i have a potenetiometer between the 5 v and the LCD, I swiched to the 12v with the pot, and the LCD is finished
|
i have a potenetiometer between the 5 v and the LCD, I swiched to the 12v with the pot, and the LCD is finished
|
Sorry to hear that you toasted the LCD but I didnt suggest running the LCD from the 12v supply.... just the backlight.Originally Posted by lerameur
i have a potenetiometer between the 5 v and the LCD, I swiched to the 12v with the pot, and the LCD is finished
If you had read the other threads about this you would see the reason behind it. The LCD only takes a couple of milliamps but the backlight takes 50-80mA which is a lot of extra for the regulator to handle.
The backlight doesnt need a regulated supply, just a current limited one hence the use of a series resistor which you calculate according to the forward voltage of the backlight , the required current through the backlight and the maximum voltage of the unregulated supply.
Keith
www.diyha.co.uk
www.kat5.tv
|
a ok , i get it,
By the way , anybody knows why My h_bridge, L298N get really really hot even with a heat sink and just 1.8 amp ?and yes it is connected to the 12v battery. Getting hot, and its not working anymore...
Last edited by lerameur; - 14th January 2007 at 22:22.
|
Country Fried
Hi Leramuer, sounds like the magic smoke escaped from that device. 12v x 1.8 a
= 21.6 watts, I assume thats the running current under normal load. That figure increases exponentialy when you reverse direction and that's a whole lot of heat. What do you have for a heat sink? Maybe in addition to more heat sink you should put in a thermal shutdown circuit.
JS
|
If it was me doing a project needing an H-bridge, I'd skip the H-bridge and just go with a set up using a bunch of logic-level N-channel enhancement mode MOSFETs (try saying that 3 times fast), or P-channel, whatever. That way I know for sure I can drive whatever it is I need to drive. And if the MOSFETs get too hot even after putting a heatsink on them, you can always parallel them. Which gets me to thinking...have you tried paralleling a couple of L298N's? I haven't read the datasheet, don't know if it's possible (or even wise)...might work though.
And 12v @ 1.8a does = 21.6watts, but only if the L298N has resistance across it, zero resistance = zero load. Maybe the L298N isn't being driven hard enough. (Sounds like it's time to get my butt over to the datasheets so I know what I'm talking about here).
|
I have a big ass heat sink, about 9 times he size of the chip.
I believe I was under th wattage recommended (or maybe just on it, cause the battery was fully charged at 12.85 and @ 1.9 amp 24.7 watt.
would that of killed it.
I looked at comse circuit for making my own H-bridge, but is seems a bit messy.
I have some IRFZ44N N mos, maybe get their brother P's and work with that, you have any schematic ?
I found this: http://www.armory.com/~rstevew/Publi...d/nch-brdg.htm
but I dont know
update:
I tried one IRFZ44N , it become very hot with just 5watt. I know I can put a heat sink, but this thing is suppose to support 94 watt. Is there somehting I am not getting ??
Last edited by lerameur; - 15th January 2007 at 04:39.
|
to go back to my LCD problem , I am not using backlight. I thought you where refering to the contrast adjustment. nothing is connected to th backlight supply. IS this ,my problem , From the other post you mentionned, The gentlemen did not have a problen and the backlight was not connected. Mine does.
Last edited by lerameur; - 15th January 2007 at 05:51.
|
Well, like I said, the only way something can dissipate heat is if it has resistance in the first place, zero ohms across a device = zero volts dropped across it = zero watts dissipated in it. If that MOSFET is a standard MOSFET, and you're driving it with 5v, it isn't going to work very well. You need a logic level MOSFET, one that's designed to be driven with 5v. And monster heat sinks only work well up to a point. You can only get rid of so much heat so fast, they got limits too.
Why not post a schematic...we'll get a better idea of what you're up to. (on a side note, I haven't gotten over to the L298N datasheet yet).
|
well eventually I would like to use 15v at 2 amps, so that h-bridge might to be ideal for now.
To follow your idea on using MOSfet, I found a web site talking about the IRF540, which is very similar to the one I have IRFZ44N., Except they use Pmos also, I guess I can use 4 Nmos and using an inverter instead of using 2 Nmos and 2 Pmos.
|
B A
Sounds good, how about some "B/A" bypass capacitors, or snubber diodes to protect those transistors, motors throw off some outrageous spikes which may well cause your bridge to get "Kentucky Fried".
Always better, I think.
Last edited by Archangel; - 15th January 2007 at 20:40. Reason: Add
Members who have read this thread : 0You do not have permission to view the list of names.
Posting Permissions
Bookmarks