Creating a 5v reference from 3.3v

[somespirit]

Can someone recommend a way to create a 5v reference voltage from 3.3v? No more than 500uA will be drawn from it.

I'm about to breadboard this- File:Boost conventions.svg - Wikipedia, the free encyclopedia

.. as it seems like it will do what I need with only a few external components (I can generate the switching from a microcontroller output).

Are there any other convenient ways to do this, bearing in mind that I don't need regulation?

 

[crutschow]

You could use a swtiched-capacitor DC-DC converter such as these.

 

[Sceadwian]

And then run a 5V reference from THAT. No charge pump will ever make an adequate voltage reference alone. Since your current draw is so low you could also use high precision resistors to voltage divide the 5V source down to something the 3.3V device can measure directly.

 

[colin55]

For a simple 3v to 5v:
**broken link removed**

 

[somespirit]

Many thanks for the suggestions! I hadn't considered a transformer (as per the last suggestion), and I didn't know that LT made inductor-less DC-DC switchers, so I've got a bunch of research to do around these

I'm still going to attempt the basic charge pump, since the 5v doesn't need to be exact, regulated, or particularly ripple free... but the other options presented look more stable and reliable, so the eventual solution will probably be one of those. Appreciate it!

 

[Sceadwian]

What's the point of the 5V refrence then?

 

[somespirit]

The device on the other end looks for 5V to detect a connection and I can't be sure whether it'd successfully 'detect' if I supplied the 3.3V I have available.

 

[Mikebits]

For a simple 3v to 5v:
**broken link removed**

This would be simpler.
https://www.electro-tech-online.com/custompdfs/2010/07/MAX1896.pdf

 

[MrAl]

Hi there,


If you already have a micro controller chip that is to be used for this project and you happen to have an available output pin, then you can simply use that pin to drive a small transistor and that transistor drive a small inductor and with a Schottky diode you have a boost converter that should easily boost 3v up to 5v no problem with a set duty cycle.
An unregulated boost converter is a lot easier to build then a regulated one so you're getting off easy here
Parts List:
1k resistor
2N2222A transistor (or whatever you have around)
Small inductor (100uH or higher for say 50kHz operation)
Small Schottky diode like 1N5817 or even smaller
Small electrolytic output cap
Probably set the duty cycle to around 50 percent maybe with some cutback when the voltage rises or use a zener perhaps, keeping the input to the booster at 3.3v while supplying 5v to the other parts of the circuit.

As the voltage starts out at 3.3v the booster will start creating a higher voltage, which should reach at least 5v rather quickly.
The required power pin may have to be diode OR'd to accept the new voltage (bootstrapped) if you need to drive the uC at 5v too.

 

[somespirit]

Thanks MrAl, that helps clarify things! I'm interested that you can bootstrap the MCU to the 5V without regulation-- is this because the MCU load is small and relatively stable? I guess if you lit a few LEDs from I/O pins the bootstrapped voltage would fall slightly, or would you calculate the inductor and duty cycle with enough voltage overhead (before the zener clamps it down) to deal with that?

 

[MrAl]

Hi again,

The more current you draw from a boost supply the more the voltage will fall unless you increase the duty cycle, unless the booster is regulated some how.
A simple zener may suffice for your app here, where the booster uses a little more power that's all. The zener across the MCU pins will limit the voltage and as the LEDs turn on they sink more current but the voltage doesnt drop too much.
If you are doing a bit of AD conversion however you may need to use a shunt regulator ic in place of the zener so you get more accurate regulation.

Using a constant duty cycle you'd have to set it with any possible loads (such as LEDs) running so that the voltage never falls below a certain level.