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Topic: Single PWM Trigger for Common Anode, and Common Cathode LED Strips (Read 1 time) previous topic - next topic

dpmattox

Aug 23, 2011, 04:53 am Last Edit: Aug 23, 2011, 04:57 am by dpmattox Reason: 1
I am looking for a simple yes or no on "will this work?":

I am building a PWM controller for light strips from DealExtreme. The strips come in both Common Anode (CA) and Common Cathode (CC) varieties depending on what is in stock at the moment... Aside from that, they use 12volts out of the box. Since I intend to buy these in quantity, I need my final product to be flexible...

To describe the fragment of my controller schematic attached:
RCHAN1 - PWM line from arduino Mega for Red LED's Channel 1
GCHAN1 - PWM line from arduino Mega for Green LED's Channel 1
BCHAN1 - PWM line from arduino Mega for Blue LED's Channel 1
RCHAN2, etc... Channel 2 Blah Blah Blah (same as channel 1)

From the above lines, a 2N2222 is triggered, further switching TIP120's setup to drive 12 Volt lines of either CA or CC.

So, Will it work?

Almost forgot, on the Common Anode half, the LED strip's +12 is connected to +12, and on the Common Cathode hale, the LED strip's GND is connected to GND. Also, the ROUT,GOUT,BOUT, etc, are broken out to screw terminals in my proposed design, along with GND/+12

dpmattox


elandd2011

for help you send the full diagram for only one channel with the diodes

Magician

It would not works as you expect.
for Q15 Q16 Q17 easier way, just put resistor in series to base and drive directly from arduino.
With other side (CC) you have to connect 2n2222 collector to base of tip120's (resistor between arduino and base 2n2222 is mandatory), emitter to ground, and VCC to resistor to base tip120.

dpmattox

You mentioned the base of the TIP120 twice in connection to the 2n2222 and didnt mention the TIP emitter at all? Could you please draw me a diagram, I am having difficulty picturing it... This isn't thread necromancy, I lost interest in this, and now I NEED to finish this...

dc42

1. Using darlingtons such as the TIP120 is generally a bad idea because of their high voltage drop aka Vce(sat). I would use a simple transistor such as BC327 (PNP) or BC337 (NPN) for up to 500mA, and a mosfet above that.

2. Using NPN transistors in common collector configuration is not good for a similar reason. Use PNP transistors or P-channel mosfets for high side switching.

3. Your circuit as shown will not work, apart from the missing base resistor for the low side switch, you need to level-shift the 5v drive to 12v for the high side switch.

The attached schematic can be used for up to 500mA per LED strip. I am assuming the LED strips have a built-in series resistor and so are suitable for operating direct from 12v.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

dpmattox

Would you do me a huge favor and draw that again, but using mosfets, as I know I will be above 500ma? I will do it myself, if you can explain to me which goes where... I am willing to do the work and learn, I just need some help.

dc42

Sure, here it is. The mosfets I have specified are overkill for the job but fairly readily available. The important thing is that the n-channel mosfet (the one I have suggested STP40NF10L for) is logic level. The P-channel mosfet does not need to be logic level and I have suggested IRF9540. There are lots of alternatives for both of these.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

dpmattox

Before I run a batch of bad boards, both the N and P channel mosfets from what I am reading are pin compatible with the IRF540 (as far as eagle is concerned). If not could someone help with eagle parts for the above schematic?

dc42

That's easy enough to check, just look at the datasheets for the mosfets you are using and for the IRF540.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

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