Help with electronics.

[m wisdom]

I'm building a "device" and need some help with part of the electronics. I got most off it working but I only have some basic knowledge about electronics and I have run into a problem I don't know how to solve.

What I have is a 9V power supply, a 3V vibrator and a control circuit that gives me a 0-8V signal.
I can't figure out a good way to get the vibrator to be controlled by the signal from my circuit.
The problem is twofold, i need to boost the current because the control circuit don't have enough power to run the vibrator and I need to get that 0-8V signal down to 0-3V.

The main problem I have is that I don't know how to boost the current without losing any voltage

Any help would be appreciated.

 

[Weird Harold]

What I have is a 9V power supply, a 3V vibrator and a control circuit that gives me a 0-8V signal.
I can't figure out a good way to get the vibrator to be controlled by the signal from my circuit.
The problem is twofold, i need to boost the current because the control circuit don't have enough power to run the vibrator and I need to get that 0-8V signal down to 0-3V.

I'm going to assume these are solid state circuits and not bread-board circuits.

First the power problem:

Current limitations are, to put it a bit simplistically, are all about heat disipation. You either need to find a circuit with bigger robust circuit components that don't heat up as much, or youneed to find a way to cool the components you do have so the magic smoke in them doesn't escape because of over-heating.

The better choice is to find higher rate components, because even cooling can only do so much when you run a circuit beyond it's designed current rating.

Second, the voltage conversion problem:

If you opt to find a higher rated component for the control circuit you might as well ask the Radio Shack guy for one in the required voltage range.

However, an additional component can solve both problems -- what you need is a power amplification circuit that also is a voltage divider. Almost any basic electronics textbook contains examples of a single transistor circuit that will do what you want.

A simple voltage dividing resistor network will reduce the voltage, but it won't do anything for your current limitations. Using your low current control circuit to control an amplifier circuit that can handle the necessary current directly from the battery is your best bet.

 

[m wisdom]

I thought it would be that easy myself but all the power amplification circuits that I have found steel some voltage. Let's say a circuit takes 1V that means that when the input is between 0-1V the output is 0V.

Any idea on how to get around that, is it possible to lift the input voltage by 1V to compensate?
I can do it by adding a battery but I'm sure there are a better solution.

 

[m wisdom]

The problem have been solved.

 

[Weird Harold]

I thought it would be that easy myself but all the power amplification circuits that I have found steel some voltage. Let's say a circuit takes 1V that means that when the input is between 0-1V the output is 0V.

Any idea on how to get around that, is it possible to lift the input voltage by 1V to compensate?
I can do it by adding a battery but I'm sure there are a better solution.

I suspect you'll need to "bread-board" a custom circuit.

I've been retire for fifteen years and seldom had a need to design circuits from scratch, but a basic transitor circuit to take a 9VDC bias voltage and control it over a 0-3VDC range proportional to your 0-8VDC low current control circuit is a really basic circuit.

Basically you put the transitor in series with a fixed (high current rated) resistance transistor so that as the control voltage changes, the voltage dropped across the transistor changes from 1/3 of the 9VDC bias voltage to no voltage.

You use the same 9V battery to bias both the control circuit and the output circuit. With the right components, that kind of simple "amplifier" circuit can provide outputs from 0V to whatever upper limit you choose and as much current as the components can handle.

In fact, it's probably what the output portion of your control circuit looks like but with components too small to take more than a few mili-amps.

ETA: The explanation of the circuit is at http://www.tpub.com/content/neets/14179/css/14179_77.htm and there are links there to the preceding discussions of basic transistor function and circuits.
http://www.tpub.com/content/neets/14179/img/14179_77_1.jpg

 

[m wisdom]

Thank you for the help
I solved it with an op-amp to change the voltage offset and and Darlington connection to get some current. I can put up to 1A throught the vib now