Hello All,

Wanted to try this circuit in a project...
https://www.instructables.com/id/LED-Light-Box-Modified-Circuit-Diagram/

Ultimate goal will be to reproduce something like this.
https://www.instructables.com/id/Music-LED-Light-Box/

I basically learn as I go with circuitry.

So, my question is will a Mosfet work in place of the TiP31 as noted in the circuits above. Reason I ask I I already have some Mosfets and trying to avoid having to buy something else of the Mosfet will work.

If you have a better solution that shared above please share. My goal will be to drive 6-12 LEDs.

Thanks,

Tru

 

Providing your MOSFETs can handle the current needed by the LEDs and can be switched on fully by the USB signals - presumably 5V - then yes N-channel MOSFETs will work.

 

You will need to select a mosfet with a low threashold voltage or increase the level of the audio signal so it is sufficient to cause the mosfet to conduct. A BJT starts to conduct with about 0.7 volts on the base. Even a logic level mosfet will need +2 volts on the gate and other mosfets probably need over 5 volts on the gate to start them conducting.

Les.

 

Providing your MOSFETs can handle the current needed by the LEDs and can be switched on fully by the USB signals - presumably 5V - then yes N-channel MOSFETs will work.

Albert,

Thanks for the reply. Let me share more information on what I have to work with.

IRF 3205 Mosfet..... With that info... do you think it should work?

Below is also the contents of a Kit that I have. As I mentioned, I learn as I go with my tinkering. Is anything in the kit better than the Mosfet for this application?



Again.... Thanks.

 

Yes, maybe, but ...

In semi equivalent terms, a TIP starts to turn on at about 0.5 V, while a typical power MOSFET starts at around 2 V. The MOSFET takes much less current and does not add distortion to the audio signal driving it (not an issue in this circuit). Also, the MOSFET will turn on and off much more gradually as the audio signal increases in volume, whereas the TIP will cause the LEDs to appear to switch on and off more crisply.

If no one has mentioned it yet, direct paralleling of LEDs is not a good practice. Minor variations if the Vf of individual LED ships will cause brightness variations. Also, you need current limiting resistors for the LEDs, or loud audio will cause them to fail. Keep the plus leads connected to the +5V, add a 100 ohm resistor in series with each minus lead, and connect the other end of the resistors to the TIP collector.

ak

 

The IRF3205 gate threshold voltage is anywhere between 2V and 4V and that is the voltage at which it just begins to conduct, so you would need more voltage than that to turn it on fully. It all depends what you are driving it with.

The MJE182 from your kit would be a good substitute for the TIP31.

N.B. The MJE182 is NPN and the MJE172 is PNP. Your kit list shows the opposite.

 

The IRF3205 gate threshold voltage is anywhere between 2V and 4V and that is the voltage at which it just begins to conduct, so you would need more voltage than that to turn it on fully. It all depends what you are driving it with.

The MJE182 from your kit would be a good substitute for the TIP31.

N.B. The MJE182 is NPN and the MJE172 is PNP. Your kit list shows the opposite.

Albert,

Thanks again. Need to try the MJE182 as you have recommended. Assuming my circuit is correct, the Mosfet allows no effect for on the LEDs. Just because I had one on hand before reading your post I replaced the Mosfet with a 2N2222 NPN. Now the lights are always on with or without the audio playing. I will be using a 9 volts to power the circuit.

If you have any other advice before I try the MJE182 feel free to share.

Thanks Again,

TRU

 

The 2N2222 should have worked. Did you use an adequately valued base resistor? If the base current is too high it'll kill your transistors.

 

What value resistor would you recommend?

 

You have to calculate that value based on the transistors parameters and the input voltage peak value, using ohms law to get a desired current.

This website has an excellent Module on transistors that would assist you greatly.

http://www.allaboutcircuits.com/textbook/semiconductors/chpt-4/bipolar-junction-transistors-bjt/

 

What value resistor would you recommend?

You need to know how much current the motor draws to be able to answer that question. The base current of the transistor should be about 1/10 of the motor current. So for 400mA motor current the base current should 40mA. Then to calculate the resistor value you need to know what the input voltage is. Suppose this is 2V, then the voltage across the resistor will be 2V - 0.7V (the base/emitter voltage of the transistor) and the required value is (2V - 0.7V) / 40mA = 33Ω. This assumes that your input voltage is capable of supplying that 40mA. If it is not then you will need an extra transistor to amplify the input signal.

 

You need to know how much current the motor draws to be able to answer that question. The base current of the transistor should be about 1/10 of the motor current. So for 400mA motor current the base current should 40mA. Then to calculate the resistor value you need to know what the input voltage is. Suppose this is 2V, then the voltage across the resistor will be 2V - 0.7V (the base/emitter voltage of the transistor) and the required value is (2V - 0.7V) / 40mA = 33Ω. This assumes that your input voltage is capable of supplying that 40mA. If it is not then you will need an extra transistor to amplify the input signal.

Yes he is correct, the transistors would have to be in a darlington configuration. There are a lot of options for your light box. You can use filter capacitors to trigger different LED's at different frequencies, larger value caps for lows(bass) and smaller values for highs(treble), but you should learn to properly use BJTs and IMHO, I think that's far more information than anyone can answer in a post which is why I suggested the module.

 

I think he's working with LED's.

Yes indeed, the motor is from a different thread.
However, the calculation remains the same, just put in the numbers from the LED circuit.

 

Yes indeed, the motor is from a different thread.
However, the calculation remains the same, just put in the numbers from the LED circuit.

I agree.

Should probably download LTSpice or the like. LT is a fairly easy to use circuit simulator.