Average diode current

Average Diode Current Inductor Current Equals Load Current here... 

Average Switch Current is lL x D Average Diode Current is lL x (1-D)... 

Average Input Current equals Average Switch Current Average Output Current Is equal to average Diode Current... 

Since the average current from the output capacitor is zero, therefore, for the buck-boost, the average diode current must be equal to the load current (where else can the current come from ). Therefore... 

The intuitive reason why the above relations are different is that in a buck, the output is in series with the inductor (from the standpoint of the dc currents — the output capacitor contributing nothing to the dc current distribution), and therefore the average inductor current must at all times be equal to the load current. Whereas, in a boost and buck-boost, the output is likewise in series with the diode, and so the average diode current is equal to the load current. 

For the buck, as the input voltage is raised, the duty cycle falls, and because the average inductor current II remains fixed at lo, the average diode current increases. That means we get the worst-case diode current (and dissipation) at Vinmax for a buck. So we can just use the numbers we already have derived from carrying out the general inductor design procedure (at Vinmax)-... 

The rule-of-thumb is to pick a diode with a current rating at least equal to, but preferably at least twice the worst-case average diode current given below (for low losses, since the diode forward drop decreases substantially if its current rating is increased) ... 

Looking at the equivalent buck-boost models in Figure 3-2, the center of the ramp on the secondary side (average inductor current, II ) must be equal to Io/(l — D), as for a buck-boost (because the average diode current must equal the load current). This secondary-side inductor current gets reflected to the primary side, and so the center of the primary-side inductor current ramp is Ilr, where Ilr = Ii/n. Equivalently, it is... 

However, in a boost or buck-boost, energy flows into the output only during the off-time. And it can only be coming via the diode. So the average diode current must be equal to the load current. By simple arithmetic, since the average diode current calculated over the full cycle is equal to II x (1 — D), equating this to the load current Io gives us II = IoAT — D) for both the boost and the buck-boost. 

Answer This is simply the converse of the previous question. For the buck, the average output current equals the average inductor current. For the boost and buck-boost, it is equal to the average diode current. 

Peak Current Switch/Diode/ Inductor (A) Average Current in Switch (A) Average Current in Diode (A) Average Input Current (A)... 

A remark appears indicated about the measurement of the power of a picosecond diode laser. The sensor in power meters for the 10 pW to 10 mW range is usually a silicon photodiode. The photodiode is connected to a transimpedance amplifier that holds the diode voltage at zero and delivers an output voltage proportional to the diode current. Of course, the amplifier is far too slow to reaet to the fast diode laser pulses. Consequently, the pulses bias the diode in a forward direction. The result is a logarithmic dependence of the voltage on the input power. At a 50 MHz repetition rate, the linearity error usually becomes notieeable above 1 mW average power and can easily reach 100% at 5 mW. The problem ean be avoided by operating the photodiode with a reverse bias. It is normally not known whether a particular power meter uses a biased or an unbiased photodiode. 

Table 3.2 Peak and Average Current and Average Power and Power Density of p-/-n and jBS Diodes as a Function of the Number of Paralleled Die ...

The C.P.D. is obtained directly by the magnetron and the capacitor (or Kelvin) methods. Other methods which have proved successful rely on the variation of anode potential in a diode with constant cathode conditions. In this case, since adsorption changes the effective anode potential, the applied potential necessary to restore the anode current to its original value is equal to the C.P.D. between the two surfaces. As considered in Sec. II, a true average work function is measured in the C.P.D. method when the two conductors are separated by a distance which is much greater than the size of the patches on the surface. These conditions are invariably fulfilled in the capacitor and the space-charge-limited diode methods. 

These results show that all three of the SPICE simulators were not equipped to handle simulations of this particular zener diode in its soft region. However, zener diodes are not well defined or tested in this region of operation, so it may just be that the circuit tested had a worse than average zener diode in it. To further explore this problem, the experiment was modified to put more current than the specified test current in the zener diode. The circuit with these modifications made is shown in Fig. 6.64. The measurements across the zener diode are shown in Table 6.6, and the the resistance-to-voltage response is contained in Fig. 6.65. 

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