01 October 2013

2N3553 Power Transistor Measurements

Looking at the Phillips data sheet for the 2N3553 transistor and then trying to compare the measurements I took for my 1.5Watt 40m transmitter based on W7ZOI design,  as follows:

Note: I am certainly not sure if the measurements are correct? Further analysis needed.

2N3553 is an NPN RF power transistor intended for VHF applications and recommended by W7ZOI as being suitable for the Universal QRP Transmitter (1.5Watts). He states that even under high SWR conditions the transistor will survive. I have not tested this (although I would love to) since I only have one of these transistors and they are quite expensive.

Case Type = TO-39. (I am running mine with no heatsink although it does get a little warm when sending normal type CW)

Vceo (Peak Collector Emitter voltage) = 40v max. My Vp-p on a 50 ohm load is 24volts (this as expected)
Icm (Peak Collector Current) = 1A. My Ic rms value is 213mA. Thus my Ic peak is 315mA. (not certain)
Ptot = 7W. This is max power dissipation. My tx has a calculated power dissipation of 1.5Watts. ie well below the rated max value and probably explains why it can run with high SWR? The spec also states an efficiency of 50%. I measured an efficiency of 53% which appears to be in the ballpark.

According to the spec. For f=175Mhz. Vce=28, Po = 2.5Watts and Gain = >10dB.

I measured as follows: f=7.020Mhz, Vce=24, Po=1.5Watts and Gain = 18dB. Seems reasonable??

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