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Explain Three pin fixed voltage regulators.
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Solution:

The $78 \times x$ series consist of 3 terminals positive fixed voltage regulators.

Fig below shows $78 \times x$ series IC for standard application.

These Ias are designed as fixed voltage regulators and with adequate heat sinking can deliver op current in excess of $1 \mathrm{~A}$. The typical dropout voltage [Via- Vout] is $2 \mathrm{~V}$.

capacitor $C_i$ is required if the regulator is located at an appreciable distance from a pows supply filter.

Even though $\mathrm{co}$ is not needed. it may be used to improve the transient response of the regulator.

The voltage options with $78 \times \times$ series are. as follows:

$$\begin{array}{|c|c|c|} \hline \text { Device Type } & \text { o/p vtg }[\text { Vo }] & \text { Max ilp vig } \\\\ \hline 7805 & 5.0 & 35 \\\\ 7806 & 6.0 & 35 \\\\ 7808 & 8.0 & 35 \\\\ 7812 & 12.0 & 35 \\\\ 7815 & 15.0 & 35 \\\\ 7818 & 18.0 & 35 \\\\ 7824 & 24.0 & 40 \\\\ \hline \end{array}\\$$

$79 \times x$ series regulators are negative 3 terminal fixed voltage regulators.

The various options available with the $79 \times x$ series are as follows:

$$\begin{array}{|c|c|c|} \hline \text { Device Type } & \text { o/p vfg [Vo] } & \text { Max i/p vfg } \\ \hline 7902 & -2.0 & -35 \mathrm{~V} \\ 7905 & -5.0 & -35 \mathrm{~V} \\ 7905.2 & -5.2 & -35 \mathrm{~V} \\ 7906 & -6.0 & -35 \mathrm{~V} \\ 7908 & -8.0 & -35 \mathrm{~V} \\ 7912 & -12.0 & -35 \mathrm{~V} \\ 7915 & -15.0 & -3 \mathrm{VV} \\ 7918 & -18.0 & -3 \mathrm{JV} \\ 7924 & -24.0 & -40 \mathrm{~V} \\ \hline \end{array}$$