English
Menu

What is Safe operating area?

The range of voltage and current combinations in which a power transistor can be used without damage, abbreviated SOA. It is shown on a log-log graph, with boundaries set by on-resistance, current rating, power (thermal) limits and breakdown voltage. The thermal limit relaxes for shorter pulse widths.

Japanese name: 安全動作領域

Safe operating area appears in 2 practice questions across 2 topics, including How to read datasheets, Bipolar transistors.

Field: How to read datasheets

Try it: questions about Safe operating area

Which is the correct way to read a power MOSFET's safe operating area (SOA) graph?

  1. AThe DC line is outermost, and for pulsed operation, the shorter the pulse, the more strictly it is limited compared with DC
  2. BThe boundary is set only by the absolute maximum ratings of VDS and ID, so it does not change with pulse width or case temperature
  3. CShorter pulses allow higher power, and most graphs are for 25 °C single pulses, so derate according to temperature
Show answer and explanation

Answer: C. Shorter pulses allow higher power, and most graphs are for 25 °C single pulses, so derate according to temperature

The SOA is a log-log graph with VDS on the horizontal axis and ID on the vertical axis, showing the combinations of voltage and current at which the device can be used without damage. The boundary is set by the RDS(on) limit, the current rating, the thermal (power) limit and so on; the thermal limit relaxes as pulse width shortens, so multiple lines such as 10 µs, 1 ms and DC are drawn. Most graphs are for a case temperature of 25 °C and a single pulse, so derate them for the actual temperature and repetitive operation. This is especially important when operating in the linear region, as in inrush-current limiting circuits.

Safe operating area in the explanations

Questions that mention Safe operating area (2)

  1. Which is the correct way to read a power MOSFET's safe operating area (SOA) graph?
  2. Which correctly describes thermal runaway in a bipolar transistor?

Books on How to read datasheets Ad

As an Amazon Associate I earn from qualifying purchases.

Related terms

Power MOSFET 5 V tolerant Absolute maximum ratings Allowable power dissipation Derating Dropout voltage Errata Exposed pad Input offset voltage MSL (moisture sensitivity level)

Back to the glossary