Searching mosfet/transistor equivalent

Thread Starter

crazybuoy

Joined Sep 19, 2010
77
Some time, we need to find equivalent N/P mosfet. I know some websites offering the list of mosfets according to given filters or characteristics.

In data sheet, mosfet has lots of characteristics. But which characteristics we should take care of while searching equivalent mosfet.
 

ian field

Joined Oct 27, 2012
6,539
Some time, we need to find equivalent N/P mosfet. I know some websites offering the list of mosfets according to given filters or characteristics.

In data sheet, mosfet has lots of characteristics. But which characteristics we should take care of while searching equivalent mosfet.
Obviously only search in the right polarity - voltage and current are the first criteria, then RDSon, if that is higher; there will be more dissipation whwn its turned fully on.

When you consider the gate specifications - the first thing you need to know is whether its logic level. If you use a standard MOSFET instead of LL type, It won't switch fully on and will have the same effect as high RDSon.

If its for an SMPSU; you probably need to take a look at the Ton and Toff specifications. Slow switching means more time between fully on and fully off, which also causes the device to dissipate excessive power. Manufacturers like to push SMPSU frequency as high as they can get away with because it means smaller cheaper inductors and capacitors - sometimes the look of a PSU can hint that you need fast MOSFETs.

High current MOSFETs sometimes have higher gate capacitance because of the larger die area - many manufacturers have developed fabrication technologies to make the best of this downside.
 

dl324

Joined Mar 30, 2015
10,722
The application is H-bridge to drive motor.
What is the current part number?

Off hand, you should be concerned with maximum current, on resistance, max SD voltage, gate capacitance; maybe turn on voltage, depends on the driver. If the existing circuit doesn't have snubber diodes, you also need to consider avalanche energy capability.
 

ian field

Joined Oct 27, 2012
6,539
The application is H-bridge to drive motor.
Probably not high speed switching - but you should make sure before selecting a substitute.

Many motor drives use IGBTs because VCEsat is usually better than RDSon, IGBTs tend to be slower than MOSFETs. but that usually isn't a problem with motor drives.

The most advanced modern MOSFETs compete pretty much on equal terms with IGBT for reducing on state losses.
 
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