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.

When you have to buffer and invert the polarity of mV input levels. This is the circuit you can use, as OP07 has uV offset. R9 and R10 can be 100K 1% MFR or better. Use a symmetrical dual supply.

Dual Polarity Analog Output Op-Amps

OP07: Ultralow Offset Voltage Operational Amplifier

Both the output are identical but opposite polarity. Only low offset opamp can make this possible. We also have to consider temperature stability, environment, emi and thermoelectric emf when working with micro-volts.

Ensure the opamp circuit including the 1% resistors are away from power electronic circuits like output drivers and power supplies. A hot Mosfet close to a 1% resistor will need Sherlock Homes to fix your design, which is flawless. The layout was kaput.

The input impedance of this module is very high, if U1 is OP07 it is in mega ohms, use CA3140 or LF356 fet input opamps to get 1 tera ohm input impedance, but for high gains OP07 is better as it is ultra low offset, this is a good amplifier for sensor outputs, as in a DC Circuit.

Non-Inverting Opamp Interactive Simulation

Non-Inverting Amplifier - Op-Amp Circuits

Vout = Vin * (Rf + Ri) / Ri

The Spice in Analog Design

The zener diodes protect the opamp inputs, R1 limits current during high voltage inputs and R1 and C1 form a filter to remove ac components C1 should be a plastic type as ceramic and electrolytic caps are leaky. A large C1 will slow the response time, the sum of Ri + Rf should be greater than 5k so that output is not loaded. also do not connect output to voltages more than vcc/vdd it will blow Opamp.

This is a Test arrangement for Leakage Testing of Diodes on Reverse Bias. The leakage current indicates the ability of the diode to withstand higher voltages. An AutoTransformer or Variac can be used to vary the test voltage. Even Plastic capacitors can be tested for leakage this way.

High Resistance Indicator – del50004

Diode Reverse Bias Leakage Tester

Safety Precautions –
Use a Isolation 1:1 transformer for safety. This circuit has to be enclosed in a insulated cabinet. A Jig or Acrylic Safety Plate with clamp can be used to connect the diode. The voltage is only applied as long as a Mains two way push switch is pressed. This adds to the safety.

Build a DMM or Digital Multi Meter

Caution Instruction –
Use this with Low voltages like 24V AC for Learning. Do not Use it with High Voltage AC. If you are learning, first work with other circuits using batteries or Low Voltage Mains Adapters.