CN113597058B - LED protection circuit and driver with overheat current reduction and constant current functions - Google Patents
LED protection circuit and driver with overheat current reduction and constant current functions Download PDFInfo
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- CN113597058B CN113597058B CN202110894170.9A CN202110894170A CN113597058B CN 113597058 B CN113597058 B CN 113597058B CN 202110894170 A CN202110894170 A CN 202110894170A CN 113597058 B CN113597058 B CN 113597058B
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- 230000009467 reduction Effects 0.000 title claims abstract description 15
- 230000005669 field effect Effects 0.000 claims abstract description 18
- 230000007423 decrease Effects 0.000 description 10
- 230000008859 change Effects 0.000 description 5
- 101100462378 Danio rerio otpb gene Proteins 0.000 description 3
- 238000010586 diagram Methods 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 239000011324 bead Substances 0.000 description 2
- 230000008033 biological extinction Effects 0.000 description 2
- 101100295841 Arabidopsis thaliana OPT3 gene Proteins 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000017525 heat dissipation Effects 0.000 description 1
- 230000020169 heat generation Effects 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
Classifications
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
- H05B45/50—Circuit arrangements for operating light-emitting diodes [LED] responsive to malfunctions or undesirable behaviour of LEDs; responsive to LED life; Protective circuits
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
- H05B45/30—Driver circuits
- H05B45/345—Current stabilisation; Maintaining constant current
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
- H05B45/50—Circuit arrangements for operating light-emitting diodes [LED] responsive to malfunctions or undesirable behaviour of LEDs; responsive to LED life; Protective circuits
- H05B45/56—Circuit arrangements for operating light-emitting diodes [LED] responsive to malfunctions or undesirable behaviour of LEDs; responsive to LED life; Protective circuits involving measures to prevent abnormal temperature of the LEDs
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
- Y02B20/00—Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps
- Y02B20/30—Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]
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- Led Devices (AREA)
- Circuit Arrangement For Electric Light Sources In General (AREA)
Abstract
The invention discloses an LED protection circuit with overheat current reduction and constant current functions and a driver, wherein the protection circuit comprises a first operational amplifier circuit OP1, a third operational amplifier circuit OP3 and a field effect transistor, two voltage input ends of the OP3 are used for inputting a variable voltage and a reference voltage, two voltage input ends of the OP1 are used for inputting a voltage Viadj and a constant current threshold voltage, a current output end of the OP3 is connected with a current input end of the OP3 through a resistor R2 and a resistor R3, the current output end of the OP3 is connected with a power end of the OP1 through the resistor R2 and the resistor R1, the current output end of the OP3 is grounded, the power end of the OP1 is connected with a power supply, the voltage Viadj input end of the OP1 is connected with the current input end of the third operational amplifier, a drain electrode of the field effect transistor is connected with the power supply, a source electrode is connected with the current input end of the OP3, and a grid electrode is connected with the output end of the OP 1. The invention has a constant current function, and the reduced lamp current can be kept constant.
Description
Technical Field
The invention relates to the technical field of LED lamps, in particular to an LED protection circuit with overheat current reduction and constant current functions.
Background
As with most integrated circuit drivers, conventional LED drivers have only a thermal shutdown function. When the junction temperature of the driver exceeds the set temperature, the controller turns off the driving output, and the LED lamp is turned off. In order to solve the problem of extinction of the LED lamp at high temperature, a few LED drivers incorporate a current foldback circuit. When the junction temperature of the driver reaches the set temperature, the driver outputs reduced LED current to reduce the heat generation of the LED lamp. The LED lamp has the advantages that the extinction of the LED lamp can be avoided, and the LED lamp can continue to work under the condition of low current. However, after the LED current is reduced, the brightness of the LED lamp is reduced, the heat of the LED lamp is reduced, the junction temperature of the driver is reduced, the output of the driver increases the LED current, the brightness of the LED lamp is improved, and the heat of the LED lamp is increased. The LED current will change constantly in the foldback interval, and the LED lamp will appear suddenly and suddenly effect.
