Home     Forum     Projects     Experiments     Circuits     Theory     BLOG     PIC Tutorials     Time for Science

### Author Topic: kids oven and stove led circuit  (Read 11917 times)

0 Members and 1 Guest are viewing this topic.

#### kam

• Hero Member
• Posts: 1849
##### Re: kids oven and stove led circuit
« Reply #15 on: September 06, 2015, 16:31:42 PM »
which circuit are you talking about?

#### EricD

• Newbie
• Posts: 25
##### Re: kids oven and stove led circuit
« Reply #16 on: September 08, 2015, 04:05:08 AM »
http://www.pcbheaven.com/circuitpages/Simple_Linear_Fan_Controller/

It's in fact a 8-12v and not 5-12v so i'll need to decrease R3 for sur but what about the rest? (As asked in my previous post)

#### kam

• Hero Member
• Posts: 1849
##### Re: kids oven and stove led circuit
« Reply #17 on: September 08, 2015, 16:35:07 PM »
using the pot like i do with the 3 pins, it is an effective voltage divider. R2 is used to prevent overcurrent through the transistor when the pot is set to max voltage. R3 is used to unbalance the pot-voltage divider and thus set a minimum voltage other than 0 volts.

#### EricD

• Newbie
• Posts: 25
##### Re: kids oven and stove led circuit
« Reply #18 on: September 09, 2015, 06:20:23 AM »
My DC power supply is 12.2V. I'm using a 4.7Kohm pot with a switch that I want to enable so the circuit is off. I guess that my + wire will enter one side and a jumper wil go from the exit to the right pin.

The pot have in fact 4.3Kohm when test with my multimeter. R1 is 222ohm for 11.70V max output and R3 is 916ohm for 6.4V min output. I started decreasing R3 from 3.3Kohm giving 8.7V and tried different resistors.

My transistor is an LM317T so at first I tough that it was the reason why I was having an higher minimim voltage output but a 1.5Kohm resistor still gave me 6.85V. I tried with a 560ohm but the output rise so i'm scratching my head right now.

Each circuit of the stove will power 24 smd led (3528) for 167mA of current. Each series ofn3 led have a 330ohm built in smd resistor.

#### kam

• Hero Member
• Posts: 1849
##### Re: kids oven and stove led circuit
« Reply #19 on: September 09, 2015, 17:15:20 PM »
Oh! The LM317 is not a transistors, it is a linear regulator...

http://www.st.com/web/en/resource/technical/document/datasheet/CD00000455.pdf

#### EricD

• Newbie
• Posts: 25
##### Re: kids oven and stove led circuit
« Reply #20 on: September 09, 2015, 17:31:36 PM »
That's probably why my output is very stable  . Im using 2x .1uf ceramic capacitors btw. It have his own resistance but i can't remember the number i had yesterday. I'll check tonight.

#### EricD

• Newbie
• Posts: 25
##### Re: kids oven and stove led circuit
« Reply #21 on: September 10, 2015, 04:46:32 AM »
Ok I think that i have everything in place to do something great buddy!

I switch the LM317T for one of my TIP121 and manage to drop the voltage to 4.8V. I jump the output of the emitter to the fade in/fade out simple circuit as my voltage input.

Doing this I've notice that under 6.8V it doesn't look good so I put my LM317T back in place with a 1.5kohm since it was giving me the perfect match.

I'll send some pics and/or a link to a video to show you the result.

#### kam

• Hero Member
• Posts: 1849
##### Re: kids oven and stove led circuit
« Reply #22 on: September 10, 2015, 20:26:40 PM »
a video would be great!

#### EricD

• Newbie
• Posts: 25
##### Re: kids oven and stove led circuit
« Reply #23 on: September 11, 2015, 05:31:51 AM »
With the LM317T the voltage go directly to the other circuit (fade n delay) or maybe i did something wrong when wiring.
So I placed 2 tip121, one for each circuit but I lose 2V at the max output. Another thing is the instead of being lit just a bit at 6.8V (my min output) it drop somewhere aroud 5V.

I'm wondering why they turn on at a different voltage now and what would happen if I place the LM317T on the fade circuit, will it work better?

It's not perfect and I know I can improve it but i'll solder some parts so they hold together in i'll film the rough results i'm getting at the moment.

