I wanted to build a CCS as a plate load for a 6SN7 using the schematic shown here. So off I went to the electronics store... they didn't have the DN2540 FET (as always they don't have what I want), so I looked for an alternative high-voltage N-channel FET and went home with a bunch of IRF830 MOSFETs. Once the circuit was done using the IRF830 instead of the DN2540 I found that there is zero current flowing through my CCS. I double checked my work. I built another one (I thought that maybe one of my MOSFETs is dead). I tried with only the lower part of the CCS (without the upper "buffer" FET). No luck.
Is this because the IRF830 won't work in this circuit? Any ideas what's wrong?
Is this because the IRF830 won't work in this circuit? Any ideas what's wrong?
Hi,
DN2540 is a depletion mode mosfet while IRF830 is enhancement mode. They are not interchangeable.
DN2540 is a depletion mode mosfet while IRF830 is enhancement mode. They are not interchangeable.
Oh well, those black sand critters all look the same, so I thought they must be the same ;-) I am more of a glass guy, an I like to see what's inside. Thanks for illuminating me!
The original circuit is calculated for 20mA current draw. Is your setup for 20mA draw? If not, you need to recalculate the source resistor. Also, the source/gate voltage may be bit different different on the IRF830
Depletion mode N Mosfet such as DN2530, DN2535, DN2540, IXTP01N100D, IXTP08N100D and a few others are rare part.
Since CCS circuit using enhancement mosfets tend to be a lot more complex, I suggest you procure the more appropriate DN2540N5-G for the CCS circuit through online channel. N3 designation is low power and N8 is SMD.
Since CCS circuit using enhancement mosfets tend to be a lot more complex, I suggest you procure the more appropriate DN2540N5-G for the CCS circuit through online channel. N3 designation is low power and N8 is SMD.
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