2N3418 Operation Over Temperature
2N3418 Temperature-Power Derating Curve [2N3419, 2N3420, 2N3421]
NPN Medium Power Switching Silicon Transistor. Package, TO-39, TO-5 metal Can.
2N3418 Derating Curve, Maximum Operation
Use the Graph to determine how much to derate power [wattage] based on ambient temperature [Ta]. See additional Transistor Derating Curves for other BJTs.
Temperature derating is a standard design practice to insure that the operating characteristics fall below the maximum temperature that would damage the transistor. The graph covers 2N3418, 2N3419, 2N3420, and the 2N3421 transistors in either a TO-5 or TO-39 package.
As common with these type curves, the line that intersects 200 degrees centigrade represents the maximum junction temperature, which should not be approached, used or exceeded. The line that intersects 150C represents the junction temperature used was used to gather the electrical characteristics found in a data sheet. The line that intersects at 125C and 110C show power ratings where most users want to limit Tj in their application.
An alternative method of derating base on the temperature of the case;
Derate linearly 5.72 mW/C for TA > 25C.
Use the following equation when deal with air temperature and not case temperature;
Derate linearly 150 mW/C for TC > 100C
Which means the power dissipation found in the data sheet should be used up to the case or air temperature provided. Above that temperature the power should be reduced by the amount shown for each degree in temperature rise.
Refer to MIL-PRF-19500/393; Semiconductor Device, Transistor, NPN, Silicon Power, Types 2N3418, 2N3418S, 2N3418U4, 2N3419, 2N3419S, 2N3419U4, 2N3420, 2N3420S, 2N3420U4, 2N3421, 2N3421S, and 2N3421U4, as JAN components, [TO-39, or TO-5]
2N3418 Maximum Ratings:
Collector Emitter Voltage = 60 volts [2N3418, 2N3420]
Collector Base Voltage = 85 volts [2N3418, 2N3420]
Collector Emitter Voltage = 80 volts [2N3419, 2N3421]
Collector Base Voltage = 125 volts [2N3419, 2N3421]
Emitter-Base Voltage = 8.0 volts [all devices]
Forward-Current Transfer Ratio = 60 max [2N3419, 2N3421]
Forward-Current Transfer Ratio = 120 max [2N3419, 2N3421]
Operating Temperature = -65 to +1750C
Power Dissipation 250C [ambient air temp] = 1 Watt
Power Dissipation 1000C [case temp] = 15 Watt
The 2N3418 and 2N3420 devices have similar ratings, as do the 2N3419 and the 2N3421 devices. However the Collector to Emitter breakdown current and Collector to Emitter cutoff currents are different.
How to read the chart; Use the upper curve as a guideline for a 'not to exceed' limit.
Determine the maximum junction temperature that the 2N3418 should operate at.
Draw a line parallel to one of the curves on the chart, that determines the operating characteristics of the 2N3418.
Best practices should force the design to use the 110C curve, for longest life.
Implementation recommendations: Lead length plays a role in power dissipation, so use the shortest possible leads. Read more about Power Dissipation through Component Terminals. The case of the device should not be permitted to make contact with the Printed Circuit Board [PCB]. When the lead terminals are reduced to enhance current flow, they should not be so short that the metal case makes contact with the board. An insulating spacer should be used between the board and the case to separate the heat dissipating case making contact with the board, or with any copper traces running under the conductive case. A heat-sink might also be used to assist in dissipating heat away from the component. High current devices should also not be placed near the transistor, as they may effect the temperature seen by the component. That is, the ambient temperature seen by 2N3418 is not the air temperature, but the temperature around the component, which is the air tmperature and the additional heat generated by other near-by devices.
2N3418 SMD Version
The surface mount 2N3418 version defined in the specification can dissipate far more power than the leaded package. The SMD page has three terminals or pads which reside under the package. For what ever reason the emitter pad is about 3 times the size of either the base or collector pads [which are both the same physical size].
The maximum allowed power dissipation of the SMD version is 15 watts up to 45 degrees centigrade, falling to 110C [60C down to 125C for the second curve]. The maximum junction temperature begins to fall at 130C and terminates at 200C
The 2N3418, 2N3419, 2N3420 and 2N3421 appear to still be in production in either a TO-5 or TO-39 package
