Hey,
I driving 3 small electrovalves. This model of electrovalve must be supplied with a 250 mA current in order to open.
Here is an extract of the valve datasheet :
Operating current : 250mA
I'm using 3 mosfet to drive these valves with my STM32 mcu.
The mosfet is LB8721.
Gate Threshold voltage : 1.8V < 3.3V of GPIO mcu output.
Continuous Drain Current V GS @ 10V is 62A which is largely enough.
I tested the valve alone and here is what I got :
So you can check that the valve has an internal resistance when working of approx 4 ohm.
But when I build the mosfet low side switch circuit above, the current in the valves decrease a lot and isn't the same in every valve.
From what I tested it seems that it's working better when I connect only low-side switch than when the 3 of them are connected.
With 3.3V supply :
- 0.150 A flowing in a valve when 1 of mosfet gate is supplied with 3V.
- 0.100 A flowing in a valve when 2 of mosfet gate are supplied with 3V.
- 0.050 A flowing in a valve when 3 of mosfet gate are supplied with 3V.
With 5V supply (i'm using supply to power the mosfets gate in the test not the 3.3V mcu output) :
- 0.180 A flowing in a valve when 1 of mosfet gate is supplied with 5V.
- 0.160 A flowing in a valve when 2 of mosfet gate are supplied with 5V.
- 0.140 A flowing in a valve when 3 of mosfet gate are supplied with 5V.
I tried increase the supply voltage (that's why I have a supply of 5V instead of the recommanded 3V with 10ohm resistor) to increase current but it's not really a good solution because i don't want some random 6.4V supply in my system.
I don't think the issue comes from my power supply because it should be able to output 3.5A and I need less than 1A.
Do you have any idea where the issue could come from ?
I saw that in some cases, you use an other transistor to drive the gate of the mosfet, would it be helpfull ?
What other circuits could I use to drive the valves properly with my mcu ?
Thx,
Adrien
I driving 3 small electrovalves. This model of electrovalve must be supplied with a 250 mA current in order to open.
Here is an extract of the valve datasheet :
Operating current : 250mA
I'm using 3 mosfet to drive these valves with my STM32 mcu.
The mosfet is LB8721.
Gate Threshold voltage : 1.8V < 3.3V of GPIO mcu output.
Continuous Drain Current V GS @ 10V is 62A which is largely enough.
I tested the valve alone and here is what I got :
So you can check that the valve has an internal resistance when working of approx 4 ohm.
But when I build the mosfet low side switch circuit above, the current in the valves decrease a lot and isn't the same in every valve.
From what I tested it seems that it's working better when I connect only low-side switch than when the 3 of them are connected.
With 3.3V supply :
- 0.150 A flowing in a valve when 1 of mosfet gate is supplied with 3V.
- 0.100 A flowing in a valve when 2 of mosfet gate are supplied with 3V.
- 0.050 A flowing in a valve when 3 of mosfet gate are supplied with 3V.
With 5V supply (i'm using supply to power the mosfets gate in the test not the 3.3V mcu output) :
- 0.180 A flowing in a valve when 1 of mosfet gate is supplied with 5V.
- 0.160 A flowing in a valve when 2 of mosfet gate are supplied with 5V.
- 0.140 A flowing in a valve when 3 of mosfet gate are supplied with 5V.
I tried increase the supply voltage (that's why I have a supply of 5V instead of the recommanded 3V with 10ohm resistor) to increase current but it's not really a good solution because i don't want some random 6.4V supply in my system.
I don't think the issue comes from my power supply because it should be able to output 3.5A and I need less than 1A.
Do you have any idea where the issue could come from ?
I saw that in some cases, you use an other transistor to drive the gate of the mosfet, would it be helpfull ?
What other circuits could I use to drive the valves properly with my mcu ?
Thx,
Adrien