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Author Topic: Using BC327 instead of BC337 but not working as expected?  (Read 6615 times)
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dc42 That would do it but I would like to see the Led's data sheet he may be able to just use the TLC to sink them without the
PNP it can sink 120mA @ 3.6 VCC with the led voltage at up to 17 volts.
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Hi all, DC I have another similar thread about controlling these bulbs, http://arduino.cc/forum/index.php/topic,138969 but I started this thread because I couldn't get the 327s to work without heating up.

I now have the other bulb that I was waiting for
#1 http://www.ebay.co.uk/itm/251095501994 uses a ZXLD1360 controller http://www.diodes.com/datasheets/ZXLD1360.pdf
#2 http://www.ebay.co.uk/itm/270758491217 uses a MT7201 controller http://www.maxictech.com/en/UploadFiles/MT7201_rev1.1_EN.pdf

I think I can cross bulb #2 off the list, it only draw's about 150mA so the stated 5w is a joke!

I'm pretty confused now about my options. I could just use digital pins and BC337's to turn them on and off, but I would really like to have PWM control of them and I thought TLC5940's would be the answer.

Would the best option be to drive the VADJ pin on the controllers from the TLC5940? If so how would I go about doing this? Or try the method David has just explained?

Or am I completely barking up the wrong tree?

Thanks


* ZXLD1360a.jpg (260.01 KB, 1141x874 - viewed 30 times.)

* ZXLD1360b.jpg (241.76 KB, 990x816 - viewed 29 times.)
« Last Edit: December 30, 2012, 07:12:29 pm by dtokez » Logged

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I looked at the datasheets for the controllers, but cant get the ADJ pin to do anything. Grounded the device is supposed to cut the current to the led and go into sleep mode but it does nothing when grounded. Lifted the ADJ pin on the ZXLD1360 and now managed to break it off smiley-sad

Edit, if I ground the ADJ pin on the MT7201 it does turn off (the main supply ground to the bulb) - but can't get the transistor to control it
« Last Edit: December 30, 2012, 08:24:52 pm by dtokez » Logged

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Sorry for all these updates but I'm trying lot of different things at the moment and want to keep the thread updated.

Just tried the circuit below suggested by DC and it works nicely, but with a write of 4095 (max) the transistor is pretty damn hot still, i'm measuring around 45 degrees c with a infrared thermo but when u squeeze it between your fingers it is to hot to touch for more than about 2 seconds

EDIT. just found this info sheet on the ZXLD1360, doesn't really help me but it gives slightly more info on the ADJ pin than the main datasheet ZXLD1360

« Last Edit: December 30, 2012, 09:12:51 pm by dtokez » Logged

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Are you still using the BC327 that you had backward ?  I would get rid of the  470 ohm resistor then set IREF pin of TLC5940  to a max of 10mA
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No I have swapped that BC327 out!

Ok, just tried a 3.9k on the iref pins so should be around 10mA. taken out the 470R but still gets blisteringly hot


edit. DOH looks like I had this one back to front too! I'm getting mixed up with the symbols!

Seems to work OK now and keep the heat down! Only thing is the range seems inconsistent, with writes of anything >1000 (range is 0 - 4095) the bulb seems almost at max intensity? Is the 1K pullup effecting the base too much?
« Last Edit: December 30, 2012, 10:43:38 pm by dtokez » Logged

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Pnp are bad players. Have you checked to see how much current there sourcing.  I still stay there not t turning on like they should    

What I see happening is your not pulling the PNP low enough. If your feeding 12 volts the base is only pulling down to 2.5 volts it needs to be below 2 volts if your using pwm. take some readings at the base to see if it's going low enough. 
« Last Edit: December 30, 2012, 11:06:04 pm by be80be » Logged

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Quote
Seems to work OK now and keep the heat down! Only thing is the range seems inconsistent, with writes of anything >1000 (range is 0 - 4095) the bulb seems almost at max intensity? Is the 1K pullup effecting the base too much?

The 1 k pullup is to switch the PNP off 1 K looks about right the 470 set the base voltage to high because the dang TLC is doing the same thing.

The only thing I see would be to change the IREF to 25mA

The gray scale takes
Quote
Figure 18 shows the grayscale data packet format which consists of 12 bits x 16 channels, totaling 192 bits. The
format is Big-Endian format. This means that the MSB is transmitted first, followed by the MSB-1, etc.

