Power supply with temperature compensated current foldback

Claim 2

In combination in a power supply circuitry for effecting foldback current limiting, series pass transistor means including first and second terminals having a main conduction path therebetween and a control terminal, a power supply output terminal, current sensing impedance means disposing intermediate a first one of said series pass main conduction terminals and said power supply output terminal, feedback amplifier means including means for comparing a measure of the output potential at said power supply output terminal with a fixed reference voltage and for supplying at said control terminal of said series pass transistor means an output potential dependent upon said comparison, an additional transistor having collector and emitter terminals thereof respectively connected to said control terminal of said series pass transistor means and said power supply output terminal, a potential source, foldback impedance means connecting the base of said additional transistor with said potential source, said current sensing impedance means comprising temperature responsive resistance means connected in parallel with the base-emitter junction of said additional transistor for offsetting the temperature dependent conduction threshold of said additional transistor wherein said current sensing impedance means and said temperature responsive resistance means comprise a first load current passing impedance, resistive voltage divider means connected in parallel with said current passing resistance, said voltage divider including in one branch thereof said temperature responsive resistance means.

Claim 3

In combination in a power supply circuitry for effecting foldback current limiting, series pass transistor means including first and second terminals having a main conduction path therebetween and a control terminal, a power supply output terminal, current sensing impedance means disposing intermediate a first one of said series pass main conduction terminals and said power supply outpUt terminal, feedback amplifier means including means for comparing a measure of the output potential at said power supply output terminal with a fixed reference voltage and for supplying at said control terminal of said series pass transistor means an output potential dependent upon said comparison, an additional transistor having collector and emitter terminals thereof respectively connected to said control terminal of said series pass transistor means and said power supply output terminal, a potential source, foldback impedance means connecting the base of said additional transistor with said potential source, said current sensing impedance means comprising temperature responsive resistance means connected in parallel with the base-emitter junction of said additional transistor for off-setting the temperature dependent conduction threshold of said additional transistor wherein said potential source comprises means for providing a constant output potential independent of line voltage variations further comprising a diode connected in series with said foldback impedance means, and wherein said potential source includes means for providing a voltage of sufficiently small value wherein said diode is reverse biased during normal power supply operation.

Claim 4

In combination in a power supply circuitry for effecting foldback current limiting, series pass transistor means including first and second terminals having a main conduction path therebetween and a control terminal, a power supply output terminal, current sensing impedance means disposing intermediate a first one of said series pass main conduction terminals and said power supply outpUt terminal, feedback amplifier means including means for comparing a measure of the output potential at said power supply output terminal with a fixed reference voltage and for supplying at said control terminal of said series pass transistor means an output potential dependent upon said comparison, an additional transistor having collector and emitter terminals thereof respectively connected to said control terminal of said series pass transistor means and said power supply output terminal, a potential source, foldback impedance means connecting the base of said additional transistor with said potential source, said current sensing impedance means comprising temperature responsive resistance means connected in parallel with the base-emitter junction of said additional transistor for off-setting the temperature dependent conduction threshold of said additional transistor wherein said potential source comprises means for providing a constant output potential independent of line voltage variations further comprising a diode connected in series with said foldback impedance means, and wherein said potential source includes means for providing a voltage of sufficiently small value wherein said diode is reverse biased during normal power supply operation.