the voltage. It can be AC/AC, AC/DC, DC/AC or DC/DC.
This voltage step-up is a DC/DC adjustable voltage regulator. Usually a voltage regulator is fed by a higher input than output voltage, for example 9V IN to 5V OUT. This circuit will take a low voltage (down to 0.7V) and step it up to adjustable 2.7-5.5V. Since it is a regulator, the output voltage will stay constant regardless input voltage (0.7-5.5V), as long as output voltage is higher than input. It cannot step-down, only step-up. Are there any ICs that can do both?

I build it for usage in this project:
http://www.instructables.com/id/Battery-Charger-Powered-by-Fire/

Applications:
This is a typical circuit for a battery-powered USB-charger, for example two AA batteries (3V) to power 5V USB. There are tons of DIYs how to create that. They are often hard-specified to 5V output power. This construction can be used in a range of other applications. Many electronic devices work within 3-5 V and often you want to power them by low voltage power sources.

Some input examples:
  • Solar panels
  • Generators
  • Batteries
  • Peltier elements (TEC/TEG modules)
Some output examples:
  • ICs
  • Displays
  • Motors
  • LEDs
  • Battery/USB charger
Costs:
All components cost me about 7€ but it's totally possible to find cheaper components!

If you want to construct this one, then continue reading!

Next Step: Specifications
 
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thanks for giving such a beautiful and knowledgeable details............

TroyL23 months ago
I need a item like this to detect .7v-5v no more load then 20ma and trigger a 5v relay
TroyL23 months ago
Is there a way to make this detect 0.7v and less then 20ma and output 5v
micro.maspil4 months ago

sir i am thinking to make this project, to make a portable 5v charger for my android phone with my 6v lead acid battery may i ask if i can change the IC maybe LM2623 by T.I. or LM2621 by T.I because it can go input from 0.8v to 14v? please reply thanks

are there any replacements for the IC

because there arent any in my electronics store ..

did you connect anything to LB1

need some help i built the above schematic but it didtn work was wondering if you had any advice

52625spm5 months ago

HI Joohansson,,,I'm doing this as my miniproject. But my faculty is asking me to simulate this circuit first. So can you please suggest me any simulation softwares which has MAX757 IC and IN5817 diode.I tried with ORCAD PSPICE I could not get the schottky diode library there.

Joohansson (author)  52625spm5 months ago
Sorry, I have no experience with simulation software.
Oh ok ok,,,,,thanks for your immediate response..
52625spm5 months ago

HI Joohansson,,,I'm doing this as my miniproject. But my faculty is asking me to simulate this circuit first. So can you please suggest me any simulation softwares which has MAX757 IC and IN5817 diode.I tried with ORCAD PSPICE I could not get the schottky diode library there.

AK.aka.KayEy6 months ago

I don't know if someone already told you that LT1073 does Step-Up and Step-Down. Just telling because you asked if there is an IC that can.

Greetz and thank you for writing this. :)

i want to get all the accessories of this project ,from wher I can ourchase in Pakistan

i want to get all the accessories of this project ,from wher I can ourchase in Pakistan

i want to get all the accessories of this project ,from wher I can ourchase in Pakistan

pmccourt7 months ago

Found Step-up/Step-down IC's while looking around for 757's :D

The MAX167x series!

http://www.alldatasheet.com/view.jsp?Searchword=MAX167

Joohansson (author)  pmccourt7 months ago
Nice! Only 300mA output current but still quite useful for some applications like LED driver.
Joohansson (author)  Joohansson7 months ago
My mistake, it support even higher current. 500mA at 3V, seems to be better than the 757.

Yeah :D Seems they discontinued the 757 in favour of it.
It was a fortuitous find :3

pmccourt pmccourt7 months ago

P.s. Love the campfire TEG btw! I'll be adapting it into something similar for a college project/infinite music from my phone while camping :3

Joohansson (author)  pmccourt7 months ago
Cool!
arjunmenon9 months ago

You mentioned -

Since it is a regulator, the output voltage will stay constant regardless input voltage (0.7-5.5V), as long as output voltage is higher than input.

Shouldn't it be that "as long as the input voltage is higher than output"?

By going what you mentioned, so if I have a 2.4V battery cell, I can power a 5V load, even if the cell drops to 1.8V after sometime? It will still output 5V and have the load running.

