Zener Voltage Regulator (1N53)

Thread Starter

MadJ

Joined Feb 18, 2011
11
I have built a simple voltage regulator using the 1N53 zener diode ( 3.9v )
The input source is 5v at 500mA, at the output i need 3.9v.
But when i measure the voltage across the diode, it shows same as input voltage (5v).
I tried changing the zener diode, but to no avail.
What could be the issue ?
 

JDT

Joined Feb 12, 2009
657
Should be OK then. If you are getting 5V out, there is no current in the diode.

Have to say, I looked up 1N53 and it wasn't a zener. Are you sure? have you got a data sheet?
 

JDT

Joined Feb 12, 2009
657
Well, according to the datasheet it has a nominal Vz of 3.9V at 320mA so it should work. The voltage you will get will be higher than 3.9V due to the effective zener resistance of 2Ω. But, yes, it should be doing something. Certainly should be conducting current and getting quite warm.

You can't get a circuit much simpler than this so I can't explain why it's not working. Sorry.

Unless the diode is open circuit. Does it conduct in the forward direction? (with about 0.6V drop - just like a normal diode?)
 

Thread Starter

MadJ

Joined Feb 18, 2011
11
Yes, it does conduct in forward direction.

Also, i tried replacing the diode with a 1W zener ( glass casing it seems ), this diode would warm up and at the output i get 3.9v
 

Thread Starter

MadJ

Joined Feb 18, 2011
11
I specifically asked for a zener diode.
The text on the body of the diode says 1N53 35B
Did you check the datasheet i have attached in my previous posts ?
 

SgtWookie

Joined Jul 17, 2007
22,210
Are you certain that you have the Zener connected correctly?
Zeners are shunt regulators.
The +5v output should connect to one side of the current limiting resistor, the other side of the resistor connects to the cathode of the Zener, and the anode of the Zener connects to the supply return (ground); the output voltage is taken across the Zener.

Using a power Zener in this manner will result in terrible efficiency; most of the power in your circuit will be dissipated in the current limiting resistor and the Zener itself. Output regulation will probably not be very good.

Why don't you tell us more about your load requirements? What are you trying to power with the 3.9v output; what current does it (your load) require?
 

Thread Starter

MadJ

Joined Feb 18, 2011
11
Yup, i have connected the Zener just in the manner you described above (reverse biased).

The load would be 4 IR Lasers, each running at 3.9v @ 60mA
 

SgtWookie

Joined Jul 17, 2007
22,210
You really need to control the IR lasers by current rather than by voltage, and they each need their own current limiters.

Is your 500mA 5v supply well regulated?
If so, you might use individual resistors for each IR laser.
Rlimit >= (Vsupply - VfLaser) / DesiredCurrent
Rlimit >= (5v-3.9v) / 60mA
Rlimit >= 1.1v / 0.06A
Rlimit >= 18.333... Ohms.
That is not a standard value of resistance. 20 Ohms is the closest standard value.
I=E/R, so 1.1v/20 Ohms = 55mA.

Power dissipation in the resistors will be 1.1v*55mA = 60.5mW, double for reliability = 121mW; you can use 1/8W or higher rated resistors.

Four IR lasers in parallel would then use 55mA x 4 = 220mA


If the supply is not regulated, you'll need to use a different approach.
 

Thread Starter

MadJ

Joined Feb 18, 2011
11
Ohhk.
Yes, the 5v supply is through 7805, so it is regulated.
And ill even go with just a 20Ω resistor in series.

But i am just curious as to why the zener regulator is not producing a desired output !
 

SgtWookie

Joined Jul 17, 2007
22,210
Ohhk.
Yes, the 5v supply is through 7805, so it is regulated.
OK. Do you have the required 0.33uF cap on the input to ground and 0.1uF on the output to ground, as close as possible to the regulator? These are not optional.

What is the input voltage to the 7805?
And ill even go with just a 20Ω resistor in series.
OK.
Keep in mind that you need to verify the Vf of the lasers by measuring the voltage drop across the current limiting resistors. If you are getting more than 1.1v across the 20 Ohm resistors, then you risk early failure of the IR laser diodes.
E=IR, so if the 7805 is giving exactly 5v output, then the most you should read across the resistors is 0.06A x 20 Ohms = 1.2v.

But i am just curious as to why the Zener regulator is not producing a desired output!
It might be mis-marked, it could be a counterfeit part if you didn't buy it from an authorized distributor, you may have an error in your wiring - only three of several possibilities.
 

Thread Starter

MadJ

Joined Feb 18, 2011
11
OK. Do you have the required 0.33uF cap on the input to ground and 0.1uF on the output to ground, as close as possible to the regulator? These are not optional.
No, i don't have it. I did go through the Sticky Post on Bypass Caps. I will try adding it and let you know if that makes any change.

What is the input voltage to the 7805?
6V - 10V ( its from a wallwart, which contains a multi tapped transformer, a bridge rectifier and a huge capacitor inside )


OK.
Keep in mind that you need to verify the Vf of the lasers by measuring the voltage drop across the current limiting resistors. If you are getting more than 1.1v across the 20 Ohm resistors, then you risk early failure of the IR laser diodes.
E=IR, so if the 7805 is giving exactly 5v output, then the most you should read across the resistors is 0.06A x 20 Ohms = 1.2v.
oh Yes.


It might be mis-marked, it could be a counterfeit part if you didn't buy it from an authorized distributor, you may have an error in your wiring - only three of several possibilities.
Quite possible
 
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