Selecting right components for capacitive supply - Page 1
Forum section: electronics / beginners

author: Vindhyachal.takniki
author_rank: Frequent Contributor
timestamp: March 26, 2016, 07:21:11 am
content: This post is continuation to this(https://www.eevblog.com/forum/beginners/capacitive-transformerless-supply-with-zero-cross-detect/msg902139/#msg902139)Ckt is attached.1. I have 1uF cap as in attached picture. Purchased it from local market.I have searched for its part number on google & did image result but didn't find its exact details.I have made ckt on PCB & tested by this capacitor. It is working.However microchip app note says cap should be X2 type. I don't know if it is X2 type.I have designed the power supply for 185Vac to 265Vac/50Hz. Max load current on +5V out is 50mA. Is this cap ok?2. POV purchased from local market has this link (http://www.shenzhen2013.eb80.com/gongying____11284485_1.html).Again link is in chinese, so couldn't download its daatsheetWill this POV work.(Haven't tested the ckt with POV)3. zener is 9.1V, 1W. 1N4739A. I think it should work ok.4. I have removed 0.15uF & 1M in parallel with POV at input. Because I have seen then microchip app note didn't have these placed.Is it ok?5. 100ohm Resistance selected is of 1W. I have seen that when voltage is 265Vac at input & load across +5Vdc is 100ohm,then drop across 100ohm resistor is around 7Vac.6. all 1M resistor are 1/4W in ckt, standard non smd type. Is it ok?7. 7805 is in TO92 package. & cap across it are electrolytic, 1000uF/25V.8. 1N4007 & 1N4148 are nominal diode

author: Ian.M
author_rank: Super Contributor
timestamp: March 26, 2016, 07:38:54 am
content: 1. No. It doesn't have an X rating or an AC voltage rating so you risk it failing with extended use. Best case, it may loose capacitance or go open circuit, but its just as likely to fail short circuit, which is certain to destroy the Zener, and may blow everything fed by it, and may also catch fire.6. No. they almost certainly don't have enough voltage rating. Its usual to use two or even three equal lower value resistors in series to get the desired resistance and an adequate voltage rating to survive the peak mains voltage + expected spikes.Next time, don't start a new topic unless you have a different project/problem or discussion in the old topic has gone off out of control in a direction that you have absolutely no interest in!

author: Vindhyachal.takniki
author_rank: Frequent Contributor
timestamp: March 27, 2016, 01:22:43 pm
content: 1. Is this 1uF cap is ok. Can I select 275V one.http://www.digikey.com/product-detail/en/panasonic-electronic-components/ECQ-U2A105ML/P10736-ND/281399http://www.digikey.com/product-detail/en/epcos-tdk/B32923C3105M/495-2324-ND/7789862. POV purchased from local market has this link (http://www.shenzhen2013.eb80.com... ).Again link is in chinese, so couldn't download its daatsheetWill this POV work.(Haven't tested the ckt with POV)6. all 1M resistor are 1/4W in ckt, standard non smd type. Is it ok?http://www.digikey.com/product-detail/en/stackpole-electronics-inc/CF14JT1M00/CF14JT1M00TR-ND/1741316or I can use two 500K in series. I dont have much space.

author: Vindhyachal.takniki
author_rank: Frequent Contributor
timestamp: March 29, 2016, 09:46:26 am
content: Comments/suggestions on ckt. Ckt is attached.1. First section is Main with switch & MOV with EMI filter cap. It has MOV installed with fuse on line. Then switch is connected after which a EMI filter is used. Instead of one 1M resistor, I have now used two 500K resistor.2. Second is zero cross detect ckt. Is it ok?3. Third is +5V supply. I have checked this on breadboard. It is working giving +5Vdc at 50mA.4. Fourth is MCU driving a triac using MOC3021. Since load is 100% resistive so I haven't used snubber circuit here.5. Fifth is thermal fuse section. I don't understand how it works here. I have copied it from other board.Load is a resistance with a isolated wire along along it.The two ends of this wire are shorted & connected to J2 connector-thermal point. When load gets excessive heat up beyond safe point, the isolation gets punctured & this shorts load with wire. This leads to current flow in this wire & current flows through two parallel 4.7K resistor. Thermal fuse is placed in between these two resistor. After they gets heat up they blow the thermal fuse.But how does this ckt works I don't understand

author: orolo
author_rank: Frequent Contributor
timestamp: March 29, 2016, 02:28:29 pm
content: QuoteThis cap is not required to be X2, since it is in series with the power supply (seethis reference). Of course, a X2 cap, guaranteed to fail open circuit, is probably safer than a regular cap.Quote from: Vindhyachal.takniki on March 26, 2016, 07:21:11 amBe very careful if you test it. If you purchased a 5mm 05d470k MOV,it is rated for 30V AC max,if I got it right. Connecting it to mains voltages should either blow it, or gradually overheat and fry it.QuoteThis cap is intended to filter EMI, either coming from mains or that which is generated by your circuit. If you add it, the capmustbe X2 (see the above reference). You should decide if it is needed in your design; better safe than sorry.In order to test the zero-cross, what I did was to program the MCU to flip a led every 60 crosses. You should see regular flashes half a second long. Using a regular 'scope here is a bad idea, for obvious reasons.

author: Vindhyachal.takniki
author_rank: Frequent Contributor
timestamp: March 31, 2016, 03:45:01 pm
content: 1. Two caps 0.15uF & 1uF in power supply, I will use these. These are mentioned as X2 type & for 305Vac.I have designed supply for 185Vac to 265Vac. Are these caps ok?http://www.digikey.com/product-detail/en/epcos-tdk/B32922C3154M/495-4425-ND/2651655http://www.digikey.com/product-detail/en/epcos-tdk/B32923C3105M/495-2324-ND/778986Can I use these 275Vac caps also?http://www.digikey.com/product-detail/en/panasonic-electronic-components/ECQ-U2A105ML/P10736-ND/2813992. I found two MOV from local market unfortunatley both lead to some chinese website. DOn't know if they are ok. If one of them is ok, they are very cheap & easy to source for me.http://www.shenzhen2013.eb80.com/gongying____11284485_1.htmlhttp://www.elecfans.com/soft/IC/2010/2010030570497.htmlHow abt this , it is mentioned for 300Vac max.http://www.digikey.com/product-detail/en/epcos-tdk/S14K300E2K1/495-4292-ND/2269501