It seems similar to the device asullivan suggested. Microswitches and motor operated cams today reminds me of a Chistmas hobby. Most devices nowdays use bytes. Programmed devices can use bits which is essential to most electrical interfaces.

You may not want to use a Sallen and Key Butterworth filter unless you want this particluar response, which can be varied. An RC filter has 20db/decade attenuation. A gain dependant on frequency opamp filter circuit can produce 40db/decade ideally. More likely it will have better filtering with added distortion.

I'll add that the inductor capacitor filter is not acting as a filter, but is dividing voltage. The frequency of the PWM is based on the frequency of the PWM.

The input voltages are very high, making the control circuit difficult to design. An ordinary opamp and PWM couldn't be used. The main pass transistor should be a low on Vds FET or bipolar transistor operated between cutoff and saturation to achieve higher efficiency. The inductor capacitor filter is absolutely necessary. Choosing the values might be done by load testing.

An opamp can be used out of saturation to amplify a digital signal. A very high gain, which would not be needed with the 12v signal from the pulse width generator, would be less stabile.

A sort of variation of a buck converter could be used in this case. A simple fixed pulse width generator can allow the control opamp to supply input to a regular 5V voltage regulator. An electrolytic capacitor would be needed at the input to the regulator. The opamp could be made stabile enough out of saturation, possibly.

Indulis, are buck converters used very often? They're not standard regulators which I have seen more often. Maybe they can only be used for certain applications.

Are analog ammeters worth purchasing? I'd like to buy a few low current ones. I've never seen them used in low current circuits.

That's a good question. I've seen those flashing light displays at Christmas time. A specialty store of some sort if you can't find them at the local stores.

200m of cable carrying 2 KVrms sinewave at 2 KHz requires only a small guage stranded wire.

Looking again at the design, the ground symbol is very similar to the the voltage source signal. So the design isn't over engineered and is a basic H-bridge. It has two main series circuits which supply voltage to the device. Only one of the series circuits is used at one time. The desired result is normally AC which will not be referenced from the H-bridge ground.

The circuit looks alright. Input A and input B are not specified, but the circuit is much over engineered and needs simplification. What type of device uses this?

Many analog IC's require very large external design to be compatible with a system. Aren't there more variations to IC's that are more useful and less accurate? The whole of the circuit design is very limited. Not knowing much about the availability, are there more manufacturers with better variations of IC's.

Another aspect, is not only will the 5v charging system need to regulate at 5v, it must also not overcharge a low battery to quickly. The same as the slow charge fast charge switch on an automobile battery charger.