Turning on/off LCD 1602 on HIGH side

Other Hardware General Electronics
1

Hi, i want to turn on and off my lcd module 1602 with a i2c adapter with my arduino, i've done this before with a NPN transistor + 5v regulator and worked well but now i want to build it using a p mosfet

So i've done this circuit (made by me) and the lcd is turning on but the regulator is getting super hot, i also measured the current from the output of the reg to the lcd and it does not exceed 30mA
'

also, is there a problem that the module is running at 5V and the arduino at 3.3V, about the i2c

2

So the regulator is dropping 12-5V = 7V and with 30mA of current that is 7 * 0.03 = 0.21W
Also I don't see any capacitors either side of that regulator. Also when you turn the LCD off you have to first make the lines driving it into inputs so that you don't pump current into the unpowered device. A device with no power just looks like a diode to ground and feeding a signal into it is going to burn power.

3

Hi,
When you turn the MOSFET ON, check the volts at the regulator input and output.

As Mike has said, you need bypass capacitors around the pins of the 7805, look up the data sheet and see the suggested circuits.

Tom.. :slight_smile:

4

TomGeorge:
Hi,
When you turn the MOSFET ON, check the volts at the regulator input and output.

As Mike has said, you need bypass capacitors around the pins of the 7805, look up the data sheet and see the suggested circuits.

Tom.. :slight_smile:

I solder them now, but actually not the regulator was the one who got hot but the transistor does, very very hot

the input/output are fine, the circuit works

5

Hi,
Can you please post a picture of your project so we can see how you have got it layed out?

Can you measure the voltages around your circuit and note them on your circuit please?

The 10K in the base of the BC337 may be to large and the BC337 not saturating, try 1K.

Thanks.. Tom... :slight_smile:

6

, but actually not the regulator was the one who got hot but the transistor does, very very hot

So it is not wired like the schematic. The 10K resistor will stop the transistor getting any more than just over a mA, so the only way it can possible get hot is if it is misswired. Or you have a faulty FET with a gate drain short.

7

there is nothing to understand from a photo :smiley: ..

I tought there is something wrong with the schematic so this is why it's happening
Nothing is misswired from my view and nothing is touching anything else then there is supposed, i checked with my multimeter

I suppose that the Mosfet is a bad one, even if i tested it before i may broked it with my big solder gun
Because it was hidden down there i didn't realised that it was getting hotter and this is why the transistor is hot too

Edit: i removed the transistor, conntect gate directly to ground
Result: magic smoke

8

Nothing is misswired from my view and nothing is touching anything else then there is supposed

That basically is your problem, you think there is nothing wrong.

Edit: i removed the transistor, conntect gate directly to ground
Result: magic smoke

And this surprised you?

9

Hi,
You need to spread your circuit out to let components fit properly.
When you replace your components, can you please measure the input and output voltages at the regulator please?

Thanks.. Tom... :slight_smile:

10

Why the diode on the bjt base? That means 2 diode drops with a 3.3v input. I'm thinking with the 10k base resistor, you are not putting the bjt into saturation, and therefore not driving the mosfet fully on. A check with a meter would show voltage on the gate of the mosfet when the circuit is on, when the voltage should be 0. I would drop the base resistor down to 1-2K.