Disclosure of Invention
The invention aims to solve the technical problem of rising power consumption of a detection circuit caused by short circuit detection of an LED backlight panel, realize the purpose of reducing the power consumption of a short circuit detection chip, and simultaneously reduce the pin number of the short circuit detection circuit chip so as to reduce the manufacturing cost of the chip.
In order to solve the technical problems, the invention provides a short circuit detection circuit for an LED backlight panel, which comprises a short circuit detection unit, an on-chip driving MOS tube, an operational amplifier, a DAC current module and a voltage switching unit;
The short circuit detection circuit is also provided with a G port and an S port, the G port is connected with the grid electrode of the off-chip driving MOS tube at the low potential end of the LED lamp string in the LED backlight panel, and the S port is connected with the source electrode of the off-chip driving MOS tube;
The short circuit detection unit is connected to the S port and is used for detecting the voltage value at the S port;
The drain electrode of the on-chip driving MOS tube is connected to the S port, the source electrode of the on-chip driving MOS tube is connected to the DAC current module, the DAC current module is connected to the ground, and meanwhile, the DAC current module generates a first working current and a second working current of the LED lamp string;
the non-inverting input end of the operational amplifier is connected with a reference voltage, and the inverting input end of the operational amplifier is connected with the source electrode of the driving MOS tube in the chip;
the voltage switching unit is connected with the G port, the output end of the operational amplifier and the grid electrode of the drive MOS tube in the chip at the same time;
The voltage switching unit is switched to a first voltage input state when the DAC current module outputs a first working current; when the voltage switching unit is in a first voltage input state, the grid electrode of the on-chip driving MOS tube is controlled by a first voltage to enable the on-chip driving MOS tube to be in a conducting state, and when the voltage switching unit is in a second voltage input state, the grid electrode of the off-chip driving MOS tube is controlled by a second voltage to enable the off-chip driving MOS tube to be in a conducting state;
the first working current is larger than the second working current, and the short circuit detection unit detects the short circuit of the LED lamp string only when the DAC current module outputs the second working current.
In one embodiment, when the DAC current module outputs the first working current, the output terminal of the operational amplifier is controlled to be connected to the G port so as to be connected to the gate of the off-chip driving MOS transistor.
In one embodiment, when the DAC current module outputs the second working current, the output terminal of the operational amplifier 3 is controlled to be connected to the gate of the driving MOS transistor in the chip.
In one embodiment, the DAC current modules are controlled by the PWM signals to switch between on and off states, and when each DAC current module is in an on state period, the DAC current module provides a first working current or a second working current, and an average current value provided by the DAC current module is consistent with an average working current value of an LED preset by the LED backlight panel.
In one embodiment, the driving MOS transistor 2 in the chip and the driving MOS transistor 200 outside the chip are both NMOS transistors.
The invention also provides a short circuit detection circuit for the LED backlight panel, which comprises a short circuit detection unit, an on-chip driving MOS tube, a first operational amplifier, a second operational amplifier, a voltage switching unit and a DAC current module;
the short circuit detection circuit is provided with a G port and an S port, the G port is connected with the grid electrode of the off-chip driving MOS tube at the low potential end of the LED lamp string in the LED backlight panel, and the S port is connected with the source electrode of the off-chip driving MOS tube;
The short circuit detection unit is connected to the S port and is used for detecting the voltage value at the S port;
The drain electrode of the on-chip driving MOS tube is connected to the S port, the source electrode of the on-chip driving MOS tube is connected to the DAC current module, the DAC current module 6 is connected to the ground, and meanwhile, the DAC current module generates a first working current and a second working current of the LED lamp string;
The non-inverting input end of the first operational amplifier is connected with a first reference voltage, and the inverting input end of the first operational amplifier is connected with the source electrode of the on-chip driving MOS tube;
The non-inverting input end of the second operational amplifier is connected with a second reference voltage, the inverting input end of the second operational amplifier is connected with an S port, and the output end of the second operational amplifier is connected with a voltage switching unit;
The voltage switching unit is connected with a control voltage; the voltage switching unit is switched to a second operational amplifier input state when the DAC current module outputs a first working current; the voltage switching unit is switched to a control voltage input state when the DAC current module outputs a second working current, and when the voltage switching unit is in a second operational amplifier input state, the output end of the second operational amplifier is connected with the G port;
the first working current is larger than the second working current, and the short circuit detection unit detects the short circuit of the LED lamp string only when the DAC current module outputs the second working current.
