Heavy current high speed switching - Electronic Circuits Projects Diagrams Free

jbelectric777 · 19th May 2007, 03:05 AM

Hey Everyone,

I am building a PCB for flashing headlights on my freinds vehicle (he is a volunteer fireman) I am using a basic 555 timer with a 1Kuf capacitor and a 300 Ohm resistor for the flash timing. I utilize the high and low states of the 555 and thats o.k when using LED's because the polarity can be reversed. Now I want to use (2) 555's and switch the headlight lamps (wig-wag) ... I don't think a PCB miniature relay could switch that fast, and even if it could it would'nt last very long. Now I am hoping someone can help me find an IC or other component that is capable of switching heavy lamp loads very fast and can do it by the 555 pulse I send to it. All suggestions appreciated very much. Jim P.S I pondered the idea of having enough 555's in paralell to handle the load but that would be a heck of a lot of timers because I think they are maxed at 200ma.....

audioguru · 19th May 2007, 03:24 AM

555s in parallel would fight each other then blow up.

A 555 can drive a Mosfet that can switch very a high current light. Then an inverting transistor and another Mosfet can drive the other light as a wig-wag.

jbelectric777 · 19th May 2007, 03:29 AM

Would'nt want a meltdown ! I'll look into MOSFET's , do you suggest any certain type ? Or should I just go by the load it's serving ?

audioguru · 19th May 2007, 03:56 AM

Over-rate the current for the Mosfet because an incandescent light bulb draws up to 10 times its rated current when it is cold. Its filament gets pretty cold between flashes.

jbelectric777 · 19th May 2007, 04:15 AM

60-100V 5A ( IRF510 ), That should do it, ya think ? and one more thing scrooge, should I put capacitors across the lamps ? Or dont I need em... and if I do what size ?Thanks again

jbelectric777 · 19th May 2007, 04:36 AM

I just checked the data sheet, I don't think the 510 will work because I am only looking at 12V switching voltage and mv gate voltage ? Goin to bed I'll check more in morning, any suggestions ? Thanks

Hero999 · 19th May 2007, 09:59 AM

Quote:

Originally Posted by audioguru

555s in parallel would fight each other then blow up.

It is possible to connect 555s in parallel but you hve to parallel all the pins and a small current balancing resistors in series with the outputs are still a good idea in case the comparators have slightly different switching levels.

**Nigel Goodwin** · 19th May 2007, 10:14 AM

Quote:

Originally Posted by Hero999

It is possible to connect 555s in parallel but you hve to parallel all the pins and a small current balancing resistors in series with the outputs are still a good idea in case the comparators have slightly different switching levels.

But it's a completely pointless, really stupid, thing to do!

Russlk · 19th May 2007, 02:16 PM

Quote:

Originally Posted by jbelectric777

60-100V 5A ( IRF510 ), That should do it, ya think ? and one more thing scrooge, should I put capacitors across the lamps ? Or dont I need em... and if I do what size ?Thanks again

NO capacitors! you already have a problem with high peak current, don't make it worse. The headlamp draws several amps, so look for a mosfet rated 20 amps with low Rds(on).

audioguru · 19th May 2007, 02:24 PM

A car's headlight is 60W isn't it? Then its current at 13.8V is 4.3A when it is hot, and maybe 43A when it is cold.

An IRF510 Mosfet is very old and cannot switch such a high current.
An IRF540 Mosfet is also pretty old and fairly cheap and conducts 11 times better.
There are hundreds of newer and better Mosfets. The IRFZ44 has a max current rating of 200A for pulses and a max on-resistance of only 28 milli-ohms. If it has the proper driver circuit then it would do a good job to flash headlights.

jbelectric777 · 19th May 2007, 02:46 PM

Will the MOSFET's you all mentioned switch the low 12V ? Thats where I am confused , the datasheet states 60-100V does that mean max value ? Because I saw (on the spec sheet ) minimum V as 60..... So I just need to know if the one you said was better to use will switch 12V Thanks, Jim

audioguru · 19th May 2007, 02:56 PM

The max voltage rating of a Mosfet is the max voltage allowed. A higher voltage will break it. It will switch a voltage as low as 1V.

**Nigel Goodwin** · 19th May 2007, 03:26 PM

Considering this is a fairly 'important' function, and the OP doesn't seem exceptionally electronics minded, I would suggest the easiest (and most relaible) way would be a 555 timer feeding a transistor and car type relays - minature relays are probably too small. Flashing speed isn't a problem, it has to be fairly slow due to the thermal inertia of the bulbs - car relays will be more than fast enough.

justDIY · 19th May 2007, 04:54 PM

JB,

this thread I wrote a while back may be of interest to you. the circuit was originally designed to flash led tail-lights, but choose the right mosfets and it should be able to switch headlights just fine.

http://forums.linear1.org/index.php/...9.html#msg5129

jbelectric777 · 19th May 2007, 05:34 PM

Thanks for all your help..... much appreciated..

