When a Inverting Opamp Configuration is at a steady state, we say the Inverting Input is at a Virtual Ground. That means it is at 0V w.r.t to the dual power supply ground, but it cannot drive or draw any current. It is at a high impedance, but still at 0V. When you buffer this 0 V, you get a low signal ground for a opamp supply.

Analog Buffer and Inverter Switching with logic – del20016

Opamp Supply on Buffered Virtual Ground

This gnd. can sink and source in a couple of mA. You can use it with low power opamp circuits for portable battery operated devices. This creates a virtual +/- 6 V dual supply from a 12V battery. This may be needed in cases where some instrumentation opamps need the negative supply or your design demands a measurement around zero.

You may get a more loadable ground using a Power Opamp, i have not tried. The above circuit gnd cannot be used as a return path for LED’s or Relays. You can drive these, between VCC-VDD, but translate levels to drive them.

A Center tap 50Hz Step Down Transformer with two diodes is used to get a train of Positive Sine Pulses at 100Hz which is applied to Q6 base via R51.

2N2646 is a unijunction transistor(UJT) in a TO-18 metal package. The control voltage or voltage proportional to error is fed to R56-Q3, The UJT drives a pulse transformer which provides isolation from the Load which the SCR bridge is controlling.

2N2646 based Voltage controlled SCR Pulser

This phase angle control gives a near Linear closed loop control for a SCR bridge which may be used in Electroplating or a Preregulator of a big power supply.

High Energy Circuits

MOSFET and IGBT based systems are now more in use than Thyristor – Triac – SCR based designs in power electronics. Thyristors are more robust than many power devices.

This is a Regulated Power Supply based on the LM317 IC. It will need a Boost Power Transistor and heatsink for higher currents. It is a versatile building block for stable instrumentation supplies. Consumer Electronic gadgets can use a SMPS chip. In case you wish to use a SMPS for a Precision Instrumentation Block, then take extreme care on Shielding and EMI-RFI.

LM317 based Regulated Power Supply

This is a General Purpose Chip, Series Regulation. It can be varied or trimmed. There is an Internal temperature compensated reference. The minimum trim value is around 1.2. In case you want a Low value voltage like 0.5 with a good current, then use a good negative supply to offset the 1.2 V.

Power supply with battery backup for DMM

The transformer can be s Split Bobbin with Pri-Sec copper shield foil.  This can be earthed along with the metal enclosure. C4 sends any hi-freq components to earth.  It is better if you do not earth the ground but use such capacitors. A Supply should simulate a a battery with both ends floating wrt Earth. A option to eartth the ground is fine. This also helps the user to configure his own dual supplies.

Q1 and R5 form a Short Circuit OR current fold back OR constant current mechanism. TP1 can be used to vary the output voltage.  Better use something like a Bourns 10T trimpot. An open preset may introduce a noise due to dust and vibration. I don’t remember why i added a zener DZ1, a diode may suffice.

See more at my Power Supplies Section.

This is a 9V power supply which will work even on power failure. It uses a rechargeable battery and regulators. A transformer with 15-0-15 AC volts output is required.

From my Power Electronic Circuits

Battery Backup Supply

In the first regulator U1 the output is lifted up by 1.4V and in the second regulator U2 by a resistor divider. In the second regulator the voltage across resistor R3 is 5V, so the current is 5V / 1K = 5mA this adds to the quiescent current of 5mA from the regulators ground terminal and flows into the resistors R1 and R2 in parallel which form 404 ohms, 10mA thru 404 ohms is 4V. So the output will be 5 + 4 = 9V. Note that the charge and discharge paths of the battery are separated with diodes.