MOSFET shunt regulator substitutes for series regulator

You would normally use a series linear regulator or a DC-to-converter 3V DC from a obtain higher. However, when breadboarding a concept, your may is able to use a shunt regulator, especially if a series regulator of the C Orrect voltage is unavailable. The MOSFET in Figure 1 can replace a Zener diode in a shunt regulator and provide lower output impedance than a Zener diod E.

the MOSFETs are self-biased by connecting their drain to their source. The difference between the input voltage and the gate-to-source threshold voltage, v_{gs, sets th E Current. The IRF521 in this example have a threshold voltage of 2 to 4V at 250µa. The upper curve Of figure 2 shows The IRF521 achieves a gate-to-source voltage of 3V at a current of about 200µa. MOSFETs can vary from device to device, but the typical MOSFET have a threshold at approximately the mean between T He maximum and the minimum limits.}

the Lower curve in figure 2 is the output impedance, which you obtain from the upper curve By differentiating the upper curve. Although the output impedance, r_{out, is near 800ωat A current of 100µa, it rapidly drops to L ESS than 6ωat MA. Because operate the MOSFET at or near Threshold, its on-resistance spec doesn ' t apply, and the output impedance of thi s circuit is far higher than you would expect from the on-resistance. However, in general, the lower the on-resistance, the lower the output impedance at a specific current near Threshold.}

This circuit could require that R2 and C1 stop the oscillation in the MOSFET. Add a filter capacitor to the output to minimize the effect of load transients. Connecting a large filter capacitor from the gate to the source with short leads eliminates the need for R2. You can use the other MOSFETs families and other voltages if necessary.

Although you are unable to get the exact output voltage you need at the current you prefer, many devices tolerate wide Variations in operating voltage. For instance, many 3.3V-DC microcontrollers can operate as low as 2.5V DC and as high as 3.6V DC. Note that operating a mosfets near its threshold causes a large negative-temperature coefficient of the Gate-to-source volt Age. This circuit have significant change on output voltage over a wide temperature range; It is suitable for only limited temperature ranges.

MOSFET shunt regulator substitutes for series regulator