Hi,
I want to supply a led ring of type “angel eye” who have a constant current driver included and works from 9V to 30V, 9W, but since I want to control and decrease the light, I would like to try to use a PWM supply.
Since I would like to not use any transistor for simplicity, I wonder if I could use directly the enable pin of U3V70A powered with a 5V USB “charge” (with enough power) to send the PWM command, and if yes, what the maximum frequency could be used, and is there more risks with spikes with a fast on/off on command than with a PWM directly on output?
Thanks for your help!
Hi.
I do not recommend PWMing the enable pin of the U3V70A regulator. Each time the regulator is re-enabled it will take up to 6ms turn on and gradually ramp up the output voltage. I do not expect there to be much increased risk of spikes, but the regulator is just not designed for that kind of operation, so it is possible you would see some other odd behaviors.
If you do not want to implement your own transistor circuit, you could use something like our mini MOSFET slide switch.
-Claire
Thanks for your answer, I forgot that I have 2 Mini Pushbutton Power Switch, are they suitable for PWMing ?
EDIT : should be ok with the CTRL pin, can be drived by a 3V3 µc.
What speed do you want to PWM at?
-Claire
Not sure exactly, but for LED 200Hz to 1kHz would be sufficient I think.
Reading your first post again I realize that you mentioned using a constant current driver for your LEDs. The point of most constant current drivers is that they keep the current (and thus brightness of the LED) constant when there are fluctuations in input voltage (or other parameters). Unless you have a driver that is specially designed to take an analog voltage to set the LED current, PWMing will not work.
As for PWMing the control pin on the pushbutton power switch, 200Hz would be too fast. The latching circuit on the board is analog so there is not exactly a strict cutoff, but I tested one here and do not expect anything more than 1Hz to work. The mini MOSFET slide switch I mentioned earlier does not have the same latching circuit, so it should handle PWMing at 1kHz and much faster speeds easily.
-Claire
Is there somewhere a schematic of your boards, the technical data available are very succinct, access to the datasheet of components and the schematic could help us to understand the functional and the limits of your boards.
Some of our boards, like the mini MOSFET slide switch, have schematics or other additional documentation available on the resources tab of their product pages, for example:
-Claire
Some, yes, but for the one I have, the diagram schema contains a “black-box” and we have no clue of the component used, nor the real schema, so it’s not possible to see PWM is not feasible even with the “ctrl” pin.
Those boards are so simple, that someone who wants to “copy” your work for selling it could spend a short time in reverse engineering to rebuild the schema, so the lack of those technical data is not really good protection, but the real customer is not able to know the capacity and the limits of those boards, I think offering real datasheet to your customer is more valuable than the weak protection of keeping those data secrets…
Whatever, thanks for your help.
Thank you for your feedback. There are a lot of considerations that go into what information we choose to share or withhold for certain products. If you are interested in a more detailed discussion, I recommend reading our company president’s blog posts on open source hardware and commenting if you wish:
-Claire