Disclosure of Invention
The invention aims to provide an LED protection circuit with overheat current reduction and constant current functions, which solves the technical problems that the LED current is continuously changed in a foldback interval and the LED lamp is suddenly darkened after the LED driver is added with the current foldback circuit in the prior art,
the invention is realized by the following technical scheme:
the utility model provides a LED protection circuit with overheat current reduction and constant current function, includes first operational amplifier circuit OP1, third operational amplifier circuit OP3 and field effect transistor Q1, third operational amplifier circuit OP3 has two voltage input ends, is used for input change voltage Viadj2 and reference voltage Vref respectively, first operational amplifier circuit OP1 has two voltage input ends, is used for input LED lamp normal operation setting voltage Viadj and constant current threshold voltage Vtemp. respectively, third operational amplifier circuit OP3 is used for converting voltage signal into current signal, the current output end of third operational amplifier circuit OP3 passes through resistance R2, resistance R3 in proper order and is connected with its current input end, the current output end of third operational amplifier circuit OP3 passes through resistance R2, resistance R1 in proper order and is connected with the power end of first operational amplifier circuit OP1, the current output end of third operational amplifier circuit OP3 is connected with ground, the power end of first operational amplifier circuit OP1 is connected with the power, the voltage Viadj of first operational amplifier circuit OP 1's normal operation setting voltage and constant current threshold voltage Vtemp. respectively, the current output end of third operational amplifier circuit OP3 is connected with the drain electrode of drain electrode operational amplifier circuit OP1, the drain electrode of drain electrode is connected with the current output end of the drain electrode of the third operational amplifier circuit OP 1.
Further, the circuit further comprises a second operational amplifier OP2 and a field effect transistor Q2, wherein the second operational amplifier OP2 is provided with two voltage input ends respectively used for inputting the variable voltage vidij 2 and a turn-off threshold voltage Vtempb, the turn-off threshold voltage Vtempb is smaller than a constant current threshold voltage Vtempa, a grid electrode of the field effect transistor Q2 is connected with an output end of the second operational amplifier OP2, a drain electrode of the field effect transistor Q2 is connected with a current input end of the third operational amplifier OP3, and a source electrode of the field effect transistor Q2 is connected with a current output end of the third operational amplifier OP 3.
The LED driver comprises an LED protection circuit with overheat current reduction and constant current functions, the driver comprises a driving chip, the driving chip comprises an IADJ2 pin, a VREF pin, an IADJ pin, a TEMPA pin and a TEMPB pin, the variable voltage Viadj2 and reference voltage Vref input end of a third operational amplifier circuit OP3 are respectively connected with the IADJ2 pin and the VREF pin, and the voltage Viadj and constant current threshold voltage Vtemp input end of a first operational amplifier circuit OP1 are respectively connected with the IADJ pin and the TEMPA pin.
Further, the IADJ2 pin is used for being connected to a voltage divider circuit comprising a thermistor and used for obtaining a temperature signal of the LED lamp panel.
Further, the TEMPA pin is used for setting a derating curve of the LED current when the LED lamp is overheated, and the TEMPB pin is used for setting an overheated shutdown temperature threshold.
Compared with the prior art, the invention has the following advantages and beneficial effects:
according to the LED protection circuit and the driver with the overheat current reduction and constant current functions, the constant current function is added on the basis of enabling the LED driver to have the current turn-back function, and the reduced LED current can be kept constant in a high-temperature environment, so that the LED lamp is prevented from suddenly changing into a dark state.
Drawings
In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the drawings that are needed in the examples will be briefly described below, it being understood that the following drawings only illustrate some examples of the present invention and therefore should not be considered as limiting the scope, and that other related drawings may be obtained from these drawings without inventive effort for a person skilled in the art. In the drawings:
FIG. 1 is a schematic diagram of an LED protection circuit with overheat current reduction and constant current functions according to the present invention;
FIG. 2 is a graph of temperature points (e.g., LED panels or LED beads) detected by an LED protection circuit with overheat current reduction and constant current functions according to the present invention;
FIG. 3 is a circuit diagram of an exemplary application of an LED driver according to the present invention;
FIG. 4 is a graph of LED current versus IADJ2 voltage for an LED driver according to the present invention;
FIG. 5 is a graph showing the relationship between LED current and LED lamp panel temperature in an LED driver according to the present invention;
FIG. 6 is a schematic diagram showing the effect of IADJ2 function on LED lamp panel temperature and LED current in an LED driver according to the present invention.
Detailed Description
For the purpose of making apparent the objects, technical solutions and advantages of the present invention, the present invention will be further described in detail with reference to the following examples and the accompanying drawings, wherein the exemplary embodiments of the present invention and the descriptions thereof are for illustrating the present invention only and are not to be construed as limiting the present invention.