Thanks.

arjunmenon9 months ago

You mentioned -

Since it is a regulator, the output voltage will stay constant regardless input voltage (0.7-5.5V), as long as output voltage is higher than input.

Shouldn't it be that "as long as the input voltage is higher than output"?

By going what you mentioned, so if I have a 2.4V battery cell, I can power a 5V load, even if the cell drops to 1.8V after sometime? It will still output 5V and have the load running.

Thanks.

Joohansson (author)  arjunmenon9 months ago
A better description is "as long as input is lower than output". 1.8V should be fine as long as the output current is not too high. I think I have a graph you can look at or it was in one of my other instructables.
Fragmaster10 months ago

If I needed to supply up to 1A output at 5.5V and a supply (battery) of 3V minimum, would this circuit be able to handle it? the Efficiency graph only goes up to 500mA, so I think I would need another regulator to do the job. Do you know of a variable output regulator that would work?

shina-ct11 months ago

i constructed the circuit on a breadboard, but on testing, it only produces 0.8V output for an input range of 1-6V. Please how do I know if the issue is with the connection or if the ic is damaged. Thank you.

Joohansson (author)  shina-ct11 months ago
Hard to tell. I will have to do a verification of the circuit. I will write here again when/if I have time to do that.
Ok. Thank you.

Hi, I am trying out this project. I was able to find all the parts except the Max757C. Please help me as to what to do? I was able to find 756C. What should be the circuit changes and is there any equivalent IC. Please help me. I really need more information. Thank you in advance.

You might have already found a converter that can boost, and buck. In case you haven't, you should take a look at this: http://en.wikipedia.org/wiki/Single-ended_primary-inductor_converter . It's called a SEPIC converter, it can even go from buck to boost, or vica versa, without an interuption in the output power, you won't even notice when it crosses the input voltage.

Thom
Joohansson (author)  Thom Kouwen1 year ago
Thanks, I might try that circuit some day =) Looks easy to build.
lraggio1 year ago
Hello! Thanks for this instructables :)
I've a question: Why on the scheme on pin 6-2 there's a P1 and R1 but on the "shopping list" and the board scheme there's also P1R1 and a P1R2?
Thanks!
Joohansson (author)  lraggio1 year ago
Hi,
I had to think a bit and now I remember! It´s actually in the description in some way. In the layout i have simplified P1 to make the drawing easier to understand. But P1 in the drawing consists of P1+P1R1+P1R2 in serie. P1R1+P1R2=57Kohm and P1=100Kohm. That create the correct interval of 57-157kΩ instead of 0-100Kohm if you just use P1.

That make sense?
Samuel kos1 year ago
Joo where did you happen to find theses maxim 757 ICs I cannot find them anywhere
Joohansson (author)  Samuel kos1 year ago
https://www.elfa.se/elfa3~se_sv/elfa/init.do?item=73-076-31&toc=0&q=max757
Thank you very much for the link! ( is it in German?)also would the product ship from Germany or where ever it comes from ?
Joohansson (author)  Samuel kos1 year ago
It was Swedish. You can choose other countries:
https://www.elfa.se/elfa3~se_sv/StartPage.do?ignorecookie=true
smartablet2 years ago
Hello, I appreciate your contributions but my question is, it possible to build a DC-DC step-up with input voltage of 6V/ 2Amh to out-put of 12V/7Amh if your answer is yes, email me kingjoejoe29@yahoo
jimvandamme2 years ago
You're exceeding the maximum rating on the boost switch output (pin 8, LX). Somewhere between 5 and 10,000 volts, it will fry. At 5.5V out, you're probably OK but if somebody wanted higher voltage, it would be cool to put an extra stage in there to take the extra voltage so you could get more out.
dutado2 years ago
Hi, if you want to make it a tiny bit more effective for low output current, replace the 1N5817 diode for some other with lower junction capacitance (such as 1N4937 or 1N60).
Generally:
Standard silicon diodes are great for non-critical use. (usable as HF varactors, low Q)
Schottky diodes are good for use as high power rectifiers and varactors (they're great, but have a bit higher ESR than serious varactors, so do zener diodes).
Germanium point-contact diodes are great for RF equipment and low-drop rectifiers. Low capacitance. Not very good as varactors cos' they have high parasitic reverse current.
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