Can I connect the AC ground and DC ground together in this circuit?

ac dc ground



This is the diagram which is included in my project.The Vcc and Ground of transistor are of DC +5V and Gnd.Now I must get square wave of the half wave sinusoidal wave coming from AC source 220/50Hz.I wasn't getting neither the square wave and nor the sinusoidal.So I replace the NPN emitter ground with the AC ground, now I can see the pulsating DC on the cathode of the diode, but no square wave is outputing from the transistor collector.I have used different values of resistors.I don't understand as why the Ground of the DC power supply doesnot produces the pulsating DC at the cathode of the diode, I only get this when AC ground is connected.When dealing with center tap transformer, I put one black lead to the ground(middle one) and I measure voltage on the other two sides in AC mode, I get different values slightly altered.Although I bought the "6 0 6" transformer.As we get 6V on either side which are 180' out of phase.I read some what 7.80V and 7.85V


Can I connect the AC ground and DC ground together?
This circuit is very simple, I don't know why this is not working.



I also make the power supply for my project, I use the 220-12V transformer and 470uF capacitor on the 12V side, bridge rectifier and I use 7805 voltage regulator to get the +5V.

Please tell me as how can I get the square wave from this circuit and why my laboartory power supply and my home built power supplies have different values of AC/DC voltage when measured by multimeter.

ac dc grounding

My problems had got solved now.I call my teacher today, he advises me to short the center tap transformer ground with the power supply ground.After doing so, I still didn't get the square wave, then I short the resistance, because the center tap transformer don't provide much current.It was a small transformer, so I thought may be 1kOhm resistor is too much for it and cannot provide the base current to the transistor.So I short the resistor, then I use the oscilloscope and with respect to ground (AC+DC) I checked the signal on the collector of the NPN transistor, there was a perfect square wave and a smile on my face

I don't understand the concept of shorting the AC ground with the DC ground, as why we do it and my another teacher while teaching us the circuit of microcontroller 8051 that was turning ON/OFF the electric bulb powered by 220V/50Hz through the help of RELAY.He said you don't short the 8051 GND with the Ground of the bulb.I don't remember the circuit, but it was something like this one.



But in above circuit shorting the AC ground with DC ground is giving me correct result.When do we short the AC ground with DC ground???

transformer with dc ground

ANOTHER QUESTION:
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Can I connect the ground of two center tap transformer of (12,0,12) and (9,0,9) together??

Re: About AC DC ground

umery2k75 said:

ANOTHER QUESTION:
==============

Well you can short two center tap transformer grounds without any hesitation........But first see ur requirement?

Do u want Isolated supply ? If no then short it otherwise dont


Can I connect the ground of two center tap transformer of (12,0,12) and (9,0,9) together??

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