Example 1
Referring to fig. 1 and 2, the embodiment of the invention provides an LED protection circuit with overheat current reduction and constant current functions, which comprises a first operational amplifier circuit OP1, a third operational amplifier circuit OP3 and a field effect transistor Q1, wherein the third operational amplifier circuit OP3 has two voltage input ends for inputting a variable voltage vidj 2 and a reference voltage Vref, the first operational amplifier circuit OP1 has two voltage input ends, an inverted input end and a homodromous input end of the first operational amplifier circuit OP1 are respectively used for inputting a normal operation set voltage vidj and a constant current threshold voltage Vtempa of the LED lamp, the third operational amplifier circuit OP3 is used for converting a voltage signal into a current signal, a current output end of the third operational amplifier circuit OP3 is connected with a current input end of the third operational amplifier circuit OP3 sequentially through a resistor R2 and a resistor R3, a current output end of the third operational amplifier circuit OP3 is connected with a power supply end of the first operational amplifier circuit OP1 sequentially through the resistor R2 and the resistor R1, a current output end of the third operational amplifier circuit OP3 is connected with a current input end of the third operational amplifier circuit OP1, and the current output end of the third operational amplifier circuit OP1 is connected with a drain electrode of the third operational amplifier circuit OP 1.
As a specific implementation manner, the circuit further comprises a second operational amplifier OP2 and a field effect transistor Q2, wherein the second operational amplifier OP2 is provided with two voltage input ends, an inverted input end and a homodromous input end of the second operational amplifier OP2 are respectively used for inputting the variable voltage vidj 2 and a cut-off threshold voltage Vtempb, the cut-off threshold voltage Vtempb is smaller than the constant current threshold voltage Vtempa, a grid electrode of the field effect transistor Q2 is connected with an output end of the second operational amplifier OP2, a drain electrode of the field effect transistor Q2 is connected with a current input end of the third operational amplifier OP3, and a source electrode of the field effect transistor Q2 is connected with a current output end of the third operational amplifier OP 3.
The working flow of the embodiment of the invention is as follows:
when the LED lamp works normally, namely before overheat protection does not work, the current of the LED lamp is controlled by the normal working set voltage of the LED lamp, namely the input voltage Viadj. The input voltage Viadj is a fixed voltage set by the voltage dividing resistors fixed by R1 and R2, and the fixed voltage is used for setting current when the LED lamp works normally.
When the external circuit temperature is too high, the thermistor changes, and the change of the thermistor value changes the voltage Viadj2. When the voltage Viadj2 is lower than the reference voltage Vref, the third operational amplifier OP3 starts to operate to generate a sink current source. This current source acts as a bypass current, causing current to flow through resistor R3, thereby changing voltage vidj. After the voltage Viadj decreases, the LED current decreases accordingly. With the gradual increase of the voltage Viadj2, the LED current gradually decreases, the fixed slope adjustment of the current is realized, and the lamp gradually darkens.
One of the voltage input terminals of the first operational amplifier circuit OP1 is set to a constant-current threshold voltage Vtempa through a single resistor, when the voltage vipaj is reduced to the constant-current threshold voltage Vtempa, the first operational amplifier circuit OP1 and the field effect transistor Q1 start to operate, the voltage vipj is locked, and thereafter, the LED current is kept constant.
One of the voltage input terminals of the second operational amplifier OP2 is set to an off threshold voltage Vtempb input through a single resistor. If the external circuit temperature continues to rise, the voltage Viadj2 continues to decrease. When the voltage Viadj2 is lower than the turn-off threshold voltage Vtemppb, the second operational amplifier OP2 starts to operate, and the voltage Viadj is pulled down to 0V through the field effect transistor Q2, so that the LED current is reduced to 0. And the LED current is turned off.
Referring to fig. 2, OTP1 is a start temperature point of a reduced current, OTP2 is a start temperature point corresponding to a constant current state of the LED current, and OTP3 is a temperature point corresponding to a driver turned off. The temperature interval corresponding to OTP1 to OTP2 is a foldback current region, and in the temperature interval, the LED current changes along with the temperature change; the temperature interval corresponding to OTP2 to OPT3 is a constant current region, and in the temperature interval, the LED current is kept constant, and the LED lamp can work at constant low brightness. OTP3 is the overtemperature Guan Duandian, and when the detected temperature point reaches the temperature, the driver output is closed, and the LED lamp is turned off.
According to the LED protection circuit with the overheat current reduction and constant current functions, the constant current function is added on the basis of enabling the LED driver to have the current foldback function, the reduced LED current can be kept constant in a high-temperature environment, the condition that an LED lamp suddenly changes is avoided, and the technical problem that the LED current continuously changes in a foldback interval and the LED lamp suddenly changes after the current foldback circuit is added in the LED driver in the prior art is solved. The invention can be widely applied to various power supply circuits, including DC-DC constant voltage power supply, LED constant current power supply and constant power supply, and can avoid instability caused by repeated change of output voltage or current when over temperature occurs.
