Offset Voltage Elimination Circuit Structure for Dimming Device Protection Mechanism

Abstract

An offset voltage cancellation circuit structure of a dimming apparatus protection mechanism is disclosed. The offset voltage cancellation circuit mainly comprises a constant current source capable of outputting constant current; the output end of the constant current source is connected with a dimming signal input end through a current-limiting resistor; the dimming signal input end is connected with an external conventional dimmer output end; when current passes through the current-limiting resistor, a current-limiting resistance voltage that causes voltage offset is generated; an input end of a subtracter is communicated with the constant current source; an offset reference voltage can be imported into another input end of the subtracter; a non-inverted input end of a hysteresis comparator is connected to the output end of the subtracter; and a sawtooth wave can be input to the inverted input end of the hysteresis comparator. Therefore, the offset reference voltage is set to be equal to the current-limiting resistance voltage; the current-limiting resistance voltage can be cancelled by the subtracter, so that the hysteresis comparator can obtain a correct dimming signal voltage, and a GD pulse signal capable of adjusting the luminance of light rays is output.

Description

[0001] Technical field: [0002] The present invention relates to an offset voltage elimination circuit structure for the protection mechanism of a dimming device, in particular to a structure that can provide current output when connecting an external resistor type dimmer, and effectively eliminate the external current limiting resistor used for the protection circuit. Circuit configuration for voltage difference (offset). [0003] Background technique: [0004] Light-emitting diodes (LEDs) have the characteristics of low energy consumption and long service life, so they have gradually been matured and widely used in various lighting requirements; however, due to the great differences between LED light source components and traditional light source Physical characteristics are different, and the dimming circuit suitable for traditional light source components cannot directly control the brightness change of LED light source components, so a conversion circuit is used to connec...

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Problems solved by technology

[0011] However, in practical applications, a current-limiting resistor is usually set at the above-mentioned dimming signal input terminal Adj_in to protect the constant current source A and related circuits from damage caused by excessive voltage or reverse voltage polarity; therefore, in Under normal use conditions (especially for resistive dimmers, the dimming signal voltage input from the dimming signal input terminal Adj_in is formed by a constant current source A outputting a current on a variable resistor RT), any current Flowing through the current-limiting resistor will inevitably produce a voltage drop of the current-limiting resistor. The voltage drop of the current-limiting resistor is added to the voltage introduced or generated by the dimming signal input terminal Adj_in, and a voltage offset (offset) will be generated. This voltage The offset will affect the GD pulse output (dimming control voltage) output by the subsequent hysteresis comparator CMP1, so it must be eliminated in order to obtain the real required dimming signal voltage input

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