10-14W Class A Amplifier -  I have built this amplifier and it does sound good. It requires a preamp as it hasn't got much gain. It requires big heat sinks and a large transformer and a great power supply and careful wiring, but in the end it is extremely simple and it sounds very good. The zener diode rejects any ripple coming from the power supply, But you still only want a ripple of 10mV max. The ripple reaching the input is amplified, so the zener gets rid of that, but whatever ripple there is will still reach the power stage. . . . 

12 volt battery monitor -  R1 controls the trip-point of the circuit. when the voltage falls below the trip-point, the led lights. adjust it to the desired level. to use this circuit to monitor a 6v battery, substitute D1 for a 3. 3 volt zener diode and adjust R1 accordingly. . . .  [Andy Wilson's site]

2 Watt Switching Power Supply -  In this small switching power supply, a Schmitt trigger oscillator is used to drive a switching transistor that supplies current to a small inductor. Energy is stored in the inductor while the transistor is on, and released into the load circuit when the transistor switches off. The output voltage is dependent on the load resistance and is limited by a zener diode that stops the oscillator when the voltage reaches about 14 volts. Higher or lower voltages can be obtained by adjusting the voltage divider that feeds the zener diode. The efficiency is about 80% using a high Q inductor. . .  [Bill Bowden's website]

2-wire Game Show Time -  Several Game Show timers included, scroll to find this one. The game show timer determines which contestant presses their button first by lighting a lamp and ringing a bell and the slower  contestants are locked out. The circuit is convenient in that only two wires are needed to interconnect the stations and the wires may all go back to the base unit or they may be "daisy-chained" between stations. There is no electronic limit on the number of stations. The circuit uses a 24 volt power source and 12 volt lamps when built as shown but the experienced experimenter may scale these voltages along with the zener voltages if desired. If the SCR triggers when the power is applied or when the reset button is pressed, add a 0. 1uF capacitor from anode to cathode. (A sudden increase in voltage across some SCRs can trigger them, especially if the gate impedance is high. ) . . .  [Charles Wenzel (unless otherwise noted)]

30W Class AB amplifier -  This is an instrument amplifier for monitoring music when on stage. It provides 21W output power of this little design. Previously I had a decent 10W amplifier (RED Free Circuits) , but we blew that one somehow. Now I will put this into the old box. I haven't built it yet, but the simulations say it works as I designed. In this design, wiring is important due to no differential amplifier. I might need to add ripple rejection with a zener as in the above design. . . .  [designer identified as Marc]

4 Ch Digital Logic Analyzer and 5 Ch Digital Oscilloscope in Parallel Port -  This is one of the simplest circuit for a PC parallel port based DLA. The Circuit is mainly used to protect the port which is fabricated on the motherboard itself. The IC 74LS04 is an inverter and acts as a buffer. The Zener is used for undervoltage and overvoltage protection. If a voltage > 5V appears on the input, The buffer will not transmit this voltage to the PC. . . .  [by Huzaifa S. Sidhpurwala, India]

4-Channel Digital Logic Analyzer  and 5 Channel Digital Oscilloscope by using PC Parallel Port -   This is one of the simplest circuit for a PC parallel port based DLA. The Circuit is mainly used to protect the port which is fabricated on the motherboard itself. . . .  [by Huzaifa S. Sidhpurwala, India]

60V, Synchronous Step-Down High Current LED Driver -  03/01/14 EDN Design Note   This circuit provides much better performance and higher power handling than a Zener diode The meaning of the term “high power LED” is rapidly evolving. Although a 350mA LED could easily earn the stamp of “high power” a few years ago, it could not hold a candle to the 20A LEDs or the 40A laser diodes of today. High power LEDs are now used in DLP projectors, surgical equipment, stage lighting, automotive lighting, and other applications traditionally served by high intensity bulbs. . .  [by Hua (Walker) Bai, also see Linear Technology Design Note 508]

7 by 10 LED Moving Sign -  This sign I designed uses no microprocessor. It has an eprom and multiple counters. As in most electric signs, the LEDs are matrixed, and strobed very quickly. . . .  [Bob Blick's design]

Amplified Zener -  A 13 volt Zener diode will work well for charging a 12 volt battery on Standby use. Or use a 14 volt zener a diode for a Standard 14. 6 volt charge. . . .  [G.L. Chemelec]

