Circuit Design of Regulator Test Circuit

In this tutorial, we are going to learn about Circuit Design of Regulator Test Circuit.

A switching– regulator test circuit was constructed of the type shown in image, A buck converter power stage operated in the inductor continuous –current mode, and a modulator of the fixed-frequency variable on –time type. The switching frequency was 100 KHZ. One of the principal considerations in design of a regulator is the loop- gain frequency response. In a switching- mode regulator, the loop gain T contains the two – pole response of the averaging filter, and at least one additional source of phase lag from the “Transport Delay” inherent in the switching process, and so the loop is at best marginally stable unless corrective measures are taken. Hence, some frequency compensation in the error amplifier is mandatory.

In the test circuit, the error amplifier was an A741 OPAMP and frequency compensation was accomplished by local feedback around the error OPAMP in conjunction with two-loop sensing of both the averaging filter output voltage and capacitor current. The complete small – signal ac model of the test circuit, which corresponds to the general model of image, . From table1, for a buck regulator µ =1/D, λ =1/D, and Le= L. Also, f(s) = 1 and for the simple comparator – special- case expressions are shown in image.

Also shown in image are numerical values of all parameters. The regulator dc loop established the output voltage V = 10V, and the input voltage was set so that the dc duty ratio was D = 0.7; these values were maintained for all the tests. Direct dc measurement on the test circuit showed that a dc control voltage range of 2.50v was needed to sweep the dc duty ratio over its full range of 0 to 1, so the modulator parameters was VM = 2.50V,leading to the dependent – generator parameters V/DVMR= 1/53Ὠ. Direct ac measurements of the modulator/converter transfer function v/vc disclosed the values Le = L= 82µF, and the effective damping resistance, from the observed Q- factor, was Re= L= 82µH and C= 19µF, and the effective damping resistance, from the observed Q- factor, was Re= 3.5Ὠ. This value is considerably greater than the actual series dc (loss) resistance, the excess being accounted for by modulation resistance (5).

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