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Help on Cascode DN2540 CCS

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swordsman

Member
Joined 2005
What is the minimum Vds for a Cascode DN2540 CCS to work properly to 160mA?

Looking at the DN2540 spec, it stated a Idss of 100mA minimum and looking at the curve, it shouldn't have any problem delivering up to 160mA i wanted. On my test rig, i have a 11V supply for the cascode CCS and only able to get maximum 105mA sink therefore suspecting the low supply voltage might be limiting the current sink achievable. This is the measurement i got from my test rig:

Upper DN2540
Vds = 10.4V
Vbs = -1.4V

Lower DN2540
Vds = 1.4V
Vbs = -0.15V

My intention is to use this Cascode CCS replacing a cathode bias resistor which is dropping 20V at this moment. Therefore, the supply to the Cascode CCS when placed in the actual circuit is 20V. Will this increase in supply voltage over the 11V supply in my test rig increase the available current sink from 105mA to 160mA? The cascode CCS will be dissipating 3.2W and i already attached a heatsink to the upper DN2540 for that purpose.

Anyone here uses DN2540 to sink more than the quoted 100mA in the spec? If 100mA is the absolute current sink, what can i do to increase the current sink to 160mA?
 
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