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Topic: Constant current power supplies (Read 6973 times) previous topic - next topic

retrolefty

Quote
Let's see a show of hands how many of you have used cel phone charger even like the iphone charger  or any of the newer smart phone chargers. Well how may hands are up in the air Guess what there constant current supply that do to things one
there output is fixed at 5 volts till you over load them then it drops off to a point that they shut down.


Not sure what you are trying to say here exactly. However as far as cell phone charger modules most are indeed just fixed DC voltage regulators, typically rated at 5.1 or 5.2 vdc output and at some maximum current rating. The chip that handles how much constant current to allow to charge the phones Li battery and when to shutdown charging current when the cell is fully charged is inside the phone itself. I find these power modules at second hand stores for usually $1-2 and they work fine for powering small digital projects drawing an amp or less.

Lefty

westfw

I believe that the root of the question is essentially: "look!  Cheap switchmode power supplies being produced in the millions for the LED lighting market!  While they're supposed to be "constant current", don't they have a practical limit on output voltage that falls in the range needed at the input of an Arduino?"

Answer: maybe.  But the cheap switchmode power supplies being produced by the millions for the cellphone/etc market are more appropriate and not that different in price.  (although, the price goals of the supply for a $10 lightbulb are probably lower than the goals for the supply for a $100 cellphone/videogame/whatever.)

be80be

Cel phone charger are a constant current supply fixed at 5 volts. That's the newer one's like the iphone use's and most smart phones use

What part don't you understand I'm talking about the charger that plugs in the wall
not how it disconnects the battery from it.  

retrolefty

#18
Dec 01, 2012, 09:09 am Last Edit: Dec 01, 2012, 09:11 am by retrolefty Reason: 1

Cel phone charger are a constant current supply fixed at 5 volts. That's the newer one's like the iphone use's and most smart phones use

What part don't you understand I'm talking about the charger that plugs in the wall
not how it disconnects the battery from it.  


No, you are giving these cell phone charger modules more functionality then they actually have. I've used many in my projects, they put out a constant regulated +5vdc voltage only, and not at a constant current. I have wired one up to power my arduino board via It's 5V and ground shield pins and the board draws about 80ma and the voltage is fixed at 5.1vdc. The constant current part is performed by a chip inside the cell phone that handles the chore of properly charging the battery at a proper constant current, using the regulated voltage supplied by the external cell phone charger module.

Again a typical 'cell phone charger module' is simply a switch mode DC voltage regulator outputting a regulated nominal +5vdc (most are rated at 5.1 or 5.2vdc) and can supply any current demand from 0 to typically 1 amp.

Lefty

be80be

#19
Dec 01, 2012, 09:15 am Last Edit: Dec 01, 2012, 09:47 am by be80be Reason: 1
I not giving them any thing there I just tested about 100 of them as to there rating
and did a lot of digging on the net

Quote
TND329
5 W Cellular Phone CCCV
(Constant Current Constant
Voltage) AC-DC Adapter

better charger like the smart phones and iphone use these in them and there
Not this same chip but one like it.
Quote
This reference document describes a built-and-tested,
GreenPoint solution for a cellular phone Constant Current
Constant Voltage (CCCV) AC-DC adapter. This design is
intended for isolated, low power, universal input off-line
applications where a constant current/constant voltage
output (CCCV) is required for charging NiCd, NiMH,
Lithium-ion or similar batteries. Typical applications would
include cell phone chargers or cordless phone chargers.


Back to the Op you may be able to use the supply you posted if like I said they fit the happy spot of 7 to 12 volts but may need to add a regulator and filtering  

See I have a bunch of these old ones and new ones and got to wondering why some of the old one where no way near there rated voltage and the newer one where dead on 5 volts and I got my kids two new phones so we had 4 of the same
chargers that open the door to cut one open and have a look and as I figured
they have CCCV
So draythomp test it for output voltage and see what it is you may be able to use
the E-Bay supply but I have to say one thing if the output is 350mA and it's 2 watts it's only good for about 5.7 volts at that load

retrolefty

#20
Dec 01, 2012, 09:37 am Last Edit: Dec 01, 2012, 09:58 am by retrolefty Reason: 1

I not giving them any thing there I just tested about 100 of them as to there rating
and did a lot of digging on the net

Quote
TND329
5 W Cellular Phone CCCV
(Constant Current Constant
Voltage) AC-DC Adapter

better charger like the smart phones and iphone use these in them and there
Not this same chip but one like it.


Well I guess we will just continue talking past each other. I will state that from an ohms law point of view that a 'constant current constant voltage output 'module' could only work with single fixed value resistance load, and thus would be of very limited usefulness. You can't have both a constant current and a constant voltage at the same time with a variable resistance load.

A DC power supply module either changes it's output voltage to maintain a constant current when presented with variable resistance loads, or it maintains a constant voltage by supplying more or less current to match a variable resistance load, it can't do both simultaneously except at one 'perfect' load resistance value.  I've used these modules with different value loads, the current didn't stay constant but the voltage did, hence they are indeed simply fixed output voltage regulators.

