There`s not much to this circuit. The two RJ-11 jacks are set up to feed the telephone circuit through from the wall to the phone. The active signal for a single phone is on the red and green wires. Yellow and black are usually used for a second phone line. The 0.22uF capacitor blocks any DC current from flowing through the transformer. The 4.7K resistor limits the current of the 90V ringing signal. The transformer isolates the telephone side of the circuit from the tape recorder side. The zener diodes clamp the 90 volt ringing signal and other transient spikes to protect your recorder. The 10K potentiometer is used to adjust the level to the tape recorder.

Using a single 555 Timer IC and a small transformer to generate a high voltage, this circuit will test zener diodes of voltage ratings up to 50VDC. The 555 timer is used in the astable mode, the output at pin3 drives a small audio transformer such as the LT700. This has a primary impedance of 1K and a secondary impedance of 8 ohms. Used in reverse the unloaded ac voltage is around 120volts ac.

Here is a handy zener diode tester which tests zener diodes with breakdown voltages extending up to 120 volts. The main advantage of this circuit is that it works with a voltage as low as 6V DC and consumes less than 8 mA current. The circuit can be fitted in a 9V battery box. Two-third of the box may be used for four 1.5V batteries and the remaining one-third is sufficient for accommodating this circuit. In this circuit a commonly available transformer with 230V AC primary to 9-0-9V, 500mA secondary is used in reverse to achieve higher AC voltage across 230V AC terminals. Transistor T1 (BC547) is configured as an oscillator and driver to obtain required AC voltage across transformer`s 230V AC terminals.

TR1 provides a constant current to a bank of three zener diodes, thus maintaining a constant voltage independant of supply voltage variations. The resistor Rx is used to sense the PSU output current and to switches off the current to the zener diodes should the output current become excessive. The 1M0 (logarithmic taper) pot causes the current sensor (TR2) to "kick-in early", so providing a variable current threshold limit. The value of RX should be (0.7/Amperes) ohms, where Amperes is the maximum output of the bench PSU. The prototype was set to 1-ampere, so Rx should be 0.5 / 1.000 = 0.5 ohms. The resistor should be rated at 1-watt, or 2x 1R0 500mW resistors in parallel for 1-ampere maximum output. I have used 4x 1R0 ohms in parallel (0.25 ohms) and have achieved 2-amperes (with a bigger heatsink).

Here is a circuit that implements phase-control of heaters, adjusting their power smoothly from zero to around 95% of the rated power, keeping the room temperature to within 1 or 2 degrees, while using few components. Notice that this is entirely an AC design. The TRIAC, DIAC, capacitor, resistor, potentiometer and thermistor are all AC devices. I did not have a suitable MOV at hand, so I used two Zener diodes in back-to-back fashion. The poorest aspect is that I don't know of the existence of any AC transistors, so I had to pair two complementary ones, joining the collectors through diodes, thus creating my AC transistor from 4 parts!

This battery allows the indicator to the car battery voltage monitor. The indicator has four LEDs which indicate power. The more LEDs, the higher the voltage. The last LED is a flashing LED. It comes on when the accuspaning limit of about 15 V limit. This is a sign that something is wrong with the alternator or voltage regulator. The other LEDs light up in 9 V (D5: bad battery), 11 V (D7: battery doubtful) and 13 V (D9: battery ok). Build the circuit and verify the above activation points. If the measured values ??much different from the above, try other Zener diodes. Of 300 mW Zener are sufficient for the circuit.

This circuit derives its supply voltage, Vcc and Vdd from <£c. This factor, together with the neon lamps and zener diodes in the phase inputs, establishes 50% threshold that detects low voltage or absence of one or more phases.

This circuit will make the appropriate or above the value determined by zener diodes LED

This circuit provides a low cost and reliable method of testing zener diodes. RVl can be calibrated in volts, so that when LED 1 just lights, the voltage on pins 2 and 3 are nearly equal. Hence, the zener voltage can be read directly from the setting of RVl. The supply need only be as high a value as the zener itself

An external power supply that gives a voltage higher than the highest expected rating of the zener diodes to be tested is required. Potentiometer RVl is adjusted until the meter reading stabilizes

This simple circuit gives a positive and negative supply from a single transformer winding and one full-wave bridge. Two zener diodes in series provide the voltage division and their centerpoint is grounded

A limiter circuit that requires matched zener diodes can instead use one zener with a full-wave diode bridge. The

This circuit uses a pair of Zener diodes to monitor battery voltage of a 12-V battery. If below 11 V, 1)1 ceases to conduct, pin 3 of 102 goes high, setting FF IC2 turning on Ql, Kl, and the battery charger.

The IN914 (little glassy diode) and the zener diodes all have bands on the body which must be put in the direction shown on the drawing. The bands ar ` e at the K end of the diodes. A magnifying glass will help to locate the bands and also to check the values of the zeners. To identify them, the following procedure will help : with a magnifying

The power supply has been simplified. Power transformers and rectifiers have been omitted and some parts have been omitted from the MOSFET voltage regulator circuits: 1N5242 zener diodes between the source and gate and 10k resistors in series with the gate. These parts serve as protection in case of accidental short circuits, but don`t affect the

Rf = 100 k preset - The slider is set about a quarter of the way round. This is used to control the gain. The gain should be as small as possible consistent with the oscillator starting up reliably. The zener diodes limit the oscillator output by decreasing the amplifier gain if the output rises above their breakdown voltage. They also decrease th

Using a single 555 Timer IC and a small transformer to generate a high voltage, this circuit will test zener diodes of voltage ratings up to 50VDC. The 555 timer is used in the astable mode, the output at pin3 drives a small audio transformer such as the LT700. This has a primary impedance of 1K and a secondary impedance of 8 ohms. Used in reverse

Although this may be a basic question but I`m still struggling with it. In this schematic, two zener diodes D1 and D2 are connected back-to back across relay coil L1. The BVds = -30V for Q1. Can I use 15V(Vz = 15V) zeners for D1 and D2 instead of 5. 1 V zeners Will the relay coil or contacts can get damaged during turn-off of relay If required, I

This is a circuit to test zener diodes. It hooks up to a 120V AC line and boosts the output ..

Used Zener Diodes to derive the stabilized voltage for the Hartley oscillator (although I did find a couple of suitable voltage stabiliser valves (CV287) whilst sorting through a box of valves this morning). Whilst sniffing around in that box of valves mentioned above, I was adding to my catalogue of valves "in stock", in which I like to include links to a data sheet. Whilst doing that,