Frequency Switching

Very low switching frequency, but a GTO is suitable for frequent switchings. 

Power MOSFF.Ts and IGBTs can handle much higher switching frequencies, compared o a thyristor. In an a.c. motor control, fast switching is mandatory and therefore transistors are preferred. 

It is generally seen that a human body can sustain a much higher current at a lightning or switching frequency (5 kHz or above) due to the extremely short duration of such surges (30 /is or less). 

As discussed above, a cttpacitor circuit is an L-C circuit, and the switching frequency can be expressed as... 

This will be the surge frequency of the switching circuit when the sixth capacitor is switched on a circuit that has five capacitor units already switched. The improved value of this switching frequency, /s, af si the introduction of inductance 42.93 uH in each capacitor circuit will become. 

There are two major types of power switches used today the bipolar power transistor (BJT) and the power MOSFET. The IGBT (integrated gate bipolar transistor) is used in the higher power industrial applications, such as 1 kW power supplies and electronic motor drives. The IBGT has a slower turn-off than does the MOSFET, so it is typically used for switching frequencies of less than 20 kHz. 

The power switch and rectifier ac-current loops contain very high trapezoidal current waveforms typical in PWM switching power supplies. These waveforms are rich in harmonics which extend far above the basic switching frequency. These ac currents can have peak amplitudes two to five times that of the... 

The gain eross-over frequency of the closed loop should not be any higher than 20 percent of the switching frequency (or 20 kHz). I have found that gain crossover frequencies of 10 kHz to 15 kHz are quite satisfactory for the majority of applications. This yields a transient response time around 200 uS. 

The current-mode controlled forward converter has one additional consideration there is a double pole at one-half the operating switching frequency. The compensation bandwidth normally does not go this high, but it may cause problems if the closed-loop gain is not sufficiently low enough to attenuate its effects. Its influence on the control-to-output characteristic can be seen in Figure B-14. 

For this example, the switching frequency is assumed to be 50 kHz. The corner frequency to produce -24 dB of attenuation at this point is... 

A Q-switched, frequency-quadrupled Nd—YAG laser (X, = 266 nm) and its accompanying optical components produce and focus the laser pulse onto the sample surface. The typical laser spot size in this instrument is approximately 2 pm. A He-Ne pilot laser, coaxial with the UV laser, enables the desired area to be located. A calibrated photodiode for the measurement of laser energy levels is also present... 

Dynamic domain imaging or Kerr microscopy of low coercivity thin films at MHz domain-switching frequencies allows one to examine domain wall motion in detail. ... 

Starting at the switching frequency, we need to invariably fix the harmonic amplitude at that point at -4dB. This follows from the basic governing equations (for more details, see the chapters on EMI in my A to Z book). Note that OdB corresponds to the full amplitude of the pedestal (1A in our example). 

The last resort for reducing the clamp losses is to reduce the switching frequency, since the clamp loss term is purely a switching loss term and is therefore proportional to the switching frequency. 

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