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CTL503, when to use Continuous, Pulsed 300us and Pulsed 80us modes

When measuring power devices with the CTL503 it is useful to understand what the limitations are.

The CTL503 comes with a 12V 1.5A mains adaptor, this limits the maximum available power to around 18W.  Clearly testing a power device continuously at 50V, 3A (150W dissipation) is not possible, or desirable (most DUT are not going to be heat sunk during testing). This is where we test using pulsed modes.

Pulsed test modes are necessary to reduce heating in the DUT and to work within the limitations of the CTL503 power supply.

There are two options for pulsed mode testing: 300us and 80us (these are chosen as historically many curve tracers use these values). The 300us setting is the most accurate (it takes 4 consecutive ADC samples and averages these, as opposed to 80us sampling in which the ADC samples just once per cycle.

Sampling intervals are by default 1/50th of a second (50Hz) - this is adjustable between 10 and 100Hz using the sampling menu.

The effective duty cycle of the sampling system is given by:
SampleRate x PulseDuration e.g. 300us @ 50Hz would be 1.5% dutycycle.

For a 100V/3A peak dissipation (300W) test we end up with only 4.5W (300W x 1.5%) using the example pulse settings - even this would be quite alot for a DUT that wasn't heat sunk - Under these test conditions we would suggest a slower sample rate (perhaps 10Hz) and/or the faster pulsed setting (80us).

Collector set to Continuous mode (showing limitation):

Collector set to 300us mode:

Both the collector supply and the base generator can be set to continuous or pulsed modes (although they cannot be set to different timings if both set to pulsed mode).

Future revisions of ASA (the PC software) will display the peak estimated power automatically.


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