If you study the datasheet for the TND329 device you talked about, you will find that it is in fact a regulated constant voltage regulator when operating at any current demand from 0ma to 1 amp. If however the load attempts to draw more then 1 amp (load resistance decreases below 5.1 ohms) the module enters a current limiting mode where it will lower it's output voltage to maintain the maximum current drawn by the load to a constant 1 amp value. So that one acts like a simple fixed 5.1vdc output voltage regulator up to it's maximum rated output current, above that value it enters a fixed current limiting mode by lowering it's output voltage to maintain 1 amp. So no ohms laws broken and does never at any time maintain a constant current and a constant voltage at the same time, the load resistance always has a say in the matter.

Lefty

be80be

lefty I'm not trying to get you mad or any thing but your missing a part here

Take a Iphone charger there made to do to things one is supply 5 volts .
Now if the battery is dead you want a fast charge these supply's can dump a amp on the battery and still keep the voltage at 5 volts and charge current at there rating but at no load they just keep the voltage at 5 volts they use CCCV

https://www.google.com/webhp?sourceid=chrome-instant&ion=1&ie=UTF-8#hl=en&sugexp=les%3Bernk_cprob&gs_nf=3&gs_rn=0&gs_ri=hp&gs_mss=cel%20phone%20chargerconstant%20current&tok=uaof38zD-Ak5L0pEYPwIcQ&cp=34&gs_id=k&xhr=t&q=cell+phone+charger+constant+current&pf=p&tbo=d&sclient=psy-ab&oq=cel+phone+charger+constant+current&gs_l=&pbx=1&bav=on.2,or.r_gc.r_pw.r_cp.r_qf.&fp=de6c3c9910299377&bpcl=39314241&ion=1&biw=1137&bih=570

westfw

I'm pretty sure that a constant current switchmode power supply (LED Driver) and a constant voltage switchmode power supply (cell phones) are awfully similar.  One would take feedback from the load voltage, and the other would take feedback from current sense resistor om series with the load.  Any switchmode chip ought to be able to implement either type of supply with minor changes in wiring.

In "Lab" power supplies, "CCCV" generally means "constant voltage with a current LIMIT", and defines the way the supply behaves when the current limit is exceeded.  This is supported by the TND329 datasheet:
Quote
(section 5: "Circuit operation")
For output currents less than 1 A the circuit performs as a constant voltage source.  ... Although very simple, this current sense circuit will provide a constant current output of approximately 1 A all the way down to an output voltage of 1 V.

In other words, a "CCCV supply" provides a constant voltage up to the current limit, and then decreases the voltage as needed not to exceed the desired current.  (as opposed to simpler regulators, that might just shut down in over-current situations.)  Some Li-ion battery charging chips assume that the power supply has a current limit built-in to it, but a cell phone supply will normally operate in a constant voltage mode.

In general, that's not quite the behavior you'd want from an LED driver style of CC supply.  In that case, you want the voltage to go to any value needed to force the target current through the load.  This permits you to use varying numbers of LEDs in series in your light, for instance.   I haven't studied the current flood of "LED driver" chips to see how they're different from other switchmode chips; there may be other simplifying factors that permit a cheaper design and justify having a separate chip (oh, like not needing to provide clean DC, for instance.)

retrolefty


I'm pretty sure that a constant current switchmode power supply (LED Driver) and a constant voltage switchmode power supply (cell phones) are awfully similar.  One would take feedback from the load voltage, and the other would take feedback from current sense resistor om series with the load.  Any switchmode chip ought to be able to implement either type of supply with minor changes in wiring.

In "Lab" power supplies, "CCCV" generally means "constant voltage with a current LIMIT", and defines the way the supply behaves when the current limit is exceeded.  This is supported by the TND329 datasheet:
Quote
(section 5: "Circuit operation")
For output currents less than 1 A the circuit performs as a constant voltage source.  ... Although very simple, this current sense circuit will provide a constant current output of approximately 1 A all the way down to an output voltage of 1 V.

In other words, a "CCCV supply" provides a constant voltage up to the current limit, and then decreases the voltage as needed not to exceed the desired current.  (as opposed to simpler regulators, that might just shut down in over-current situations.)  Some Li-ion battery charging chips assume that the power supply has a current limit built-in to it, but a cell phone supply will normally operate in a constant voltage mode.

In general, that's not quite the behavior you'd want from an LED driver style of CC supply.  In that case, you want the voltage to go to any value needed to force the target current through the load.  This permits you to use varying numbers of LEDs in series in your light, for instance.   I haven't studied the current flood of "LED driver" chips to see how they're different from other switchmode chips; there may be other simplifying factors that permit a cheaper design and justify having a separate chip (oh, like not needing to provide clean DC, for instance.)



