| 摘要 |
PURPOSE:To reduce power loss of a bias resistance and also prevent burning loss of a chalk transformer without forming a protecting circuit by inserting a Zener diode into the gate reverse bias circuit of a thyrister SCR in the reverse bias direction. CONSTITUTION:During the negative period (c point to e point) of a commercial power source AC, a power source voltage is raised to above an (c) point in the negative direction, and then a current is started to flow through a bias circuit and an operating voltage -VB (g point) is the reverse direction voltage -VG of SCR + the operating voltage VZD of a Zener diode ZD, and a bias resistance R4 is decided so that the reverse bias current of the SCR is caused to flow between g point and h point after the g point. Under these conditions, the preheat current of the SRC becomes less than a holding current, and a high voltage is generated at d point by the action of a bias current. The temperature rise of a chalk transformer is thereby restrained and also power loss of a bias resistance R4 in the reverse bias circuit is reduced. |
