Zener (a.ka. avalanche or breakdown) diodes are p-n junction semiconductor products made to operate in the reverse dysfunction region of these VI characteristic curve. By maintaining their opposite recent within particular restricts, the voltage decline throughout the diode can stay constant. If preserved in that setting of function, the diode can behave as a voltage reference.
Study the spec sheet for a on average avalanche diode – Vz is the Zener voltage calculated at certain check recent Izt. The knee recent Izk, is the minimum current through the device to maintain a continuing Vz. Since the vibrant weight at the leg of the of the result curve is high, if recent through the device is below Izk, regulation is going to be poor. Izm is the most Zener current which can be passed without exceeding the most permissible energy dissipation. Break that and the device may become smoke before your eyes.
For function as a voltage reference, a Zener diode should be opposite biased. When the reverse voltage is smaller than Vz just the normal diode opposite saturation recent is allowed to flow. When forward partial it functions like a typical silicon diode – a big ahead recent passes, and the forward diode voltage is usually 0.7 V. Avalanche diodes are available with sustaining currents from several voltages a number of thousands volts and with energy dissipation scores up to 50 Watts.
The temperature tenderness of a Zener diode (temperature coefficient) is provided as a percentage modify in guide voltage per centigrade stage modify in diode temperature. That number is usually in the product range of +/- 0.1 per cent per deg C. The direction of the change relates to the system of description (avalanche multiplication versus Zener breakdown). Usually, if the research voltage is over 6V the coefficient is good, if below, negative.
Some producers have made temperature compensated research diodes by mixing a confident heat coefficient dysfunction diode with a ahead partial, negative heat coefficient, silicon diode within a offer (i.e. the generic 1N829, a 6.2V research diode with a temperature coefficient of +/- 0.0005 % per deg C around a variety of -55 to +100 deg C). As opposed to use a single greater diode it is often greater to position multiple description diodes in series when developing a top voltage reference. This mix allows higher voltage, higher energy dissipation, decrease heat coefficient, and lower dynamic resistance (the reciprocal mountain of the volt-amp curve in the functioning region). Of course, this is a more costly answer when compared to a single diode.
Diodes come in many designs and sizes. High-current diodes in many cases are mounted on a heat-sink unit to lessen their running temperature. It is probable to position diodes in similar to increase the current-carrying volume, nevertheless the VI characteristics of both diodes must certanly be directly matched to make sure that recent separates equally (although a tiny resistor can be put into collection with each diode to simply help equalize the currents). All diodes have some leakage recent (current that gets through when a diode is reverse-biased).
This leakage current-better called the reverse recent (IR)-is very small, an average of within the nano ampere range. Diodes also provide a optimum allowable reverse voltage, peak opposite voltage (PRV), or peak inverse voltage (PIV), over which a big recent may flow in the incorrect direction. If the PIV is surpassed, the diode could get zapped and may become forever damaged. The PIV for diodes ranges from a couple of volts to around several thousand volts. One approach for achieving an effectively larger PIV is to put diodes in series. Again, it is important that diodes are matched to make sure that the opposite voltage divides similarly (although a tiny resistor put in similar with each diode can be utilized to equalize the reverse voltages 2cl77).