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Output voltage on 5V In/Out pin


#1

Hi ,

could somebody check the voltage level on the 5V In/Out pin.

I read only 4.5 volts at my board. It seems a little bit low. I also check the level directly at the voltage regulator (IC1) with the same result only 4.5 volts.

The 3.3 voltage levels are ok.

BR

cypher


#2

I notice this when i supplying it with USB voltage only. Once i powered with a external supply the lower voltage went away.


#3

That is normal. You are measuring the power level of your USB port. Try a power pack and it will be 5V


#4

Check the type of USB cable you are using as well. Cheaper ones use 28 AWG wire pairs for both the data and power which is OK for short cables and low current draws. With higher current draws and a longer cables you can see 0.2V~0.3V dropped across the cable. You can get better quality USB cables that use 20~22 AWG power conductors.


#5

What chimp and jeff said is right.

I would suggest to everyone who uses this (and other) board(s) to not just rely on usb power. I would suggest to ALWAYS use external supplies. Mostly it saves you a lot of worries and time. Connecting and external supply takes 10 seconds, finding a bug cause by power drops can take hours.


#6

I have used a power supply. And I think that was my problem.

The first days the board runs smooth.I noticed that the 5V regulator getting really hot.

I have used a 12V/2A power supply. Yesterday I noticed when I have connect the power supply and after plugging in the USB cable , the USB hub shut down the port. A windows message occurs sounds like an overcurrent protection.

Without a power supply it works well.

Fortunately I had a 5V LM1117 regulator and so I have exchanged the IC. Now it runs normal , but when I connect a 12V power supply the regulator getting hot.

When I reduce the voltage to 7V the regulator getting slightly warm.

Have somebody check the current(only board and display)?

My power supply shows 280 mA in idle mode.


#7

The Cobra schematics show that the regulator is a LM1117MP-5.0.

This is a 800mA Low Drop Out linear regulator. The drop out voltage at 800mA is 1.2volt.

If this regulator has to regulate 12v to 5v, it will have to dissapate a lot of heat. This is why you see the regulator heat up and since the heat sink tab is on the PCB, you may see the power section of the PCB being warm.

Although the Cobra schematics show the input external voltage as 12v, I would try something like 6v or lower. The silkscreen of the Cobra says 6v.

HTH.

-Rajesh


#8

I would absolutely stay at 6V and not 12V. Although it “should” be possible, 6V is a safe voltage.


#9

@ Rajesh and Foekie

Could you check the current? Maybe there is something wrong with my board.

As I said 280 mA at idle mode.

My EM-TFT dev board shows 260 mA @ 9V


#10

Use 6v and you will never have any problems. 12v is not okay. See the “6v” printed by power connector

7.5v is okay too


#11

Then you have to change the documentation :smiley:

The brochure says 6-12 volts and on the silk screen (expansions pins) is also printed 6-12V.


#12

Correct. We are working on docs :slight_smile:


#13

BTW:

The maximum current of the LM1117 is 800mA. The current of the Cobra board is around 280 mA (in my case). The USB host can use up to 500 mA. So there is not so much room for extension.

Maybe it is better to use another voltage regulator? Like on EM-TFT dev board (MIC4680)?

I know that you have to change the layout and the deadline for production is not so far away (or maybe the board is still in production)


#14

or a LT1085CT


#15

The USB host port is meant to be used with minimal current consumption. Something like Joystick, thumb driver…etc. If higher power is needed then a powered hub must be used.

The documentation will be updated to explain this