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15v 150w Lamp Dimmer problems.

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sccs

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Hi guys,

ive been using PWM DC Motor Controller for a while now as a fan controler and small lamp dimmer and i must say works great.

my problem is i now find myself with the need to add a dimmer to a 15v 150w lamp.
to be totally honest im stumped as to where to go from here, from my reading im thinking i need to add a darlington pair to the output to allow the control of the lamp. problem is i havent got a clue where to start looking.

the supply to the lamp is AC altho i can convert to DC if easier

any help or if you have a better way to do it im open to ideas.
 
Hi guys,

ive been using PWM DC Motor Controller for a while now as a fan controler and small lamp dimmer and i must say works great.

my problem is i now find myself with the need to add a dimmer to a 15v 150w lamp.
to be totally honest im stumped as to where to go from here, from my reading im thinking i need to add a darlington pair to the output to allow the control of the lamp. problem is i havent got a clue where to start looking.

the supply to the lamp is AC altho i can convert to DC if easier

any help or if you have a better way to do it im open to ideas.

A 15 volt 150 watt lamp would be 150 / 15 = 10 Amps @ 100%. The MOSFET called out in your link as Q1 is a STP36NF06L MOSFET LOGIC N 60V 30A which with an adequate heatsink should drive your 15 volt 150 watt lamp if the 12 volt supply were increased to 15 volts.

A standard lamp filament type will not care if it is powered from an AC or DC source.

Ron
 
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Hi Ron.

thanks for the quick reply. i have been using 2n3055's in place of the STP36NF06L and so far all is well.
but when i tried it first time with the lamp it some how fried the pic and the 2n3055, both instantanly got super hot
looks like ill have to get some STP36NF06L. and try again
 
For PWM apps like this, run with the MOSFET. Nice thing about the one called out is it is a logic level MOSFET meaning the 5 Volts from your PIC to the gate will turn that sucker on all the way as in right now and that is what you want for PWM. While the old 2N3055 is a good power transistor and will handle a 15 amp collector current you likely were not getting it into saturation. That caused the 3055 to get hot and the needed base current was likely giving your PIC a PIC fit. The total power dissapation of the 3055 is only 150 watts also. I believe if you use the suggested or like logic level MOSFET capable of the needed current with a good heat sink things will work out fine.

Ron
 
Great thanks. when i first used the circuit i couldnt find the STP36NF06L localy, and didnt have facility of rs/farnell, but had a bunch of 2n3055 lying around,
currently ordering them on rs/farnell once i work out what else i need to order to get min order value.
heat sink wont be a problem as i have a giant one from an old psu to bolt it to once its done.

thanks again for the help, turned out was much easier than i thought.
 
Should work out fine.

Ron
 
the STP36NF06L and other parts arrived this am,
and not that i didnt trust you;) but its working fine.

i have another question, whats the best way to convert ac-dc,
atm im using a bridge rectifier but pulling 10A through it is making it hot,
this and the heat from the mosfet is alot of extra heat, whilst this is not a problem
it does make me wonder if there is a better way to do it.

Thanks again.
 
With only 15 volts and 10 amps you have to pay attention to voltage drop. A bridge rectifier will have two diode drops so you lose about 1.7 volts from the AC supply to start with. The bridge rectifier will dissipate about 15 watts which requires a good sized heat sink.

With 5 volts gate drive the Rs of the STP36NF06L is about 0.045 ohms so MOSFET will dissipate (10A^2) * 0.045 ohms = 4.5 watts and will have a Vds voltage drop of 0.45 volts.

So you have about 2.15 volts drop. You can do as good, maybe slightly better, with a triac dimmer approach.
 
Since I don't know what bridge you are using I can't say much but just make sure the MOSFET and Bridge are well heat sinked and rated for the load. I know the MOSFET is.

Ron
 
The bridge is a KBPC2501, 25A so should be plenty, i have run the lamp through the bridge prior to adding the dimmer and it did get hot but worked fine.

going to sink it all up in a bit and give it a proper test.
 
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