Different voltage requirements for components

[Salsa Stint]

Hi,

I'm creating a circuit with an arduino clone (https://moderndevice.com/product/bare-bones-board-bbb-kit/) and an LED driver (MM5451, pdf datasheet: **broken link removed**). Currently I'm powering everything via USB FTDI cable attached to the arduino clone.

On the FTDI pins attached to the arduino, I see 5v. However, on the other side of the arduino, the +5V/GND pins actually report ~3.5V. Now, the IC datasheet says that it needs "4V-11V" as supply. Does this mean I can't power the IC with the "remaining" voltage?

How are issues like this normally addressed in circuits? My feeling is that if I power the circuit with a higher voltage (non-USB) source, everything would work?

I've also come across "voltage multipliers," but I don't know enough about them to know if this would help me as well.

Thanks!

 

[MikeMl]

Is your arduino 3.3V or 5V?

All of my Arduino projects are stand-alone, so the last thing I would want to do is to power the project from USB. Once the code is debugged, The USB cable goes away.

I prefer to use 5V Arduinos, and typically, I start with a 12Vdc supply, either a SLA battery or a Wall-Wart, or a Wall-Wart charger for the SLA implemented inside the Arduino. The regulator on the Arduino usually has enough capacity to power some extra stuff...

 

[Salsa Stint]

Hi Mike,

It is a 5V board, linked above... but the datasheet says it can handle a 6-12V supply, by adjusting some jumpers. When do I have to worry about "burning out" the arduino board, though?

Wall-Wart charger for the SLA implemented inside the Arduino

Can you describe what you mean by this? If SLA is "sealed lead acid" battery, what is meant by "implemented inside the Arduino"? Do some arduino's have on-board batteries?

Thanks!

 

[MikeMl]

It is a 5V board, linked above... but the datasheet says it can handle a 6-12V supply, by adjusting some jumpers. When do I have to worry about "burning out" the arduino board, though?

Powering just the Atmel chip byitself, you can go up to about 15V input. You may have to lower the input voltage if you are expecting the Arduino's on-board 5V regulator to supply 5V to shields or other external hardware that you add. The limitation is caused by heating of the on-board regulator IC. Just feel the regulator with your finger. If you get burned, it is too hot

Can you describe what you mean by this? If SLA is "sealed lead acid" battery, what is meant by "implemented inside the Arduino"? Do some arduino's have on-board batteries?

No. One of my recent Arduino projects was a drive-through swing-gate controller. The gear-motor that moves the gate is 12Vdc. I used a 12V sealed lead-acid battery to provide the high-current to run the 12Vdc motor. The battery also powers the Arduino, the RF remote-control receiver, limit switches, etc. I added an AC wall-wart charger to keep the battery charged. The Arduino ADC measures the battery voltage and the Arduino program I wrote turns-on and turns-off a transistor switch between the wall-wart and the battery. The battery will run the gate for several days in the event of an AC power failure. The battery is recharged automatically when the power comes back on.

I used a similar approach to make a high-current smart charger for my electric golf cart. However, since the battery voltage goes all the way to 48V, I couldn't use the Arduino's on-board regulator directly. I made a "pre-regulator" which drops 48V to ~10V to power the Arduino mini...

 

[Salsa Stint]

Interesting!

I made a "pre-regulator" which drops 48V to ~10V to power the Arduino mini.

Do you remember the components and/or design of this? I'd like to learn more about how that's done.

I remember hearing from many EE types that "separating" the arduino voltage source from the rest of the "high power" parts of a design (such as motors, actuators, solenoids,) but it's still not clear how that's actually done. Does this mean two actual voltage sources? Do you have a general tip for this aspect of design?

(Thanks for all your tips, and sorry for all the follow-ups, often one question leads to many more, as I learn. )

 

[KeepItSimpleStupid]

Does this mean two actual voltage sources? Do you have a general tip for this aspect of design?

You need to understand ground/common/earth etc. and that's tough. You need to understand how ground loops are formed.

The general tip is your 0V reference needs to be one place. The best thing you can do is put all of the high current grounds together, the analog grounds together, the digital grounds together and then connect them at one point

 

[MikeMl]

I used a similar approach to make a high-current smart charger for my electric golf cart. However, since the battery voltage goes all the way to 48V, I couldn't use the Arduino's on-board regulator directly. I made a "pre-regulator" which drops 48V to ~10V to power the Arduino mini...

...Interesting! Do you remember the components and/or design of this? I'd like to learn more about how that's done...

The schematic is on another computer across the parking lot...

The problem is that most IC regulators (or cheap Chinese Buck Regulators) will not tolerate an input voltage as high as 48V, besides I like to build things from parts I have laying around without waiting for the Brown truck. I had some NPN power transistors which would dissipate >5W and had a Vce(max) of ~100V. I also have a collection of 1W Zener diodes, so I threw together some thing like this using a 12V Zener:

I ran a simulation to help explain how it works. AFAICR, the Arduino and its associated stuff draws about 50mA from its Vin pin. The simulation shows what happens when the battery voltage is 30V (fully discharged, GREEN trace) and again when the battery voltage is 48V (peak under charge, YELLOW trace) as the simulated Arduino current varies from 20mA to 70mA (x-axis).

I show two sets of plots. The upper pane shows what the Arduino's V(in) will be as a function of battery voltage and the Arduino's current demand. About all we can say is that at any given Arduino current, the Arduino's input voltage will be between the green and yellow trace. However, this is well within the allowed range, and the fact that it is not perfectly regulated doesn't matter because the Arduino's on-board regulator will take care of that.

The lower plot pane shows the power dissipation in the NPN transistor Q1. Note that when the battery voltage is 48V (Yellow Trace) and the Arduino current is 70mA, the power dissipation in the NPN Q1 is 2.5W. This is the range where the NPN has to be bolted to a heatsink. AFAICR, in my Golf Cart charger, I bolted it to the sheet steel enclosure using an insulated mounting kit. R1 should be a 1/2W resistor.