Pixel driving circuit for oled display device and oled display device

A pixel driving circuit for OLED display device, comprising:

• a first thin-film transistor, wherein a gate electrode of the first thin-film transistor T1 is electrically connected to a first node, and a source electrode of the first thin-film transistor is electrically connected to a second node;
• a second thin-film transistor, wherein a gate electrode of the second thin-film transistor receives a second scanning signal, and a drain electrode of the second thin-film transistor is electrically connected to the first node;
• a third thin-film transistor, wherein a gate electrode of the third thin-film transistor receives a third scanning signal, a drain electrode of the third thin-film transistor is connected to a drain electrode of the first thin-film transistor, and a source electrode of the third thin-film transistor is electrically connected to a direct-current power positive electrode;
• a fourth thin-film transistor, wherein a gate electrode of the fourth thin-film transistor receives the first scanning signal, and a drain electrode of the fourth thin-film transistor is electrically connected to the second node;
• a capacitor, wherein one terminal of the capacitor is electrically connected to the first node, and the other terminal of the capacitor is electrically connected to the second node;
• an organic light-emitting diode, an anode of the organic light-emitting diode is electrically connected to the second node, and a cathode of the organic light-emitting diode is electrically connected to a direct-current power negative electrode;
• when the organic light-emitting diode display device is turned off or turned on, the source electrode of the second thin-film transistor receives a first data signal, the source electrode of the fourth thin-film transistor receives an initialization signal or a threshold voltage detector, the threshold voltage detector is used for detecting a threshold voltage of the first thin-film transistor, and generating a threshold voltage signal;
• when the organic light-emitting diode display device operates normally, the source electrode of the second thin-film transistor receives a second data signal formed by the threshold voltage signal and an original data signal, and the source electrode of the fourth thin-film transistor receives the initialization signal;
• and
• wherein each of the initialization signal and the first data signal has a constant low voltage level, and the original data signal has a pulse high voltage level.