# Diode felt warm

1. Dec 7, 2009

### ramonegumpert

Dear Experts,

I have recently soldered some diodes to maintain a constant voltage. This i learnt from this nice forum.

But when using it, the diode can become quite warm.

My doubt is, when diodes become warm to touch, like about 60 degrees celsius , is it something wrong with the diode?

I am not sure what kind of diode i am using but it has some aphabets and numbers on it which reads
"CT" and
"2 A 0 5"

I suspect it means 2 Amps diode.

Someone told me that if your diode is hot, something is wrong.
I wonder is this true?

sincerely
Ramone :)

2. Dec 7, 2009

### vk6kro

Diodes can stand more heat than your fingers can. If you can't hold it for more than 5 seconds, it is getting too hot.
If it stops being a diode and conducts equally in each direction, then it is faulty.

The power dissipated in a diode depends on the current and voltage. The voltage is about 1 volt for a diode carrying high current.
Yours isn't really carrying high current so it shouldn't get very hot.

Silicon diodes do get hot if they are carrying high frequency current. If this was the case, you might need Schottky diodes.

3. Dec 7, 2009

### sophiecentaur

You seem to be describing a very simple shunt regulator and I assume you are using the diodes to provide bias for something.
If the circuit that you are using involves a resistor R from Vss in series with the diodes (forward biased), then the maximum power that the diode will dissipate is
Vd X (Vss - Vd)/R where R is the series resistor value. How much current does the circuit need? If the diodes are getting too hot, you may just be passing more current down this bias chain than is needed. Increase the pullup R value to something more sensible (if this circuit involves milliAmp circuit currents, then you don't need many mA down your bias chain) or use another biasing method - an emitter follower or something.

4. Dec 8, 2009

### mabs239

Using diodes for voltage regulation is a not a very good selection. You might consider using fixed voltage regulator IC's like 7805 (A 3-terminal device with 5 volts output), 7809 etc or LM17.

5. Dec 8, 2009

### sophiecentaur

What is the specific application which requires this voltage limit?