Tip31c drops voltage output? - Page 1
Forum section: electronics / beginners

author: toxicnos
author_rank: Contributor
timestamp: November 13, 2013, 12:26:18 am
content: Hello i am only 13 so please refrain from making fun of :wtf:my technical knowledge about transistors or electronics in general. Now that we have gotten that out of they way here is my question. A wile back I had seen kipkays video on an LED beatbox (basicaly a colour organ) the project called for 2 tip31 transistors because it was dual changed when I went to my local electronics shop they only had tip31c transistors duto my lack of electronics at the time i bought them thinking they where same thing. I was mistaken the problem is when i tested the circit usi g only one channel on the 12v powersupply i was instructed to use the leds where very faintly glowing to the sound of the music keep in mine there where 4 3v leds on 12v in series. The perfect voltage for them. So i would assume the transiser droped the voltage. I am going to put a multimeter to it and do an update if i can find the parts and say the voltage. Thank you for helping meand have a great day.

author: Nerull
author_rank: Frequent Contributor
timestamp: November 13, 2013, 12:41:54 am
content: The C specifies the maximum breakdown voltage rating of the transistor, there are A, B, and C grades of TIP31s. All have otherwise identical specs and it should not affect the working of your circuit otherwise. Something else is likely wrong.Does your headphone out provide enough voltage to drive the transistor? Headphone outs can range anywhere from +/- .5V to 2V depending on the system used.Red LEDs generally want about 2V, driving 4 of them without a current limiting resistor from 12V (or driving any LEDs without current limiting in general) is a pretty bad idea. This circuit design seems a bit shoddy.

author: toxicnos
author_rank: Contributor
timestamp: November 13, 2013, 01:36:48 am
content: The LEDs run off 3v each and there are four. what you are saying about the voltage of the headphones sounds like its the problem. I will use my multimeter to check the voltage. I didn't design the layout will post a link to the video. I was not happy with the way he just soldered everything with wires so i went the extra step in buying a perf board to avoid shorts.this is the video a found the projecthttp://kipkay.com/?wpdmact=process&did=MzkuaG90bGluaw==the download link to the schematic i would make the file an attachment but this way you can see the url is from kipkay's website.

author: Nerull
author_rank: Frequent Contributor
timestamp: November 13, 2013, 01:44:50 am
content: Yes, I looked up the schematic. It is not well designed. Exactly what LEDs are you using?

author: Frenchie
author_rank: Regular Contributor
timestamp: November 13, 2013, 01:57:57 am
content: Quote from: Nerull on November 13, 2013, 01:44:50 amTo clarify further, if the channels are outputting peaks of less than ~0.6V or so your transistor probably isn't turning on. Any higher than that and your base emitter junction is effectively short to ground which won't be nice for the music player. You'll want a small resistor in series with the base to limit the current through that junction. 1k will give you more than enough drive current on the base (No calculator was harmed in this ballpark figure).The other obvious problem is the lack of a current limiting resistor in the LED strings, if the transistor does turn on hard one (or more) of the LEDs will more than likely act as a fuse. Assuming you want about 10mA drive on the LEDs you'll need a (12-4*2)/0.01 = 400 ohm (use a 390) resistor in series with the string.

author: toxicnos
author_rank: Contributor
timestamp: November 13, 2013, 02:17:13 am
content: Quote from: Frenchie on November 13, 2013, 01:57:57 amI am fairly new to electronics would you mind explaining how i would incorporate the resistors. Maybe edit the schematics or some other way. Thanks you for your help.

author: Frenchie
author_rank: Regular Contributor
timestamp: November 13, 2013, 03:30:43 am
content: I'm at work so can't draw you a schematic so I hope this makes sense. To make your circuit robost you'll need to update the red and green lines to look like:Signal in ---- 1k Resistor ---- BaseAnd then each of the LED strings to be:+12V --- LED --- LED --- LED --- LED --- 390 Ohm Resistor --- Collector.Of course, as Nerull has mentioned, the line out of your music player might not output peaks with enough voltage to switch the transistor on - in which case you might need an amplifier before it. Without the resistors however you're going to kill something in that setup be it the transistor the LEDs or your music player.If you've built the circuit as it has been drawn originally I'd probably recommend testing the components haven't been destroyed. The diode setting on even cheap multimeters should be able to check Red & Green LEDs without too much hassle. NPN transistors can also be checked with the diode test, for an NPN put the positive probe on the base and you should get a reading when you put the negative probe on each of the collector and emitter.

author: toxicnos
author_rank: Contributor
timestamp: November 13, 2013, 12:47:14 pm
content: Quote from: Frenchie on November 13, 2013, 03:30:43 amAlriht i'll try it in the coming days and tell you how it goes.