Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

Help me understand some parameters on a datasheet of IRFL4315

Status
Not open for further replies.
N

Nischitha

Junior Member level 1
Junior Member level 1
Joined
Nov 25, 2011
Messages
15
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,391
Hi,

Can anybody help me how to understand the Maximum safe operating Area Graph in the MOSFET IRFL4315 datasheet. i.e graph Id vs Vds, with the duration of the pulse.
 

The SOA defines a safety zone and you should not go outside it. An example: Look at the line for 1msec and see where it touches the coordinates of 5A and 20V. It means that, with a 1msec pulse of 20V, the current must not exceed 5A. Look at other points along the 1msec curve and you'll see other combinations of voltage and current like 10V & 10A, 50V & 2A, etc. Since the products are all 100VA, it is clearly a linear function and you can derive a max current for any voltage and vice versa, e.g. 16V and 6.25A.

Similarly, the limit for a 100usec pulse is a VA product of about 320. And whatever the pulse length, you should never exceed 21A or 150V.
 
Thank you,
And I have still more questions on this,

Again form the datasheet of IRFL4315, graph Id vs Vd (fig 2), which is given for the 20usec pulse width. For Vgs=15V, it is found that Id (21A) has Rds(on) curve upto Vds=10V, and Id=21A. After that the curve is found to be linear. Now my question is what if the current increases above that.
1) Does the current saturates(FET starts go linear) or FET turns OFF?
2) Since the above current rating is given for 20usec pulse, can my current be 25A for 16usec??
 

Nischitha said:
Thank you,
And I have still more questions on this,

Again form the datasheet of IRFL4315, graph Id vs Vd (fig 2), which is given for the 20usec pulse width. For Vgs=15V, it is found that Id (21A) has Rds(on) curve upto Vds=10V, and Id=21A. After that the curve is found to be linear. Now my question is what if the current increases above that.
1) Does the current saturates(FET starts go linear) or FET turns OFF?
Click to expand...
Before I can answer that, I have to be sure exactly what it is you're asking. By "After that....." do you mean that part of the curve that goes down from about 10V & 20A towards 0.1V and about 0.25A?

2) Since the above current rating is given for 20usec pulse, can my current be 25A for 16usec??
Click to expand...
No, because that would push it outside the SOA. The SOA limits the permissible Id to an Absolute Maximum Rating of 21A no matter how brief the pulse is. The Absolute Maximum Ratings are also given near the top of the document.
 
Yes, you are absolutely right.
 

OK, now going back to your question about the transistor going linear on the left-hand portion of the graph: In a way, it could be said that it's linear because the drain-to-source resistance (Rds) is approximately linear in that region and current changes approximately in proportion to voltage.

But another, more often encountered, application of the term 'linear' is to the relation between the input and output of a device. In the case of a MOSFET, that would be the relation between gate voltage Vgs and output current (Id) and/or voltage (Vds). In that sense, that region is the most non-linear part of its characteristics because changes in Vgs cause little corresponding change in the output.
 
Thank you,
For the above graph(same curve)
1)Does the current saturates to 20A, eventhough my current is increased above 20A.?
2)Does MOSFET turns off, if the current through the drain increases above 20A or MOSFET burns out?? To be more clear what happens if my current is increased the limit(20A)?
 

1) Yes, the saturation current is about 20A at Vds of 10V because Id cannot increase even if you increase Vg. But Id will increase if you increase Vds. The curve is not drawn above about 21A simply because it exceeds the maximum ratings. It can go higher than 21A but with risk of damage to the transistor.
2) No. The transistor is fully on at 20A and 10V. The term 'on' here means presenting the least resistance in a given condition such as when you close a mechanical switch. If you go above 20A, it may or may not burn out immediately, but you'll be exceeding the safe limit.
 
Thank you very much for the useful information
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top