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<p>The micro-variable equivalent circuit is when a part of the circuit is replaced by its equivalent circuit, the unreplaced part of the voltage and current do not change, that is to say, the part with constant voltage and current is only the circuit outside the equivalent part.</p><p><br></p><p>Characteristics of the <a href="https://www.pst888.com/power-<a href="https://www.pst888.com/power-diodes" target="_blank">diode</a>s" rel="noopener noreferrer" target="_blank"><strong>diode</strong></a> micro-variable equivalent circuit:</p><p><br></p><p>Slightly changed the equivalent circuit of the object only on the change. Therefore, the equivalent circuit of NPN tube and PNP tube is identical.</p><p><br></p><p>(2) the micro-variable equivalent circuit is obtained at the correct point Q, such as point Q set wrong, that is, when point Q is selected in the saturation or cut-off area, the equivalent circuit is meaningless.</p><p><br></p><p>(3) can not use the micro - variable equivalent circuit to find the static working point.</p><p><br></p><p>The voltage and current in the equivalent circuit are all expressed by the effective value of ac. The direction of voltage and current is defined by the network. Do not change it at will.</p><p><br></p><p>Diode micro - equivalent circuit</p><p><br></p><p>If there is only dc on the diode, then the volt-ampere characteristic for this dc is its common volt-ampere characteristic curve. If a small ac is superimposed on this dc, what is the relationship between voltage and current for this small ac signal? Or what circuit the diode is equivalent to for this ac signal, this is the microvariant equivalent circuit. Of course, for this ac signal, the diode is equivalent to a resistance, which is also related to the dc.</p><p><br></p><p>Ideal diode equivalent circuit</p><p><br></p><p>In the circuit, if the diode turn-on of the positive pressure drop is far less than the voltage of series and its components, diode as the reverse current is far less than the element in parallel with the current, so you can ignore the pipe of the diode forward voltage drop and reverse current ideal into a switch, when plus forward voltage, the diode conduction, positive pressure drop to zero, is equal to the switch is closed, when coupled with reverse voltage, deadlines, reverse current is zero, the diode is equal to the switch, the equivalent circuit of the ideal diode. Using ideal diode to represent the actual diode circuit analysis and calculation can be obtained more satisfactory results, but a little error.</p><p><br></p><p>The micro-varying equivalent circuit conditions are applied to diodes</p><p><br></p><p>The ideal model is applicable when the supply voltage is much higher than the diode voltage drop. The constant voltage drop model is used when the current flowing through the diode is greater than or equal to 1ma. The broken line model is used when the voltage at the diode terminal is between 0.5V and 0.7V. The small signal model is used when the signal at the diode end is small, that is, when the fluctuation range is small, the micro-variable diode equivalent circuit is applied.</p>
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