CN210137471U

CN210137471U - Pulse input detection circuit for white light LED dimming

Info

Publication number: CN210137471U
Application number: CN201920600656.5U
Authority: CN
Inventors: 方建平; 赵鹏冲
Original assignee: XI'AN TUOER MICROELECTRONICS CO Ltd
Current assignee: Tuoer Microelectronics Co ltd; Xi'an Tuoer Microelectronics Co ltd
Priority date: 2019-04-28
Filing date: 2019-04-28
Publication date: 2020-03-10
Anticipated expiration: 2029-04-28

Abstract

The utility model provides a pulse input detection circuitry for white light LED adjusts luminance before traditional pulse low pass filter, has added the level shift circuit and the voltage divider network circuit by the reference voltage power supply. When a pulse signal for changing the brightness of the white light LED is required to be provided, only the duty ratio information of the pulse signal is required to be set, and the high level voltage of the pulse signal is not required to be changed, so that a direct current voltage signal in linear and direct proportion relation with the duty ratio of an input pulse signal can be obtained, the level range of the input pulse signal is greatly expanded, the requirement on the output level of a preceding stage circuit is reduced, and the method has universality.

Description

Pulse input detection circuit for white light LED dimming

Technical Field

The invention relates to the field of circuits, in particular to a pulse input detection circuit.

Background

White LEDs need to change their brightness according to the environment when providing backlight for applications such as mobile phones, tablet computers, and various portable multimedia player screens. The current white LED driver chip usually designs a Ctrl pin to detect the input pulse signal. The purpose of adjusting the current flowing through the LED is achieved by changing the high level and the duty ratio of the pulse signal and converting the pulse signal through the LED driving chip. However, since the pulse signal with duty ratio information is generally generated by a previous stage circuit of the LED driver chip, the high level of the pulse signal has a certain value in some application occasions, and it is inconvenient to change the voltage level, which limits the application of the pulse detection method.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention provides a pulse input detection circuit for dimming a white light LED.

The technical scheme adopted by the invention for solving the technical problems is as follows:

a pulse input detection circuit for white light LED dimming comprises a band gap reference circuit, a buffer circuit, an inverter circuit, a PMOS (P-channel metal oxide semiconductor) tube M1, an NMOS (N-channel metal oxide semiconductor) tube M2, a resistor R1, a resistor R2, a resistor R3, a resistor R4, a capacitor C1 and a capacitor C2; the band-gap reference circuit generates a reference voltage VREF and inputs the reference voltage VREF to the buffer circuit; the buffer circuit outputs a voltage signal V1; the grid electrode of the PMOS tube M1 is connected with the grid electrode of the NMOS tube M2, the source electrode of the PMOS tube M1 is connected with the voltage V1, the drain electrode of the PMOS tube M1 is connected with the drain electrode of the NMOS tube M2, the source electrode of the NMOS tube M2 is grounded, the M1 tube and the M2 tube form a level conversion circuit, and a voltage signal V1 serves as a power supply signal of the level conversion circuit; the inverter circuit shapes the pulse input signal into a square wave signal V2, and the square wave signal V2 is output to the gates of the M1 tube and the M2 tube; a level conversion circuit composed of M1 tubes and M2 tubes converts the square wave signal V2 into a pulse signal V3, wherein the high level value of the pulse signal V3 is the voltage value of V1, and the pulse signal V3 is output from the drain connection point of the M1 tube and the M2 tube; voltage V3 is connected with one end of resistor R1, the other end of resistor R1 is connected with one end of resistor R2, the other end of resistor R2 is connected with ground, resistor R1 and resistor R2 form a voltage dividing circuit, voltage division is performed on pulse signal V3, and divided signal V4 is output at the connection point of resistor R1 and resistor R2; one end of the resistor R3 is connected with the voltage V4, and the other end of the resistor R3 is respectively connected with one end of the capacitor C1 and one end of the resistor R4; the other end of the capacitor C1 is coupled to ground; the other end of the resistor R4 is connected with one end of the capacitor C2; the other end of the capacitor C2 is coupled to ground; the resistor R3, the capacitor C1, the resistor R4 and the capacitor C2 form a two-stage low-pass filter, the signal V4 is filtered, the direct-current level Vdc is output from the other end of the resistor R4, and the signal controlling the magnitude of the current flowing through the LED is controlled.

The invention has the beneficial effect that a level conversion circuit and a voltage division network circuit which are powered by reference voltage are added before the traditional pulse low-pass filter. When a pulse signal for changing the brightness of the white light LED is required to be provided, only the duty ratio information of the pulse signal is required to be set, and the high level voltage of the pulse signal is not required to be changed, so that a direct current voltage signal in linear and direct proportion relation with the duty ratio of an input pulse signal can be obtained, the level range of the input pulse signal is greatly expanded, the requirement on the output level of a preceding stage circuit is reduced, and the method has universality.

Drawings

FIG. 1 is a block diagram of an embodiment of a detection circuit of the present invention.

Detailed Description

The invention is further illustrated with reference to the following figures and examples.