Example two
Referring to fig. 1 to 6, an embodiment of the present invention provides an LED driver, including the LED protection circuit with overheat current reduction and constant current functions, where the driver includes a driving chip, the driving chip includes an IADJ2 pin, a VREF pin, an IADJ pin, a TEMPA pin, and a TEMPB pin, input ends of a reference voltage VREF and a variable voltage vidj 2 of the third operational amplifier OP3 are respectively connected to the IADJ2 pin and the VREF pin, and input ends of a voltage vidj and a constant current threshold voltage Vtempa of the first operational amplifier OP1 are respectively connected to the IADJ pin and the TEMPA pin.
The driving chip can adopt a PT16751 chip, and as a specific implementation mode, the IADJ2 pin is used for being connected to a voltage divider circuit comprising a thermistor and used for obtaining a temperature signal of the LED lamp panel. As a specific implementation mode, the TEMPA pin is used for setting a derating curve of the LED current when the LED lamp is overheated, and the TEMPB pin is used for setting an overheated shutdown temperature threshold.
PT16751 chips provide advanced over-temperature protection. The current derating curve and the off-point are customized by setting Radj5, rtempa and Rtempb. Typical application as shown in fig. 3, an NTC thermistor is typically placed on the LED board to detect the temperature of the LED board. The NTC thermistor value is reduced along with the temperature rise of the LED lamp panel, and the voltage of IADJ2 is also reduced. As shown in fig. 4, when vidj 2 drops to 2.17V, the LED current begins to decrease to reduce the LED board heating. However, if the temperature of the LED lamp panel continues to rise, the NTC thermistor value continues to decrease, and the corresponding via 2 also continues to decrease, thereby further reducing the LED current. When the LED current drops to X% (Radj 5 and Rtempa settings), the LED current remains unchanged. If the temperature of the LED lamp panel continues to rise, the NTC thermistor value continues to decrease, and Viadj2 continues to decrease. When the Viadj2 voltage drops to Y [ V ] (set by Rtempb), the GATE pin of PT16751 stops working and the LED current drops to zero.
As shown in fig. 5, the LED rated current is 300mA, the first overtemperature protection threshold OTP1 is set to 120 ℃, vidj 2 is 2.17v, and the LED current starts to decrease. The second over-temperature protection threshold OTP2 is set to 130 ℃ (Radj 5, rtempa set) and the LED current remains constant at 120mA (40% of nominal). The third over-temperature protection threshold OTP3 is set to 140 ℃ (Rtempb set), the Viadj2 corresponding voltage is Y [ V ] (FIG. 4), and the LED lamp is turned off. Fig. 6 shows the effect of IADJ2 over-temperature protection (0 TP) function on LED panel temperature and LED current. Without IADJ2 OTP functionality, the LED current remains unchanged (Line 2), but the LED panel temperature continues to rise (Line 1). With the increase of working time, if the heat dissipation of the LED lamp panel is poor, the LED lamp beads can burn out. After the IADJ2 OTP protection function is used, the temperature of the LED lamp panel is increased, the LED current is reduced, and the temperature of the LED lamp panel can be kept unchanged.
The foregoing description of the embodiments has been provided for the purpose of illustrating the general principles of the invention, and is not meant to limit the scope of the invention, but to limit the invention to the particular embodiments, and any modifications, equivalents, improvements, etc. that fall within the spirit and principles of the invention are intended to be included within the scope of the invention.
Claims (4)
1. The LED protection circuit with the overheat current reduction and constant current functions is characterized by comprising a first operational amplifier circuit OP1, a third operational amplifier circuit OP3 and a field effect transistor Q1, wherein the third operational amplifier circuit OP3 is provided with two voltage input ends which are respectively used for inputting a variable voltage Viadj2 and a reference voltage Vref, the first operational amplifier circuit OP1 is provided with two voltage input ends which are respectively used for inputting a normal working setting voltage Viadj and a constant current threshold voltage Vtemp. of an LED lamp, the third operational amplifier circuit OP3 is used for converting a voltage signal into a current signal, the current output end of the third operational amplifier circuit OP3 is connected with the current input end of the third operational amplifier circuit OP3 through a resistor R2 and a resistor R3 in sequence, the current output end of the third operational amplifier circuit OP3 is connected with the power end of the first operational amplifier circuit OP1 through the resistor R2 and the resistor R1 in sequence, the current output end of the third operational amplifier circuit OP3 is grounded, the power end of the first operational amplifier circuit OP1 is connected with the power supply end of the third operational amplifier circuit OP1, and the current output end of the third operational amplifier circuit OP3 is connected with the drain electrode of the third operational amplifier circuit OP 1;
the second operational amplifier OP2 is provided with two voltage input ends, the two voltage input ends are respectively used for inputting the variable voltage Viadj2 and the turn-off threshold voltage Vtemppb, the turn-off threshold voltage Vtemppb is smaller than the constant current threshold voltage Vtemppa, the grid electrode of the field effect transistor Q2 is connected with the output end of the second operational amplifier OP2, the drain electrode of the field effect transistor Q2 is connected with the current input end of the third operational amplifier OP3, and the source electrode of the field effect transistor Q2 is connected with the current output end of the third operational amplifier OP 3.
