A linear constant current circuit with overvoltage protection

Abstract

The invention provides a linear constant current circuit with overvoltage protection. The linear constant current circuit with overvoltage protection comprises a linear constant current circuit which further comprises a voltage stabilizing element, a first switching element and an impedance element, wherein the linear constant current circuit is connected to a load to realize a constant current output of the load; and a protection circuit for reducing an operating current flowing through the load when an input voltage exceeds a specified voltage range. The protection circuit is connected to both ends of the voltage stabilizing element and includes a sampling circuit and a second switching element. The sampling circuit is used for detecting a voltage value of the input voltage. The second switching element is connected to the sampling circuit, and when the sampling circuit detects that the input voltage exceeds the specified voltage range, the second switching element begins to work so as to reduce the working current passing through the load. The linear constant current circuit with overvoltage protection of the invention can effectively ensure that the current flowing through the load is constant so as to improve the stability and reliability of the linear constant current circuit with the overvoltage protection.

Description

technical field [0001] The invention relates to the field of circuit protection, in particular to a linear constant current circuit for overvoltage protection. Background technique [0002] The triode constant current circuit is a commonly used LED constant current drive circuit, which is widely used in the drive circuit because of its simple structure and low cost. However, the existing triode constant current circuit generally has a big disadvantage. With the increase of the input voltage, the excess voltage is loaded on the triode or the parallel resistance, which is easy to cause a large loss of the triode or the parallel resistance. , and these losses are usually reflected in the form of heat, which affects the reliability and stability of the entire product, and even causes a fire, resulting in irreparable and serious consequences. [0003] figure 1 It is a triode constant current circuit commonly used in the prior art. This circuit mainly clamps the base voltage of ...

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Problems solved by technology

[0004] in the figure 1 Among them, the voltage Vce between the emitter and the collector of the power transistor Q1=Vin-Vout-VR3, and according to the characteristics of the LED, when the LED is in normal operation, Vout basically remains unchanged, and since the Ic is constant, VR3 remains unchanged. Therefore, when the input voltage Vin changes, Vce will change accordingly. When Vin continues to rise, Vce will also rise. Since the power dissipation of the power transistor Q1 is PQ1=Ic*Vce, when Vce rises, the power transistor Q1 A constant collector current Ic will cause the power PQ1 of the power transistor to continue to rise, and this loss is often reflected in the form of heat, which further leads to a substantial increase in the temperature of the power transistor Q1, which in turn affects the reliable operation of the entire circuit. start a fire

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