Build a DS1621 PC Thermometer -  Since I have no time to build a million pcTHERMs, I give you the plans and the software to build one on your own. This project is easy enough for beginners, the only difficulties possibly arising from serial port hardware incompatibility from PC to PC. In the single-sensor version, you need only the sensor IC, a voltage regulator and and handful of diodes and resistors. Build it, and learn the secrets of IIC bus, how to implement IIC bus using only two resistors and a couple of zeners, how to drive it on a serial port using Visual Basic. . .  [Alberto Ricci Bitti]

Design Notes: 60V, Synchronous Step-Down High Current LED Driver -  03/01/14 EDN Design Note   This circuit provides much better performance and higher power handling than a Zener diode The meaning of the term “high power LED” is rapidly evolving. Although a 350mA LED could easily earn the stamp of “high power” a few years ago, it could not hold a candle to the 20A LEDs or the 40A laser diodes of today. High power LEDs are now used in DLP projectors, surgical equipment, stage lighting, automotive lighting, and other applications traditionally served by high intensity bulbs. . .  [by Hua (Walker) Bai, also see Linear Technology Design Note 508]

Four-Ch Digital Logic Analyzer and 5 Ch Digital Oscilloscope in Parallel Port -  This is one of the simplest circuit for a PC parallel port based DLA. The Circuit is mainly used to protect the port which is fabricated on the motherboard itself. The IC 74LS04 is an inverter and acts as a buffer. The Zener is used for undervoltage and overvoltage protection. If a voltage > 5V appears on the input, The buffer will not transmit this voltage to the PC. . . .  [by Huzaifa S. Sidhpurwala, India]

Handy Zener Diode Tester -  This circuit can test zener diodes with a breakdown voltage up to 120 volts. It takes only 6 volts as power supply and consumes less than 8 mA current. . . .  [© EFY Enterprises Pvt. Ltd. All rights reserved.]

High Voltage Generator for Geiger Tubes -  The following two circuits are an improvement over the older circuits below. The are shown generating 500 volts but they may be modified to supply a couple of hundred to nearly 1000 volts by changing the zener diodes. The difference is subtle; the feedback signal increases the voltage on the base of the 2N4403 to stop the oscillator instead of stealing current from the capacitor on the emitter. The result is much lower power dissipation when there is little or no load on the high voltage. . .  [Charles Wenzel, designer]

Homemade Serial to Nokia MBus Interface on a PCB, without using Zener diodes -  . . . 

Interfacing 5 Volt CMOS to 12 Volt loads -  The circuit above is designed to be used with the bi-directional lamp sequencer shown above on this same page. Two additional transistors are used to increase the current from the 74HCT138 decoder to control 12 volt 25 watt lamps. A 6. 8 volt/1 watt zener diode is used in series with the ground connection of all the CMOS ICs (74HC14, CD4516 and 74HC138s) so that the total voltage across the CMOS devices will be about 5. 2 volts and the outputs will move from +12 to about +7 when selected. The 2N2905/PNP transistor stage is connected as an emitter follower which provides a high impedance to the. . .  [Bill Bowden's circuit]

LED Indicates Power Source -  08/26/10 EDN Design Idea   A zener diode lets detects the presence or absence of a power source. . . .  [by Brian Conley, PE, Circuitsville Engineering LLC]

Measure Zener Voltages and Test LEDs -  06/10/10  EDN Design Idea   You can use this circuit to measure zener voltages as high as 40V. To measure a zener diode's breakdown voltage, you need a dc voltage source whose voltage exceeds that of the zener voltage. In Figure 1, resistor RSER provides voltage drop between VIN and VZEN. In any case, VIN should exceed VZEN. Resistor RSER must provide current, IZEN, that can keep the zener diode in reverse breakdown. That is, the current must be more than IZEN-IZENMIN and less than IZEN-IZENMAX. You also need to consider the current that flows through the load. Otherwise, VZEN will be unregulated and less than the nominal breakdown voltage. Also, the power that the zener diode dissipates should not exceed the manufacturer's specifications. Except for the value of IZEN-IZENMIN, all necessary data appears in zener-diode data sheets. . . .  [by Vladimir Oleynik, Moscow, Russia]