Zener Diode Regulation

The Un-Regulated Power Supply, in the previous section, is fine to use as a start for a new project. But you may be working with a device that already has an internal power supply. You might want to get a little better regulation or need a slightly different voltage for a modification. Probably, the Basic Zener Regulator is the simplest approach. The Basic Zener Regulator only requires one resistor and one Zener diode but will maintain an output voltage within a tolerance of 5%. At 9 Volts that's better than +/- 0.5 volts. And this is as the input voltage, or output load current, changes.

Vishay Semiconductors - 1N4728A to 1N4764A Part Number Zener Voltage Range Test Current Reverse Leakage Current Dynamic Resistance f = 1 KHz Surge Current Regulator Current VZ at IZT1 IZT1 IZT2 IR at VR ZZT at IZT1 ZZK at IZT2 IR IZM V mA mA uA V Ω mA mA NOM. MAX. TYP. MAX. MAX.

1N4728A 3.3 76 1 100 1 10 400 1380 276 1N4729A 3.6 69 1 100 1 10 400 1260 252 1N4730A 3.9 64 1 50 1 9 400 1190 234 1N4731A 4.3 58 1 10 1 9 400 1070 217 1N4732A 4.7 53 1 10 1 8 500 970 193 1N4733A 5.1 49 1 10 1 7 550 890 178 1N4734A 5.6 45 1 10 2 5 600 810 162 1N4735A 6.2 41 1 10 3 2 700 730 146 1N4736A 6.8 37 1 10 4 3.5 700 660 133 1N4737A 7.5 34 0.5 10 5 4 700 605 121 1N4738A 8.2 31 0.5 10 6 4.5 700 550 110 1N4739A 9.1 28 0.5 10 7 5 700 500 100 1N4740A 10.0 25 0.25 10 7.6 7 700 454 91 1N4741A 11.0 23 0.25 5 8.4 8 700 414 83 1N4742A 12.0 21 0.25 5 9.1 9 700 380 76 1N4743A 13.0 19 0.25 5 9.9 10 700 344 69 1N4744A 15.0 17 0.25 5 11.4 14 700 304 61 1N4745A" 16.0 15.5 0.25 5 12.2 16 700 285 57 1N4746A 18.0 14 0.25 5 13.7 20 750 250 50 1N4747A 20.0 12.5 0.25 5 15.2 22 750 225 45 1N4748A 22.0 11.5 0.25 5 16.7 23 750 205 41 1N4749A 24.0 10.5 0.25 5 18.2 25 750 190 38 1N4750A 27.0 9.5 0.25 5 20.6 35 750 170 34 1N4751A 30.0 8.5 0.25 5 22.8 40 1000 150 30 1N4752A 33.0 7.5 0.25 5 25.1 45 1000 135 27 1N4753A 36.0 7 0.25 5 27.4 50 1000 125 25 1N4754A 39.0 6.5 0.25 5 29.7 60 1000 115 23 1N4755A 43.0 6 0.25 5 32.7 70 1500 110 22 1N4756A 47.0 5.5 0.25 5 35.8 80 1500 95 19 1N4757A 51.0 5 0.25 5 38.8 95 1500 90 18 1N4758A 56.0 4.5 0.25 5 42.6 110 2000 80 16 1N4759A 62.0 4 0.25 5 47.1 125 2000 70 14 1N4760A 68.0 3.7 0.25 5 51.7 150 2000 65 13 1N4761A 75.0 3.3 0.25 5 56 175 2000 60 12 1N4762A 82.0 3 0.25 5 62.2 200 3000 55 11 1N4763A 91.0 2.8 0.25 5 69.2 250 3000 50 10 1N4764A 100.0 2.5 0.25 5 76 350 3000 45 9

The chart on the right gives you an idea of the Zener voltages that are available. Zener diodes in the chart range from 3.3 volts to 100 volts. And in current capabilities from 9 to 275 ma. The lower voltage zener diodes can handle the higher currents. All are considered to be 1 Watt devices.

A Zener Diode Regulator only requires a series resistor, to limit diode current, and a Zener diode to stabilize the voltage. The Zener, ZD1, will then maintain the output voltage within a tolerance of about from about 0.1 to 0.9 Volts. This is even as the input voltage, or output load current, changes. It's extremely useful regulator for cases where you need to add say a small low current circuit to a larger system that is powered by a larger voltage.

The calculator below shows the schematic of a Zener Diode Regulator (RS and ZD1) connected to a Source on the left and a Load (Z_Load) on the right. The Source is the voltage source that you are using to drive the zener regulator. This can be a regulated source, internal/external to your project, that is stable with load. Or, the Source can be a Un-Regulated Power Supply, that varies with load. In the case of a Un-Regulated Power Supply, you need to check the V Min voltage specified on the source. If the Source voltage drops below that value, V Min, the Zener diode may drop out of regulation.

Initially, the Output Voltage is used to select a zener diode, from the list of Vishay diodes. The selected zener will be less than, or equal to, the specified Output Voltage. This zener voltage is then used to calculate the minimum source voltage, V Min (V Min = Zener Voltage * 1.4).

Then various circuit parameters are calculated. If the Load is specified in "Ohms", the load current is calculated. If the Load is specified in "ma", the load resistance is calculated.

The Load Power is then use to calculate the required Zener Power and Zener Current. These two values need to be checked against the actual Zener power and Zener current (I_ZM) listed in the specifications, (Z_P = V_Z×I_ZM).

The Series Resistor (RS) is then calculated using V Max, Safe Zener Voltage (Z_V), and Safe Zener Power (Z_P).