How is the values of R that it is connected to +5Vcc?

 

hi,
As I said in my first reply post you cannot use a bss138 in that Source load circuit.
Do you have any P MOSFETs or NPN transistors on the bench.?
E

 

hi 1995,
Post a sketch of the project, the driver section, giving details of the load and I will post a design.
E

hi,
As I said in my first reply post you cannot use a bss138 in that Source load circuit.
Do you have any P MOSFETs or NPN transistors on the bench.?
E

Actually in the picture, ive kept the source on top and drain at the bottom. So, the driver is connected to drain itseld

 

How is the values of R that it is connected to +5Vcc?

About 10 kohms? in order to simplify the circuit, ive attached a circuit.
Im giving input to the source with gate pulled upto 3.3 volts. The drain is connected to the motor driver. When my input is 3.3 volts, Vgs = 0 and the mosfet is off, hence the drain voltage is 5 volts. When my input is 0 volts, Vgs=3.3 volts and mosfet is on and the drain is at 0 volts ( same as input).

 

Two 10K are the false load at the output.



RZM002P02T2L : Pch MOSFET, Vds = - 20 V, Id = - 200 mA, Rds(Set) = 1.2 Ω, Vgs(DS[on])= - 4.5 V.

 

I haven't read the full datasheet in detail, but it looks like it has enable pins which would do exactly what you want without any additional components. Maybe I'm misreading it, but here's what I was looking at:

 

hi 1995.
Consider the current level and path into the MCU pin when using your circuit, when PB8 is Low.
E

 

I think i can just use a PMOS as follows. My microcontroller pin to gate will be floating when it is asleep.

 

When the gate is floating or the gate is 3.3V then the Vs will be connected to Gnd and when the Vgs is 0V then the Vs will be as output 5V, but this is not a good way to output a low level to control the P MOSFET in this case, especially when the uC initialing that the output is a low level and it could be causes the Vs goes high.

 

I think i can just use a PMOS as follows. My microcontroller pin to gate will be floating when it is asleep.

I thought earlier the driver was getting 5V supply. Also, the microcontroller was 3.3V logic, right? If so, your circuit is a bad idea, because you'll be exposing the microcontroller to 5V on its GPIO pin when it's off.

Again, why not just use the enable pins on the driver? No extra components needed (unless I'm misreading the datasheet.)

*** EDIT: I see now that the quiescent current of the driver is relatively high. I can understand why you wouldn't want to rely on enable pins alone if this were a battery powered device and power management was important.

 

I thought earlier the driver was getting 5V supply. Also, the microcontroller was 3.3V logic, right? If so, your circuit is a bad idea, because you'll be exposing the microcontroller to 5V on its GPIO pin when it's off.

Again, why not just use the enable pins on the driver? No extra components needed (unless I'm misreading the datasheet.)

*** EDIT: I see now that the quiescent current of the driver is relatively high. I can understand why you wouldn't want to rely on enable pins alone if this were a battery powered device and power management was important.

My microcontroller pin is 5 volt tolerant

 

If you need a level shifter, just use use a simple BJT. They usually have lower capacities than fets and are cheaper. Additionally, you don't have to worry about not completely turning them on with only 3.3V. Why use a mosfet here?

 

If you need a level shifter, just use use a simple BJT. They usually have lower capacities than fets and are cheaper. Additionally, you don't have to worry about not completely turning them on with only 3.3V. Why use a mosfet here?

A MOSFET can easily have a much lower voltage drop (a function of Rds-on and current) than a BJT's CE voltage drop, so there's at least one reason.

As for turning it on, the last circuit proposal uses a P-MOSFET and a pull-up resistor, then uses an active low signal from the microcontroller to turn on the MOSFET. As such, there will be 5V across gate and source when MOSFET needs to conduct, not 3.3V.

 

If you need a level shifter, just use use a simple BJT.

Did you see the post #20, the TS said that he used this circuit to drive L293D motor driver and it needs 60mA.

 

Did you see the post #20, the TS said that he used this circuit to drive L293D motor driver and it needs 60mA.

60 mA on the input or output? If that was an issue, you could use a higher gain BJT or a darlington transistor setup. But then I guess you may as well use a mosfet, unless speed was really an issue.

 

60 mA on the input or output? If that was an issue, you could use a higher gain BJT or a darlington transistor setup. But then I guess you may as well use a mosfet, unless speed was really an issue.

I think you should reread from the first post, it seems that you missed many points.