2N4931 Transistor Derating Graph

2N4931 TO-39 Transistor

2N4931 Temperature-Power Derating Curve [2N4930, 2N3743]
PNP Silicon High Voltage Transistor. Package, TO-39 metal Can [Through-Hole].

2N4931 Temperature-Power Derating Curve
2N4931 Transistor Operational Power Derating Curve

Use the Graph to determine how much to derate power [wattage] based on Case temperature [with a Heat Sink, Tsink]. For best results or longest life use the lowest curve possible. How to read the curves; Interpreting Deraring Curves. The highest curve is normally Thermal Runaway and should be avoided in any design. In fact thermal runaway is basically the point in the operating curve when the transistor is no longer functioning within the design parameters or under the control of the circuit designer. Thermal runaway is sort of self explanatory, the heat inside the semiconductor has reached a point that it is self generating. The increase in semiconductor temperature is causing a higher current flow which in turn is generating additional heat. It than goes without saying that any condition that could cause thermal runaway should be avoided at any cost.

Another derating method would be use the linear equation found in many data sheets;
Derate the 2N4931 linearly 5.71 mW/0C for TA > +250C [ambient temperature]
Derate the 2N4931 linearly 28.6 mW/0C for TC > +250C [case temperature]

These equation are almost always using worst case numbers, or absolute maximum numbers. In most cases one or more of these calculations will be found just after the absolute maximum rating table, which indicates that they begin with the maximum power dissipation indicated in the data sheet [usually provided at 25C] and they terminate at 200 degrees centigrade [the maximum junction temperature]. The curves, on the other hand, allow the designer to select operating points below the maximum ratings to insure that the semiconductor junction temperature never even approaches the maximum temperature.
How to Derate Transistors over Temperature
Temperature derating is a standard design practice for electrical engineers.
If possible define larger than needed pads on the circuit board to help conduct heat away from the transistor and into the board. Shorter component leads also help to dump heat into the board copper.

Refer to MIL-PRF-19500/397; Semiconductor Device, Transistor, PNP, Silicon, Types 2N3743, 2N3743U4, 2N4930, 2N4930U4, 2N4931, and 2N4931U4, qualified under JAN, JANTX, JANTXV, JANS, JANHC, and JANKC, [TO-39, U4 surface mount, Semiconductor-Die]

2N4931 Maximum Operational Ratings:
Collector Emitter Voltage = 250 volts dc [Vce]
Collector Base Voltage = 250 volts dc [Vcb]
Emitter Base Voltage = 5 volts dc [Veb]
Power Dissipation = 1 Watt [250C]
Collector Current = 200mA dc
Operating Temperature = -65 to +2000C [Tj], 2N4931
Storage Temperature = -65 to +2000C [Tstg], 2N4931

Refer to the data sheet for additional electrical characteristics

2N4931 SMD Transistor

2N4931-U4 Temperature-Power Derating Curve [2N4930U4, 2N3743U4]
PNP Silicon High Voltage Transistor. Package, U4 SMD [Surface Mount].

2N4931U4 Temperature-Power Derating Curves
Transistor Operational Power Derating Curve

Use the chart to determine the maximum allowable power dissipation with increasing ambient temperature [still-air]. Note that the graph does use case temperature to derate the device.
Note that the curve relates to the devices case temperature of the surface mount package shown to the left. Additional package styles are available, refer to the links to the left. The reference to the term U4 is just a generic reference to this particular package style, as there is no commercially available package type to call out. So in this case, U4 only relates to the package shown to the left. The over-all case dimensions are provided, but because the pad to pad dimensions could change, they are not shown in the graphic.
Also refer to additional Transistor Derating Curves.
Another page covers How to Interpret Transistor Derating Curves.

TO-39 metal Transistor Through Hole Package
TO-39 metal Package

PNP High Voltage Transistor, BJT
Derating curves for a 2N4930 BJT
2N4930U4 SMD BJT version
Derating curves for a 2N3743 BJT
2N3743U4 SMD BJT version

PNP Transistor Derating guide

Electronic Component Derating

Transistor Manufacturers and vendors.

Surface Mount Transistor Package
Surface Mount Package

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Modified 1/21/12
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