3v to 5v using MAX666

[soadrage7654]

Hey
I am kinda new at electronics, so this might be something very simple that I am overlooking. I heard that you can use a MAX666 to convert 3vDC to 5vDC, which is what I need for a project I am working on. I have the circuit wired exactly the way that the MAX666 datasheet describes for the programmable voltage regulator settings, but no matter what I do, I can never get the output higher than ~2.6 volts.

My value for R1 is 1MΩ. R2 = 2.9MΩ

Any help would be appreciated. Or if there were an easier way to do this.

Thanks

 

[crutschow]

You have it backwards. The MAX666 is a linear regulator which can convert a higher voltage to a lower voltage, not the other way around.

To convert 3V to 5V you need some type of switching regulator.

What amount of current do you need at the output?

 

[soadrage7654]

I need 30-40 mA.

Hm. I guess that would explain why I could never get a higher Vout than Vin. Is there any way to use a MAX666 along with some other circuit to convert 3v to 5v? Or would it just be easier to get a switching regulator?

 

[crutschow]

Yes, you need some type of switching device. For currents under 100mA you can use a switched capacitor device such as the LTC3200 from Linear Technology (Linear Technology - LTC3200 - Low Noise, Regulated Charge Pump DC/DC Converters LTC3200 LTC3200EMS8#PBF LTC3200ES6-5#TRPBF LTC3200ES6-5#PBF LTC3200ES6-5#TRMPBF LTC3200ES6-5 LTC3200EMS8#TR LTC3200ES6-5#TRM LTC3200EMS8#TRPBF LTC3200ES6-5#TR LTC3200EMS8).

 

[soadrage7654]

Thanks for the help.

 

[crutschow]

It helps to understand voltage if you realize that it is the pressure of the current. Thus it is easy to reduce pressure by running it through a throttle valve (such as a linear regulator) but it requires a more elaborate mechanism to increase the pressure (such as a switching regulator).

 

[soadrage7654]

So is it the voltage or the current that powers the components. I'm guessing it is a combination of the two, but I'm not really clear on how exactly it works.

For example, I know you can't power and LED if the voltage is too low, but does increasing the current to a certain extent make up for it?

 

[blueroomelectronics]

If you're just trying to light a white LED with 3V then here's a very simple circuit that can do that.
Make a Joule thief.

 

[crutschow]

To continue the analogy, voltage is the pressure and current is the amount of flow. Power for a resistive type load is simply volts times amps or P = V x I (things can get more complicated for AC circuits if you include inductors and capacitors but we'll ignore that for now). For a resistor the current can be calculated with Ohms law, I = V ÷ R.

A semiconductor junction such as a diode or LED has a sort of threshold voltage, below which is doesn't significantly conduct in the forward direction (it blocks current flow in the reverse direction). When you exceed that threshold voltage (about 0.6V for a silicon diode or 1.5 to 4V for an LED depending upon the type) then the diode will start to conduct.

The resistance of a diode is quite low once it starts to conduct current above its threshold voltage so you need some method to limit the current (often a series resistor or sometimes a more elaborate current control circuit) to avoid burning it out.

 

[soadrage7654]

I was just using the LED as an example.

Ok, so in order for the current to be able to flow through a diode like an LED, the voltage must first be higher than the threshold voltage. This is what causes the voltage drop, right? I knew that silicon diodes did this but I never made the connection with LEDs.

Thanks again.

 

[crutschow]

Yes, LEDs are also diodes (hence the name Light Emitting Diode) but the visible light ones are typically made of gallium arsenide, silicon carbide, or other compound semiconductors, instead of silicon.