Short circuit detection circuit

Abstract

The invention discloses a short circuit detection circuit. The short circuit detection circuit comprises a voltage source, a current conversion circuit, a protection circuit, a current limiting circuit and a sampling circuit; when the second end of a load is grounded, an external power supply supplies power to the load, and when the second end of the load is not grounded, the resistance of the load is calculated according to the second end voltage of the current conversion circuit, or by using the voltage of the voltage source, the voltage of the second end of the current conversion circuit and the internal component parameters of each circuit of the short-circuit detection circuit, and whether the load is short-circuited is judged. Through the method of detecting the voltage of the second end of the current conversion circuit or reversely calculating the resistance under the condition that the load is powered off, whether the load is short-circuited or not is detected before the load is started, output can be directly not started any more, and the defects that in the prior art,under the condition that the load is powered on, short-circuit protection failure are caused by power supply voltage and power supply current and heating of a detection resistor is serious are solved, and the risk of device damage caused by instant large current is avoided.

Description

technical field [0001] The invention relates to the technical field of detection, in particular to a short circuit detection circuit. Background technique [0002] LED power supplies on the market are currently divided into two categories: constant voltage power supplies and constant current power supplies. In the constant voltage circuit scheme, because the output voltage is constant, the output current will change according to the size of the load. Therefore, when the constant voltage power supply fails and causes a short circuit, the current of the constant voltage power supply will surge in a short time after the output is turned on. If the short-circuit fault cannot be detected quickly and protected in time. In the slightest, it will damage the power supply, and in severe cases, it will cause a fire accident. The current idea of ​​short-circuit detection is roughly divided into detecting the power supply voltage and detecting the power supply current. Among them, the ...

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Problems solved by technology

The current idea of ​​short-circuit detection is roughly divided into detecting the power supply voltage and detecting the power supply current. Among them, the circuit for detecting the power supply voltage is as follows: figure 1 As shown, when the output is short-circuited, since the load is 0, the output current will far exceed the output capability of the power supply VCC, which will cause the voltage of the power supply VCC to drop. Therefore, it is only necessary to detect that the voltage at the check point is lower than a certain threshold to determine the device. When a short circuit occurs, it is enough to protect the device. However, when the output power of VCC is large, or the short circuit has a certain resistance value, the VCC voltage drops very slowly, or even falls below the detection threshold, resulting in short circuit protection. fail

The circuit that detects the power supply current such as figure 2 As shown, when the output is short-circuited, the output current will increase instantaneously because the load is 0, and then flow through the resistor R L The current increases, causing the resistor R L The voltage at both ends increases, so it is only necessary to detect that the voltage at the check point is higher than a certain threshold to determine that the device is short-circuited and protect the device. However, when you want to process the signal at the check point, whether it is a single-chip ADC Or use an op amp to amplify the signal, you need a resistor R L The voltage at both ends can only be processed when the voltage reaches a certain level. When the power supply is large, the resistance R L The power is very high and the heat is serious, so it is not suitable for short-circuit protection scheme of high-power constant voltage power supply

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