Hello, I am a student who is not really familiar with electronics, and these days I start studying several circuits which is being used in our experiments.
I have a circuit we insert between room ground and the circuit with power supplies. I made a diagram from the photo of the circuit that I took.
As far as I know, to avoid too high floating voltage between the circuit with power supplies and the ground, the circuit is to make negative voltage ~ MAX -50V relative to ground. (Zener diode 1N5347B are actually 5 in series, not one. I omitted for the simplicity in the diagram)
I sort of understood by Googling and learning myself that the capacitor and the diode is a safe circuit for sudden voltage peaks (am I right?) But, the center part in the circuit diagram, still no idea after several days study. Only figured out that 1N5347B Zener diode 10V 5W is to endure max -50 V.
Here are my questions..
- What would this circuit be called, if it has a name?
- How may the capacitor size 1 uF and resistor size 10 ohms be chosen?
- Why and in what role are those resistors (cement resistors) and transistor connected additionally to the zeners? I thought to have max -50V, only the 5 zener diodes may be sufficient.
- Is it sort of isolation circuit or floating regulation circuit?
----------------------added at 20:52 pm, 6th March, 2016 ----------
Thank you for all who had commented.
The following figure is the edited schematics. U1 - U3 are some user equipment boxes powered by DC power supplies 1, 2, 3 sharing Vcg with their '-' port. (PSs have '+, -, GND' ports, and'GND' ports in PSs are not connected to its own '-' ports.) So, the right side of Vcg are grounded, not to earth, but to the node Vcg. The circuit in the photo is the left side of Vcg.
So far what I learnt about the circuit (left side of the node, Vcg) are,
- to keep 'Vcg' negative potential relative to earth. (which doesn't really have its own power supply), but up to max ~ -50V.
- thanks to @transistor, the roles of the capacitor, diode, and shunt regulator.
Here, additional questions came up to me.
- What role does the circuit itself have when it doesn't have a power supply to itself? would it be just being connected between Vcg and earth, and would start work when Vcg tends to go further negative than -50V?
- In what case (I guess, when what happens in the right side circuit for operation of equipment), Vcg would tend to go more negative?
- and let's say when it goes -51V, without any power supplies on the circuit, the current through R2 to turn on Q1 is going to come through the earth?
- What kind of improvement would I be able to make for this circuit?
(from the previous question) 5. How may C1 1 uF and R2&R3 10 ohms have been chosen? (got to know about R1 to limits the current through D2, thanks to @transistor)
p.s. Am I asking too many questions in one? is putting additional questions not quite the thing?
I think @transistor answer makes sense, and I understood its role. But my schematics may have error still, and the figure in p. 338 doesn't show clearly how the circuit will be closed during the thruster operation, I am trying to give as much information as possible. @transistor mentioned about 'closing circuit', and I added a drawing for that. Generated plasma near anode (inside in U1 in the drawing) accelerate to the vacuum chamber wall which is earth ground, so I expect this is the mechanism closing the circuit. In the drawing, the big square grounded is the vacuum chamber. I hope this help to comprehend the circuit for the additional questions.