The paper deals with the theory and design of the non-linear Wheat-stone bridge circuits used in voltage stabilizers. It is restricted to the use of the bridge as a source of voltage proportional to the change in the supply voltage and to non-linear elements obeying the lawV=kIn, wherenandkare constants. Four circuits are considered, and formulae are deduced for the general case of a resistive load across the output terminals. The effect of changes in the various parameters is discussed. Formulae are also given for the load required for maximum power output from the bridge for a given change in input voltage. The paper concludes with a review of the advantages and disadvantages of the various circuits.