pic16f84 powered from mains power supply without transformer?

B0

You want the Microchip application note #AN958. Also useful is AN954.

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Abacus-Ri ha scritto:

Search: transformerless power supply

In Microchip (TB008 and other..)

and in GOOGLE!

Emanuele

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thanks for answer to both of you, but in theory everything is ok.In real design is something else. I could not receive zero crossing input from mains. It si 10 MOHM resistor conect to B0. In simulator everything is ok. Power from mains is taken over 0,47uF capacitor and diode bridge to 78L05.

any idea?

i search with google without success.

thanks in advance, Damir

It would be helpful if you could show your schematic, especially if it is in LTSpice ASC format. I assume your simulator is MPLAB SIM?

The FWB from the power line through a capacitor loses the ground reference you need for an accurate zero crossing. A better way to get the power to the PIC is with a zener to neutral, a diode to a capacitor, and then a regulator for 5VDC. You should have a current-limiting resistor in series with the capacitor, especially if there may be high frequency spikes in the line. I have used a similar approach, and found that an 18 ohm 1/2 W series resistor would overheat, indicating much higher current than expected.

I assume your 1M resistor goes to a comparator input or possibly a Schmitt trigger digital input. For zero crossing detection, make sure the input to the PIC never goes more negative than one diode drop. Even better, bias the input so that the signal stays within the power rails, and use a comparator to pick up the zero crossings. Make sure there is no appreciable phase shift from the resistor and any capacitance at the PIC input.

Paul

Thanks Paul,

that what you say have sence. In fact originaly drawing was with transformer, and everything was ok. Meantime, I try to take out transformer and change schematic. Instead of transformer I put 0.47uF capacitor on one side connected to phase, on other side connected to diode bridge ACinput. Zero from mains going to second input of diode bridge. Positive from diode bridge going to diode and after it to 78L05. Point between diode bridge and diode is connected to 2 serial resistor to zero from main. Middle point is connected to zener diode 5,1 and to B0 input on PIC for zero crossing. Latter I change some things but still without proper result. I try to find similar drawings, just to copmare, because this is my first project without transformer and PIC together.

Thansk for your time,

Damir

"Abacus-Ri" wrote in message news:epk38c$hhk$ snipped-for-privacy@ss408.t-com.hr...

I just tried two simulations, one with a FWB, and the other with a two diode doubler type circuit. Both have essentially the same zero crossing waveform, with positive level of about 4 volts, and negative excursions of

650 mV. You can add a little positive bias to make sure the input to B0 does not go negative. For both circuits the simulation shows a logic state change within 30 uSec of actual ZC, so phase error at 60 Hz is less than 1 degree. The 5 VDC supply will provide at least 5 mA, and the circuit current draw from a 240 VAC 60 Hz line is about 43 mA RMS. The LTSpice circuits follow:

