Amplify DC Voltage (from 5v to 12v)

d123 said:

I think there are many ways to do this, but I'm convinced you will need an external power supply capable of powering 1 or 5 motors. The few Arduino circuits I've seen for motors have an external power supply. Post #12 explanis why. You can put lots of ICs between the Arduino and the motor(s) but it won't change the a) power requirements of the circuit and b) power capability of the Arduino.
A simple solution, that could work, ...using an external 12V supply..., is to use a buffer IC - like the 7404, between the Arduino output and fan out one 7407 output to some transistors, the transistors used to drive your motors. If the motors have such small current requirements that 130mA is enough for 5, then even a BC547/557 could suffice, but better a slightly more powerful one (e.g. more than 100mA capability each transistor), or a small mosfet.
My first circuit is embarrassing to remember, as I spent two weeks trying to match my ill-informed wishes to components that could not perform magic, and by the hundredth time some-one explained it to me, I realised that a momentary pushbutton will only keep a circuit on momentarily, no matter what I might want it to do - I'm not sure if you aren't doing the same thing - re fixed idea that won't work - with the Arduino power capability, if you don't mind me saying.

Why not try using a buffer IC and a transistor array (and an external power supply/USB power hub if the Arduino can pass large currents)?

If you could explain why it has to be through the Arduino without an external power supply, and any other fixed parameters you must follow, it is easier for other people trying to help understand your needs.

Click to expand...

d123 said:

Okay, it's a non-negotiable issue.

This Step-Up voltage regulator has a picture/schematic on page 2 of the datasheet ("Typical Application"), that is tailor-made for your requirement: 5V in > 12V out (and up to 800mA out), that should cover 5 motors, and no doubt if you have been set this as a project/homework by another person then it is to be assumed that 5 motors can be powered by the Arduino GPIOs. I still have my doubts...

Anyway, it looks basically the same as the schematic you posted with another converter IC.

https://www.ti.com/lit/ds/symlink/lm2577.pdf

Rather than PWMing the converter, that is repetition, I'd put a diode from GPIO out pin to the ground pin.

Click to expand...

Audioguru said:

Nominal current of your motor? But that is when it is running and its back EMF is reducing its current. What about when the motor starts running then it needs its rated "stalled current" that is MUCH HIGHER than its nominal current? Then the overloaded L293 will smoke and die. The stalled current is much higher than its nominal running current because when it starts it is not turning so it is stalled and not generating a back EMF voltage so it is simply a long piece of wire that draws a very high current.

You keep saying the 5V comes from your Arduino board. But do you mean the 5V is coming from the 5V power supply that feeds your Arduino board? Or does the Arduino board already have a 5V power supply on it and will it provide enough current to do what you want?
Then will you use a voltage stepup IC to convert the 5V power to 12V power? Did you know that the 5V current will be 12/5= 2.4 times or more higher than the 12V current?
Then will you use the logic outputs of the Arduino to feed the logic inputs of the L293 to turn the motors on and off?

Click to expand...

Audioguru said:

5V from the USB on a pc does not produce enough current to boost to 12V then run a high current motor.
The motor with a 0.95A starting current is powered from a boost converter with an efficiency of maybe 85%. Then its current from the 5V USB is (0.95A/85% x 12V/5V=) 2.68A!

Click to expand...

in post 2 someone reminded something about pwm and 555 ic.

Click to expand...

KlausST said:

Hi,


OK, the "PWM" of post#2 confused you.

Here my advice:
If you are not sure whether to believe in the datasheet or a post of a forum (mine included) then trust the datasheet.
Especially when they are from big reliable companies.

I see six parts in the schematic of your post#15. This is enough. It makes 5V to 12V.
You can run a simulation with LTspice or other simulation tools.

*****
I don´t know what you mean with "current amplifier".
The motor needs power. More than the USB can supply. There is no overcome. You need an extra power supply.

Klaus

Click to expand...

d123 said:

Try increasing the value of the output capacitor for a smoother output voltage. That's probably about as good as it gets... and if you imagine that image of 0.025 seconds but zooming out 40 times, that'd be a pretty respectable DC straight line output.

Click to expand...

d123 said:

I don't know..., from googling the info., the Arduino One official web says 20mA per output pin, and 50mA on the 3.3V pin, that you can use an adapter that is 5 to 12 or even 20Vdc, but best stick to 9Vdc max. for more than one reason, that the adapter you use has to provide current from 250mA, up to 1 Amp...
And if your computer USB connection (is that what you're using?) can provide the necessary current, and the boost converter doesn't draw more current than the Arduino pins can supply, which your simulation might simulate better than I can guess, then I'll just say yes, whatever, could work, who am I to know, but 0.95A is 1 Amp.

You should check that the Arduino GPIO output pin won't have to supply the converter with more than 20mA... 0.02A at any one time. I don't have an Arduino, maybe you know something that I don't understand about how it works.

The capacitor on the output is presumably to smooth the ripple, it is a reservoir capacitor, so in my opinion if you make it smaller the output will have more ripple - bigger spikes, not smaller spikes - you could put a much smaller capacitor in parallel to the 100uF one for high frequency, might help.

Best of luck, hope this design works for you.

- - - Updated - - -

Just to see in your simulator, it's not really the same as a motor, but the best I can think of... I think you could put a 12.65 ohm resistor as a load on the 12V output (if your motor really is 0.95A start-up), and first try to configure the input voltage and current parameters to the converter in the simulator as best you can (presumably 5V/20mA, unless I've misunderstood anything), to see if it will work or not.

Click to expand...

Audioguru said:

An L293 turns on with an output signal from your Arduino then passes its 12V power supply current to the load. It does not amplify the current, it simply switches the current, but you do not have enough current.
For an output of 12V at 0.95A the 5V to 12V boost converter needs 2.68A from the 5V.

An amplifier or a switch does not work with magic, instead it has a powerful power supply. It passes some of its power supply to the load.
An L293D has a typical input current of 0.1mA and can switch an output connected to its power supply with a current of up to 600mA.

Click to expand...

Audioguru said:

An amplifier simply passes some of its power supply current to the load. An amplifier does not increase its input level, instead it increases its output level and its output has a power supply.
But an L293 is not an amplifier, it is a switch. When its input has a tiny current then its output switches on its power supply to the load.
A ULN2003A has a typical input current of 0.93mA then its output switches on its power supply to the load.

A transistor amplifies signal levels. It has a power supply connected between its output and the load to pass some of the power supply current to the load.
An audio amplifier and a video amplifier also amplify signal levels. They have a power supply connected between their outputs and their loads to pass some of the power supply current to the loads.

Click to expand...