Hi, I'm new in here and my knowledge about electronics is very little. From time to time I have some small circuits to build and I like to do them, but other times I find only diagrams and I don't know how to read them and convert them to the board. I try hard but sometimes I get mixed up and even end up burning some components. The following is a simple diagram which I tried to read, but I would like someone to tell me if I've done this good or not.
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and this is how I thought it has to be connected
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This has to be fitted into a very small space, so I don't know if I can assemble it onto a strip board.
If you looked on the datasheet for the LM317 then you will see your circuit but it uses a more expensive LM117, not an LM317.
The LM317 needs to have a 120 ohm resistor and a 2.5k trimpot so its output voltage doesn't rise when there is no load.
You connected the trimpot wrong and did not connect the input ground to the output ground.
I need this circuit to use it with a 1.5Volts (max. 3V ) bulb or LED, so that it lights up to a full brightness at low voltage but when more voltage is applied it won't burn out. The maximum voltage to be used is not more then 16 VDC ( mostly it will be 14.8 VDC )
Kindly advise if this is still possible with the components I have at hand.
I need this circuit to use it with a 1.5Volts (max. 3V ) bulb or LED, so that it lights up to a full brightness at low voltage but when more voltage is applied it won't burn out. The maximum voltage to be used is not more then 16 VDC ( mostly it will be 14.8 VDC )
Kindly advise if this is still possible with the components I have at hand.
hi,
If the maximum voltage is say 15Vdc
Setup your LM317 to give say, +9V.
If the LED has a forward voltage drop of 1.5V at 20mA ,then you require a resistor in series with the +9V and the LED.
The value of the resistor is calculated as:-
Rseries= (9 - 1.5)/0.02 = 375hm: , nearest pref value is 390hm:
If you use a 3V LED operating with say 30mA
Rseries =(9-3)/0.03 = 200hm: nearest 220hm:
I assembled it as Audio showed me, ( cause I started before you posted yours Eric. It works, so to say with the bulb, but when I try to regulate the pot, it doesn't add light slowly, but sort of in steps, from dimm to bright, even if I just turn it a few millimeters.
I will try next adding the other resistor as you suggested
For a 3V light bulb to be dim then it needs about 2V.
Your circuit has an output voltage that will try to go as high as 28V. So 2V is turning the trimmer up only a few millimeters.
Look at the schematic on the datasheet that I attached. Its minimum input voltage is 28V when the resistor is 240 ohms and the pot is 5k.
When the resistor is 120 ohms then a 200 ohm pot will let the max output voltage be 3.33V and the minimum voltage is 1.25v.
Ok, this is done and works, but is there any other, more compact way of replacing this whole circuit. I am trying to put all this in a very tight place, and the only space I have is for a bulb and maybe a transistor.
I will use the above for other projects, but for the one I'm in at the moment, its too big.
Ok, this is done and works, but is there any other, more compact way of replacing this whole circuit. I am trying to put all this in a very tight place, and the only space I have is for a bulb and maybe a transistor.
I will use the above for other projects, but for the one I'm in at the moment, its too big.
but the resistors reduce the voltage, so if I make a reduction for teh 3V LED, it will only light up at its full brightness when the voltage is at 16 VDC*. I am applying this light to a voltage controller that goes from 0 to 16 VDC*, at 4 volts I have something else that will be activated, so what I want is for teh bulb or LED to be at full brightness before the controller is set to 4 Volts or higher.
but the resistors reduce the voltage, so if I make a reduction for teh 3V LED, it will only light up at its full brightness when the voltage is at 16 VDC*. I am applying this light to a voltage controller that goes from 0 to 16 VDC*, at 4 volts I have something else that will be activated, so what I want is for teh bulb or LED to be at full brightness before the controller is set to 4 Volts or higher.
OK this is nothing out of this world, the whole project is about a model Railroad. The loco engines normally have a 16 VDC lamp on them, but since the locos are never run at ful speed, but normally at the lowest speed ( approx 6 volts ) the lamps are very dim, and not realistic. So I wanted to create something to make this more realistic, and the first item that came to my head was teh above, actually someone suggested me to use a TO-92, but then this was rated in milliamps and was not good to light a 1.5V bulb.
Now there are people who run DCC layouts, but I'm still on manual and not looking forward for DCC, even because my layout is small and not worth investing in DCC. Certain engines then have very little and compact space in them, so there's not much possibility in placing large components in them, like one that I'm trying on, it only has a space for approx a transistor or 2 as an extra space inside.