 When VPRG is set to GND, the TLC5940 enters the grayscale data input mode. The device switches the input
shift register to 192-bit width. After all data is clocked in, a rising edge of the XLAT signal latches the data into   
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I think the problem is that the LED lamps contain capacitors, so every time you turn them on there is a big current surge. Controlling them via the ADJ pin is the way to go. See the attached schematic. I included the diode because I know there is a bridge rectifier between the lamp supply pins and the regulator chip, and you don't want to drive the ADJ pin below the local ground of the regulator chip.


* Scan 123.JPG (61.35 KB, 1653x1165 - viewed 61 times.)
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Thanks all, I will give that circuit a go controlling them via the ADJ pins, shame I broke the leg off of the ZXLD1360 though smiley-sad

I see you show an arduino output, will it work on the TLC5940 outputs?

maybe in the meantime I will try a higher current on the base of the 327's and see if that increases PWM performance, only set to 10mA at the moment?

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I just tried that circuit from DC on the MT7201, could see some dimming, but i'd only say 75%-100%. I tried a few different resistors on the base but still the same. I tried it connected to the arduino and running the 'Fade' sketch from the basic examples.

I keep thinking the ADJ pins are connected to something, I could measure about 0.5M ohm between it and some of the others so I tried lifting it, but managed to snap this one too. No ADJ pins to play with anymore, but I have some more bulbs on order smiley-sad
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The datasheet for the MT7201 says of the ADJ pin:

Multi-function On/Off and brightness control pin:
 Leave floating for normal operation.(VADJ=VREF=1.2V giving nominal average output current IOUTnom=0.1/RS)
 Drive to voltage below 0.2V to turn off output current
 Drive with DC voltage (0.3V<VADJ<2.5V) to adjust output current from 25% to 200% of IOUTnom
 Drive with PWM signal from open-collector or open-drain transistor, to adjust output current. Adjustment range 25% to 100% of IOUTnom for f>10kHz and 1% to 100% of IOUTnom for f<500Hz
 Connect a capacitor from this pin to ground to increase soft-start time. (Default soft-start time=0.8ms. Additional soft-start time is approx. 0.8ms/nF)

So you should be able to get 1% to 100% of Iout using the Arduino default PWM frequency of 490Hz. Note that the PWM will work in reverse, i.e. analogWrite(pin, 255) should turn the LED off, while analogWrite(pin, 0) should turn the LED fully on. I'm assuming that you haven't bypassed the bridge rectifier in the current regulator, that's why I included the diode in the circuit (to prevent Vadj going more than 0.3V below the ground connection of the MT7201).

To drive it from a TLC5940 I suggest this circuit. I've moved the diode to the emitter so that you can share 1 diode between all the channels.

To avoid breaking off the ADJ pin, I suggest you use a fine enamelled copper wire to make the connection to it.


* Scan 124.JPG (60.68 KB, 1653x1165 - viewed 53 times.)
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Thanks DC! I notice that the same info is in the ZXLD1360 datasheet too. I hope the that the other bulbs use the same regulators. Shame I will have to wait for them to arrive, hopefully won't be too long.

I'm looking forward to trying your circuit when they do get here, hopefully I won't break the pins off! I used some kynar wire to connect to them but I tried to lift the pins in case the PCB connected them to anything else but I don't think it did smiley-sad

I have not removed the diode bridge from them, it would be nice not to have to modify them too much. So am I right in thinking that I should connect all the emitters to the the same diode?

Many thanks
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I'm looking forward to trying your circuit when they do get here, hopefully I won't break the pins off! I used some kynar wire to connect to them but I tried to lift the pins in case the PCB connected them to anything else but I don't think it did smiley-sad

The only thing it might be connected to is a capacitor, to increase the soft-start time. You could use a multimeter to see whether the pin is connected to anything else, in particular to any capacitors.

I have not removed the diode bridge from them, it would be nice not to have to modify them too much. So am I right in thinking that I should connect all the emitters to the the same diode?

Yes. Make sure that each lamp you are controlling has a good connection between one of the pins and ground. To avoid damage in the event of a broken ground connection, you might want to connect a resistor of about 470 ohms or 1K between the transistor collector and the ADJ pin.
« Last Edit: January 02, 2013, 04:36:18 am by dc42 » Logged

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Thanks DC! I don't think they were connected to anything, I lost the pad on the MT7201 but the pad on the ZXLD1360 seems to be O/C

Looking forward to the other bulbs arriving now for more testing! Hopefully we can get it to work smiley
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