China
Africa
Explore chapters and articles related to this topic
Harmonics Generation
Published in J.C. Das, Harmonic Generation Effects Propagation and Control, 2018
An SCR can be turned on by applying a short pulse to its gate and turned off due to natural or line commutation. The term thyristor pertains to the family of semiconducting devices for power control. The angle by which the conduction is delayed after the input voltage starts to go positive until the thyristor is fired is called the delay angle. Figure 1.14b shows waveforms with a large dc reactor, and Figure 1.14c shows waveform with no dc reactor but identical firing angle. Thyristors 1–4 are fired in pairs as shown in Figure 1.14b. Even when the polarity of the voltage is reversed, the current keeps flowing in thyristors 1 and 2 until thyristors 3 and 4 are fired, see Figure 1.14a. Firing of thyristors 3 and 4 reverse biases thyristors 1 and 2 and turns them off. (This is referred to as class F-type forced commutation or line commutation.) The average dc voltage is
Harmonics Generation
Published in J.C. Das, Power System Analysis, 2017
A silicon-controlled rectifier (SCR) can be turned on by applying a short pulse to its gate and turned off due to natural or line commutation. The term thyristor pertains to the family of semiconducting devices for power control. The angle by which the conduction is delayed after the input voltage starts to go positive until the thyristor is fired is called the delay angle. Figure 17.12b shows waveforms with a large dc reactor, and Figure 17.12c shows waveform with no dc reactor but identical firing angle. Thyristors 1 and 2 and 3 and 4 are fired in pairs as shown in Figure 17.12b. Even when the polarity of the voltage is reversed, the current keeps flowing in thyristors 1 and 2 until thyristors 3 and 4 are fired, Figure 17.12a. The firing of thyristors 3 and 4 reverse biases thyristors 1 and 2 and turns them off (this is referred to as class F type forced commutation or line commutation). The average dc voltage is
Semiconductors
Published in Mike Tooley, Electronic Circuits, 2019
Thyristors (or silicon controlled rectifiers) are three-terminal devices which can be used for switching and a.c. power control. Thyristors can switch very rapidly from a conducting to a non-conducting state. In the off state, the thyristor exhibits negligible leakage current, while in the on state the device exhibits very low resistance. This results in very little power loss within the thyristor even when appreciable power levels are being controlled. Once switched into the conducting state, the thyristor will remain conducting (i.e. it is latched in the on state) until the forward current is removed from the device. In d.c. applications this necessitates the interruption (or disconnection) of the supply before the device can be reset into its non-conducting state. Where the device is used with an alternating supply, the device will automatically become reset whenever the main supply reverses. The device can then be triggered on the next half-cycle having correct polarity to permit conduction. Like their conventional silicon diode counterparts, thyristors have anode and cathode connections; control is applied by means of a gate terminal (see Fig. 5.13). The device is triggered into the conducting (on state) by means of the application of a current pulse to this terminal. The effective triggering of a thyristor requires a gate trigger pulse having a fast rise time derived from a low-resistance source. Triggering can become erratic when insufficient gate current is available or when the gate current changes slowly. Table 5.4 summarizes the characteristics of several common thyristors.
A 92.95%-efficiency high-voltage dual-mode buck converter using 0.5-µm HV CMOS process
Published in International Journal of Electronics, 2023
Chua-Chin Wang, Lean Karlo S. Tolentino, Pin-Chuan Chen, Ralph Gerard B. Sangalang, Oliver Lexter July A. Jose
The performance of the DC–DC converter mainly depends on the conversion efficiency. To improve the conversion efficiency, the power control part becomes critical. There are two commonly used power control methods: pulse width modulation (PWM) and pulse frequency modulation (PFM) (Park et al., 2015). However, each of these two modulation methods has its advantages and disadvantages (Park et al., 2015; Wang et al., 2021). PFM converters work best at light loads, while PWM converters perform excellent at medium to heavy loads.