Hello,
I have an old ultimaker 2 controlled by a Mks robin nano v1.3 Motherboard, i’d like to control a 24v COB led strip with an IRF520 module like this :
The VIN+ and GND Pins are conencted to my psu
The V- and V+ to the Led strip
The gnd pin to gnd on the motherboard and SIG pin to pin PA5 on the motherboard.
It works, but the light is very low compared to the case when i connect the led directly to PSU.
When pin value is set to 1, i measure 3.2v on pin PA5 and 19v on the led strip
Could someone help me with this problem please ?
Thanks
You’ll see that the device is designed to operate with a 4.0 to 5.0V Drain Voltage (this is RDSon in the datasheet).
If you go down to the Ids/Vds characteristic graph:
You’re only going to get around 20% of the maximum current through the device (which is what I believe you’re seeing).
Looking at the schematics for the Robin Nano 1.3 001/002 boards, there are two heater outputs (HEATER0 and HEATER1) which provide a switched Vin that I would recommend that you look at using and skip the IRF520 board all together.
I think it will work. I believe the opto-isolator built into the board allows for 3.3V operation - I can’t be sure because there are no datasheets, schematics or part lists available for the board.
It’s cheap and shouldn’t blow up your Robin controller board - just make sure you keep your grounds constant.
Small sidenote:
Do not believe the marketing blabla of the current rating. Stay below 60% of their rated current and you will be fine. These boards will never ever survive switching 15 A continuously and even less on inductive loads.
I saw those when I was looking for what @Acca is looking for (namely 3.3V full on as opposed to 4V-5V full on).
Personally, I would not control them with 3.3V - their Ids to Vgs curve is similar to what @Acca was originally using:
Like with the IR520, with the AOD4184A at 3.2V, you’re only going to get about 20% of the maximum current. I’m guessing that because there are two MOSFETs in parallel you get twice the current sink (for 40% of the maximum).
which is followed by some test results showing that the MOSFETs on the board starts to get very hot when you try to sink more than 5A on them with a 3V to 3.3V on the Gate (“Vgs”).
For @Acca 's application, the board should work fine - especially if he keeps the current draw less than 2A (I’m more conservative than Proto Supplies).
My led strip is 9W/m and I use less than 1m, so I should not need more than 0,4A
Since I need a very low current, I don’t understand why the 20% current limit is a problem
Sorry, you say the LED strip is 9W/m and then say you’re using less than 1m with a current draw of 400mA (I’m not sure if “0,4A” is a European value)?
If it’s 0.4A (North American), and applying 24V, then the LED strip is using 9.6W and the length is 1.067m. Is this correct?
The lower gate voltage than specified means that the MOSFET is operating with a significantly higher Drain to Source equivalent resistance (called “Rds” in the datasheet) than it would in normal operation.
This causes two problems:
If you are drawing 0.4A (Assuming how I interpreted what you are saying correctly), that means your equivalent resistance (at 24V) is 60Ω. When I look at the IR520 datasheet (which I still have up) it looks like Rds is around 8Ω. This is a total resistance of 68Ω and the voltage across the MOSFET is 2.8V which means the voltage across the LED array is just about 21V which is not optimal for your LEDs and is probably the primary reason why your LEDs are dim with the single MOSFET.
Power = I^2 x R which means that as you draw more current, the power dissipated within the transistor increases as the square of the current passing through it. The more the chip heats, the less efficiently it works. The less efficiently the MOSFET works, the higher the Rds, which means more voltage across the MOSFET and less voltage across the LEDs.
Going with the board that has two MOSFETs should halve the overall Rds (at least I think that’s why the board was designed that way) which means the voltage drop across the MOSFETS (if they were IR520s) would be 1.5V and the LEDs would have a 22.5V drop which is probably closer to the specified operating voltage for them and they should be brighter.
Here is the LED strip that I use (24V, 480 LEDs/m. 5W/m):
Finally, as @Sineos noted, it is surprisingly hard to find a MOSFET board that will take a 3.3V control voltage for LEDs. I spent quite a bit of time looking around for you and I couldn’t find anything I was absolutely sure that would work.
