Soft start circuit for regulated power supply
AssigneeTexas Instruments Incorporated
InventorsKristopher K. Neild, David A. Williams
Life of this patent
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Abstract
A power supply feedback circuit includes a regulating element at an input side of an optical isolator. The control lead for the regulating element is connected to a voltage divider to receive the divided voltage. A bypass circuit is provided on the voltage divider to change the resistance in a bypassed branch of the voltage divider during start up of the circuit. The bypass time depends on charging of a capacitor at a control lead, base or gate, of an active element by the bypass circuit. The output voltage of the circuit is brought gradually to the desired level as the capacitor charges and the active element removes the bypass from the voltage divider or applies the bypass to the voltage divider.
Claims16
A power supply feedback circuit, comprising:
- an optical isolator having an input side with a light emitting element and an output side with a photosensor;
- a regulator connected to said light emitting element at said input side of said optical isolator, said regulator having a control lead;
- a voltage divider having a tap for a divided voltage connection, said tap being connected to said control lead;
- and
- a bypass circuit connected to said tap of said voltage divider, said bypass circuit operating to apply a first voltage level to said control lead during start up of said power supply feedback circuit which differs from a ongoing operating voltage to be applied during ongoing operation of said power supply, said bypass circuit operating to change a voltage applied to said control lead from said first voltage to said ongoing operating voltage over a predetermined time.
An isolated feedback circuit, comprising:
- an optical coupler having an output connected to a control and having an input;
- a shunt regulator element connected to said input, said shunt regulator element having a control lead;
- a voltage divider having a tap connected to said control lead of said shunt regulator element, said voltage divider having first and second resistors;
- a transistor connected as a bypass of said first resistor of said voltage divider, said transistor a having a control input;
- and
- a resistor and capacitor circuit connected to said control input of said transistor, said capacitor charging upon startup of said feedback circuit to cause a gradual change in voltage at said control lead of said shunt regulator element from an initial value to an ongoing operational value.
A soft start circuit, comprising:
- a voltage divider having first and second branches and a tap therebetween;
- a control lead connected to said tap for controlling a device to be started;
- a bypass connected to across said first branch of said voltage divider, said bypass being controlled to apply a first voltage level to said tap during start up which differs from a ongoing operating voltage, said bypass circuit operating to change a voltage applied to said tap from said first voltage to said ongoing operating voltage over a predetermined time.
Dependencies are inferred from the claim text.