If this circuit can be called a 12v,5A zener regulator, then I know that 12v here is the varying input voltage. What is the 5A current here,I mean where can it be represented in the picture?

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  • \$\begingroup\$ What circuit or picture? \$\endgroup\$ Jun 4 '15 at 2:41
  • \$\begingroup\$ now can you see @PeterBennett \$\endgroup\$
    – ema
    Jun 4 '15 at 2:43
  • \$\begingroup\$ Vout MAX = V zener | Vout = Vin - (R x Iload) | This can fall to below Vzener. | Power in resistor = (Vin-Vzener)^2/R \$\endgroup\$
    – Russell McMahon
    Jun 4 '15 at 3:21
  • \$\begingroup\$ Since you haven't provided values for either component, it's impossible to say what its voltage or current rating might be, but trying to use a zener shunt regulator to supply more than a few milliamps is insanity. \$\endgroup\$ Jun 4 '15 at 6:25
  • \$\begingroup\$ This kind of circuit does work as a voltage regulator. Only operating it with currents of 5A would be very impractical. This is a consequence of simplicity of this circuit. At a few milli Amperes it would work fine. But in theory: yes it can be a voltage regulator. Now calculate how much power goes in and how much comes out when Vin = 12V, Vout = 9 V and I = 5A You will find that a lot of power is turned into heat. That's why it's impractical for 5A. \$\endgroup\$ Jun 4 '15 at 6:54

Making regulator with Zener for 5A is nonsense. This regulator will dissipate power whith low load instead high. Why would you even need it? There are many regulators on the market, linear and switching, and all are better than that.

  • \$\begingroup\$ However, you can use this simple circuit to generate stable 12V at low current, and use that to control a transistor to supply 5A at a stabilised voltage. \$\endgroup\$ Jun 4 '15 at 10:16
  • \$\begingroup\$ Indeed. Actually, simple but good for mqny cases voltage reference is exactly that. But for very low currents. \$\endgroup\$
    – user76844
    Jun 4 '15 at 11:29

The circuit is clearly a voltage regulator.Suppose supply is 14v and required output is 12v, then zener needs to handle the difference which is 2v. Zener always needs a series resistor to limit the current otherwise zener will blow up. To calculate the resistor value you need to know how much current the zener diode needs and how much current should go into the load, you need to know zener specification for high currents. Lets suppose zener rating for high current is approximately 5ma and the load needs 50ma. Total current then becomes, 55ma. Resistance (R)= (difference in voltage)/Total current .i.e R=(2V/55ma) ohms

  • \$\begingroup\$ Here 12v,5a means the out put voltage and current? @Arjun \$\endgroup\$
    – ema
    Jun 4 '15 at 3:11

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