Paul

========================== OffLineSupplyFWB.ASC ===========================

Version 4 SHEET 1 880 680 WIRE -208 80 -304 80 WIRE -32 80 -208 80 WIRE 0 80 -32 80 WIRE 384 80 80 80 WIRE -304 96 -304 80 WIRE 64 224 -32 224 WIRE 160 224 128 224 WIRE 176 224 160 224 WIRE 304 224 256 224 WIRE 432 224 304 224 WIRE -304 240 -304 176 WIRE -208 240 -208 80 WIRE 384 256 384 80 WIRE -304 272 -304 240 WIRE 160 272 160 224 WIRE 304 272 304 224 WIRE 432 272 432 224 WIRE 64 288 16 288 WIRE 128 288 128 224 WIRE 256 288 256 224 WIRE -32 352 -32 224 WIRE 64 352 -32 352 WIRE -304 416 -304 352 WIRE -256 416 -304 416 WIRE -208 416 -208 320 WIRE -208 416 -256 416 WIRE 16 416 16 288 WIRE 16 416 -208 416 WIRE 64 416 16 416 WIRE 128 416 128 352 WIRE 160 416 160 336 WIRE 160 416 128 416 WIRE 256 416 256 352 WIRE 256 416 160 416 WIRE 304 416 304 336 WIRE 304 416 256 416 WIRE 384 416 384 320 WIRE 384 416 304 416 WIRE 432 416 432 352 WIRE 432 416 384 416 FLAG 304 224 Vout FLAG 384 80 Vzc FLAG 384 416 0 FLAG -304 240 Vi FLAG -256 416 Vn SYMBOL cap -48 160 R0 SYMATTR InstName C1 SYMATTR Value 0.47µ SYMATTR SpiceLine V=600 SYMBOL diode 64 240 R270 WINDOW 0 32 32 VTop 0 WINDOW 3 0 32 VBottom 0 SYMATTR InstName D1 SYMATTR Value MUR460 SYMBOL diode 64 304 R270 WINDOW 0 32 32 VTop 0 WINDOW 3 0 32 VBottom 0 SYMATTR InstName D2 SYMATTR Value MUR460 SYMBOL diode 128 336 R90 WINDOW 0 0 32 VBottom 0 WINDOW 3 32 32 VTop 0 SYMATTR InstName D3 SYMATTR Value MUR460 SYMBOL diode 128 400 R90 WINDOW 0 0 32 VBottom 0 WINDOW 3 32 32 VTop 0 SYMATTR InstName D4 SYMATTR Value MUR460 SYMBOL voltage -208 224 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value SINE(0 350 60 0 0 0 100) SYMBOL zener 272 352 R180 WINDOW 0 24 72 Left 0 WINDOW 3 24 0 Left 0 SYMATTR InstName D5 SYMATTR Value 1N750 SYMATTR Description Diode SYMATTR Type diode SYMBOL res 272 208 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R1 SYMATTR Value 270 SYMBOL polcap 144 272 R0 WINDOW 3 24 64 Left 0 SYMATTR Value 100µ SYMATTR InstName C2 SYMATTR Description Capacitor SYMATTR Type cap SYMATTR SpiceLine V=16 Irms=135m Rser=0.8 MTBF=1000 Lser=0 mfg="Nichicon" pn="UPR1C101MPH" type="Al electrolytic" ppPkg=1 SYMBOL cap 288 272 R0 SYMATTR InstName C3 SYMATTR Value 1µ SYMATTR SpiceLine V=10 Irms=0 Rser=0.009 MTBF=0 Lser=0 mfg="TDK" pn="C1608X5RIA105K" type="X5R" ppPkg=1 SYMBOL res 96 64 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R2 SYMATTR Value 1000k SYMBOL res 416 256 R0 SYMATTR InstName R4 SYMATTR Value 1k SYMBOL res -320 80 R0 SYMATTR InstName R5 SYMATTR Value 100k SYMBOL res -320 256 R0 SYMATTR InstName R6 SYMATTR Value 5k SYMBOL zener 400 320 R180 WINDOW 0 24 72 Left 0 WINDOW 3 24 0 Left 0 SYMATTR InstName D6 SYMATTR Value 1N750 SYMATTR Description Diode SYMATTR Type diode SYMBOL res -48 64 R0 SYMATTR InstName R3 SYMATTR Value 20 TEXT -240 504 Left 0 !.tran 200m startup

========================== OffLineSupply.ASC ===========================

Version 4 SHEET 1 880 680 WIRE -208 80 -304 80 WIRE 0 80 -208 80 WIRE 384 80 80 80 WIRE -208 128 -208 80 WIRE -160 128 -208 128 WIRE -32 128 -80 128 WIRE -304 192 -304 80 WIRE -32 224 -32 192 WIRE 64 224 -32 224 WIRE 160 224 128 224 WIRE 176 224 160 224 WIRE 304 224 256 224 WIRE 448 224 304 224 WIRE -208 240 -208 128 WIRE 384 240 384 80 WIRE 160 272 160 224 WIRE 304 272 304 224 WIRE 448 272 448 224 WIRE -304 288 -304 272 WIRE -32 288 -32 224 WIRE 256 288 256 224 WIRE -304 304 -304 288 WIRE -304 416 -304 384 WIRE -208 416 -208 320 WIRE -208 416 -304 416 WIRE -32 416 -32 352 WIRE -32 416 -208 416 WIRE 160 416 160 336 WIRE 160 416 -32 416 WIRE 256 416 256 352 WIRE 256 416 160 416 WIRE 304 416 304 336 WIRE 304 416 256 416 WIRE 384 416 384 304 WIRE 384 416 304 416 WIRE 448 416 448 352 WIRE 448 416 384 416 FLAG 304 224 Vout FLAG 384 80 Vzc FLAG 448 416 0 FLAG -304 288 Vi SYMBOL cap -48 128 R0 SYMATTR InstName C1 SYMATTR Value 0.47µ SYMATTR SpiceLine V=600 SYMBOL diode 64 240 R270 WINDOW 0 32 32 VTop 0 WINDOW 3 0 32 VBottom 0 SYMATTR InstName D1 SYMATTR Value MUR460 SYMBOL diode -16 352 R180 WINDOW 0 24 72 Left 0 WINDOW 3 24 0 Left 0 SYMATTR InstName D2 SYMATTR Value MUR460 SYMBOL voltage -208 224 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 WINDOW 3 -97 213 Left 0 SYMATTR InstName V1 SYMATTR Value SINE(0 350 60 0 0 0 100) SYMBOL zener 272 352 R180 WINDOW 0 24 72 Left 0 WINDOW 3 24 0 Left 0 SYMATTR InstName D5 SYMATTR Value 1N750 SYMATTR Description Diode SYMATTR Type diode SYMBOL res 272 208 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R1 SYMATTR Value 470 SYMBOL polcap 144 272 R0 WINDOW 3 24 64 Left 0 SYMATTR Value 100µ SYMATTR InstName C2 SYMATTR Description Capacitor SYMATTR Type cap SYMATTR SpiceLine V=16 Irms=135m Rser=0.8 MTBF=1000 Lser=0 mfg="Nichicon" pn="UPR1C101MPH" type="Al electrolytic" ppPkg=1 SYMBOL cap 288 272 R0 SYMATTR InstName C3 SYMATTR Value 1µ SYMATTR SpiceLine V=10 Irms=0 Rser=0.009 MTBF=0 Lser=0 mfg="TDK" pn="C1608X5RIA105K" type="X5R" ppPkg=1 SYMBOL res 96 64 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R2 SYMATTR Value 1000k SYMBOL zener 400 304 R180 WINDOW 0 24 72 Left 0 WINDOW 3 24 0 Left 0 SYMATTR InstName D3 SYMATTR Value 1N750 SYMATTR Description Diode SYMATTR Type diode SYMBOL res 432 256 R0 SYMATTR InstName R3 SYMATTR Value 1k SYMBOL res -320 176 R0 SYMATTR InstName R4 SYMATTR Value 100k SYMBOL res -320 288 R0 SYMATTR InstName R5 SYMATTR Value 5k SYMBOL res -64 112 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R6 SYMATTR Value 20 TEXT -306 458 Left 0 !.tran 100m startup

