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Linear Control of Phase-Controlled Rectifiers

IP.com Disclosure Number: IPCOM000041313D
Original Publication Date: 1984-Jan-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 2 page(s) / 40K

IBM

Related People

Bonnet, Y: AUTHOR [+3]

Abstract

Power supplies operating from an AC source frequently use phase-controlled rectifiers to gate the AC input signal variably to a load in response to a control signal. Conventional methods using a linear ramp do not provide a linear relationship between the AC voltage across the load and the control signal. This disclosure proposes a simple way to generate an S-shaped ramp whose use yields a linear relationship between the AC voltage across the load and the control signal. Fig. 1 illustrates a conventional control circuit and the proposed improvements thereto. In the conventional circuit, the upper terminal of resistor R is connected to a DC voltage source + V and path 10 does not exist. (This is illustrated by switch SW set in position 1.

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Linear Control of Phase-Controlled Rectifiers

Power supplies operating from an AC source frequently use phase-controlled rectifiers to gate the AC input signal variably to a load in response to a control signal. Conventional methods using a linear ramp do not provide a linear relationship between the AC voltage across the load and the control signal. This disclosure proposes a simple way to generate an S-shaped ramp whose use yields a linear relationship between the AC voltage across the load and the control signal. Fig. 1 illustrates a conventional control circuit and the proposed improvements thereto. In the conventional circuit, the upper terminal of resistor R is connected to a DC voltage source + V and path 10 does not exist. (This is illustrated by switch SW set in position 1.) The signal at node A is a linear sawtooth signal, and comparator 14 produces a firing angle signal r which varies linearly with the second signal, Vc. This can be expressed by the following relation: r = K Vc (1) when K is a constant. The RMS value, V eff, of the AC voltage across the load is a function of sin r and can be expressed in the form: V eff = f (sin r) (2) Combining relations (1) and (2) yields: V eff = f (sin (K Vc)) (3) Relation (3) clearly shows that V eff is not linearly dependent on Vc. According to the proposed improvements to the control circuit briefly described above, the upper terminal of resistor R is not connected to the DC voltage source +V but to the (+) inpu...