The post discusses a simple method which can added with ordinary inverters for achieving an automatic output voltage regulation in response to varying loads or battery voltage.

Circuit Objective


I have been repeatedly requested for presenting one such design which would enable ordinary inverters with an automatic output voltage control or correction feature.

The idea is simple, as soon as the output voltage crosses a predetermined danger threshold, a corresponding circuit is triggered which in turn switches OFF the inverter power devices in a consistent manner thereby resulting a controlled output voltage within that particular threshold.

The above can be implemented by using an ordinary transistor or by an opamp.

Using opamp and Transistor


The drawback behind using a transistor could be the involved hysteresis issue which could make the switching fairly over a wider cross section resulting in a not so accurate voltage regulation.

Opamps on the other hand can be immensely accurate as these would switch the output regulation within a very narrow margin keeping the correction level tight and accurate.

The simple inverter automatic load voltage correction circuit presented below could be effectively used for the proposed application and for regulating the output of an inverter within any desired limit.

The proposed inverter voltage correction circuit can be understood with the help of the following points:

A single opamp performs the function of a comparator and a voltage level detector.

Simulation and Working


The high voltage AC from the transformer output is stepped down using a potential divider network to about 14V.

This voltage becomes the operating voltage as well as the sensing voltage for the circuit.

The stepped down voltage using a potential divider corresponds proportionately in response to the varying voltage at the output.

Pin3 of the opamp is set to an equivalent DC voltage corresponding to the limit which needs to be controlled.

This is done by feeding the desired maximum limit voltage to the circuit and then adjusting 10k preset until the output just goes high and triggers the NPN transistor.

Once the above setting is done the circuit becomes ready to be integrated with the inverter for the intended corrections.

As can be see the collector of the NPN needs to be connected with the gates of the mosfets of the inverter which are responsible for powering the inverter transformer.

This integration ensures that whenever the output voltage tends to cross the set limit, the NPN triggers grounding the gates of the mosfets and thereby restricting any further rise in the voltage, the ON/OFF triggering continues infinitely as long as the output voltage hovers around the danger zone.

It must be noted that the NPN integration would be compatible only with N-channel mosfets, if the inverter carries P-channel mosfets, the circuit configuration would need a complete reversal of the transistor and the input pinouts of the opamp.

Also the circuit ground should be made common with the battery negative of the inverter.

CAUTION: THE PROPOSED DESIGN IS NOT ISOLATED FROM INVERTER MAINS VOLTAGE, EXERCISE EXTREME CAUTION DURING THE TESTING AND SETTING UP PROCEDURES.

Circuit Diagram


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