Low-Line Overstress of Constant-Power Loads(3 of 4) |
SolutionOnce the problem is understood, the solution is usually straight forward. - Select the turn-on voltage for the power supply
- design a sense circuit for this voltage with hysteresis
- use the circuit to inhibit turn-on until the proper voltages are reached
- add soft start to minimize the load transient at turn-on
- and then by means of simulation and lab measurements, check the transient stress on components during turn-on and turn-off, especially the V-I trajectories of semiconductor switches in relation to their safe-operating area
Do not use this information for design without independent verification of the information. Editor: Jerrold Foutz |
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Low-Line Overstress of Constant-Power Loads(2 of 4) |
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Low-Line Overstress of Constant-Power Loads(1 of 4) |
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Underestimating Complexity of SMPS Design(4 of 5) |
Personal AnecdoteThe first resulted in an 18 month schedule slip on a system schedule that was 18 months from go-ahead to completion of qualification testing. At the beginning of the program a buy decision was made and the power supply development was awarded to the lowest bidder. When it became apparent the design activity could not deliver, the contract was pulled and awarded to the next lowest bidder. When it became apparent that they also could not deliver, the power supply was pulled inside. However, instead of drawing on a group of designers who had strong experience in switching-mode power supply design, the company gave it to some excellent designers with strong backgrounds in communications and analog design (one of the engineers I talked with). When they ran into trouble, the corporation finally tapped their power supply design experts (the other engineer I talked with) and the job was completed. The rest of the system was completed on the original schedule up to the start of qualification testing and waited on the dock for qualification testing for 18 months before the power supplies were available. The final result was an 18 month schedule slip for underestimating the complexity of power supply design. |
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Read more... [Underestimating Complexity of SMPS Design(4 of 5)]
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Underestimating Complexity of SMPS Design(3 of 5) |
SolutionThroughout the 1960's and 1970's, many program managers learned the hard way (though experience) that power supplies were the critical-path item on their program, causing embarrassing schedule slips and cost overruns on an otherwise successful program. Unfortunately, people talk about their successes and not their failures, especially when it is something as embarrassingly simple as a power supply. Hence, the trouble with power supplies was one of the best kept secrets of these decades. |
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Read more... [Underestimating Complexity of SMPS Design(3 of 5)]
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