Unbreakable LDMOS BLF578XR Power Transistor

NXP’s Unbreakable LDMOS: BLF578XR Power Transistor

When you are looking for RF power products for the most demanding applications NXP is your partner of choice.  If you’re tired of replacing dead power transistors then make this a thing of the past with NXP’s new XR extremely rugged.  So rugged are these new transistors that there is a very good claim that they are unbreakable.  How rugged is extremely rugged?  We’ll show you (DEMO)


We have the BLF578XR in a class amplifier, delivering 1200 watts into a 50 out loud.  We create a very transistor unfriendly open circuit situation by disconnecting the output load.  We switch on the power and quickly short the output with a screwdriver.  You can see the extreme amount of energy at the terminal, a condition that would kill most LDMOS devices.  We return to the normal situation, 50 volts 1200 watts into a 50 watt load and see that the amplifier still works perfectly.  

The next test of ruggedness is with a controlled load mismatch through all phases, enabled by the test fixture now in view. The mismatch unit is connected to a network analyzer.  Through a network control we can set it to work through all phases of the Smith chart.  This mismatch unit will create voltage standing waves with ratios from 55:1 up to a maximum of 125:1.  With the normal situation, standard, 50 volts 1200 watts into a 50 watt load, so at this moment the amp is operating at full power.  The mismatch unit now replaces the dummy load connected to the output of the amp and the test set up is powered up again.  The mismatch unit is now varied to expose the LDMOS transistor to a range of extreme mismatch conditions and positions on the Smith chart.  The extreme conditions vary from VSWR from 55: 1 to 125: 1. Now we show the transistor is still alive by going back to the original load and showing the 1200 watt output power.  It still works.

Would you ever treat a transistor worse than this?  Check out the next test.

Even though the transistor is normally used at 50 volts, we test at 55 volts to challenge the extremely rugged BLF578XR.  We set up the transistor at 55 volts 1200 watts into 50 ohm.  We disconnect the output load creating a very unfriendly open circuit situation.  We power up the transistor to 1200 watts.  We screw the short to the output of the amp while the transistor is powered up.  We go back to the 50 ohm load and power up the transistor to 1200 watts and we see that it again survives and works perfectly.  This is what we mean by extremely rugged.  This transistor seems to be unbreakable.  What do you think?

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