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Topic: Power Supply (Arduino and TLC5940) (Read 2736 times) previous topic - next topic

Hicksy

Hi

I'm having a bit of trouble regulating voltage and current from my power supply its a S-150-5 (5v 30A) but i want to reduce it to 3.3v 150ma to drive TLC5940's, i have tried using a LM317 to get the voltage down to about 3.3v but every time i connect one of the chips it blows. All i can think of is the current is still to high. if anyone has any ideas it would be really helpful

thanks

AWOL

What voltage are you reading on Vout of your regulator?
What is the "it" that blows - the reg or the TLC5940?

Can you post your circuit?
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

Hicksy

its the tlc5940's that keep blowing the voltage coming out of the regulator is 3.374 i noticed when i turn the power supply on it spikes at about 7v could that be whats blowing them ? how can i stop that spike ?

AWOL

Quote
how can i stop that spike ?

You can check your regulator circuit - it shouldn't be spiking!
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

Hicksy

I'm using the following diagram



And I'm Using a 130ohm for R1 and a 220ohm for R2

this has me puzzled

Mike Mc

What about a switch after the resistors? Power it up THEN flick the switch to on.

Hicksy

Yeah that would work, even maybe some type of delayed relay ? but i would still like to know why this circuit is not working.

Groove

I would have expected some caps for transient suppression - have you got any fitted?

What does the datasheet suggest?
Per Arduino ad Astra

RuggedCircuits

I agree with the capacitors suggestion.

Also, how did you map pin numbers to Vin, Vout, and ADJ? Any chance you got that wrong (1=ADJ, 2=VOUT, 3=VIN for the TO-220 package).

BRuTuS

MUST have output caps with the LM317.

Their voltage fluctuates wildly without them.

Recently we blew up  the .1uF output cap we had on ours and decided to just desolder it and forget it.

Toasted 2 sensors in a row before scoping the PS and finding the spikes.  Solder in a new .1 and all has been well since.

We also have a 2200uF on the input side of the 317 to ensure it gets a nice steady voltage in, coupled with another .1uF

hcgilje

I followed the advice with .1uF capacitor on the output of the LM317, except that I had managed to put the capacitor between ADJ and ground instead of VOUT and ground. For some reason this worked fine though.
When I discovered my mistake I put the capacitor between VOUT and ground, and now I have blown 3 capacitors.
Looking at the datasheet they first of all say that it is an option to use a output capacitor, but also they indicate a value of 1uF.
Could this be the reason why the caps are blowing up, that they are too small?

hc

Grumpy_Mike

Quote
and now I have blown 3 capacitors.


I find this amazing, you just don't blow up capacitors unless you over voltage them or connect electrolytics the wrong way round or exceed the ripple current. I don't see how on earth you could be doing either of these things.  :o

What input voltage are you applying?

hcgilje

Glad to amaze you.
Vinput is +9v, I have a 1.8 ohm resistor between ADJ and Vout, and the schematic is like in this picture (from an instructable). I first placed the .1uF between 1(ADJ) and gnd, then moved it to 2(VOUT) and gnd.


in my setup the pwm pin is an output from the tlc5940 (with a 10k pullupresistor).

As I mentioned before, it worked flawlessly when the capacitors were between ADJ and gnd.

hc

Grumpy_Mike

Quote
it worked flawlessly when the capacitors were between ADJ and gnd.


Now that don't surprise me. What does surprise me is that any idiot would think what you posted could possibly work.

How do you know the capacitors have 'blown', is there physical damage?

pwillard

#14
Jul 14, 2009, 02:50 pm Last Edit: Jul 14, 2009, 02:51 pm by pwillard Reason: 1
I'm just glancing at this... but...  HC

To me... that's the CURRENT regulator configuration... which means you are NOT controlling the voltage...  I realize that you are PWM'ing the ADJ... but that's not a good voltage regulator circuit.

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