a little help with capacitive power supply values

[Dennis]

Hi all

Melanie..

Regarding SMD, I have seen some designs showing SMD components placed after the rectification section section, is it a bad thing to consider SMD in a transformer-less design ?

The voltage ratings are 0805 = 150V and for 1206 = 200V it's quite a whack but not enough for the rectifying stage here.

Would you suggest I utilize that PSU degin you posted mentioned in #2 ?
Just curious as to why the MOV is placed where it is ?
EDIT **** OK I saw it in the forum post ..It's to accomodate for a weakspot at the the zener ****
Did you ever try replacing the 5V regulator with a 5V1 or 5V6 zener instead ?
Have you had any strange anomalies in the PSU's use ?
Have you had any blow?
Is there any ripple or noise encountered on the outputs ? The reason I ask is because I was wondering if it would be ok to add a wireless module to the circuit which the supply would power.

Steve.. the prices certainly are expensive and even for an X2 cap no surface mount !

Those transformers you found certainly are well priced !

Regarding the PIR sensors ...WOW and they do what they do at such a low voltage too ...awesome!
You could easily pack something like that into a matchbox or smaller and have it as a bed-side alarm !
Problem is that it would trigger every time either you or your partner moved in your sleep :-)

Will definitely be looking into those too !

Keep well

Kind regards
Dennis


-

[Melanie]

> Would you suggest I utilize that PSU degin you posted mentioned in #2 ?

I make no recommendations... use at your own risk after taking your own requirements and circumstances into account.

> Did you ever try replacing the 5V regulator with a 5V1 or 5V6 zener instead ?

No, because I was using the PICs ADC in my design, and wanted a closer repeatable tolerance and higher current than a Zener could provide.

> Have you had any strange anomalies in the PSU's use ?

None

> Have you had any blow?

No, the design is short-circuit proof and failsafe.

> Is there any ripple or noise encountered on the outputs ?

None beyond the design specification of the 78L05.

[Byte_Butcher]

Steve.. the prices certainly are expensive and even for an X2 cap no surface mount !

Those transformers you found certainly are well priced !

Yes, they're pretty reasonable... and now I notice that they come in an even smaller size!

http://ww2.pulseeng.com/products/dat...2007_02-04.pdf

13 mA @6V, with the same 22mm x 23 mm footprint as the others, but only 12mm high! With a SMD rectifier, regulator, and caps, it's probably not much bigger than a xformerless supply with it's big cap, MOV, and all the
rest.
I'm sure it's still a little more expensive. But maybe not much...

Regarding the PIR sensors ...WOW and they do what they do at such a low voltage too ...awesome!

Those are cute, aren't they? And tiny! I'm starting to use them around the house to turn LED "night lights" on and off. When I stumble into the bathroom at night there's enough lumens to find my target without having to fumble for a light switch.


steve

[Melanie]

The efficiency of a Transformer at 50/60Hz is dependent on the amount of iron in it's core... once you drop below about 1.5VA (which is just over an inch cube with an EI30 core) the amount of iron is so small that half the power consumption is used just to heat up the core and windings the efficiency plummets to only 50% or less.

[boroko]

Melanie, you never cease to amaze me with your practical grasp of such a wide range of issues.

You never know, keep it up and you might just have a future in this "electronics" thing.

Bo

[Byte_Butcher]

The efficiency of a Transformer at 50/60Hz is dependent on the amount of iron in it's core... once you drop below about 1.5VA (which is just over an inch cube with an EI30 core) the amount of iron is so small that half the power consumption is used just to heat up the core and windings the efficiency plummets to only 50% or less.

Well, I'm sure those little transformers aren't the greatest for efficiency, but I don't think the medium small ones (6v@83mA) I've been using are all that bad.
I've got one sitting here on the bench for days with a light (10-15mA?) load on it, and it's only barely warmer than it's surroundings. It can't be dissipating very much energy. Maybe one of these days when I'm feeling less lazy I'll attempt to measure the efficiency on one.
It certainly doesn't heat up like cheap chinese wall wart transformers do.

But how efficient is a xformerless supply if it's not "precisely loaded"? Input current is always the same regardless of load! And unless that fancy X2 cap is sized exactly to the needs of the circuit, it looks like that zener is gonna be dissipating a good dose of heat.

If your load draws a constant current and the cap is sized correctly I can see how it could be very efficient. If the load varies over a wide range as the PIC switches stuff on and off, but the power supply draws the maximum current all the time, then I don't see how that can be very efficient...



steve

[dhouston]

But how efficient is a xformerless supply if it's not "precisely loaded"? Input current is always the same regardless of load! And unless that fancy X2 cap is sized exactly to the needs of the circuit, it looks like that zener is gonna be dissipating a good dose of heat.

