Current Amplification

[Marco203]

Hello,
I have a function generator to generate a sinusoidal voltage waveform (+5-5 V) and a coil. I have to design a circuit that allows to change AMPLITUDE and FREQUENCY of the current flowing in the coil. To amplify current I have a transistor (MJE) (both pnp and npn). How should I design the circuit?
I'm using LTspice as simulator.

Thank you

Marc

 

[Alec_t]

Welcome to EP!
As this is a Homework question, show us your best efforts so far at a design, then we can give guidance.

 

[Marco203]

this is what I have so far. I don't know how to have an alternating current in the coil where I can change its frequency and amplitude

 

[AnalogKid]

I think you should check with the instructor about the requirement to change the frequency. That is very difficult. For example, if you have a 1.0 kHz input frequency and you want to change it to 1.2 kHz, you can heterodyne it with a 200 Hz signal in an analog multiplier. This sounds like it is way beyond the level of the course.

ak

 

[Marco203]

well, so just focusing on the transistor, how can I know how to have a precise alternating current (like +1/-1 Amperes) flowing into the coil, given the sinusoidal voltage in input? the coil is represented in spice with a resistance and an inductance in series.
thanks

 

[AnalogKid]

For precision you must have a feedback circuit that compares the current into the coil against a reference value. The forward gain of a single transistor varies significantly with temperature and with collector current. I don't think you can get "precise" current regulation out of any variation of the circuit in post #3.

What part of Italy?

ak

 

[CDRIVE]

My guess is that your instructor requires that the circuit be capable of functioning over an audio frequency spectrum that can be changed via the signal generator. It's either that or your instructor is also expecting you to build a variable frequency signal source but I doubt it.

I would also suggest that you Google "Push-Pull Amplifier Circuit" and "Complimentary Symmetry Amplifier Circuit".

Chris