It is also possible that your circuit board is very old and has been corroded. Maybe chip 7201 has been damaged也有一种可能，我看到你们电路板是很旧的，有过腐蚀的情况，可能芯片7201已经损坏Funny you should post that at this time.
I was just looking over the spec sheet for my personal "electronics 101" session.
Anyways what I "see" is the chip has an internal reference signal of 1.2V. I assume that is to keep the chip "on"
if no input on the ADJ pin.
Second it contains a lowpass filter (R/C) to convert a pwm to a dc voltage (triangle wave??)
not sure about where the diodes kick in here anyways, assuming a full 2.4V dc applied to the pin the equation is
2.4/1.2/.1 (for 1000ma) Which is 20??? when it should be 2
1.2/1.2/.1 1/.1??
Have I lost all my math skills?
Anyway guessing .. at 3.3V DC on the adj pin and a .1 Ohm sense resistor (ignoring pwm atm) the output current would be 2.75A
except for the diodes? Exactly where are they?
And if it did this (2.75A) "in practice" I assume either the driver or led string would not last long.
I've dabbled in using the voltage drop in diodes to cut the voltage down but that is external.
I guess one could compensate by using different sense resistors..
Say you wanted 1A max when applying 3.3v dc to adj pin one would use a .275 Ohm sense resistor.
.1/.275 = .363A x 2.75 =1A ?
I'm missing something.. AFAICT the max voltage on the Adj pin should be 1.2
3.3v regardless of pwm or not just seems wrong. Even averaging the voltage over the duty cycle
still puts higher than spec-d voltage especially at 100%.
Oh also going to reiterate that unless there is an overriding reason the PWM frequency should be <500Hz
A 100:1 brightness control range sure beats 5:1
Cameras may not like it as much though.
since this driver seems to actually adj. current (unlike say an LDD which has a PWM output so current is equal at all on times) there will be some color shift as you dim.
Led hacking help for robotank
- Thread starter Cantankerous
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Sral
Valuable Member
I believe we have looked at the wrong datasheet. There seem to be two versions of the MT7201 and the „C“ version accepts PWM with 2.5-5.5V amplitude and is limited to 100% nominal output current.
Under normal conditions, the maximum output current of the circuit board is about 1a, and there will be no large current. The actual test results show that正常情况下，电路板的输出电流拉满最大也就是1a左右，不会出现大电流，实际测试得出的结论Maybe we have been consulting the wrong datasheet. This one for the MT7201C+ mentions a higherDC ADJ voltage that is also clamped to a maximum current of 100%. It also says that the nominal PWM amplitude is supposed to be between 2.5 and 5.5 V.
If that’s the circuit our informant was absolutely right. One way To check would be to power the driver board and measure the voltage on the disconnected PWM_IN. If that’s 2.4V we have the MT7201C circuit with a different ADJ-behavior
And can therefore simply drive it with a 3.3V PWM @ 500 Hz. Case closed XD
Sral
Valuable Member
Exactly, this indicates, that you are using a different MT7201 than the datasheet linked in the first post, which we have been referring to up to this point.
Thank you for bringing us this info, we otherwise would have noticed our error a lot later !
The MT7201 component has not been replaced, and its parameters can only reach a maximum current of 1a. A higher current will burn the 7201 component. Friend, what do you want to do? Make your own controller? I haven't heard of reefpi in China, and I don't know much about it. Can you send me some informationMT7201这个元件没有更换过，他的参数只能最大1a的电流，更大的电流会烧毁7201元件的，朋友，你想做什么？自己制作一款控制器吗？我在中国没有听过reefpi，不太了解这个它，有资料可以发给我看一下吗
Well that is interesting.
I did see references to a "new" 7201.
Changes really seem to make it a new chip.. not a "c+".
The changes include a 2.3V internal reference signal and 1.2A max current
And..
Well think I'm done here, thanks all, it def was fun.
Sral
Valuable Member
I believe we are misunderstanding each other, consider these two datasheets:
MT7201
MT7201C+
The first one on page 2 explicitly mentions 200% of I_OUTNOM, whereas the second one does not. Both are called MT7201, but behave differently. Thanks to you friend, we have figured that out.
My motivation here is helping others with their projects and learning something about electronics in the process.
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Sral
Valuable Member
Thank you very much for the offer, but as you can see in my build thread I'm currently aiming for my first freshwater aquarium and already have a lamp for it, so I don't think I would be a well suited tester/user for your product right now. Maybe @Cantankerous would be a better candidate
It's a pity. Thank you for your appreciation非常感谢您的提议，但正如您在我的构建线程中看到的那样，我目前正在瞄准我的第一个淡水水族馆，并且已经有一盏灯，所以我认为我现在不是一个适合您的产品的测试人员/用户。也许@Cantankerous会是一个更好的候选者
I would love to, but we need a way to integrate this with reef-pi , otherwise it’s a headache to co figure/control the lights .
This is a great thread by the way. Thank you for sharing the learnings folks. Much appreciated
Sral
Valuable Member
Yeah, but as long as there is no easy protocol with which ReefPi can send for example an http request to control the lamp over WiFi, this is not really useful for us.
This is our latest control module, which can be Bluetooth+wifi. More powerful
exactly, right now all this is like a pretty house of which we dont have any access to. Without any api/integration path this systems are less compelling :-(
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