Sunrise and sunset for an Aquarium lit by LED strips

[sa]

I believe this can be related to my project for the high voltage supply.

Xantrex 300V 4A Power Supply Teardown
http://www.youtube.com/watch?feature=player_embedded&v=27c4RTntAPw#t=466s

[kam]

basically, the theory behind this filtering-rectify-smoothing unit is awesome!!!

[sa]

Do you have some links about how to make simple high voltage power supplies with circuits (and theory)?

I'm still asking myself what is the least dangerous, high voltage or high current?
I could also stay at 12V and split in more PWM controllable circuits but that might be a hasle.

Can't wait to play with the MSP430 microcontroller!

[kam]

As a beginner, i suggest you stick to transformer with linear regulator, a set of capacitors and bridge rectifier. That will be enough. Safe voltage is generally considered anything below 50 VDC.

Here is a page how to make a linear regulator.
http://www.satcure-focus.com/tutor/page5.htm

[sa]

Thanks, I've been looking at a lot of designs and I begin to have a better understanding of the process!

There is an IC inside the 12V power supply named SDC7500.
I could only find the datasheet in chinese but it may be interesting.

It is a DC/DC converter and in the title of the document, there is PWM written.
Is the chip using PWN to achieve its duty or can it be controlled by PWM?
I need a little help on this one, thanks!

Chinese datasheet for SDC7500 DC/DC:
http://www.sdc-semi.com/UploadFile/SDC7500_CN.pdf

[kam]

SMPS converters use PWM pulses to achieve the desired output, by altering the duty cycle of the pulses. Usually there is some sort of feedback from the output back to the chip, and according to this feedback it increases or decreases the duty cycle. I suppose that this feedback is the pin 1 (page 5 of the datasheet) which gets the output voltage. The PWM pulses are then applied to the switching transistor (top-right), so they musty come from pins 8 and 11 (C1-C2). Why are 2 pins? Not a clue! 

Anyway, the point is that the chip probably generates the PWM pulses to maintain stable output.

[sa]

You're quick!

So there might be a possibility to hijack the feedback from the output and to control it from there.
Whether I can do it is another  big question.

I think I will try to spy the signals with the voltmeter in the first time.

--

You suggested to go with a linear regulator.
From what I read, those circuits are efficient if the input and output voltage don't differ much.

Now, I'm also questioning myself if I really want high voltage in the tank, I'm not current Mohan.

I have found this chip, it looks interresting, it can drive up to 20A current:
http://www.linear.com/product/lt3743

[kam]

Have you decide how you will connect your LEDs? If they are close to water, i strongly suggest that you use transformers (220 to 48V for example), for 2 reasons: first to have lower voltage to play safe, and second (and most important) to isolate between earth and your circuit.

Now, regarding the linear supplies, you are right. in mathematical words, you need to dissipate the amount of power you don't want to be delivered. It goes something like this:
If you have 48 volts supply but you want to regulate it to 40 volts, and your circuit draws 1 ampere, no matter what sort of linear supply you will use, there will be 8 watts of power that must be dissipated as heat. That is because your power transistor must "hold" 8 volts (48-40=8) at 1 ampere. Generally, anything above 1 watt will need a TO220 transistor with heatsink. Above 4 watts you may consider using a small fan or a large heatsink, otherwise the transistor will fry in seconds.

On the other hand, SMPS deliver only as much power needed, and that is why they achieve that high efficiencies. I've just made an SMPS LED driver with the A6210 and a PIC. The controller gets 2x18 volts AC and drives up to 8 3W LEDs in series, a total of 24 Watts at 700 mA. The chip can drive up to 3 amperes (!!!) so i can scale it up (almost easily) to about 65 Watts, but i certainly need to change the linear supply with something else (not sure what). The AC power comes from a transformer (for isolation) which is driven to a linear regulator (only to sink the over-voltage from the transformer). I can fully dim the LEDs with PWM pulses with 1024 duty-cycle steps. That is only possible with SMPS, otherwise, i would need to sink 24 watts (3watts x 8 leds) to maximum dim the LEDs

Now, why i wrote all these? 
Oh yeah, to point out that you may consider using both linear and SMPS

[sa]

Lights will be close to the water, it is very important for plant growth.
I will go with 48V, I don't want the fishes or their owner to die.


I enjoy reading you, it's enlightening!
And now i don't know if I want to do this project for the result or the fun of it!

I'm considering ordering samples of a chip, but there are two references:
LT3743EFE#PBF
LT3743IFE#PBF

I don't know what EFE and IFE mean.
From the specs, FE is for TSSOP 28 design (there is also QFN but i believe TSSOP will be easier to solder).

Does the "E" and "I" mean something special?
Which one should I chose?

[George]

Refer to Note 2 on page 3 of the datasheet E is spec'd 0C -125C junction temp, I is spec'd -40C - 125C junction temp

[sa]

Thank you George!

[sa]

From http://www.edaboard.com/thread221063.html

Re: Control 20A- 12V DC motor
Yes, you can use PWM to control this motor. To control the speed only, you can use one MOSFET/BJT to control the motor. To control the direction as well, you need to implement a full-bridge circuit.

At this power level, I'd recommend that you use a MOSFET. What is the frequency of PWM that you are going to use?

You can use a POWER MOSFET, which has a low Rds(on). So, you minimize power loss and increase efficiency. However, this will require a driver circuit that will provide the MOSFET with around 10v from the logic level of the microcontroller and also supply more current.

Alternately, you can use a logic level MOSFET. However, they tend to have higher Rds(on). By using a logic level MOSFET, you can drive the MOSFET directly from the microcontroller. STP55NF06L is among the better logic level MOSFETs I've come across. It has an Rds(on) of about 18mohm. This is quite low for a logic level MOSFET and even comparable to POWER MOSFETs. The IRFZ44N has a higher Rds(on) than STP55NF06L. Using a logic level MOSFET simplifies the drive circuit.

Hope this helps.
Tahmid.