X10 Home Automation using PIC16F877

[CMOS]

Hi,
I am constructing "X10 Home Automation using PIC16F877" (AN236) from microchip. It consists of a transformerless power supply and a zener regulator of 5.1V. Since my country has 230V AC @ 50Hz, I have changed the power supply circuit. Both the original and modified circuits are given below.

Calculations for Irms output from ac coupling capacitor is.
Original circuit : Irms = Vrms * 2 * Pi * f * C = 117 * 2 * 3.14 * 60 * 4.4uF = 194mA

Modified circuit : Irms = 230 * 2 * 3.14 * 50 * 2.2uF = 159mA

The problem I am facing is that when the circuit starts X10 transmission, its current consumption increases from 30mA to about 80mA and voltage drops from 4.99V to 4.1V. But the circuit is capable of delivering 159mA. Even then there is this voltage drop. Due to this the circuit fails to work properly. If I supply the circuit from 7805 regulator and transformer, it works absolutely fine.

Can anyone explain why there is so much variation in the output voltage? Any suggestions to make it stable?

 

[Borber]

Re: Zener Regulator

Your calculation of rms current through capacitor is correct. But you have half wave rectifier where max awerage (DC) current is only 70mA. Allso voltage ripple is too high, about 0.7Vpp. I suggests to use bridge rectifier and increase of smoothing capacitor to 4.7mF. In this way, max output DC current will be increased by 2. Your circuit should then work. But bridge (Graetz) rectifier will not allow you to ground your circuit.

 

[IanP]

Re: Zener Regulator

Other option is to increase current to 5.1V zener to a level which will allow this additional 50mA. (zener rated for higher currents and possibly with a heatsink). This may mean another 0.47µF (or so) in parallel with 2.2µF and also more µF added to the smooting capacitor.
To decrease voltage ripple you may consider adding >10µH inductor between existing cap and zener diode and add another 1000µF next to zener diode.

 

[Borber]

Re: Zener Regulator

Sorry 10µH inductor at 50Hz means eaqual to nothing. But 10H inductor is OK.

 

[IanP]

Re: Zener Regulator

Miniature suppression chokes (>10µH ...) have dc resistance, and it is something >0.5Ω, in some cases Ohms or tens of Ohms..
If you still think that it is not enough, 10Ω (or bigger) resistor in series will not harm..

 

[Borber]

Re: Zener Regulator

Rectifier can look like this. Power dissipation of zenner diode is about 0.5W with no load. Max output current is about 100mA and output ripple is about 30mVpp.

 

[CMOS]

Re: Zener Regulator

Hi Borber,
I will try your circuit. Can you tell me what should be the volatge rating of 4.7mF capacitor?

 

[trigger74]

Zener Regulator

I think this type of circuit is a constant current source, am I right??

If there is no load, all current will be eat up by the zener diode. If the Watt rating of the zener is not enough, the zener will die.....

 

[IanP]

Re: Zener Regulator

Previous post:
Circuits like this (and on many occasions with added transistor to increase current range) are often called "parallel regulators". The type is not current but voltage source (obviously limited with amount of current it can supply).

Circuit:
I would add 10V zener diode in parallel with 4.7mF cap and rate this cap for, say, 16V or 25V.. similar rating for 1mF.

 

[Borber]

Re: Zener Regulator

Voltage on 4.7mF capacitor will not exceed 7V, so 15V capacitor will be OK.

 

[CMOS]

Re: Zener Regulator

Thanks a lot brober. The circuit worked well.

But there is one problem.
Is there any way to supress mains spikes. I have already connected MOV between live and neutral. I can't connect snubber to my circuit since it will supress the carrier also. Yesterday while pulgging in the circuit, the switch was on which caused some arcing taking away 4069 inverter. I connected a new one, tested it for some time and did same the same mistake of plugging in the circuit while switch was on. The arcing once again blew 4069. How do I protect it.

There are two possible ways spike could enter the circuit. One is through power supply and another is through AC signal coupling. 4069 is coupled to mains using 0.1uF capacitor and another passive RC high pass filter. There are two 6.8V zenere diodes (anti-series combination) connected after 0.1uF capacitor to limit the input voltage.
Any solutions please.

 

[Borber]

Re: Zener Regulator

One possibility is to use coupling transformer and another to use high voltage transistir buffer.

 

[rmcrmc]

Re: Zener Regulator

Dear Friends,

I trying to build AN236 from Microchip, but I don't know very much electronics, I'm a good programmer and need you help if you don't mind.

Can some one send me the modifications for using it with 220V?

Thanks,
Rui Caridade

 

[CMOS]

Re: Zener Regulator

You only need to change the power supply section. Use the above circuit suggested by "Borber". I've tested it and it works all right.

 

[rmcrmc]

Zener Regulator

I'm going to use only N and L. Only 2 Pins from mains.

Ok, I tested the power circuit and works ok, but what about XOUT and XIN?


The Highpass Filter on sheet 4, uses .1uF 275VAC is it ok?

Is there other parts that I must replace?

Thanks

 

[CMOS]

Re: Zener Regulator

Oh yes, I forgot to mention that. You need to change the voltage rating of all the capacitors connected to power line to atleast 400V. Note that all capacitors must be non-polarized polyester type. No electrolytics at all in the power or Xin Xout section.

 

[rmcrmc]

Zener Regulator

Ok, but in power section the one made by "Borber" it seems to be 2 electrolytics, one 4700uF 16V and other 1000uF 16V they are polarized.

"Voltage on 4.7mF capacitor will not exceed 7V, so 15V capacitor will be OK."

Is this correct?

Thanks,
Rui Caridade.

 

[Borber]

Re: Zener Regulator

Yes it is correct. Both capacitors can be only electrolitics. But capacitors, used for X10 signal coupling, has smaller value and they should be of foil type and 400V rating voltage minimum.

 

[rmcrmc]

Zener Regulator

What do you mean with capacitors 400V AC or DC?

Thanks

 

[Borber]

Re: Zener Regulator

Capacitor rating is 400V DC or 275V AC.