Power SuppliesZener Diode

Triple Power Supply Schematic Circuit Diagram

Generating Additional Higher Voltage from a Transformer:

In typical cases, budget-friendly miniature transformers provide one or two secondary voltages, which suffice for creating positive and negative supply voltages required for various circuits, like operational amplifier setups. However, what do you do when you need an extra voltage higher than either of these supply voltages, say, for a tuning voltage in a receiver? This circuit provides a straightforward solution to this issue, and its versatility can be adapted for diverse applications.

Creating 24-V and 12-V Supply Voltages:

Utilizing a 2×15-V transformer, this circuit generates positive 24-V and 12-V supply voltages along with a negative 12-V supply voltage. The key to generating the +24-V output lies in utilizing IC1 to establish a virtual ground. This is achieved through a familiar setup employing a voltage divider composed of two equal resistors. These resistors divide the voltage (Ub) across the rectifier, reducing it from approximately 40 V to 20 V. This Ub/2 potential is then buffered by an op-amp, allowing the virtual ground to drive a load.

In this circuit, the same principle is applied, but with a slight twist: the voltage across the rectifier (around 40 V) is divided unevenly by resistors R1 and R2. Consequently, the resulting potential, buffered by the op-amp and the subsequent transistor output stage, rests approximately 15 V above the lower potential, roughly 25 V below the upper potential. This ingenious setup ensures the generation of the necessary higher voltage.

Triple Power Supply Schematic Circuit Diagram

Stabilizing Multiple Voltages:

In the schematic, standard 100-mA voltage regulators are employed to stabilize the three generated voltages. Additionally, the supply voltages for the op-amp are intentionally made asymmetric. This imbalance is efficiently managed through the utilization of two Zener diodes, thanks to the op-amp’s low current consumption.

Managing Voltage Fluctuations:

It’s crucial to consider that an unloaded miniature transformer yields a secondary voltage considerably higher than its rated value. A test circuit utilizing a 1.6-VA transformer with two 15-V secondary windings demonstrated promising results. The positive and negative 12-V outputs could bear a load of approximately 10 mA each, and the 24-V output could accommodate a load of about 20 mA. Remarkably, these loads didn’t cause any voltage drop in any of the output voltages. For simpler circuits like a 0(4)–20-mA instrumentation loop, this performance is entirely satisfactory. However, for more intricate circuits or those involving switched loads, additional compensation might be necessary.

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