Powering Circuits Using Series Capacitor
In numerous circuits, direct power can be sourced from the mains by employing a series capacitor (C1). However, this method has a drawback: typically, only one-half cycle of the mains waveform can be utilized to generate a DC voltage. To overcome this limitation, full-wave rectification can be achieved using a bridge rectifier. This approach enhances the available current supply and allows for a smaller filter capacitor. The featured circuit adopts this technique, albeit in a clever manner that utilizes fewer components. The strategy capitalizes on the dual nature of a Zener diode, which functions as both a Zener diode and a regular diode conducting current in the forward direction.
Full-Wave Rectification with Dual Diode Operation
During one half-wave of the cycle, the current path involves flowing through D1, the load, and back via D4. Conversely, during the other half-wave, the current passes through D3 and D2. It’s crucial to note that in this circuit (as well as in the bridge rectifier version), the zero voltage reference of the DC voltage isn’t directly linked to the neutral line of the 230-V circuit. Consequently, it’s generally impractical to utilize this supply for driving a triac, which typically requires such a connection. However, circuits incorporating relays can benefit from full-wave rectification.
Voltage and Current Determinants
The supply voltage’s magnitude relies on the specifications of the chosen Zener diodes, allowing for flexibility in selection. C2 must have the capacity to handle at least this voltage. The deliverable current is contingent upon the capacitance of C1. With a specified value of 220 nF, the current amounts to approximately 15 mA.
Safety Precautions for Mains Voltage
A crucial disclaimer: this circuit is directly linked to mains voltage, which can be life-threatening. Any direct contact with this circuit must be strictly avoided. It is imperative to securely encase this circuit within an appropriate enclosure, adhering to the safety guidelines outlined in publications like Elektor Electronics.