Yes, you have explained it all very well and better then me I' sure. There is a difference between a DC power module that has automatic current limiting protection and a true constant current regulator. I'm just trying to make sure that people understand that ohms law is still applicable here no matter what name a DC power module uses.  ;)

Lefty

Krupski


Let's see a show of hands how many of you have used cel phone charger even like the iphone charger......


Let's see a show of hands how many of you built your first computer in the 1970's with an 8008, 256 bytes of static ram and toggle switches for address and data input.

Let's see a show of hands how many of you know the difference between a triode and a pentode (and have actually built circuits using both).

Lots of people here have forgotten more about electronics than you know. Don't be smug.

(rant off).
Gentlemen may prefer Blondes, but Real Men prefer Redheads!

Grumpy_Mike

Me on all counts, although it was 2650 processor and it was 1976.

Quote
Cel phone charger are a constant current supply fixed at 5 volts

That sentence is so wrong unless the charger has the ability to change the impedance of its load. But as others have pointed out this is just sloppy talk.

dhenry

A constant voltage smps can be easily modified to become a constant current power supply.

The same holds true for a linear power supply.

draythomp

Wow, I finally got a discussion started.  Thank you folks.

A bit more inspection of the device shows that it really can power an Arduino, but there are things that concern me.  First, it does have a top voltage limit (open circuit) that falls within the range an Arduino can handle as well as a current limit that, when exceeded, shut it down.  It doesn't taper off, it just quits.  The killer though is that it is very noisy.  I don't have a scope so I can't paint you a picture of the noise, but measuring voltage through various capacitors to block the DC shows a substantial noise or ripple coming out of the supply.  Comparing that to an apple two board wall wart ( one of the 1 inch cubes ) the apple one has almost no noise at all and the CC supply has a ton.  This noise wouldn't make any difference to an LED, but it could to a more complex device, and it appears the Arduino has enough filtering on board to work.  This may not be true of something that I threw together in the garage one evening.

I can't tell you what the chips are that it uses, the markings are blurred or missing on almost every part; the inductor has rings, but I can't tell exactly what colors they are.  You've all seen this before. 

Regarding the size, the two CC supplies I have are about 3/4" x 1/2" x 1/2", and I got two of them under 5 bucks, so you see why they are appealing as a possibility.  Remember, the link I posted was just the first one I hit on ebay, that may have been a mistake since several folk grabbed on that as a negative.  The point was that these CC devices are incredibly easy to find and don't cost much, which only a couple of people noticed.  Tiny little constant voltage supplies that run off wall power are not anywhere as numerous or cheap.  I venture to say that you'll find 10 or so CC led supplies or more for each little CV supply and they'll cost substantially more (not counting getting a usb charger and gutting it).

In answer to the various comments about the apple chargers ( 1" cubes ) the one I have torn apart provides a constant 5.1 volts regardless of the state of the battery in the device it's hooked to.  If I hook it to a resistor and force it past the rating of 1A by lowering the resistance, it drops below the 5V level until it reaches some point where it shuts off.  That's usually just after the resistor burns a blister on my hand.  This little device lists a ton of certifications on the bottom in print so small I have to get the big magnifier out to read it.  So, it appears that something in the device with the battery helps the charge cycle along somehow.  I don't own a single apple device to look at to see; I probably wouldn't pull an expensive device apart to check either.

See, I don't just discount a possibility simply because it doesn't have the right name; I want to actually see if it will work or not.  Bouncing it off other folks helps fill in the gaps that I don't think of or understand (yet).  That's why I asked for your thoughts in the very first post.

Your various comments led me to check for noise in the output, so I don't think this particular kind of device is the answer to my need for a tiny power supply, even if it was a compelling possibility.

Trying to keep my house under control http://www.desert-home.com/

dhenry

Get a scope and put it on that sucker, you will be surprised.

Mine (a large collection of apple stuff) shows 100mv or so Vpp, ranging well into Mhz. Linear regulators have practically zero rejection to those ripples.

retrolefty

Quote
300mA+/-5%. Now, why on earth would I want to power my Arduino board using something
like this?
Can anyone explain why my board would want to have a device trying to drive a
fixed 300mA current into it? Makes no sense, unless maybe the p/s were jiggered after the
fact.


You would never want to power an arduino board with a true constant current power supply. An arduino board with nothing wired to it's output pins or 5V or 3.3 pins draws only around 80ma, and a true CC power source would raise it's output voltage as high as it could trying to force 300ma into the arduino board, which would most likely burn up many components on the board due to the high voltage.

There are some Asian DC constant current LED driver modules designed to power 1 and 3 watt power leds that also have a TTL level input that allows for PWM control for the module effectively allowing a dimming function if one wants to use such a feature, or as a simple on/off control using an arduino digital output signal. However you have to look carefully at the maximum PWM frequency that is allowed for the specific CC drivers that have this extra feature.

Lefty

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