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19th May 2007, 03:05 AM	(permalink)
jbelectric777	Heavy current high speed switching Hey Everyone, I am building a PCB for flashing headlights on my freinds vehicle (he is a volunteer fireman) I am using a basic 555 timer with a 1Kuf capacitor and a 300 Ohm resistor for the flash timing. I utilize the high and low states of the 555 and thats o.k when using LED's because the polarity can be reversed. Now I want to use (2) 555's and switch the headlight lamps (wig-wag) ... I don't think a PCB miniature relay could switch that fast, and even if it could it would'nt last very long. Now I am hoping someone can help me find an IC or other component that is capable of switching heavy lamp loads very fast and can do it by the 555 pulse I send to it. All suggestions appreciated very much. Jim P.S I pondered the idea of having enough 555's in paralell to handle the load but that would be a heck of a lot of timers because I think they are maxed at 200ma..... __________________ "Yesterday is History, Tomorrow's a Mystery"

19th May 2007, 03:24 AM	(permalink)
audioguru	555s in parallel would fight each other then blow up. A 555 can drive a Mosfet that can switch very a high current light. Then an inverting transistor and another Mosfet can drive the other light as a wig-wag. __________________ Uncle $crooge

19th May 2007, 03:29 AM	(permalink)
jbelectric777	Thanks Would'nt want a meltdown ! I'll look into MOSFET's , do you suggest any certain type ? Or should I just go by the load it's serving ? __________________ "Yesterday is History, Tomorrow's a Mystery"

19th May 2007, 03:56 AM	(permalink)
audioguru	Over-rate the current for the Mosfet because an incandescent light bulb draws up to 10 times its rated current when it is cold. Its filament gets pretty cold between flashes. __________________ Uncle $crooge

19th May 2007, 04:15 AM	(permalink)
jbelectric777	Irf510 ? 60-100V 5A ( IRF510 ), That should do it, ya think ? and one more thing scrooge, should I put capacitors across the lamps ? Or dont I need em... and if I do what size ?Thanks again __________________ "Yesterday is History, Tomorrow's a Mystery"

19th May 2007, 04:36 AM	(permalink)
jbelectric777	I just checked the data sheet, I don't think the 510 will work because I am only looking at 12V switching voltage and mv gate voltage ? Goin to bed I'll check more in morning, any suggestions ? Thanks __________________ "Yesterday is History, Tomorrow's a Mystery"

19th May 2007, 02:24 PM	(permalink)
audioguru	A car's headlight is 60W isn't it? Then its current at 13.8V is 4.3A when it is hot, and maybe 43A when it is cold. An IRF510 Mosfet is very old and cannot switch such a high current. An IRF540 Mosfet is also pretty old and fairly cheap and conducts 11 times better. There are hundreds of newer and better Mosfets. The IRFZ44 has a max current rating of 200A for pulses and a max on-resistance of only 28 milli-ohms. If it has the proper driver circuit then it would do a good job to flash headlights. __________________ Uncle $crooge

19th May 2007, 02:46 PM	(permalink)
jbelectric777	o.k now the big question Will the MOSFET's you all mentioned switch the low 12V ? Thats where I am confused , the datasheet states 60-100V does that mean max value ? Because I saw (on the spec sheet ) minimum V as 60..... So I just need to know if the one you said was better to use will switch 12V Thanks, Jim __________________ "Yesterday is History, Tomorrow's a Mystery"

19th May 2007, 02:56 PM	(permalink)
audioguru	The max voltage rating of a Mosfet is the max voltage allowed. A higher voltage will break it. It will switch a voltage as low as 1V. __________________ Uncle $crooge

19th May 2007, 03:26 PM	(permalink)
Nigel Goodwin	Considering this is a fairly 'important' function, and the OP doesn't seem exceptionally electronics minded, I would suggest the easiest (and most relaible) way would be a 555 timer feeding a transistor and car type relays - minature relays are probably too small. Flashing speed isn't a problem, it has to be fairly slow due to the thermal inertia of the bulbs - car relays will be more than fast enough. __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk

19th May 2007, 04:54 PM	(permalink)
justDIY	JB, this thread I wrote a while back may be of interest to you. the circuit was originally designed to flash led tail-lights, but choose the right mosfets and it should be able to switch headlights just fine. http://forums.linear1.org/index.php/...9.html#msg5129 __________________ If you don't have a planet, what good are gold bars? want to contact me directly? gmail gordonthree check out my project website: http://projects.dimension-x.net Favorite numbers: 09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0

19th May 2007, 05:34 PM	(permalink)
jbelectric777	Thanks Everyone Thanks for all your help..... much appreciated.. __________________ "Yesterday is History, Tomorrow's a Mystery"