Test Your Zener Diodes: 555 Timer Circuit for 1-2mA Loads

Circuit diagram:

Notes:

This schematic employs a solitary 555 Timer IC and a diminutive transformer to produce a considerable voltage, enabling the evaluation of zener diodes up to 50VDC. The 555 timer operates within the astable configuration, with its output at pin3 driving a small audio transformer, specifically the LT700. This transformer possesses a primary impedance of 1K and a secondary impedance of 8 ohms. When unloaded, the generated AC voltage approximates 120volts AC. This alternating current is subsequently rectified by the 1N4004 diode and smoothed using a 2.2u capacitor. It is crucial that this capacitor is rated for 150 VDC. The zener diode being assessed is measured with a multimeter set to DC volts as indicated. The load current switch facilitates testing of the zener diode at 1 or 2mA DC. The rectified DC current is supplied by a good zener diode, which should maintain a steady reading on the voltmeter.

More about components

The 555 Timer IC (integrated circuit) is a versatile and widely utilized timer circuit. It’s a monolithic integrated circuit that functions as an astable multivibrator, creating a continuous oscillating waveform. This IC contains a precise timing circuit, typically powered by a 5V DC source. It's commonly found in applications requiring pulse generation, timing functions, and oscillating circuits. The 555 Timer is known for its ease of use and relatively simple circuit requirements. It's a fundamental building block in numerous electronic designs.

The LT700 transformer is a small audio transformer frequently used in electronic circuits. It’s designed to efficiently transfer electrical power from one circuit to another. This particular transformer has a primary impedance of 1K ohm, meaning it presents a resistance of 1000 ohms to the input signal, and a secondary impedance of 8 ohms. It's typically used to step up or down the voltage while maintaining the desired impedance. The transformer's core is made of a magnetic material to enhance its efficiency. It’s a standard component in audio amplifiers, signal processing circuits, and various power supply designs.

The 1N4004 diode is a rectifier diode commonly employed to convert alternating current (AC) to direct current (DC). It's a small, cylindrical device designed to allow current flow in only one direction. This diode is crucial for rectifying the AC voltage produced by the transformer, enabling the construction of DC power supplies. It’s a standard component in numerous electronic devices and circuits. The 1N4004 diode is frequently used in low-power applications such as battery chargers and power adapters.

The 2.2u capacitor is an electrolytic capacitor, often utilized for filtering and smoothing electrical signals. Its capacitance value, 2.2 microfarads (2.2uF), indicates its ability to store a charge. It’s applied to reduce ripple in DC power supplies, effectively smoothing out voltage fluctuations. It is essential to ensure the capacitor is rated to withstand the peak voltage of 150 VDC to prevent damage or failure. The capacitor is a critical component in many electronic circuits and is especially important in power supply designs.

Warning:

This circuit involves high voltages. Exercise extreme caution when working with this circuit and always ensure adequate safety measures are in place. Incorrect operation may result in serious injury or equipment damage.