2. An LED driver, comprising the LED protection circuit with overheat current reduction and constant current functions of claim 1, the driver comprises a driving chip, the driving chip comprises an IADJ2 pin, a VREF pin, an IADJ pin, a TEMPA pin and a TEMPB pin, the variable voltage vidj 2 and the reference voltage VREF input end of the third operational amplifier circuit OP3 are respectively connected with the IADJ2 pin and the VREF pin, and the voltage vidj and the constant current threshold voltage Vtempa input end of the first operational amplifier circuit OP1 are respectively connected with the IADJ pin and the TEMPA pin.
3. The LED driver of claim 2, wherein the IADJ2 pin is for connection to a voltage divider circuit comprising a thermistor for obtaining a temperature signal of the LED lamp panel.
4. The LED driver of claim 2, wherein the TEMPA pin is used to set a derating curve for LED current when the LED lamp is overheated, and the TEMPB pin is used to set an overheated shutdown temperature threshold.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202110894170.9A CN113597058B (en) | 2021-08-04 | 2021-08-04 | LED protection circuit and driver with overheat current reduction and constant current functions |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202110894170.9A CN113597058B (en) | 2021-08-04 | 2021-08-04 | LED protection circuit and driver with overheat current reduction and constant current functions |
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| Publication Number | Publication Date |
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| CN113597058A CN113597058A (en) | 2021-11-02 |
| CN113597058B true CN113597058B (en) | 2024-04-05 |
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| Application Number | Title | Priority Date | Filing Date |
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| CN202110894170.9A Active CN113597058B (en) | 2021-08-04 | 2021-08-04 | LED protection circuit and driver with overheat current reduction and constant current functions |
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| CN117939745B (en) * | 2024-03-20 | 2024-06-25 | 珠海市圣昌电子有限公司 | High-precision load limiting control circuit and load limiting control method based on load derating curve |
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|---|---|---|---|---|
| CN102412611A (en) * | 2011-12-07 | 2012-04-11 | 西安启芯微电子有限公司 | Constant-current charging circuit applied to linear charger |
| CN102830746A (en) * | 2012-08-15 | 2012-12-19 | 杭州科岛微电子有限公司 | Segmented linear heat foldback current generation circuit |
| CN208796137U (en) * | 2018-07-17 | 2019-04-26 | 深圳市华芯邦科技有限公司 | A kind of circuit and its battery charger of Voltage Feedback control electric current output |
| CN110856314A (en) * | 2019-12-17 | 2020-02-28 | 南京微盟电子有限公司 | LED drive circuit with overheat protection |
| CN211297044U (en) * | 2019-11-29 | 2020-08-18 | 深圳市晟碟半导体有限公司 | Multi-segment linear LED driving circuit and device |
-
2021
- 2021-08-04 CN CN202110894170.9A patent/CN113597058B/en active Active
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102412611A (en) * | 2011-12-07 | 2012-04-11 | 西安启芯微电子有限公司 | Constant-current charging circuit applied to linear charger |
| CN102830746A (en) * | 2012-08-15 | 2012-12-19 | 杭州科岛微电子有限公司 | Segmented linear heat foldback current generation circuit |
| CN208796137U (en) * | 2018-07-17 | 2019-04-26 | 深圳市华芯邦科技有限公司 | A kind of circuit and its battery charger of Voltage Feedback control electric current output |
| CN211297044U (en) * | 2019-11-29 | 2020-08-18 | 深圳市晟碟半导体有限公司 | Multi-segment linear LED driving circuit and device |
| CN110856314A (en) * | 2019-12-17 | 2020-02-28 | 南京微盟电子有限公司 | LED drive circuit with overheat protection |
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