Light source lighting circuit and lamp system for vehicle

A lighting circuit for a light source, comprising:

• a countercurrent prevention unit comprising a first control terminal and a second control terminal, the countercurrent prevention unit configured to transmit a first current or a second current that is smaller than the first current to the light source;
• and
• a current controller comprising:
• a common terminal connected to the first control terminal and the second control terminal;
• and a switching terminal connected to the first control terminal, the current controller configured to provide a first driving current or a second driving current from the common terminal to the light source, wherein the first driving current corresponds to the first current, and the second driving current corresponds to the second current,
• wherein the countercurrent prevention unit further comprises:
• a first rectifier, wherein voltage at the first control terminal is provided to the switching terminal through the first rectifier;
• a first P-FET provided between the first control terminal and the common terminal;
• a second P-FET provided between the second control terminal and the common terminal;
• and
• a second rectifier provided between the second P-PET and the common terminal, wherein the second rectifier is series-connected to the second P-PET, and
• wherein when DC power voltage is provided to the first control terminal, the first P-FET is turned-on and the second P-FET is turned-off, and then the countercurrent prevention unit transmits the first current to the light source, and
• wherein when the DC power voltage is not provided to the first control terminal but provided to the second control terminal, the second P-FET is turned-on, and then the countercurrent prevention unit transmits the second current to the light source.