Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Portable power for my device

Status
Not open for further replies.
Well, the situation is the following.
I have successfully built my touch panel device, mounting a TFT LCD over a perfboard where I put a PIC controlling it and some I/O such as LEDs and switches. It looks very neat and portable (I can hold it in my hand)

The thing is, so far in my projects I am using power from ...um I dont know what is the correct name... power devices? manufactured by COSEL. I have to connect it to a power outlet (AC), this transforms it into my required 5V (although the whole system is 3.3V, the LCD transforms this from 5V as an option- it can also receive 3.3V).

But my device seems so portable that I would love to have a portable power for it too (and free it from connecting to a power outlet). What I need is a battery of some sort.

Before I used to use batteries, and tried to get 5V from say 4 1.5V batteries but that gives 6V and although it worked to some extent I was scolded...

So my question is what is the Correct way to get this 5V (or 3.3V if that is the case) to power my device??

Thanks for your expert advice
 
See this here!!

https://www.mikroe.com/mikromedia/pic18fj/
This does EVERYTHING you are doing and has a lithium battery connector with a charger circuit that will charge from USB.... I have the pic32 version..
 
Ian has linked you to specific devices above which you may find helpful. But for completeness I'd just like to describe in more general terms the type of solution you are looking for.
  1. Linear Dropout Regulator (LDO) - this provides a fixed output voltage for a wide range of input voltages provided the input voltage is ~0.7V above the desired output voltage. It does this by 'dropping' the excess voltage over the LDO. This method is inherently inefficient and the heat generation has to be managed.
  2. Switch Mode Power Supply (SMPS) DC-DC regulator - there are a few different types here, buck or flyback for example. These are more efficient (upto 95%) but require more components and can be noisy. However they can be obtained as a discrete module so you don't have to build it yourself
I'd suggest the following for you:
Use a 9V battery as they are easier to change, from this use a DC-DC regulator to get down to 5V.
This http://uk.rs-online.com/web/p/non-isolated-dc-dc-converters/7962138/ is a 1.5A 5V DC-DC regulator
 
Not to be picky, but the L in LDO stands for Low. A low dropout regulator typically has a max input-to-output differential of less than 1 V, and in some cases only 0.1 V, while standard linear regulators have a dropout voltage in the 1.25 to 3 V range.

ak
 
Last edited:
Depends on what the datasheet for the LCD assembly says.

ak
 
forgive me if I am asking a foolish thing...
Perfectly reasonable question

If you connect it to a higher voltage power supply you'll have much greater power dissipation which will generate more heat. These linear regulators reduce the voltage by 'burning' the excess, if your LCD module has been designed to accept higher voltages and deal with the heat created then you might be ok. However if its been designed with a max of 5V then you could end up destroying the component. From the datasheet the LDO has a 12V max input but i wouldn't suggest running it at that!

You should also keep in mind that your battery voltage will drop as it discharges.

Like i said i'd get a higher voltage battery and then use a SMPS to drop down to 5V
 
5v from a single Lithium polymer battery is easier than 3.3V because a LiPo generally runs from 4.2V (at full charge) down to ~3.1V (considered discharged) so the battery voltage is always lower than the converters output (5V).
At 3.3V the converter must either have a boost and an LDO (these exist) or a buck-boost (more common) because the input can go above/below the output.

Although everything runs from 3.3V, I would go for a lipo-5V boost module. This may not be as efficient (power loss in regulators, converter loss, parts draw more power at 5V than 3.3V etc..) it will be more convenient as boards that both boost lithium polymer to 5V, and have a charging circuit for said battery are quite common:

https://www.sparkfun.com/products/11231

That is apparently a 'buck/boost' so can supply 3.3V or 5V from a lipo cell.

Lithium batteries are handy because they can have high capacity for their size, fairly ubiquitous, and for 'handheld' devices that tend to be flat, the cells themselves can be as thin as 4mm. The downside is they require specific charging circuitry, often from USB for cells with <1000mAh capacity. But with sparkfun/seedstudio/adafruit industries knocking out small charger modules for a few $$ it has become a mainstay for hobbyists to power their projects. If you're planning on going into production, of course it would be better to design your own power supply, to drive down costs and add facilities such as - powering device from charger input while the battery is charging. But for proof-of concepts, and one-off's it works just fine.

Beware of boost converters, often (but no always) when 'disabled' the output is connected to the input via a diode. This means if you disable the 5v converter to turn your device off, the battery will still power it, just at 3.7 - ~0.4V = 3.3V. Adding a switch in series with the battery works, but then you have to make sure that is 'on' when you charge it :D I think the sparkfun device above has 'true disconnect', so you can power off your device from your microcontroller.
 
Yeah the data lines won't be connected. And it breaks those pins out to a header strip on the side anyway, so if you don't want to use a USB connector on the input, or the output, you can just wire it up. It just uses USB connectors because its often used to power USB devices (for charging phones) and to be charged from USB. But it will work just fine with a 5V power supply, providing it has enough current capacity.

A word of warning though. Charging circuits use the current drawn by the battery in 'constant voltage mode' to determine when the battery has been fully charged. The upshot is, if it is powering your circuit whilst charging, that current draw is added to the battery, so the charger might not end the charge time. I wouldn't worry about it too much. With just 5V in for charging, and 5V out for your project, its a nice little module. You can experiment with various battery capacities, but 1000~15000mAh is often great for small portable things
 
well it seems the power boost 500 does not charge the batteries, just power up a circuit with batteries.
It is the PB500C the one that can charge while powering it at the same time.

maybe I ll buy it one of these days.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top