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What is the micro-variable equivalent circuit of a diode?
The micro-variable equivalent circuit is a circuit in which a portion of the circuit is replaced by an equivalent circuit, and the voltage and current that are not replaced are not changed, that is, the portion where the voltage and current are constant are only circuits other than the equivalent portion.
The characteristics of the micro-variable equivalent circuit:
1 The object of the micro-variable equivalent circuit is only for the amount of change. Therefore, the equivalent circuits of the NPN type tube and the PNP type tube are identical.
2 The micro-variable equivalent circuit is obtained at the correct Q point. If the Q point is set incorrectly, that is, when the Q point is selected in the saturation region or the cut-off region, the equivalent circuit is meaningless.
3 You cannot use a micro-variable equivalent circuit to find a static operating point.
4 The voltage and current in the micro-variable equivalent circuit are all expressed by the effective value of the AC quantity. The direction of the voltage and current is in the direction defined by the network, and should not be changed arbitrarily.
Dimorphic equivalent circuit of diode
If there is only DC on the diode, then the volt-ampere characteristic of this DC is its common volt-ampere characteristic. 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 is equivalent to this AC signal, which is its micro-equivalent Circuit. Of course, for this AC signal, the diode is equivalent to a resistor, and this resistor is also related to DC.
Ideal diode equivalent circuit
In the circuit, if the forward voltage drop when the diode is turned on is much smaller than the voltage of the component connected to it, the reverse current is much smaller than the current of the parallel component when the diode is turned off, then the forward voltage drop and reverse of the tube can be ignored. The current idealizes the diode as a switch. When the forward voltage is applied, the diode is turned on, and the forward voltage drop is 0, which is equivalent to the switch closing. When the reverse voltage is applied, the diode is turned off, and the reverse current is 0, which is equivalent to The switch is open and the equivalent circuit of the ideal diode is shown in Figure 4-4. Using an ideal diode to represent the actual diode for circuit analysis and calculation can yield satisfactory results, but with some errors.