Have you ever wanted to take a standard voltage op-amp and turn it into a high voltage output circuit? Here is a technique that requires some shunt regulators to power the chip and some current limiting transistor circuitry for the output. This example should work upto +/- 120V.
Make an Op-Amp High-Voltage Output Circuit - [Link]
This is a great video of Alan Wolke talking about op-amp power supply options. He explains the differences when using op-amps on a single supply, a split (or bipolar) supply and virtual ground.
This video discusses the power supply considerations for op amps. It talks about split or dual power supply and single supply operation, and why the op amp often doesn’t care which you use! It shows how traditional op amps designed for split supply operation can be used in single supply applications. The most important consideration generally is taking care of where the input and output voltages are with respect to the supply rails. The input voltage and output voltage range specifications are examined in a datasheet. The operation of a op amp in a single supply application is examined on an oscilloscope. This operation is compared to a modern rail-to-rail op amp in the same circuit.
Op Amp Power Supplies: Split, Single, and Virtual Ground Designs - [Link]
Kerry Wong shows how to make an adapter circuit for measuring very low voltages with a multimeter.
A typical 3 ½ or 4 ½ multimeter can measure voltage in the low mV range and current in the low mA range. Voltage measurement in the µV range and current measurement in the nA range are typically only available in the more expensive lab bench multimeters. In this post, I will show you a simple adapter circuit that can be used for precision voltage measurement down to the µV range. Using this circuit along with the current adapter circuit I discussed earlier you will be able to perform most of the low level measurements with a 3 ½ meter.
Precision Voltage Adapter For Low Voltage Measurement - [Link]
The MAX44281 is the industry’s first op amp in a 4-bump WLP package, designed for use in portable consumer and medical applications. This device is offered as a noninverting amplifier with gain (AV) of +1V/V, +2V/V, or +10V/V. The device features rail-to-rail output, low 100µV input voltage offset, and 15MHz of bandwidth with only 700µA of supply current. The device is available in an ultra-small, 0.86mm x 0.86mm, 4-bump WLP package with 0.5mm height.
MAX44281 – Ultra-Small, Ultra-Thin, 4-Bump Op Amp - [Link]
The LTC6090 is a high voltage precision operational amplifier. The low noise, low bias current input stage is ideal for high gain configurations. The LTC6090 has low input offset voltage, a rail-to-rail output stage, and can be run from a single 140V or split ±70V supplies.
The LTC6090 is internally protected against overtemperature conditions. A thermal warning output, TFLAG, goes active when the die temperature approaches 150°C. The output stage can be turned off with the output disable pin OD. By tying the OD pin to the thermal warning output, the part will disable the output stage when it is out of the safe operating area. These pins easily interface to any logic family.
The LTC6090 is available in an 8-lead SO and 16-lead TSSOP with exposed pad for low thermal resistance.
LTC6090 – 140V CMOS Rail-to-Rail Output, Picoamp Input Current Op Amp - [Link]
Gerard Fonte writes:
My client, a small manufacturer, was having a noise problem with a new batch of 1500V-dc supplies.
It had been a while since the company manufactured this product. The original engineer was long gone, and the only documentation was a schematic. The approach was a straightforward closed-loop design. An op amp controlled an oscillator that used a step-up transformer to create the high voltage, which the system rectified and filtered into dc. A small part of the output voltage fed back into the inverting input of the op amp as an error signal to adjust the oscillator frequency when necessary. The noninverting input was grounded.
Tracing down a noise problem – an interesting story - [Link]
The need for high capacitance can be fulfilled via the use of a Capacitance Multiplier. The operational amplifier circuit is used as a capacitance multiplier in such a way that multiple small physical capacitances are combined in the integrated circuit technology to yield a large overall capacitance. The aim is often to multiply the original capacitance value hundreds and thousands of times. For example, a capacitor of 10 pF capacitance could be upgraded by the use of capacitance multiplier to behave like a 100 nF capacitor.
Construction of Capacitance Multiplier Circuits:
The circuit construction of a capacitance multiplier is quite simple. Two operational amplifiers, two resistors and a capacitor are used. The second operational amplifier is an inverted amplifier. A voltage source connected to the first operational amplifier will make the amplifier operate as a voltage follower. The circuit will produce a capacitance via the load imposition created by the second amplifier acting as an inverted amplifier. The produced capacitance is isolated from the circuit with the help of voltage follower. In this way, no current flows into the input terminals of the operational amplifier – the input current will flow through the feedback capacitor of the capacitance multiplier circuit.
How Are Multiple Capacitances Produced Using An Operational Amplifier Circuit?
Critical to production of effective capacitance is the selection of good resistance values for the two resistors in the multiplier circuit. The effective capacitance produced will be the capacitance between the input terminal of the operational amplifier and the ground. This effective capacitance will be the multiple of the physical capacitance ‘C’ of the operational amplifier circuit being used as a capacitance multiplier. There is an option to limit the size of this effective capacitance by the use of an inverted output voltage limitation technique. This is a practical approach to limit the size of the effective capacitance.
Relation between Size of Effective Capacitance and Input Voltage:
The capacitance multiplication and the maximum input voltage avoiding saturation state in the operational amplifier are inversely proportional to one other. Effectively, the larger the size of the effective capacitance, the smaller the input voltage into the input terminals of the operational amplifier. Using a similar technique, a resistance multiplier circuit can also be implemented by configuring an operational amplifier circuit. Furthermore, the same operational amplifier circuit can also be designed to simulate inductance.
This is not really an app note, but more of a tutorial on DIY op-amp based linear regulators. The article describes the basics of op-amp regulator, and includes schematics and in-depth explanations of how the various circuits work. [via]
This article follows the history of a popular series of DIY linear regulators. Starting from initial concepts basically idential to the archetype block diagram above, this particular thread through history will wind up in a very sophisticated design. Because this final design developed piecemeal over the course of two decades, that’s how I’ll show it. I think showing the steps this series of designs went through aids understanding of the final design.
Op-amp based DIY linear voltage regulators - [Link]
The National Semiconductors that now belongs to Texas Instruments in 2002 brought together a large collection of circuits using operational amplifiers, are 33 pages of practical circuits with op amps, with formulas for calculations, and can adapt to your design with operational amplifiers. All together in Application Note 31 of the National Semiconductors.
Op Amp Circuit Collection - [Link]
Everyone interested in analog electronics should find some value in this book, and an effort has been made to make the material understandable to the relative novice while not too boring for the practicing engineer. Special effort has been taken to ensure that each chapter can stand alone for the reader with the proper background. Of course, this causes redundancy that some people might find boring, but it’s worth the price to enable the satisfaction of a diversified audience.
Texas Instrument – Op Amps For Everyone - [Link]