How to read graph, I want to restrict mosfet at 3A current

[kushal nandanwar]

How to read graph for gate to source voltage and drain current

https://obrazki.elektroda.pl/9565833600_1445448220.jpg


I want to restrict mosfet at 3A current.

 

[Audioguru]

The graphs on datasheets are only for a "typical" device. But when you buy one it might have the printed minimum or maximum spec's. The printed spec's guarantee how much gate-source voltage (maybe 10V) is needed for ALL of them to conduct as hard as they can which might be hundreds of Amps. What is the part number of the Mosfet so I can see its datasheet?

To limit its current you need a current sensing resistor in series with the load and a transistor or opamp to turn down the Vgs of the Mosfet when the sensing shows the limit you want.

 

[KlausST]

Hi,

It depends on what accuracy you need.
If just 2..4A is OK, then maybe a drain resistor is sufficient.
If it should be 3.000A+/-1mA, then you surely need an amplifier.

Klaus

 

[kushal nandanwar]

Hi,

It depends on what accuracy you need.
If just 2..4A is OK, then maybe a drain resistor is sufficient.
If it should be 3.000A+/-1mA, then you surely need an amplifier.

Klaus

Why need need an amplifier?

I need only 1A

 

[betwixt]

Because the voltage between to gate and source to make it pass 3A depends on the device and surrounding circuitry. To make it pass exactly (or as near as is possible) 3A you need a control mechanism that adjusts the gate to source voltage so it adapts to conditions. Typically, you would include a small resistance in the source pin, being a fixed resistance, the voltage across it will be proportional to the current through it (Ohms Law). The amplifier senses the difference between the resistor's voltage drop and a reference you provide from elsewhere, that 'error voltage' is in turn used to decide the gate voltage.

Example: You want your MOSFET to pass 3A, a 1 Ohm resistor in series withthe source pin will drop 3V. You compare that with your own 3V reference and from the difference control the gate voltage. If the 3V is too high, it means more than 3A is flowing so you reduce the gate voltage and vice versa.

Brian.

 

[KlausST]

Hi,

I need only 1A

1A or 3A?
What accuracy?

Klaus

 

[kushal nandanwar]

Hi,



1A or 3A?
What accuracy?

Klaus

I have two H-bridge one with 1A and second with 3A

 

[D.A.(Tony)Stewart]

Current limiting can be done in many ways. PTC thermistor, CC regulator with shunt R and MOSFET with OpAmp or comparator.

In most cases the current limit is done by the load resistance, but some loads are reactive with a small series resistance that determines the peak current.

So in any design, you must specify the reason for something or define, response time, Voltage, power dissipation. load and source impedance.

 

[kushal nandanwar]

Input voltage is 12VDC and 24VDC,
source impedance = variable
response time = 0.5 msec

can you provide me circuit diagram for CC regulator with shunt R and MOSFET with OpAmp or comparator

 

[betwixt]

Your requirements are conflicting. Is it a H-bridge or a simple constant current source (or sink), it can't be both!

Brian.