Question on powering LCD backlight

[kchriste]

The bypass is just to get the darn thing working in LTSpice. Myself, I'd try it just leaving bypass out to start with.

LTSpice is probably simulating it right. Q2 should have it's emitter and collector lead swapped and R4 should be a jumper. Then you can take out the bypass.

 

[mneary]

L2 (1 :mu:Hy) is probably the ESL of a 2700 uF capacitor, and not an actual component. 2700 uF sounds like serious overkill. What is the expected frequency?

 

[mvs sarma]

Hi Torben,

Thanks mate, I'll get building and good luck with the ballgame

BTW just had an idea about testing the output on the other circuit I made, wondered if I could try a Neon lamp (from an old lighted switch) across the output, but I didn't get a flicker!

Al

Hi Bigal please see whether the document in the link below could be of some help for the EL backlit inverters.

https://www.electro-tech-online.com/custompdfs/2008/04/InverterSTIMP803-pdf.pdf
If so, most probably the inverter element used in an old calculator with vacuum tube display (green) would perhaps be suitable instead of re-designing one.

 

[Torben]

LTSpice is probably simulating it right. Q2 should have it's emitter and collector lead swapped and R4 should be a jumper. Then you can take out the bypass.

Oh man, you're right. Bitten by the PNP again. I don't use them a lot and miss that sometimes.

After flipping Q2 you can remove R4 too.


Torben

 

[Torben]

L2 (1 :mu:Hy) is probably the ESL of a 2700 uF capacitor, and not an actual component. 2700 uF sounds like serious overkill. What is the expected frequency?

I imagine you're right about the inductor; I'm not sure. The target frequency is ~400Hz but the 555 circuit adjusts up and down around that. The 2700uF cap can be quite a bit lower as far as keeping the sim happy goes but I left it alone since I wasn't sure what the original author had in mind for it.


Torben

 

[mneary]

I looked at Tony's page; he definitely used an inductor. As for the capacitor,, I'd be tempted to measure the inductance of the transformer winding and see how it works when you resonate it.

 

[Torben]

I looked at Tony's page; he definitely used an inductor. As for the capacitor,, I'd be tempted to measure the inductance of the transformer winding and see how it works when you resonate it.

Mmm. Now I just need something which can measure inductance. For the transformer model I just plugged in a 1:10 ratio on the inductances without any real hope that it would be real-life-accurate, hoping that it would be close enough to a 1:10 turns ratio to at least get the voltage output in the right ballpark.

I guess it would be a good idea to at least try to make make sure the output isn't resonating.


Torben

 

[blueroomelectronics]

Here's a really simple to build L/C meter
**broken link removed**
**broken link removed**

 

[Torben]

Here's a really simple to build L/C meter
**broken link removed**
**broken link removed**

Nice! Thanks for the link. It's probably about time I moved up from 8051s anyway. If I decide to (read: get time to) build it I know I'll be buying one of your programmers.


Torben