messagenews:epk38c$hhk$ snipped-for-privacy@ss408.t-com.hr...

What happens in case of a power-line surge?

(for conveniance the schematics are copied to:

OffLineSupply.pdf)

The mains may contain surges up to 4kV with a rise time of 1us (simulating the turn-off of a inductive load).

In this supply the impedance to the shunt capacitor C2 is 20 ohms. (Actually the coupling capacitor C1 limits the current due to limited dV/dt). The maximum current is 4A - this will certainly blow the resistor.

So, I think you need a varistor to protect the circuit. If however you find a good wirewound for R6, you may get thorught using a couple of those (typically 1-2kV for very short voltage transients is ok for a wirewound)

Regards

Klaus

This may be what has caused overheating and failure of a resistor in a similar circuit I have been using as a voltage monitoring relay. The normal power should be well under 1/4 watt, but even a 1/2 watt resistor showed signs of overheating. I think we discovered that this happened on generator power, which may have more high frequency and high voltage spikes. I would not expect utility power to have very much of this sort of noise, and not at high enough duty cycles to cause overheating, but I don't know for certain.

Usually there is an "I squared t" parameter for non-repetitive (or low duty cycle) overloads. For large components like transformers, you can typically allow a 10x current overload (100x resistive wattage) for about 0.1 sec at

1% duty cycle. The maximum current of 4A might be tolerable for a surge of less than one cycle (as expected for inductive switching transients). There is probably more danger in this case that the capacitor dielectric could fail with momentary shorts, which may be self-healing (with the proper film capacitor), but could cause much higher currents that might be sustained for a while after the initial surge.

All of this points to the high risk of failure for capacitor fed line voltage supplies. Perhaps it is better to FWB rectify the voltage directly into an energy storage capacitor (as done in most switching supplies), and then use a high frequency transformer isolated step-down. Of course, this adds to complexity and cost. Switchers usually have some sort of line side inductive filtering and transient-limiting varistors, which would limit the effects of high voltage surges. Perhaps a small inductor in series with the capacitor would work in the simple circuit being discussed.

Paul

messagenews:epk38c$hhk$ snipped-for-privacy@ss408.t-com.hr...

I suggest a transil too

(5V monodirectional) near the PIC

Emanuele

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To start with, I'd be concerned about the peak-pulse-power rating of the resistor. Good resistors have this clearly spec'd, and at 230Vrms, its not hard to find a peak voltage of 350 - 400V when turning the unit on, which can frighten the hell out of an unsuspecting resistor of a kOhm or so. 470R at 230V is 225W while the cap charges. As the resistor gets smaller this of course gets worse.

I've seen 1/4W and 1/2W resistors in the hundreds of ohms die from this, and killed numerous 10R PRO2s this way.

It can be a sneaky failure mode because it depends when in the cycle you turn the thing on. For 3-phase stuff (eg damping resistors in filters) you are guaranteed to always get at least one phase exactly wrong, so the problem shows up more easily.

and yes as mentioned any spikes get dropped entirely across the resistor. But if you pick a suitable resistor, no worries :)

Cheers Terry

messagenews: snipped-for-privacy@j27g2000cwj.googlegroups.com...

Yes, we have had success using an inductor in series. However it is not straightforward - the inductor creates a LC circuit so you need to look out for peaking phenomenons (spelled wrong)

The peak current rating for the capacitor is also critical as you say, but that should be possible to find a suitable device. WRT the presense of the surges: its quite normal, so you cannot rely on them to be sporadic and seldom. If your box is next to a motor you may find these transients all the time

Regards

Klaus