Secondary battery protection circuit

A secondary battery protection circuit configured to monitor a state of a secondary battery and to protect the secondary battery when detecting an abnormal state, the secondary battery protection circuit comprising:

• a reference voltage circuit configured to generate a reference voltage by using a depletion-type transistor and a transistor unit of enhancement type connected in series with the depletion-type transistor;
• a voltage divider configured to obtain a detection voltage by dividing a power source voltage of the secondary battery, and to output the detection voltage;
• a detection circuit configured to detect the abnormal state based on the reference voltage and the detection voltage;
• a first adjustment circuit configured to adjust a size ratio of the depletion-type transistor to the transistor unit based on a threshold voltage of the depletion-type transistor and a threshold voltage of the transistor unit;
• and
• a second adjustment circuit configured to adjust the detection voltage based on the reference voltage after the size ratio is adjusted by the first adjustment circuit, such that the detection circuit can detect the power source voltage of the secondary battery reaching a predetermined voltage.