2017-06-17, 22:39
0.2 V forward drop? Wanders off to google... ah schotty 0.2 to 0.4 V, rather lower than I thought, my bad.
Only really need the series diode in the +3.3 V feed to the S1 jumper block that powers the E-field preamp. That is where a mis-jumpering or tweezer slip is going cause the +5 V and +3.3 V rails to come together. If some one chooses to power a board just resting on a work bench along with nuts/bolts and wire off cuts that's their probelm. B-)
The Blue E-field pre-amp uses the ADA4891 op-amp, minimum supply of 2.7 V, a silicon diode would drop to much. Higher end schotty would bring the supply at the controller board down to 2.9 V. Assuming 10 mA pre-amp load, 100 m of coax will only drop 0.025 V, so plenty of head room. Assuming the pre-amp design will still perform properly with a supply below 2.9 V.
Only really need the series diode in the +3.3 V feed to the S1 jumper block that powers the E-field preamp. That is where a mis-jumpering or tweezer slip is going cause the +5 V and +3.3 V rails to come together. If some one chooses to power a board just resting on a work bench along with nuts/bolts and wire off cuts that's their probelm. B-)
The Blue E-field pre-amp uses the ADA4891 op-amp, minimum supply of 2.7 V, a silicon diode would drop to much. Higher end schotty would bring the supply at the controller board down to 2.9 V. Assuming 10 mA pre-amp load, 100 m of coax will only drop 0.025 V, so plenty of head room. Assuming the pre-amp design will still perform properly with a supply below 2.9 V.