• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

6V AC (sin) generator (2A+)

Status
Not open for further replies.

ACharnley

Member
Hi all,

What's the best means of creating a 6V AC supply that ideally has variable frequency?

I thought it would be an easy off the shelf option but either I'm looking for the wrong name or it doesn't exist?

Thanks, Andrew
 

dr pepper

Well-Known Member
Most Helpful Member
If you had a transformer with 2 'outputs', one 0-6v and the other 0-12v (assuming your dc is 12v), you could drive the 12v 'output' as the primary and take the 6v off the other winding, the schem you linked us to could then be used.
Take care with frequency you couldnt go lower than the transformers rating, but you could go up to about double without major issues.
Also note this would produce mains voltages on the transformers 'primary', so be careful and dont do it if your not experienced.
You could also as you mentioned use an audio amp module, maybe a tda 2050 or similar, there are lots on ebay.
 

audioguru

Well-Known Member
Most Helpful Member
The circuit is a squarewave oscillator that is filtered a little to look something like a sinewave. if you change the frequency of the oscillator then you also must change the frequency of the filter.

Instead of a squarewave use a variable frequency sinewave circuit that feeds a powerful audio amplifier IC.
 

ACharnley

Member
If you had a transformer with 2 'outputs', one 0-6v and the other 0-12v (assuming your dc is 12v), you could drive the 12v 'output' as the primary and take the 6v off the other winding, the schem you linked us to could then be used.
Take care with frequency you couldnt go lower than the transformers rating, but you could go up to about double without major issues.
Also note this would produce mains voltages on the transformers 'primary', so be careful and dont do it if your not experienced.
You could also as you mentioned use an audio amp module, maybe a tda 2050 or similar, there are lots on ebay.
Will the TDA 2050 follow the voltage?

Only require the 6V, but varing the frequency would be useful.

In theory I only need a 1A output but I've found a 6v/12VA transformer can't keep up, 30VA is up next, but I could to the TDA route if it'll work.

A.
 

Les Jones

Well-Known Member
Most Helpful Member
You have not yet stated what current output you require. If as I suspect it is for testing your bicycle dynamo regulator it will need to provide large current pulses even though the average current will be quite low. The capacitor after the rectifier will only be charging near the peak of the waveform. Most audio amplifiers will not work down to 0.1 hZ. There are two ways around this. First is to replace all of the capaciitors with much larger value ones. Assuming the audio amplifier is designed to work down to 20 hZ then you would need to increase the value by 200 times. This is not really a practical solution. The other way is to use a split power supply design with no capacitors in the signal path.

Les.
 

ACharnley

Member
Thanks Les you are correct. So perhaps I'll just go for a bigger transformer and stick with 50hz (which is acceptable).

Current output is variable, testing different USB loads but max should be 1A @ 5V + efficiency drop so let's say 1.2A @ 6V AC. You're correct about the surge. For sure 2A @ 6V isn't enough my current transformer is rated at that and can't do it. My 15VA @ 10V can however - so roughly 4A/6V/25VA+ will be ok, I think.

Andrew
 

dr pepper

Well-Known Member
Most Helpful Member
Yes the amp module looks Ok, just make sure the frequency response of the module goes low enough, some tweaking of the circuit might be req fir 0.1hz.
Just connect the sig gen to the audio input.
Theres going to be a very small amount of distortion on the o/p, so it depends what your using it for whether its good enough or not, plus the impedance of the load needs to be over a few ohms.
 

audioguru

Well-Known Member
Most Helpful Member
The Aliexpress TDA2050 amplifier module uses a cheap Chinese copy of a "real" TDA2050 IC. The real IC costs less than a cup of takeout coffee.
OOps. The real one is not made anymore.
 

ACharnley

Member
Update, the chunky transformer doesn't work. To explain what I'm trying to do, I'm comparing the efficiency of multiple devices which convert dynamo power. A dynamo starts at low power, low frequency and builds both as the rider increase speed. Frequency builds linearly but power is inverse exponential I believe.

Some of the devices will only offer 500mA at high frequency, others (my own included) have a greater capacitance to ensure at lower frequencies the output won't ripple (and it's a large ripple!).

To avoid this ripple which is impossible to avoid at lower frequency (the key is where to trigger) some use frequency detection to shut off the power (my own included) while others use voltage drop detection (if it can't sustain 5v it shuts off).

The issue is at 50Hz I'm unable to test those that don't have the capacitance and use voltage drop detection. It means regardless of the transformers VA rating I can only draw 100mA from the output before it trips.

The only way around is it build a 200/300Hz current amplifier / voltage follower for my signal generator, I think.
 
Last edited:

ACharnley

Member
My understanding is I can build the following circuit.

At least a 12v power supply to give 6V out (realistically a bit higher).
R3 should be around 12ohm to get 1/2A out. I'd need a bit more so 8-10 ohm.

 

audioguru

Well-Known Member
Most Helpful Member
A class-A amplifier wastes a lot of power making heat, especially when it has no output signal it is still getting VERY hot. That is why most audio amplifiers use class-AB that only gets a little warm when there is no output signal.
 
Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading
Top