Voltage Regulator or Rectifier Diode?

[ronvegas]

Instead of a voltage regulator I've read a rectifier diode can be used to drop voltage.

I'm wanting to drop 6v to 5v and I've read that a IN4001 will drop 0.7v - Is this correct?

Does this work without heat like with volt regs?

Please can anyone provide info on this and what I need to get and how to wire it?

Thank you so much!

 

[rezer]

Instead of a voltage regulator I've read a rectifier diode can be used to drop voltage.

I'm wanting to drop 6v to 5v and I've read that a IN4001 will drop 0.7v - Is this correct?

Does this work without heat like with volt regs?

Please can anyone provide info on this and what I need to get and how to wire it?

Thank you so much!

First, just add to the thread you just started. By asking multiple questions related to the same topic on different threads just confuses people.

Yes, the diode can be used to drop voltage. Why can't you get another 5V adapter? I would build a 5V regulator powered from your 9V source. The other regulator may not have worked because it wasn't speced right. Check the current rating against that of the modem requirements.

 

[Torben]

Instead of a voltage regulator I've read a rectifier diode can be used to drop voltage.

I'm wanting to drop 6v to 5v and I've read that a IN4001 will drop 0.7v - Is this correct?

Does this work without heat like with volt regs?

Hi Ron,

First, ditto to what Rezer said about keep related info in one thread--it'll just make it easier for us (and for you) to keep track of it later.

On to your actual question: no, it does not work "without heat". I'm going to take a shot at walking through the numbers here. Bear with me; I'm not an EE, just some guy with a calculator and a bit of free time.

The power dissipated in Watts can be calculated with P=IE, where P is the dissipated power in Watts, I is the current flowing in the diode, and E is the voltage dropped across the diode.

Say your modem draws current of 250mA (I'm pulling that number out of the air). A 1N4001 with 250mA across it will have a forward voltage of around 0.8V. So the power dissipated by the diode will be P = 0.25 * 0.8, or P = 0.2 Watts.

At a guess I'd say that in your situation that putting a 1N4001 in series with the +6VDC supply would be a more economical solution than using a regulator, even though you are effectively having to burn off that extra 200mW as heat--the regulator would have to burn it off as heat anyway.

As always, if I'm leading you down the garden path I hope a real EE will step in and beat me with a clue stick. The above is how I understand things to be.

Reference:


Torben

 

[Boncuk]

Hi Ron,

I'd go along with Torbens idea. It's practical and cheap for the desired effect.

You can increase the effect by using a filament type (or two paralleled bicycle head light lamps) with a resistance of 4Ω for a current flow of assumed 250mA and a desired voltage drop of 1V and doesn't require any cooling.

The lamp will glow dimly when the power supply is OK.

Best bet however is using a low dropout voltage regulator. (LM2940-CT5).
It has the same regulation characteristics as the well known LM7805, but for a low drop out regulator the input voltage can drop to VIN=VOUT+1V (LM7805 - VIN=VOUT+3V).

Boncuk

 

[Torben]

Hi Ron,

I'd go along with Torbens idea. It's practical and cheap for the desired effect.

You can increase the effect by using a filament type (or two paralleled bicycle head light lamps) with a resistance of 4Ω for a current flow of assumed 250mA and a desired voltage drop of 1V and doesn't require any cooling.

The lamp will glow dimly when the power supply is OK.

Best bet however is using a low dropout voltage regulator. (LM2940-CT5).
It has the same regulation characteristics as the well known LM7805, but for a low drop out regulator the input voltage can drop to VIN=VOUT+1V (LM7805 - VIN=VOUT+3V).

Boncuk

Hi Hans!

I must admit that the idea of the 1N4001 was not mine originally, but LeftyRetro's (in this thread). I was just trying to work through how it might work.

I agree that the lamp idea would look cooler and the regulator idea would be ideal, but both are more expensive and complex--relatively speaking. Any of these ideas would be cheap and simple to implement, I think.


Torben

 

[Boncuk]

... the regulator idea would be ideal, but both are more expensive and complex--relatively speaking. Any of these ideas would be cheap and simple to implement, I think.

Torben

Hi Torben,

an LM2940-CT5 costs the fortune of 50C.

Dealing with electronics money shouldn't be the primary question. Failing to spend money for appropriate components will result in overproportional heat production, hence more money is necessary for sufficient cooling devices.

Hans

 

[Torben]

Hi Torben,

an LM2940-CT5 costs the fortune of 50C.

Dealing with electronics money shouldn't be the primary question. Failing to spend money for appropriate components will result in overproportional heat production, hence more money is necessary for sufficient cooling devices.

Hans

Hi Hans,

Sorry, I may have phrased my response poorly. That's essentially what I was getting at: the primary question should be "will it work", and I think that the answer is "yes" for all three solutions, with only very minor differences in cost and complexity between them. In this situation (IF my totally random 250mA current value is correct, which it probably isn't) I don't think cooling will be needed for any of the solutions given. I could be wrong on that though, of course.


Torben

 

[Boncuk]

Hi Torben,

I don't consider a current flow of 250mA being strong current. Even if it's an assumption which I guess pretty close - maybe even less - with a device like a modem.

I just wanted to point out that saving with the wrong (weak) part can lead to more expensive solutions.

Considering power supplies I've never built one with full load temperatures exceeding 35degC at ambient temeratures of 20degC. Everything else is HOT. I had to deal with heavy industrial environment and temperatures in the switching cabinets of 80degC. So any extra heating would have meant sudden and early death of any device I built in there.

Within a time period of 18 years none of my circuits failed. (six circuits in a 19" rack with 13 Euro-size (160X100mm) PCBs each) There were just a few LEDs never extinguishing fully when they were supposed to. (visible in the dark only)

Hans

 

[Torben]

Yessir! Building something right is better than building it again.


Torben

 

[Boncuk]

Yessir! Building something right is better than building it again.


Torben

with one exception: a dress tailered with the so called "hot needle" takes care of good looking girls - almost naked.

Hans