I have measured several X10 modules, when idle, to see how much power they waste. It's not much. http://davehouston.org/x10-power.htm

Some of the highest use transformer supplies. SMPS tend to have the best efficiencies.

[Byte_Butcher]

Hmmm. 0.4 to 1.4 watts when idle sounds like quite a chunk to me.

Say, I've got a couple of Kill-A-Watt's lounging around here somewhere... I'll take one of these little transformers and put it to the 100 hour test like you did with the X-10 modules.

Edit: I just plugged one in and these little transformers, unloaded, show .02W and .09VA. I'll let it run for a few days and see how the watt-hours add up.

I kind of forget about the Kill-A-Watt's unless the grid power is down and I'm running on backup generator. Then I drag 'em out to keep track of voltage and frequency...

steve

[dhouston]

Hmmm. 0.4 to 1.4 watts when idle sounds like quite a chunk to me.

The 0.4 was the capacitive supply that really was idle; the 1.3 & 1.4 have superregenerative RF receivers which are never truly idle. The point was that capacitive supplies are not inherently wasteful.

Tle last 5 devices all use transformer PSUs as they have serial ports and require isolation.

[Dennis]

Hi All

This is turning out to be a very interesting discussion..(well at least for me anyway!)
If you look right the way back to the start of this thread I as asking for a little help regarding the calculations mentioned in the Microchip appnote 954.Plenty have been referenced and suggested since then, and thanks to all who have contributed!

To tie things up I wonder if we could start from scratch again and take a close look at (and discuss) the circuit as we build the circuit up in 3 stages.
Hopefully we could get to a circuit which is able to supply a PIC in the correct way and be as safe as an UNSAFE and DANGEROUS circuit could be.

And the stages are :
1. The mains supply stage up to where it becomes DC
2. The circuit-load stage (where we use the 'DC' portion to power the circuit
(a possible zero crossing detector here and LED and pushbutton)
3. The output-load stage (where a load is switched either by means of a relay or a triac.

To start the ball rolling I would like to draw your attention to the attached diagram which depicts the basic types of transformer-less AC to DC power supply.

Each has its own unique chartacteristics (see AC circuit theory study notes or Google them). Understand that there may be phase shifting to consider as well as the zero crossing (these two will not be discussed yet)

SOMETIMES you may need to power a low voltage circuit such as a

microcontroller with HV AC line current.

The basic steps would be to :

1. Use a reactance to limit the current,

2. Rectify the voltage with a diode (half-wave rectification or bridge
rectifier for full-wave rectification),

3. Regulate the voltage with a zener,

4. Add a large electrolytic capacitor to filter out the ripples.

Transformerless supplies don't offer isolation from the HIGH VOLTAGE

line and present a MAJOR SAFETY ISSUE. I will put all of the possible safety tips together in point form and outline the reasons why each one is used or practiced.

I would like to be using a transformer-less CAPACITIVE circuit with common NEUTRAL (although we still have not discussed the effect on the PIC pin and the triac when there is no load!!)

I have not drawn a fuse in the diagrams yet although it is generally agreed that it is a best practice to place the fuse on the LIVE line not NEUTRAL and also not have a second fuse for example one fuse on LIVE and one on NEUTRAL!

With this in mind please could you confirm the following calculations for 220VAC and 50Hz, max current would be +-30mA.
(check the appnote and posts #14 and #16 for the calculations(Thanks Amgen and Melanie))

Calculations as per Microchip Application Note 954 :
(Please note .. Microchip are using a COMMON LIVE example - I am still not 100% sure why)

NOTE - VOLTAGE is either 230V and 240V (RMS) see appnote for 120V


VRMS 230 240
VZ 5 5.1
C1 0.00000047
R1 100
Freq 49.5 50.1

Equation 4
IIN-Min 0.018482937 Amps 18.48 ma
IIN-Max 0.029218819 Amps 29.22 ma

Equation 6
PR1 0.199702245 Watts 0.399404491 Double Watt

Equation 7
PD1 0.217302793 Watts 0.434605585 Double Watt

Equation 8
PD2 0.020453173 Watts 0.040906347 Double Watt

Please feel free to check my values and comment back.

So at this stage all I would like is some consensus on the values calculated and the different types of circuit.

Can we all agree on this so far ?

Kind regards
Dennis