How to read this mosfet datasheet parameter

[fasf]

Hi,
i have a question about how to read this datasheet

http://www.onsemi.com/pub/Collateral/BS170-D.PDF

in first page i read:

Maximum drain current 0.5A

but in page 3 fig 5, i read current up to 1.8A...what's wrong?

 

[Phil Allison]

"fasf"

Hi,
i have a question about how to read this datasheet

http://www.onsemi.com/pub/Collateral/BS170-D.PDF

in first page i read:

Maximum drain current 0.5A

but in page 3 fig 5, i read current up to 1.8A...what's wrong?

** You have to read all the notes, see page 2: " On Characteristics ( Note
1) ".


..... Phil

 

[Don Klipstein]

In <a6697a5b-9367-4833-b055-c6c186d22195@w7g2000pre.googlegroups.com>,
fasf wrote:

i have a question about how to read this datasheet

http://www.onsemi.com/pub/Collateral/BS170-D.PDF

in first page i read:

Maximum drain current 0.5A

but in page 3 fig 5, i read current up to 1.8A...what's wrong?

The maximum on 1st page is maximum continuous drain current, and they
caution that you may need continuous drain current to be limited to even
less to not exceed the power dissipation limit. The power dissipation
limit varies with ambient temperature, and Rds(on) varies highly directly
with junction temperature, and the nominal maximum Rds(on) is specified
at junction temperature of 25 C.

The Page 3 Fig. 5 higher drain currents appear to me to be ones that
are surviveable only briefly and intermittently.

I do find this datasheet lacking what I see in most transistor and
power MOSFET datasheets - how long a pulse at whatever power dissipation
with whatever duty cycle (often either 10% or one shot) allows how much
current or power dissipation.

Bipolar power transistor datasheets usually show "safe operating area"
"envelopes" for different pulse durations (non-repetitive) as well as
continuous operation, and they often show another multi-trace graph for
effective thermal resistance from junction to case as a function of pulse
duration and duty cycle.

My guess is that this particular device can pass 1.8 amps at some low
duty cycle at most 10%, maybe less, with pulse duration either low enough
to get repetition rate every second or maybe faster, or maybe 1.8 amp
pulses are limited to however many milliseconds (??? 100 or less for
non-repetitive, 10 or 1 milliseconds if repeated with duty cycle 5% or
more???)

--
- Don Klipstein (don@misty.com)