As shown in fig. 1, a pulse input detection circuit for dimming a white LED includes a bandgap reference circuit, which includes a bandgap reference circuit, a buffer circuit, an inverter circuit, a PMOS transistor M1, an NMOS transistor M2, a resistor R1, a resistor R2, a resistor R3, a resistor R4, a capacitor C1, and a capacitor C2; the band-gap reference circuit generates a reference voltage VREF and inputs the reference voltage VREF to the buffer circuit; the buffer circuit outputs a voltage signal V1; the grid g of the PMOS tube M1 is connected with the grid g of the NMOS tube M2, the source s of the PMOS tube M1 is connected with the voltage V1, the drain d of the PMOS tube M1 is connected with the drain d of the NMOS tube M2, the source s of the NMOS tube M2 is grounded, the M1 tube and the M2 tube form a level conversion circuit, and a voltage signal V1 is used as a power supply signal of the level conversion circuit; the inverter circuit shapes the pulse input signal into a square wave signal V2, and the square wave signal V2 is output to the gates g of the M1 tube and the M2 tube; a level conversion circuit composed of M1 tubes and M2 tubes converts the square wave signal V2 into a pulse signal V3, wherein the high level value of the pulse signal V3 is the voltage value of V1, and the pulse signal V3 is output from the connection point of the drains d of the M1 tube and the M2 tube; voltage V3 is connected with one end a of resistor R1, the other end b of resistor R1 is connected with one end c of resistor R2, the other end e of resistor R2 is connected with ground, resistor R1 and resistor R2 form a voltage dividing circuit, pulse signal V3 is divided, and divided signal V4 is output at the connection point of resistor R1 and resistor R2; one end f of the resistor R3 is connected with the voltage V4, and the other end h of the resistor R3 is respectively connected with one end j of the capacitor C1 and one end m of the resistor R4; the other end k of the capacitor C1 is coupled to ground; the other end n of the resistor R4 is connected with one end p of the capacitor C2; the other end q of the capacitor C2 is coupled to ground; the resistor R3, the capacitor C1, the resistor R4 and the capacitor C2 form a two-stage low-pass filter, the signal V4 is filtered, the direct-current level Vdc is output from the other end n of the resistor R4, and the signal of the LED current is controlled to flow.

As shown in fig. 1, the working flow of the detection circuit of the present invention is as follows: an external pulse signal is input into an inverter circuit, and after the inverter circuit shapes an input pulse, a signal V2 is output; the V2 signal is input into a level conversion circuit composed of a PMOS transistor M1 and an NMOS transistor M2. The band-gap reference circuit generates a band-gap reference voltage VREF; the band-gap reference voltage VREF is input into a buffer circuit, and the buffer circuit outputs a voltage signal V1; the voltage signal V1 is connected with the source electrode of the PMOS tube M1 and is used as the power supply voltage of the level shifter; after the V2 signal is converted by the level shifter, the high level voltage of the output pulse signal V3 is converted to the level V1; the voltage signal V3 is connected into a voltage division network consisting of a resistor R1 and a resistor R2; the product of the level V1 and the voltage division ratio of the voltage division network is the magnitude of the DC level Vdc when the pulse signal is input into the hundred percent duty cycle, i.e. the DC level Vdc is

A voltage division pulse signal V4 output by the voltage division network passes through a two-stage low-pass filter consisting of a resistor R3, a capacitor C1, a resistor R4 and a capacitor C2 to obtain a direct-current level signal Vdc; the relationship between the magnitude of the dc level signal Vdc and the duty ratio of the input pulse signal can be expressed by the formula:

wherein DC _ pulse is the duty ratio of the external input pulse signal. The magnitude of the direct current level signal Vdc output at this time is irrelevant to the magnitude of the high level of the externally input pulse signal, and is only in direct proportion to the magnitude of the pulse duty ratio, so that the level requirement for the output pulse signal of the preceding stage circuit can be reduced, and the application range of the pulse input detection circuit is widened.

Claims

1. A pulse input detection circuit for white light LED dimming comprises a band gap reference circuit, a buffer circuit, an inverter circuit, a PMOS tube M1, an NMOS tube M2, a resistor R1, a resistor R2, a resistor R3, a resistor R4, a capacitor C1 and a capacitor C2, and is characterized in that:

the pulse input detection circuit for the white light LED dimming is characterized in that the band gap reference circuit generates reference voltage VREF and inputs the reference voltage VREF to the buffer circuit; the buffer circuit outputs a voltage signal V1; the grid electrode of the PMOS tube M1 is connected with the grid electrode of the NMOS tube M2, the source electrode of the PMOS tube M1 is connected with the voltage V1, the drain electrode of the PMOS tube M1 is connected with the drain electrode of the NMOS tube M2, the source electrode of the NMOS tube M2 is grounded, the M1 tube and the M2 tube form a level conversion circuit, and a voltage signal V1 serves as a power supply signal of the level conversion circuit; the inverter circuit shapes the pulse input signal into a square wave signal V2, and the square wave signal V2 is output to the gates of the M1 tube and the M2 tube; a level conversion circuit composed of M1 tubes and M2 tubes converts the square wave signal V2 into a pulse signal V3, wherein the high level value of the pulse signal V3 is the voltage value of V1, and the pulse signal V3 is output from the drain connection point of the M1 tube and the M2 tube; voltage V3 is connected with one end of resistor R1, the other end of resistor R1 is connected with one end of resistor R2, the other end of resistor R2 is connected with ground, resistor R1 and resistor R2 form a voltage dividing circuit, voltage division is performed on pulse signal V3, and divided signal V4 is output at the connection point of resistor R1 and resistor R2; one end of the resistor R3 is connected with the voltage V4, and the other end of the resistor R3 is respectively connected with one end of the capacitor C1 and one end of the resistor R4; the other end of the capacitor C1 is coupled to ground; the other end of the resistor R4 is connected with one end of the capacitor C2; the other end of the capacitor C2 is coupled to ground; the resistor R3, the capacitor C1, the resistor R4 and the capacitor C2 form a two-stage low-pass filter, the signal V4 is filtered, the direct-current level Vdc is output from the other end of the resistor R4, and the signal controlling the magnitude of the current flowing through the LED is controlled.