hericlj

Thank you very much.....

Yes...I need that powered all the time. And as I was using a step-down transformer with a bridge rectifier to power the circuit...could I just feed the positive output of the rectifier to the transformer center tap? Cheers

No. It connects to the switched +12V side of the on-off switch. ...So what I did was to connect the center tap of the transformer to the positive node of the rectifier...How wrong was that? Is that the problem to my inverter? Could you tell me more about the switched +12V side of the on-off switch? Isn't that the DC supply to the IC? I thought it was a power switch, so I didn't make that part... Cheers...

Hi, thank you so much for your help....For me, to make the inverter seems like an endless process... Just reviewed the above post you replyed a few days ago...I just had the weird feeling maybe I did something wrong on the circuitry as well... You said that the circuit doesn't need to be earthed...So if I powered the circuit with a step down transformer(240V-12V) and a bridge rectifier from the main supply, should I connect all the nodes with triangle (including the emitterors of the transistors) to the negative node of the rectifier? And the centre tap of the transformer is connected to the positive node (12VDC) of the rectifier?The collectors to the remaining terminals of the transformer? Cheers....

Cheers.... I just found one in local supply...Could you have a look if it would be ok? http://www.farnell.com/datasheets/39823.pdf The online stor is: http://nz.farnell.com

oh....really.... I looked at some online electronics stores and they have transformers which are 100VA and have 2 0-12V at secondary...I only need the inverter to power a single incandescent lamp so i think 100VA should be enough for me... How do I know which type of transformer with two 12V output can be implemented as a 24V center tapped? Will that be mentioned in the specifications? What is the difference between those ones and the one I picked before at Jaycar? Cheers....

Hi....Now I know why the inverter didn't work....Thank you... Could you suggest any specific transformer that I could use? I am afraid I would pick the wrong one again....And my project is close to the due day....:( I am in New Zealand, and the two large supply are either Jaycar, or RS component Ltd....Could you please pick up the one needed from the websites for me? The websites are: www.jaycar.co.nz or www.rsnewzealand.com Cheers.....

sorry, i made a mistake. the transformer is rating at 60VA... I just did the measurment, the 0V terminals are not conneted together, nor they are to the frame...

Hi, thank you.... the transformer i am using is a 0-15V(multi-tapped)@2A 30VA...According to the specification, it is a type 2156 transofrmer. I can't find the data sheet...But I'll copy the specification from the supplyer here: 0 - 15V (Multi-Tapped) @ 2A 30VA - Type 2156 Transformer Specifications: Primary voltage: 240VAC Secondary Voltage: 6, 9, 12, 15V Magnetising current: ~65mA Total Power rating: 30VA Temp rise above ambient at rated output: ~60

Hi...sorry I still have problem in the inverter circuit... This time i put a rectifier circuit and used the main supply to power the inverter so that current limit won't be a problem. But still, when I switched it on, nothing comes out. The transformer is shorted between one wire's 12V and the other wire's 0V terminals. Even without powering the circuit, the transformer is still shorted so the collectors of the transistors are shorted...When I removed the transformer, the collectors are isolated again!..... Just to make sure I did it in the right way: one wire's 12V is connected to the other's 0V, and this is also connected to 12VDC...The remaining 12V and 0V is connecting to the collectors of the transistors respectively.... Or do I have to buy a centre-tapped transformer instead? Cheers...

Thank you so much....:) Actually when I did that experiment last week, I didn't connect any load to the transformer, and I was using those 3A(max) DC Power Source to power this circuit....So when I switched it on, the power source reaches its limited output current and wouln't give 12V out....I thought that was current-shorted....

Hi Audioguru: Thank you for your help...Sorry, I am a begginer in power electronics, so actually i don't know what a center-tap step up transformer looks like. I bought one with 240VAC primary and two 12V, two 9V, two 0V output terminals at secondary, and thought I could use it to step up the voltage.... I actually connect the collectors to the 12V terminals on the seconday, and 12V DC to the 0V terminals (I tied the two 0V terminals togeter), and the primary side of the transformer is conncted to the load.... So when I switch the power on, the whole thing is current shorted..... Am I seriously wrong? Great Thanks....

OK. This is the one I build my circuit. Do I common ground the two 0V terminals of the transformer and connect it to 12VDC? The collectors are connected to the 12V terminals of the transformer, am I right? Thank you....

sorry, still no output...When I connected the transformer to the collectors of those transistors. They are shor-circuited.

oh...Thank you very much... Now I know why I can't get anything from the circuit...hehe~~~ One more thing? Just wondering how does the opamp work? Is it functioning as a voltage follower? I thought the input to the opamp is 12V square wave and then the opamp should not be operating at its linear region...right? or is it like a schmitt trigger but instead of positive feedback, it is functioning in negative feedback? Thank you...really appreciate for your help...