555 inverter brightness and over current issue  - Page 1
Forum section: electronics / projects

author: dave_j_fan
author_rank: Regular Contributor
timestamp: November 28, 2019, 05:14:26 am
content: hi experts,I have used this 555 circuit for very simple inverterhttps://www.eleccircuit.com/220-volts-power-inverter-using-ne555-and-mosfeti am running it on dual 18650 i.e. approx 7.4vfor portability we cannot change this . It has to be 2 battery system .MOSFETS are Z44.observation1) with 12 - 0-12 , 2 AMP transformer coil resistance 2.5E. The inverter works very nicely300mA currentand ok brightness ( just one winding i use 0-12 and one MOSFET )so we get 7hour backup. This is fine2) As the . 12-0-12 is bulkywe used 0-6V/ 220V small 500ma transformer .coil resistance 12EBut hereit consumes 550mAbulb is not bright too .What can be the reason of increased current .i have measured coil voltage to MOSFET its approx 3V

author: Zero999
author_rank: Super Contributor
timestamp: November 28, 2019, 10:31:36 am
content: A schematic would help. The site you've linked to has two MOSFETs, yet the circuit you've describe only has one.My guess is you're overloading the transformer causing core saturation, hence the higher current and lower output power.What sort of light is it driving? LED or incandescent?My advice is scrap the inverter and replace the mains lamp with one which can be powered directly from DC. Two white LEDs in series and a linear current regulator will be much more efficient than an inverter and a mains lamp. It can be made even more efficient with a switched mode power supply for the LEDs.

author: dave_j_fan
author_rank: Regular Contributor
timestamp: November 28, 2019, 12:18:38 pm
content: Reposting the same ...here one MOSFET i use . in both cases1)with 12-0-12V 2 Amp transformer2)0-6 V ,500mA transformerload is 7W ledBoth cases led is lit, in second case total current 550mAin 1 case its 300mAI want to make it work well in 500mA transformer. so that i can case it in smal casegets portable(Not interested to run DC LEDs .. so please dont advice )

author: dave_j_fan
author_rank: Regular Contributor
timestamp: November 28, 2019, 12:31:33 pm
content: DC lamps to avoided1) need to be remotely mountable2)DC LED and additional circuits are wastage of time and work3)All DC led bulbs available in our countr are Junk and cant be used--need to run 5w or 7W led as these are super reliable by all leading brandscomes with nice cases

author: Zero999
author_rank: Super Contributor
timestamp: November 28, 2019, 12:40:10 pm
content: Why post an oversized picture with loads of empty space?Core saturation doesn't cause the iron core to heat up. It results in excess current being drawn through the primary winding. It may or may not cause noticeable heating of the transformer winding, depending on the power dissipation and mass of the transformer.DC LEDs can be mounted wherever you like.DC to AC circuits are a waste of time and just consume more power.Just make your own DC LED lamps.

author: JimRemington
author_rank: Regular Contributor
timestamp: November 29, 2019, 04:11:20 pm
content: QuoteThe single MOSFET design is very inefficient and will never work well.

author: NiHaoMike
author_rank: Super Contributor
timestamp: November 29, 2019, 05:30:29 pm
content: Use a push pull PWM controller like the UC3525A, that way you get a symmetrical waveform with adjustable duty cycle.Quote from: Zero999 on November 28, 2019, 12:40:10 pmDon't even need to make them, LED strips are cheap.

author: Zero999
author_rank: Super Contributor
timestamp: November 29, 2019, 07:11:38 pm
content: Quote from: NiHaoMike on November 29, 2019, 05:30:29 pmYes, DC LEDs are widespread but they're normally rated to 12V or 24V, not 7.4V. A boost converter would be required to power to generate 12V.

author: dave_j_fan
author_rank: Regular Contributor
timestamp: December 01, 2019, 11:08:13 am
content: Quote from: NiHaoMike on November 29, 2019, 05:30:29 pmled strips are not for bub replacement, they are just for corner lighting , come loaded with resistorsUC3525A not an option, cost issue

author: dave_j_fan
author_rank: Regular Contributor
timestamp: December 01, 2019, 11:15:36 am
content: i think the criteria is not clear to all .1)cost is one factor here so designs like PWM ic are not a possibilityBJT or basic 555 etc can be a possible choice2)Regarding SIngle MOSFET inefficiency3)forget DC lamps there re 100 reasons not to usesolutions do keeponly to small inverter designs"same circuitworks with 12 0 12 2AMP transformer .. low current 300mA "we have used just one winding 0-12Vbutsame circuitwith 0-6VSmaller transformer is 550mA approxWe can live with 300mA but need to be ready with smaller transformerso that cost of making will be low and we can put smaller case (cabinet)Any alternate circuit also is fine with lower parts cost.

author: dave_j_fan
author_rank: Regular Contributor
timestamp: December 01, 2019, 12:27:24 pm
content: probably smaller core getting saturated , i will adapt to PNP NPN designhttp://pindiagram.blogspot.com/2012/02/dc-to-ac-inverter.html

author: NiHaoMike
author_rank: Super Contributor
timestamp: December 01, 2019, 01:08:28 pm
content: Quote from: dave_j_fan on December 01, 2019, 11:08:13 amHow about TL494?

author: Zero999
author_rank: Super Contributor
timestamp: December 01, 2019, 01:54:22 pm
content: Quote from: dave_j_fan on December 01, 2019, 12:27:24 pmThat design is very inefficient due to the huge losses with the 555 driving emitter followers.If you use the original design posted at the start of the thread, with a centre tapped transforer two MOSFETs, the core is less likely to be saturated, since it will be alternately magnetised with opposite polarities, thus be used more efficiently.If you need a smaller solution forget the bulky, inefficient inverter. Use a 12V LED and a small, lightweight, efficient boost converter.

author: dave_j_fan
author_rank: Regular Contributor
timestamp: December 04, 2019, 07:23:12 pm
content: Quote from: Zero999 on December 01, 2019, 01:54:22 pmyes the core saturation was the issue--its resloved! ----- used Centertapped transformer and dual mosfets-- Achieved good brightness at230mAso 2200mAH pack will last8-10hourwith 2S4P we can get 20hour backup , which is hugedeveloped an ECO mode , slight less brightness at155mAon 2200mA ECO mode can pull till 12Long hoursAll this with palm sized inverter.test shown a 500mA transformer can take two 7Wbulbs ( lower brightness )but this centertap is very good for one 7W

author: dave_j_fan
author_rank: Regular Contributor
timestamp: December 04, 2019, 07:26:04 pm
content: Will the LOGIC mosfets give even better brightness ?AC was approx 185V and the bulbs for 220V do very well now