Overview. The vibration motor in the circuit I'm working on "tracks" the energy in a particular frequency band of an audio signal. For example, in the filter circuit below, the central frequency is about 2kHz, so when the audio signal has lots of power around this frequency, the motor vibrates a lot; otherwise, it doesn't. The problem I'm having involves getting enough current (200mA) to the little motors.
Signal Path. Specifically, an audio signal from an iPod (~1V) is inputted to a bandpass filter (attached), which has a gain of 4 and central frequency of 2kHz. So, the filter outputs ~4V when the audio signal has a large 2kHz component; however, the current isn't high enough to drive the motorsit needs to be 200mA. (The motor's impedance is about 50 ohms, and it vibrates with increasing amplitude from 3 to 5 V; there's a bridge rectifier preceding it in the actual circuit.) I've tried a power amplifier (LM386N4) between the filter and rectifier which has worked, but it's not ideal, because it needs a fair number of external components and its minimum gain is 20; I need a gain of 1.
The Problem: What is a straightforward way to boost the available output current of my filter from 20 mA to 200 mA (without changing the voltage)?
(I've looked into using an emitter follower, though I'm not sure whether a one transistor (http://inside.mines.edu/Academic/courses/physics/phgn217/lab4/lect7/sld013.htm) or two transistor (http://www.play-hookey.com/analog/increasing_output_current.html) design is suitable, and perhaps more importantly, what transistor model to use...)
Suggestions and advice would be very welcome. Thank you.
Signal Path. Specifically, an audio signal from an iPod (~1V) is inputted to a bandpass filter (attached), which has a gain of 4 and central frequency of 2kHz. So, the filter outputs ~4V when the audio signal has a large 2kHz component; however, the current isn't high enough to drive the motorsit needs to be 200mA. (The motor's impedance is about 50 ohms, and it vibrates with increasing amplitude from 3 to 5 V; there's a bridge rectifier preceding it in the actual circuit.) I've tried a power amplifier (LM386N4) between the filter and rectifier which has worked, but it's not ideal, because it needs a fair number of external components and its minimum gain is 20; I need a gain of 1.
The Problem: What is a straightforward way to boost the available output current of my filter from 20 mA to 200 mA (without changing the voltage)?
(I've looked into using an emitter follower, though I'm not sure whether a one transistor (http://inside.mines.edu/Academic/courses/physics/phgn217/lab4/lect7/sld013.htm) or two transistor (http://www.play-hookey.com/analog/increasing_output_current.html) design is suitable, and perhaps more importantly, what transistor model to use...)
Suggestions and advice would be very welcome. Thank you.
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