As a final thought, if you had two of your IR520 boards, you could wire them in parallel to get the equivalent of the board @Sineos suggested and that should give you an idea of how things will work for you when you get the boards you’ve ordered.
After writing up the previous response, I realized that i could test what I was saying here.
I made up a 0.5m long LED strip with wires and attached it to my bench supply.
The difference in the brightness when I went from 24V down to even 22V was remarkable but, unfortunately, it didn’t photograph well. There is something very interesting and useful in the following photographs, however:
Quick Edit, when reviewing this post, I realized that if you look at the green tape at the bottom of the images you get an idea of the relative brightness of the LED strip at different applied voltages by how much light comes through the tape.
At 24V, the iPhone camera is overwhelmed and this basically carries on through the images through to 20V but what I wanted to bring your attention to is the current reading on the bench supply.
At 24V, the current reading on the bench supply is 79mA, at 21V it’s 6mA and a 20V, as well as 19V, it’s below 1mA.
So, the lower the voltage applied to the LED strip, the less current is drawn with much less light output which was my point in my previous posting.
@Acca could you measure the voltage at the LED terminals of your current board? I’m guessing it will be around 20V.
Based on this quick experiment, I think by using the MOSFET board @Sineos suggested, you’re going to see an improvement but nowhere near as bright as what you would if you connected it directly to the 24V output of your power supply or if you connected them to a FAN (or heater) output.
Not sure about this. In the end the boards are also just using simple MOSFET circuits and all of them will have some voltage drop.
Probably also depends on what the OEM has laying around and the rated power. It seems that power rating and gate voltage requirements are somewhat proportional
The LED strip and MOSFET are essentially a voltage divider circuit. The higher the effective resistance in the MOSFET, the higher the voltage across it and the lower the voltage across the LED strip.
The IF520 (and AOD4184A, which is used in the board that you are using) have an optimal on voltage of 4V or more:
If you are driving the gate voltage (Vgs) at less than 4V, then you’re going to see the equivalent resistance rise from a fraction of an Ohm (0.028Ω) to several Ohms, as I pointed out above.
Every set of main controller board schematics I’ve seen either specifies an N-Channel MOSFET that has a specified Vgs of 3V (or less) or has a logic level converter circuit (taking the 3.3V output of the MCU and raising it to 5V for the N-Channel MOSFETS), like the 74HCT365 used here in the Manta M5P:
No. They are completely separate and device specific.
You said you’re sinking 7A with the board you recommended using a 3.3V MCU control. I have no reason to doubt this - however, the two N-Channel MOSFET drivers are going to noticeably warm if not outright hot. I would be interested in you taking a DVM and measuring the voltage across your load and compare it to what the power supply is pumping out.
If you were to drive them with 5V, you would find that they would be cool to the touch in the same situation. You would also see that the voltage across the load is closer to that of the power supply.
Currently on a business trip, so I can’t check. But I checked their temperature when deploying them with my thermal cam: Around 55 C, which does not concern me.
Generally, I agree with you that IF the board has some bus buffers or similar then you are on the safe side and I do not understand why pretty much none of these boards are equipped like this…
Albeit on the old Robin Nano board, I did not see any of these measures (or I missed them).
These boards were designed to work with Arduinos which has 5V logic.
MKS schematics don’t have part numbers and the part numbers on the Robin Nano 3.1 I have in front of me are barely legible (I don’t have a 1.3).
With a little bit of digging, it seems that the following N-Channel MOSFETs are used on the Robin Nano 3.1 and I would think that the same designer/philosophy would be used for the 1.3:
For the Bed, Q5 is an HYG024G03 which has a gate threshold voltage of 1.4V. At 3V, Rds is 3mΩ
For the two extruders, Q3 & Q4 are HY1403D which has a gate threshold voltage of 1.6V. At 3V, Rds is approximately 20mΩ
For the Fans, Q1 and Q2 are the CJ3400-HF which has a gate threshold voltage of 1.4V. At 3V, Rds is approximately 35mΩ
So, with the selection of these devices, I wouldn’t think that a 5V level shifter would be required on the MKS boards and the MCU can interface directly with the N-Channel MOSFETS without a large voltage drop for the load.
