# Cheapest way to amplify 40ma to 2 amps

1. Mar 14, 2015

### Superposed_Cat

Hey all, working on a pet project where I need a microcontroller with a 40ma pin output to be amplified to 2A, op-amps can't do the job, and H bridge motor drivers will be too expensive i think considering the amount of motors I need. What is the cheapest and smallest way to do this? Any help appreciated.

2. Mar 14, 2015

### zoki85

3. Mar 14, 2015

### Superposed_Cat

Ohkay but then il need to increase the voltage beforehand, is it easier (and cheaper) to add voltage then sacrifice voltage for amps or to simply add amps?

4. Mar 14, 2015

### tech99

I think a single power transistor would do this.

5. Mar 14, 2015

### davenn

you cannot just make more current out of nothing. Voltage and current are intimately related
if you need more current, then you need to have a poser supply that can do that

So for your microcontroller with its low current output, you use that to switch transistors (FETS)
connected to a power supply connected to a higher voltage/current source

Have run out of time to post a circuit for you .... will do so when I get home if you still need an example

cheers
Dave

6. Mar 14, 2015

### zoki85

As concerns active methods of the conversion, power transistor, like others said, is the simplest way to go.

As concerns passive circuit methods, I'm not sure.

7. Mar 14, 2015

### Baluncore

The obvious answer is that you should use a transformer with a turns ratio of 50 to 1. If your microcontroller output is 40mA at 5V, you will get 2amp at 100mV out of the secondary. I don't think that will operate a motor. 40mV * 5V = 200mW. 100mV * 2A = 200mW. You probably need more power from some other supply.

So you want to drive a motor. What type of motor? Bidirectional? What voltage?

8. Mar 14, 2015

### Staff: Mentor

Do you have an external power supply you can control (with your low current)? Also, what is the voltage of your output and what does the motor need? That is not really clear from your description.

9. Mar 14, 2015

### jim hardy

maybe not cheapest , but easy.

however if it's just on-off, a relay or a switching transistor as suggested above should work admirably.

10. Mar 15, 2015

### davenn

hi Superposed_Cat

I did respond earlier ..... your description of what you are wanting to do is pretty vague. hence you didn't get the responses that would have helped
Also, you cannot "amplify current" in the way I suspect you are thinking, as I hinted at earlier.

for the output of a micro controller to control a single motor, to start and stop it, here is an example....

This is a basic way to do it this is where you can have a low current output from the controller operate a relay that can switch a
higher current to a motor. My motor supply shows 5V but it can be whatever is needed for your motor. 12V, 24V, as long as the
relay contacted are rated for the voltage and current required by the motor

Another option ..... You can do away with the relay and put the motor in the relay's place and use a darling transistor instead, you just need
to again make sure that the micro can operate the darling transistor and that the transistor is rated for the current required by the motor

since you have given no other info, its difficult to know what you are trying to achieve ??

If you need to be able to make the motor go forward and reverse, that gets more difficult ... requires more circuitry
If you need to be able to control the speed of the motor, then you also need a H-Bridge. not overly difficult but again requires more circuitry

so please give us all the full project info.

Dave

11. Mar 15, 2015

### Superposed_Cat

Me and my friend are planningt o build a quadruped robot using an arduino microcontroller, each leg will have two motors, 3v each, about 1-2A. the issue was was that the microcontroller can only output 40ma. Each motor has to go both ways, we considered relays but theyre faily expensive compared to the other options. Can you still make them go two ways wit ha darling transistor?

12. Mar 15, 2015

### davenn

No, you need a H-bridge setup for that

here's some links to give you ideas ....

put this into google for dozens of other examples ....

controlling a motor with an arduino microcontroller

Dave

Last edited: Mar 15, 2015
13. Mar 15, 2015

### Staff: Mentor

The motor will be subject to just 3 fixed drive levels: full speed forward, full speed reverse, and of course, OFF?

What will your Arduino's corresponding output voltages be?

14. Mar 15, 2015

### Superposed_Cat

Do arduino's have custom voltage output? ie 0-40 not 0 or 40 only?

15. Mar 15, 2015

### davenn

have you looked at any of those links I gave you ?