Amplify voltage
alnajjar1
Posts: 110
Hello,
I have used the Tip120 and the LM395 successfully as power transistors (thanks for help from previous thread), but now want to know if it is possible to produce a flower voltage with higher current output.
Here, I would like to use the PWM command to vary voltage 0-5 and translate this into 0-12 with up to 2A in current.
Is this possible with a power transistor such as the LM395 or Tip120? I tried pulseout but didn't get good and smooth output.
many thanks in advance..
Al
I have used the Tip120 and the LM395 successfully as power transistors (thanks for help from previous thread), but now want to know if it is possible to produce a flower voltage with higher current output.
Here, I would like to use the PWM command to vary voltage 0-5 and translate this into 0-12 with up to 2A in current.
Is this possible with a power transistor such as the LM395 or Tip120? I tried pulseout but didn't get good and smooth output.
many thanks in advance..
Al
Comments
Anyhoo, you say the PWM command does not give a smoth output. That's absolutely correct. That's what PWM does..... switch on and off really fast to control speed or brightness or.... The PWM output will only be relatively smooth with an inductive or capacitive (or?) load on the other end, but even then you'll still see some ripple in the voltage.
It SOUNDS like you are wanting to design a DC-DC converter circuit. That's what you should search for. I hope that helps. Yes, you could probably design the circuit with the TIP120 as the switcher. I "Believe" you are on the right track with the PWM output, but then you need to filter it, usually through caps to remove the ripple. At a 2A output, you're talking some relatively large filter components.
P.S.
There are lots of DC-DC devices for purchase. Try Jameco or any of the other supply houses.... unless you just want the challenge
I did follow the circuit from Parallax manual and did get very steady voltage 0 - 5. Now I will try it with the capacitor on the Tip120.
Hope that will work..
man thanks,
http://focus.ti.com/lit/ds/symlink/pt5541.pdf
The op amp will probably need to be powered from 20V or so to provide enough voltage headroom to drive the power transistor. With a 2A load, the transistor will get very hot, though, and will need a large heatsink.
-Phil
Um, forget the DC-DC devices, that'll give you a 12V constant out from (for example) an input of 4.5-9V.
You could use an amp, but you'd need a >12V supply to make a 0-5 to 0-12 voltage FOLLOWER. Otherwise the only thing I can think of at the moment is feed PWM into a step up transformer, then from there build a linear power supply less the regulator. I imagine that would consume a lot of power though... like maybe 5A or more from your supply?
-Phil
1) can the transistor connected to the 15V be a TIP120?
2) how do you get a 0-12 to 22 V output when the transistor's collector is getting only 15?
3) Can I use any value capacitor at the positive pin of the LM358, let's say a 0.1uF or it needs to be a specific value? I assume it is only to smooth the signal from PWM.
I just ordered the LM358 and can't wait to try this.
Many thanks again
Al
That should work. VBE will be closer to 1.2V, since it's a Darlington. But I think there's still enough headroom.
2) how do you get a 0-12 to 22 V output when the transistor's collector is getting only 15?
Look again; it's 0 to 12.22 volts.
3) Can I use any value capacitor at the positive pin of the LM358, let's say a 0.1uF or it needs to be a specific value? I assume it is only to smooth the signal from PWM.
Yes, it's to smooth the value from the PWM. You will need to pick an RC time constant that's appropriate for your app. Too low, and you'll get ripple; too high, and it won't respond fast enough. Experiment to find the right value.
-Phil