In one embodiment, the DAC current modules are controlled by the PWM signals to switch between on and off states, and when each DAC current module is in an on state period, the DAC current module provides a first working current or a second working current, and an average current value provided by the DAC current module is consistent with an average working current value of an LED preset by the LED backlight panel.
In one embodiment, the driving MOS transistor 2 in the chip and the driving MOS transistor 200 outside the chip are both NMOS transistors.
One or more embodiments of the present invention may have the following advantages over the prior art:
According to the invention, the DAC current module is utilized to generate small current, so that short circuit detection of the LED lamp string is only carried out in a small working current state, and further, the power consumption generated by the short circuit detection chip during short circuit detection is effectively reduced.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings, in order to make the objects, technical solutions and advantages of the present invention more apparent.
Before proceeding with the following detailed description, it may be advantageous to set forth definitions of certain words and phrases used throughout this invention. The terms "coupled," "connected," and derivatives thereof, refer to any direct or indirect communication or connection between two or more elements, whether or not those elements are in physical contact with one another. The terms "transmit," "receive," and "communicate," and derivatives thereof, encompass both direct and indirect communication. The terms "include" and "comprise," as well as derivatives thereof, mean inclusion without limitation. The term "or" is inclusive, meaning and/or. The phrase "associated with" and its derivatives are intended to include, be included within, interconnect with, contain, be included within, connect to, or be in communication with, mate with, interleave, juxtapose, proximity to, bind to, have an attribute of, have a relationship with, or have a relationship with, etc. the phrase "associated with" and its derivatives are intended to include, be included within, be connected to, or be in communication with the phrase. The term "controller" refers to any device, system, or portion thereof that controls at least one operation. Such a controller may be implemented in hardware, or a combination of hardware and software and/or firmware. The functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. The phrase "at least one," when used with a list of items, means that different combinations of one or more of the listed items may be used, and that only one item in the list may be required. For example, "at least one of A, B, C" includes any one of the combinations A, B, C, A and B, A and C, B and C, A and B and C.
The description of the first end and the second end of the resistor, the capacitor or the inductor in the present invention is only for distinguishing two connection ends of the device, so as to describe the connection relation between the device and other devices, and does not specifically designate one end of the resistor, the capacitor or the inductor in actual situations. Those skilled in the art will appreciate that in an actual circuit construction, any one of the resistor, capacitor, or inductor may be defined as a first terminal in an actual device, while when the first terminal is defined, the other terminal of the device is automatically defined as a second terminal.
Definitions for other specific words and phrases are provided throughout this specification. Those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior as well as future uses of such defined words and phrases.
In the present invention, the application combinations of modules and the division levels of sub-modules are for illustration only, and the application combinations of modules and the division levels of sub-modules may have different manners without departing from the scope of the present disclosure.
Example 1
As shown in fig. 2, the short circuit detection circuit 100 for an LED backlight panel of the present embodiment includes a short circuit detection unit 1, an on-chip driving MOS transistor 2, an operational amplifier 3, a DAC current module 4, and a voltage switching unit 5.
The short circuit detection circuit is provided with a G port and an S port, the G port is connected with the grid electrode of the off-chip driving MOS tube 200 at the low potential end of the LED lamp string 300 in the LED backlight panel, and the S port is connected with the source electrode of the off-chip driving MOS tube 200.
The short circuit detection unit 1 is connected to the S port and is used for detecting the voltage value at the S port.
The drain electrode of the on-chip driving MOS tube 2 is connected to the S port, the source electrode of the on-chip driving MOS tube 2 is connected to the DAC current module 4, and the DAC current module 4 is connected to the ground.
The non-inverting input end of the operational amplifier 3 is connected with the reference voltage Vref, and the inverting input end of the operational amplifier 3 is connected with the source electrode of the on-chip driving MOS tube 2.
The voltage switching unit 5 is connected to the G port, the output end of the operational amplifier 3 and the gate of the on-chip driving MOS transistor 2. And the voltage switching unit 5 is connected with a first voltage and a second voltage.
The voltage switching unit 5 can switch between a first voltage input state and a second voltage input state according to the magnitude of the LED string operation current value of the LED string 300.
When the working current value of the LED light string is a large current (first working current), the voltage switching unit 5 connects the first voltage to the gate of the driving MOS transistor 2 in the chip, and controls the driving MOS transistor 2 in the chip to be in a conductive state. Meanwhile, the output end of the operational amplifier 3 is controlled to be connected to the G port so as to be connected with the grid electrode of the off-chip driving MOS tube 200. At this time, the driving MOS transistor 2 in the chip works in the linear region, which can be approximately regarded as a resistor with a lower resistance value, so as to ensure that the voltage of the S port is in a lower state, thereby realizing that the short circuit detection chip is in a low power consumption working state.
