The voltages directly available are from a dual-rail +14V/0V/-14V supply at a maximum output current of about 200mA.
Simple dual rail voltage regulator using zener diode circuit diagram
When electrical current flow to the Zener diode in the reverse breakdown voltage. Making the voltage across it is the constant—voltage regulator—to a load.
In the circuit above, it is so easy.
When 220V/120VAC comes to transformer-T1 through the ON-OFF switch-S1 and Fuse-F1 is a overload protection of circuit. The T1 changes 220VAC to about 30VAC (15V+15V).
Then, the rectifier bridge, D1 through D4, rectifies the AC into pulsating DC.
Next, the capacitor-C1 will smooth that pulsating DC into a steady DC. Which it is the unregulated DC voltage of about 43 volts.
The resistor-R1 connects with C1 together in series. They are a so well low filter.
After that, the DC voltage flows through R2 and ZD1. The resistor-R2 limit current for Zener diodes ZD1 and the load.
Now the voltage(VZ) across ZD1 is the constant voltage of about 28 volts.
Perform maintain one’s position voltage. Be stable and use the principle of divide Voltage. But this voltage still single rail supply.
Next, the two 47 ohms resistors, R2 and R3, it is the easiest way to do this. Dual resistors form a voltage divider. They provide a reference voltage at the output of +14V/0V/-14V.
This circuit is not suitable for a high current load. The output current is less than 200mA.
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