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US 5,475,579 AGranted
Pulse width modulator for switching power supply
AssigneeAT&T Corp.
InventorsPaul John, Walter G. Kutzavitch
Life of this patent
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Abstract
An improved pulse width modulation type switching power supply uses an opto-isolator as an output voltage error amplifier which feeds back an error signal to control pulse width modulation as well as to provide isolation between the primary and secondary voltages of the power supply.
Claims6
A switching power supply having its output terminals DC isolated from its input terminals, comprising
- an oscillator circuit connected to an input terminal of a switching transistor,
- a zener diode,
- an opto-isolator device including an input diode optically coupled to a base terminal of an output transistor, the input diode being connected in series with the zener diode across said output terminals, the emitter and collector of the output transistor connected to control the pulse width of said oscillator circuit in response to changes in current through the input dime, and
- a resistor connected between the base of the output transistor of the opto-isolator device and a source terminal of said switching transistor so as to provide a portion of a current flowing through said switching transistor as a base signal current to the output transistor so as to control a charge time of the oscillator circuit.
1 more element
Dependencies are inferred from the claim text.