Hello, I am trying to learn more about dual amp power suplies and came across the circuit below, the link is from +12V and -12V Dual Power Supply Circuit Diagram Pretty much the circuit works in 3 step
1- 230v Ac to 12v ac is achieved by a 230/12 transformer.
2- Rectifier diodes convert ac to dc (capacitors smooth voltage)
3- lastly the output is given to a 7812(+) and 7912(-) voltage regulators, which give a 12+ and 12- voltage.
My question is how does the capacitor c2 get charged to -12v?
Is it because C1 and C2 are in series and the Ground kinda acts like a reference ground or middle point, and the way C2 is biased it is negative because the capacitors negative plate feeds into the 7912 ic ( which is a negative regulator) Which will give -12v and the top of C1 would be +12?
larryd:
When you are looking at the negative side of the cct. ignore everything in the positive side and visa versa.
Remember things are referenced to GND.
Negative from the top winding goes through the cathode of the second from the top diode.
Negative from the bottom winding goes through the cathode of the bottom diode.
The negative then proceeds to pin 2 of the 7912.
So when thinking of negative flow, we are not talking about conventional current?
is the negative thought of as electron flow?
and the positive cylcle , we use conventional flow?
Anytime you find yourself using the word “kinda” to describe a circuit, start over because you’ve got it wrong.
C1 and C2 are not in series. The center tap of the transformer is the reference or ground point with two full wave rectifiers, one with a positive output connected to C1/7812 and one with a negative output connected to C2/7912. It would much wiser to discuss the circuit if the diodes had id numbers. It is the direction of the diodes that controls the polarity of the voltage with respect to ground.
If the secondary of the transformer is 12vac the no load dc voltage on C1 will be about 17 vdc, -17 vdc on C2. This is the difference between the rms and peak voltages which is 1.414. With 78xx/79xx series linear regulators, you need the input voltage to be at least 3 volts higher than the output voltage. Keep it reasonable since the delta voltage times the operating current becomes the heat the device must dissipate.
I suggest that if you want to build this or any other power supply you use DC DC converters, not linear regulators. Linear regulators waste lots of power. They are useful however for very low power applications and where low noise on the power supply is important.
So when thinking of negative flow, we are not talking about conventional current?
is the negative thought of as electron flow?
No you are talking about conventional current. Thinking it is anything else than conventional current is just self delusion.
Conventional current is that current flows from a positive point to a less positive point.
In that circuit the most positive point is the in of IC1, the most negative point is the in of IC 2. What is labelled as ground is a voltage half way between those two points. Ground is just a reference point for signals, it is not an absolute point. Ground is simply what you connect it to.
larryd:
When you are looking at the negative side of the cct. ignore everything in the positive side and visa versa.
Negative from the top winding goes through the cathode of the second from the top diode.
Negative from the bottom winding goes through the cathode of the bottom diode.
Thanks, Larry, The reason I was asking about conventional current flow, is because you mentioned that the negative of the top winding flows through the cathode of the second diode from the top and normally "conventionally" that would be a blocking diode.
That's why I was wondering if you can think of the negative half as "electron" flow.
Which i guess from what you said that i can.
Keep in mind the top and bottom windings output an AC signal.
The top winding moves through fully positive to fully negative; at the same time the bottom goes fully negative to fully positive. Referenced to the center tap.
How could current flow through a diode that is blocking it, if we are talking about conventional current?
Because some time in the cycle the voltage on the anode is more positive than the voltage on the cathode and so the diode conducts. Later on in the same cycle this situation is reversed and the anode of the diode is less positive than the cathode and the diode blocks.
You can use electron flow or convention current to describe a circuit but you have to use the same convention for the whole of the circuit, otherwise you understanding of what is going on can never work.
Grumpy_Mike:
Because some time in the cycle the voltage on the anode is more positive than the voltage on the cathode and so the diode conducts. Later on in the same cycle this situation is reversed and the anode of the diode is less positive than the cathode and the diode blocks.
You can use electron flow or convention current to describe a circuit but you have to use the same convention for the whole of the circuit, otherwise you understanding of what is going on can never work.
I am probably wrong here, but just to clarify. Could the negative cycle be thought of as sinking current instead of sourcing it?
This schematic doesn't show the correct way to show that lines are connected,
it seems silly but i took the original pic and put pink dots where i believe to be connection points for the wire.
Is how I put it correct? Thanks
Could the negative cycle be thought of as sinking current instead of sourcing it?
Yes you can think of it that way because the current ( conventional ) always flows from positive to negative. Or from the more positive to the more negative.
