| Electronics > Beginners |
| Clamping Split Rail Node to GND using Transistor(s) |
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| David Hess:
--- Quote from: Ian.M on August 01, 2019, 11:13:42 pm ---If the gate oxide is only rated for +/-20V with respect to the channel, I think you are going to have trouble driving the four terminal MOSFET gate safely if the rails are +/-15V. Worst case, with the integrator output railed and its input fully at the opposite rail, there will be nearly 30V across the capacitor, and you then have the problem of clamping the gate with respect to the more negative channel terminal (assuming NMOS). As I said earlier, it gets a lot easier with +/-9V or less rails for the OPAMP. --- End quote --- Oddly enough, many of the 3N and similar series 4 pin MOSFETs support gate and channel voltages of 30 volts or greater. |
| Mechatrommer:
--- Quote from: Ian.M on August 02, 2019, 11:06:03 pm ---As the aim is self-education, what you probably should have done is design simpler more general purpose analog computing building blocks (e.g. summers, differential amplifiers, integrators, differentiators, multipliers, lin=>log and log=> lin, etc.) to use up the spare PCB space. Add pin headers and pop them in a solderless breadboard to build your PID controller. When you have something workable, if you want to take it further then's the time to do a final PCB layout. --- End quote --- you are very sensible here. in fact i've done that in series of my pcb sent to seeedstudio. you can see in attachment, i've made soic/sot to DIP adapters to make my parts bread/perf board friendly since my stock parts now are only in soic/sot format. DIP8 parts are slowly phased out. we can also get soic to dip adapter in ebay for $1/each, but since there's space on my pcb, i'll just add them for the cost of $0 for 10-30 pcs. this PID circuit (2nd pic) will probably be used with motor (bridge-fet) driver (1st pic) that i've made in march. i've also bought few smaller breadboards similar to this to cope with many smaller designs. since from past experience if i assembled prototype circuit on my large single breadboard, i cannot do anything else except if i dissasemble the prototype under study, and then later to be assembled again, too much time needed. so breadboards + specialty/custom adapters/modules like the PID module discussed here is hoping for a better future ;D cheers and best regards. ps: the 5Vdc USB/powerbank to ±V DC-AC-DC module in 2nd attachment, i asked for the transformer to no definable success in Help Me Find This Type of SMPS/Hi-Freq Transformer Supplier/Model so it seems i have to wind one of my own ;D or to study later the links provided by some forum members there. anyway, the pcb is sent, now i'm freed after a week of rush, on to another stuffs until the board arrived ;D thanks everybody. |
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