Insulation detection circuit and method thereof

1. An insulation detection circuit, suitable for detecting an insulation status between a high voltage power and a low voltage power of a vehicle, the insulation detection circuit comprising:

a first energy storage unit, coupled to the high voltage power;

a second energy storage unit, coupled between the first energy storage unit and the low voltage power;

a constant current unit, coupled between the first energy storage unit and the second energy storage unit, and providing a constant current to charge/discharge the second energy storage unit; and

a detection unit, coupled to the second energy storage unit, for detecting a current change of the second energy storage unit;

wherein when the insulation between the high voltage power and the low voltage power is not damaged, only the second energy storage unit receives the constant current and the detection unit detects that a current flowing through the second energy storage unit is not smaller than a predetermined value; and

wherein when the detection unit detects that a current flowing through the second energy storage unit is smaller than the predetermined value, the detection unit outputs a detection signal which represents that the insulation between the high voltage power and the low voltage power is damaged, and the first energy storage unit and the second energy storage unit form a loop such that the current of the constant current unit is divided to the first energy storage unit.

2. The insulation detection circuit according to claim 1 , wherein the constant current unit includes a first amplifier, a second amplifier, and a plurality of resistors.

3. The insulation detection circuit according to claim 2 , wherein a non-inverting input terminal of the first amplifier is grounded or connected with the low voltage power, an inverting input terminal of the first amplifier is coupled to an input voltage, an output terminal of the first amplifier is coupled between an inverting input terminal of the second amplifier and the detection unit, a non-inverting input terminal of the second amplifier is coupled between the non-inverting input terminal of the first amplifier and an output terminal of the second amplifier, and the resistors are coupled to the first amplifier or the second amplifier.

4. The insulation detection circuit according to claim 1 , wherein the first energy storage unit is a first capacitor, and the second energy storage unit is a second capacitor.

5. The insulation detection circuit according to claim 4 , wherein when insulation between the high voltage power and the low voltage power is damaged, the constant current is divided to flow into the first capacitor to charge or discharge the second capacitor so that a highest voltage level and a lowest voltage level of the second capacitor change.

6. The insulation detection circuit according to claim 4 , wherein the first capacitor isolates an electrical interference of the high voltage power, so that the second capacitor receives the constant current under a condition of isolating the electrical interference of the high voltage power, and the detection unit detects the current of the second capacitor under the condition of isolating the electrical interference of the high voltage power.

7. The insulation detection circuit according to claim 1 , wherein a voltage level of the second energy storage unit changes according to the constant current, and the detection unit is used for detecting a voltage level change of the second energy storage unit.

8. The insulation detection circuit according to claim 7 , wherein when the detection unit detects that a highest voltage level, a lowest voltage level, the highest voltage level and the lowest voltage level, or a voltage amplitude is smaller than the predetermined value, the detection unit outputs the detection signal representing that the insulation status is abnormal.

9. The insulation detection circuit according to claim 1 , wherein the constant current unit provides the constant current in low frequency to the second energy storage unit.

10. The insulation detection circuit according to claim 1 , further comprising a constant current compensation unit, coupled between the second energy storage unit and the constant current unit, and the constant current compensation unit including a third amplifier, a fourth amplifier, and a plurality of resistors.

11. The insulation detection circuit according to claim 10 , wherein a non-inverting input terminal of the third amplifier is coupled to a first input voltage, an inverting input terminal of the third amplifier is coupled to a second input voltage, an output terminal of the third amplifier is coupled among an inverting input terminal of the fourth amplifier, the constant current unit, and the detection unit, a non-inverting input terminal of the fourth amplifier is coupled between the non-inverting input terminal of the third amplifier and an output terminal of the fourth amplifier, and the resistors are coupled to the third amplifier or the fourth amplifier.

12. The insulation detection circuit according to claim 1 , wherein the constant current unit is selected from the group consisting of a current mirror, a constant current diode, and a switching power supply.

13. An insulation detection method, suitable for detecting an insulation status between a high voltage power and a low voltage power of a vehicle, the insulation detection method comprising:

providing a first energy storage unit coupled to the high voltage power, and providing a second energy storage unit coupled between the first energy storage unit and the low voltage power;

providing a constant current for charging/discharging the second energy storage unit;

detecting a current change of the second energy storage unit; and

when the insulation between the high voltage power and the low voltage power is not damaged, only the second energy storage unit receives the constant current and the detection unit detects that a current flowing through the second energy storage unit is not smaller than a predetermined value; and

when detecting that a current flowing through the second energy storage unit is smaller than the predetermined value, outputting a detection signal representing that the insulation between the high voltage power and the low voltage power is damaged; and

forming a loop of the first energy storage unit and the second energy storage unit such that the current of the constant current unit is divided to the first energy storage unit.

14. The insulation detection method according to claim 13 , wherein in the step of detecting the current change of the second energy storage unit the method further includes:

detecting a voltage level change of the second energy storage unit, wherein the voltage level of the second energy storage unit changes according to the constant current.

15. The insulation detection method according to claim 13 , wherein when detecting that the current flowing through the second energy storage unit is smaller than a predetermined value, outputting a detection signal representing that the insulation status is abnormal, the step described above further including:

when detecting that a highest voltage level, a lowest voltage level, the highest voltage level and the lowest voltage level, or a voltage amplitude is smaller than the predetermined value, outputting the detection signal representing that the insulation status is abnormal.

16. An insulation detection circuit, suitable for detecting an insulation status between a high voltage power and a low voltage power of a vehicle, the insulation detection circuit comprising:

a first energy storage unit, coupled to the high voltage power;

an impedance unit, coupled between the first energy storage unit and the low voltage power;

a constant current unit, coupled between the first energy storage unit and the impedance unit, for providing a constant current to flow through the impedance unit; and

a detection unit, coupled to the impedance unit, for detecting a current change of the current flowing through the impedance unit;

wherein when the insulation between the high voltage power and the low voltage power is not damaged, only the second energy storage unit receives the constant current and the detection unit detects that a current flowing through the second energy storage unit is not smaller than a predetermined value; and

wherein when insulation between the high voltage power and the low voltage power is damaged, the constant current is divided to flow into the first capacitor, and the first capacitor and the impedance unit form a loop, so that the current flowing through the impedance unit is smaller than the predetermined value;

wherein when the detection unit detects that a current flowing through the impedance unit is smaller than a predetermined value, the detection unit outputs a detection signal representing that the insulation between the high voltage power and the low voltage power is damaged, and the first energy storage unit and the second energy storage unit form a loop such that the current of the constant current unit is divided to the first energy storage unit.

17. The insulation detection circuit according to claim 16 , wherein the first energy storage unit is a first capacitor, and the impedance unit is a resistor.