When the working current value of the LED string is small (second working current), the voltage switching unit 5 connects the second voltage to the G port so as to connect with the gate of the off-chip driving MOS transistor 200. Under the action of the second voltage, the off-chip driving MOS transistor 200 is in a conducting state. Meanwhile, the output end of the operational amplifier 3 is controlled to be connected to the grid electrode of the on-chip driving MOS tube 2. The short circuit detection chip performs short circuit detection in the low current state, in which case, once the LED string 300 has an LED bead short circuit, the voltage value of the S port will rise, thereby being detected by the short circuit detection unit 1, to implement short circuit detection of the LED string 300. Because the working current value of the LED lamp string is smaller at the moment, even if the voltage value of the S port is higher, the power consumption value of the whole short circuit detection chip can be controlled.
In this embodiment, the DAC current module 4 is used to adjust the working current of the LED string, as shown in fig. 3, where the DAC current module 4 is used to adjust the working current of the LED string to change between a large current value and a small current value. The corresponding current value can be obtained by changing COED values of the input DAC current module 4. The DAC current module 4 can also be used for adjusting the brightness of the LED lamp string.
In this embodiment, the setting basis for the large current (first operating current) and the small current (second operating current) of the operating current values of the LED strings is the average operating current value of the LED strings, which is preset by the LED backlight panel. Therefore, the first working current and the second working current are selectively matched with the LED backlight panel matched with the short circuit detection chip. When detecting the short circuit of the LED lamp, the voltage on the S port is higher, so that the working current value of the LED lamp string in the time period is reduced as much as possible, the product of the current and the voltage is not too large, the system is ensured not to trigger overheat protection because of too large power of a chip or to cause safety problem because of high power, and finally, the average value of the large current and the small current of the working current of the LED lamp string is equal to the set LED current of the system.
In this embodiment, as shown in fig. 3, under the requirement of the average working current value of the LED light string, the average working current value of the LED light string can reach the requirement of the LED backlight panel by controlling the magnitudes of the first working current value and the second working current value generated by the DAC current module 4 and simultaneously controlling the DAC current module 4 to be turned on or off by the PWM control signal, and the power consumption of the short circuit detection chip itself is reduced as much as possible.
In this embodiment, the first voltage is set to meet the gate-on voltage of the driving MOS transistor 2 in the chip, and the second voltage is set to at least meet the gate-on voltage of the driving MOS transistor 200 outside the chip, and meanwhile, the second voltage is also high enough to enable the S port to detect the requirement of the design value of the short-circuit voltage.
In this embodiment, the reference voltage Vref generally adopts a smaller voltage value, for example, 200mv, so that the source voltage of the driving MOS transistor 2 in the chip is lower in the high-current working state, and the voltage of the S port is also pulled down. So that the power consumption of the short circuit detection chip is in a lower state.
In this embodiment, the driving MOS transistor 2 in the chip and the driving MOS transistor 200 outside the chip are both NMOS transistors.
In this embodiment, the small current period and the large current period generated by the DAC current module may be adjusted according to the requirements, for example, one small current period is inserted into 64 DAC on periods, and the rest is the large current period. Or one small current period is inserted in 128 DAC on periods, and the rest is a large current period.
Or one small current period is inserted in 128 DAC on periods, and the rest is a large current period.
In this embodiment, the DAC on-period and off-period may be controlled by PWM control signals, or may be controlled by clock signals inside the chip. Meanwhile, the chip can be internally provided with a method for determining that a small current period is applied in the next current period after a plurality of large current periods (for example, 63 periods or 127 periods) are passed through by counting the periods, and meanwhile, short circuit detection is started in the small current period.
Example 2
As shown in fig. 3, the short circuit detection circuit 100 for an LED backlight panel of the present embodiment includes a short circuit detection unit 1, an on-chip driving MOS transistor 2, a first operational amplifier 3, a second operational amplifier 4, a voltage switching unit 5, and a DAC current module 6.
The short circuit detection circuit is provided with a G port and an S port, the G port is connected with the grid electrode of the off-chip driving MOS tube 200 at the low potential end of the LED lamp string 300 in the LED backlight panel, and the S port is connected with the source electrode of the off-chip driving MOS tube 200.
