Hi Eric, thanks for the response,
for my understanding, the power induced into an target is proportional to the current change rate (and therefore to the back emv) but not to the absolute current value. Of course, the longer the pulse (same emv), the bigger the start current, if it should end at zero. At 400V, 300uH and 1A it would last 0,75us. Do you think, this is long enough for smal targets like coins? Using 600V-MOSFET would reduce it to 0,5us, but with 50% more peak power ... for the same power input! Farnell is offering "Low Gate Charge" N-MOSFETs rated for 400V to 900V, even a Low Gate Charge version of the IRF740. Is there a benefit of higher voltage (peak Power) vs. Pulse length? I mean, if I double the start current value and the back emv, Pulse length will remain the same - I believe to get twice the signal for the cost of twice the power. What about doubling back emv/half pulse length? (measuring at the same delay after mosfet comes out of avalanche) After the current reaches near zero, the voltage starts to fall down. In case of dumping resistor you have a long expo decay. If no resistor, the inductor current is going down much quicker, but at the time the voltage reaches zero, current has allready negative value and so it starts ringing ... Now lets switch (with another mosfet) the damping resistor on with some delay and vary the delay - the response changes from expo decay over much quicker zero setting to overshoot and ringing. If resistor switching is done precisely enough (10-20ns resolution), you can save some time. Can you comment my idea please?
Can you figure out, please what factor of noise cancelation can be achieved with a differntial noise cancelling coil, e.g. as posted on the forum? What are the reasons not to use it in every detector (except of larger costs)?
regards Walter