Project: Fluoro Lamp Power Inverter (12v) - Page 3 - Electronic Circuits Projects Diagrams Free

Hero999 · 29th February 2008, 09:27 PM

The circuit is quite reliable when properly designed and built. This sort of circuit has been used to power fluorescent lamps of DC power in busses, trains and military vehicles for years without any problems.

HS3 · 7th April 2008, 04:32 AM

Quote:

Originally Posted by Hero999

The problem with this circuit it it drives the tube of pulsed DC not AC so it won't be as birght and it won't last as long. You need a push-pull driver and centre tapped transformer primary to get an AC output and drive the lamp properly.

I know this is an old post but I believe this is fundamentally wrong.

Speaking of forward mode transformers (not flyback) and assuming the transformer is designed so that it does not saturate in any case, then the addition of a DC current at the input does not affect the output at all and, in fact, there is NO way to tell by looking at the output if there was a DC component in the input.

Look at the output transformer of a valve amplifier. It is carrying the plate DC with the output signal superimposed. The output is the AC signal with no DC. If I give you the output of two transformers and both give the same signal you cannot know which one is carrying DC in its primary. If the input is V = K + A sin(ω*t) The output will always be the same regardless of whether K is zero, positive or negative.

The thing is that if you are carrying DC in the primary then you need a bigger transformer so it does not saturate the core. The DC current is creating a continuous flux which takes the core nearer to saturation so transformers (and chokes) which carry DC in their primaries need to be specially designed but you cannot see any difference in their outputs. None whatsoever. The DC is totally blocked and it is as if it did not exist.

Just the same happens with a capacitor. If I have a signal input blocked by a capacitor, on my side I will see the AC variations but I have no idea from this side what the voltage may be on the other side of the capacitor. To know that I have to go to the other side of the capacitor. All I can see is the AC from my side.

audioguru · 7th April 2008, 03:47 PM

Good point.

Hero999 · 11th April 2008, 10:14 PM

Quote:

Originally Posted by HS3

I know this is an old post but I believe this is fundamentally wrong.

Speaking of forward mode transformers (not flyback) and assuming the transformer is designed so that it does not saturate in any case, then the addition of a DC current at the input does not affect the output at all and, in fact, there is NO way to tell by looking at the output if there was a DC component in the input.

The circuit I am critisising is a flyback so the core does saturate. What you're saying is true that there's no DC on the secondary but there will be just negative DC pulses and no positive pulses.

I've uses a similar circuit to run a fluroscent tube from before and after a few hours of running only one end of the tube went black. This is because the current only flowed in one direction causing the cathode electrode to sputter on to the glass. Try connecting a neon lamp to this circuit and you'll see that only one electrode will glow.

Ubergeek63 · 18th April 2008, 08:40 PM

Quote:

Originally Posted by Hero999

That's exactly what I was talking about.
http://www.repairfaq.org/sam/samschem.htm#schmp1

Hero, is that guy a bit full of himself or what? In the industry that circuit is called a royer inverter and was the standard inverter circuit for many, many years.

For him to say that he improved it is quite presumptuous. There has been nothing under the sun original that could be done with that circuit for almost as many years.

hsab · 20th July 2008, 02:19 AM

hi

the simple project for building this 12v inverter to drive fluo lamp

few compenents, no commercial transformer

take a look here

http://www.talkingelectronics.com/te...ive_index.html

Hero999 · 20th July 2008, 08:38 AM

Where's the circuit?

audioguru · 20th July 2008, 12:57 PM

Quote:

Originally Posted by Hero999

Where's the circuit?

You need to search for it. I found it.

Hero999 · 20th July 2008, 01:18 PM

I've seen that circuit before. It uses an AM radio aerial so noise is broadcast everywhere, a single transistor and no DC blocking capacitor so one of the tube only gets driven with negative pulses causing one of tube the ends to blacken.

It's simple and low cost but also illegal (it doesn't comply with the EMC laws) and gives poor efficiency and tube life.

Ubergeek63 · 21st July 2008, 05:32 PM

Quote:

Originally Posted by HS3

The thing is that if you are carrying DC in the primary then you need a bigger transformer so it does not saturate the core. The DC current is creating a continuous flux which takes the core nearer to saturation so transformers (and chokes) which carry DC in their primaries need to be specially designed but you cannot see any difference in their outputs. None whatsoever. The DC is totally blocked and it is as if it did not exist.

Actual inverters use blocking caps before the transformer because they are less expensive in money and space than a larger transformer.

mneary · 21st July 2008, 08:14 PM

This has been covered many times, and misunderstood almost as much. An asymmetric primary drive usually causes an asymmetric secondary voltage. There is indeed no DC in the secondary, if the load is resistive. However, a fluorescent tube isn't resistive. The tube will only conduct when the voltage is high enough. Since the voltage isn't symmetrical, this can mean that the tube only conducts on half of the cycle and acts as a half wave rectifier.

Hero999 · 21st July 2008, 08:27 PM

Thanks, I'll post a link to your post everytime I see one of these crappy circuits.

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29th February 2008, 09:27 PM	(permalink)
Hero999	The circuit is quite reliable when properly designed and built. This sort of circuit has been used to power fluorescent lamps of DC power in busses, trains and military vehicles for years without any problems. __________________ What's so bad about Microsoft? Get Opera it's simply a superb browser.

7th April 2008, 03:47 PM	(permalink)
audioguru	Good point. __________________ Uncle $crooge

20th July 2008, 02:19 AM	(permalink)
hsab	12v Fluo Inverter hi the simple project for building this 12v inverter to drive fluo lamp few compenents, no commercial transformer take a look here http://www.talkingelectronics.com/te...ive_index.html

20th July 2008, 08:38 AM	(permalink)
Hero999	Where's the circuit? __________________ What's so bad about Microsoft? Get Opera it's simply a superb browser.

20th July 2008, 01:18 PM	(permalink)
Hero999	I've seen that circuit before. It uses an AM radio aerial so noise is broadcast everywhere, a single transistor and no DC blocking capacitor so one of the tube only gets driven with negative pulses causing one of tube the ends to blacken. It's simple and low cost but also illegal (it doesn't comply with the EMC laws) and gives poor efficiency and tube life. __________________ What's so bad about Microsoft? Get Opera it's simply a superb browser. Last edited by Hero999; 21st July 2008 at 07:03 PM.

21st July 2008, 08:14 PM	(permalink)
mneary	This has been covered many times, and misunderstood almost as much. An asymmetric primary drive usually causes an asymmetric secondary voltage. There is indeed no DC in the secondary, if the load is resistive. However, a fluorescent tube isn't resistive. The tube will only conduct when the voltage is high enough. Since the voltage isn't symmetrical, this can mean that the tube only conducts on half of the cycle and acts as a half wave rectifier.

21st July 2008, 08:27 PM	(permalink)
Hero999	Thanks, I'll post a link to your post everytime I see one of these crappy circuits. __________________ What's so bad about Microsoft? Get Opera it's simply a superb browser.