The short circuit detection unit 1 is connected to the S port and is used for detecting the voltage value at the S port.
The drain electrode of the on-chip driving MOS tube 2 is connected to the S port, the source electrode of the on-chip driving MOS tube 2 is connected to the DAC current module 6, and the DAC current module 6 is connected to the ground.
The non-inverting input end of the first operational amplifier 3 is connected with a first reference voltage Vref1, and the inverting input end of the first operational amplifier 3 is connected with the source electrode of the on-chip driving MOS tube 2. The output end of the first operational amplifier 3 is connected with the grid electrode of the on-chip driving MOS tube 2.
The non-inverting input end of the second operational amplifier 4 is connected with the second reference voltage Vref2, the inverting input end of the second operational amplifier 4 is connected with the S port, and the output end of the second operational amplifier 4 is connected with the voltage switching unit 5.
The voltage switching unit 5 can switch between a control voltage input state and a second operational amplifier input state according to the magnitude of the LED string operation current value of the LED string 300.
When the working current value of the LED string is large (the first working current), the voltage switching unit 5 is switched to the second operational amplifier input state, and the output end of the second operational amplifier 4 is connected to the G port, that is, the output end of the second operational amplifier 4 is connected to the gate of the off-chip driving MOS transistor 200, and the source voltage of the off-chip driving MOS transistor 200 is clamped to the second reference voltage Vref2, and when the second reference voltage Vref2 is set to a small voltage value, the short circuit detection chip can be controlled to work in the low power consumption state.
When the working current value of the LED string is small (the second working current), the voltage switching unit 5 is switched to the control voltage input state, and the control voltage is connected to the G port at this time, that is, the control voltage is connected to the gate of the off-chip driving MOS transistor 200, so as to control the off-chip driving MOS transistor 200 to be in the on state. In this state, when the LED string 300 has a short circuit of the LED beads, the voltage value of the S port will rise, thereby being detected by the short circuit detection unit 1 to realize the short circuit detection of the LED string 300.
In this embodiment, as in the foregoing embodiment 1, the DAC current module 4 is used to adjust the operating current of the LED string to change between a large current value and a small current value. The corresponding current value can be obtained by changing COED values of the input DAC current module 4. The DAC current module 4 can also be used for adjusting the brightness of the LED lamp string. And also controls short circuit detection only at a small current period.
In a small current state, although the voltage value of the S port is higher, the power consumption of the short circuit detection chip can still be controlled due to the smaller current value. The chip heating caused by the excessive power consumption can not occur.
In this embodiment, the small current period and the large current period generated by the DAC current module may be adjusted according to the requirements, for example, one small current period is inserted into 64 DAC on periods, and the rest is the large current period. Or one small current period is inserted in 128 DAC on periods, and the rest is a large current period.
Or one small current period is inserted in 128 DAC on periods, and the rest is a large current period.
In this embodiment, the DAC on-period and off-period may be controlled by PWM control signals, or may be controlled by clock signals inside the chip. Meanwhile, the chip can be internally provided with a method for determining that a small current period is applied in the next current period after a plurality of large current periods (for example, 63 periods or 127 periods) are passed through by counting the periods, and meanwhile, short circuit detection is started in the small current period.
Example 3
On the basis of the circuit structure of the above embodiment 1 or 2, the DAC current module 4 in this embodiment no longer outputs the large current and the small current for two weeks, but outputs only the average current value of the operation of the LED string.
In this embodiment, the DAC on period and the DAC off period are still generated by the PWM signal or the on-chip clock signal, and the DAC current module 4 outputs the average current value of the LED string light during the DAC on period.
Meanwhile, the chip can be internally provided with a short circuit detection function which is determined to be applied to the next DAC on period after a plurality of DAC on periods are passed through in a period counting mode.
In this embodiment, for example, one short detection period is inserted in 64 DAC on periods, and the rest is a normal operation period, or one short detection period is inserted in 128 DAC on periods, and the rest is a normal operation period. As long as the detection time is short and the interval time is long, the power consumption can be ensured to be low, and the problem of overheating of the chip is avoided.
Thus, the circuit state in the short-circuit detection period in this embodiment is the same as the circuit state in the small-current state in embodiment 1 or 2, and the circuit state in the non-short-circuit detection period is the same as the circuit state in the large-current state in embodiment 1 or 2.
The above description is only a specific embodiment of the present invention, and the scope of the present invention is not limited thereto, and any person skilled in the art should modify or replace the present invention within the technical specification described in the present invention.