#### kam

• Hero Member
• Posts: 1849
##### Re: kids oven and stove led circuit
« Reply #24 on: September 15, 2015, 08:10:32 AM »
The voltage loss is normal with this circuit and cannot be avoided. You should consider a 1.4V drop so if you want max 13v output use 13.4v supply voltage.

You cannot replace the transistor with the lm. But you cannot use the lm differently.Google "lm317 variable voltage regulator". Stop you will get a voltage drop due to the forward diode bias inside the transistor. The lm requires 3 volts to regulate.

#### EricD

• Newbie
• Posts: 25
##### Re: kids oven and stove led circuit
« Reply #25 on: September 16, 2015, 02:24:15 AM »
Yeah I should use a LM2941 which is a low drop out. There's is a way to use the 317 without the 1.5volts drop but it would not stabilize the voltage. (3v drop is for 40v in)
I've been able to do it by changing the pot to a 1k and use a 160 ohm near the LM and a 540 ohm near the ground.
when I add the led the minimum voltage rise higher, it reach around 7.5. I change the setting to "do as if" I want a 3.5v minimum so it was 5.5v with the led.
My max was at 11.something but with the led they don't have the reach 12v to glow at full intensity.

Since the led intensity is decided by the current running through them would it be better if I use the LM317T as a current regulator match with a 7.5 ohms (165mA) and a 470ohms pot (or less)? If so, can it still fits with your fade circuit?

I also bought pwm555 in case. I'm new to electronic* so I don't know what would be the best option for the greatest result.

*If you don't consider the strobe and lights modulator I make in a high school class when I was 16. (Secondaire 4 here in Quebec)
« Last Edit: September 16, 2015, 07:02:50 AM by EricD »

#### kam

• Hero Member
• Posts: 1849
##### Re: kids oven and stove led circuit
« Reply #26 on: September 16, 2015, 08:42:09 AM »
Pwm solution has almost 0 voltage drop, so you feed 12 you get 12. You can use my high speed 555 pwm driver in my circuit pages and win the match.

As for the current regulator... The strips are designed to operate at 12v without current regulation. Nevertheless you can make a current source to get linear light intensity regulation (current to lumens led characteristic is a straight line) but why bother? You can use the midget linear regulator for your tests. You can find the circuit in my theory pages about linear led drivers

Pwm is the ticket though.

#### EricD

• Newbie
• Posts: 25
##### Re: kids oven and stove led circuit
« Reply #27 on: September 16, 2015, 23:52:04 PM »
Ok i can go with pwm555 but how will i have a delay and fade in/out plus a brightness regulator.

I'll check the stuff in your pages but I dont know how everything will fit together inside one single circuit.

#### EricD

• Newbie
• Posts: 25
##### Re: kids oven and stove led circuit
« Reply #28 on: September 17, 2015, 06:59:39 AM »
Well it does work with an ajustable current regulator and almost perfectly to tell the truth. I even add it after your 1st fade in/out circuit.
The emiter of the TIP121 goes to the Vin of my LM317T and at the Vout there's a fix 16 ohms in serie with a 470ohms pot. The left and center pins are join together and the right pin have a wire to feed the leds and another one attached to the LM adjustment pin. The switch on the pot is used to break the +12V that runs from the supply to feed the base and gate of your circuit.

The downside is that when turned on or off I have a delay and the max brightness is also lower due to the currect that is cut-off by the TIP121 (I think).
I've also notice that when I change the intensity slowly the leds just follow the pot. When tried faster a fade is noticeable but too fast will created sudden drop in brightness before it catch back.

I want to give a try with the 555 but as said in a previous post I wondering how to do both things at the same time. Something was telling me that grabbing 556 would be a good idea.

#### EricD

• Newbie
• Posts: 25
##### Re: kids oven and stove led circuit
« Reply #29 on: September 19, 2015, 05:27:24 AM »

The downside is that when turned on or off I have a delay and the max brightness is also lower due to the currect that is cut-off by the TIP121 (I think).
I've also notice that when I change the intensity slowly the leds just follow the pot. When tried faster a fade is noticeable but too fast will created sudden drop in brightness before it catch back.

In fact the downside is not the delay cause it's what I was looking for.
The lower brightness at max can be easily fix by replacing the fixed resistor for a lower value and regain what is lost by th e circuit's components.

The real problem is:

■ When to brightness value change quickly the leds have a "drop".
● By reading your article I came across something about fixing the voltage to have a more stable circuit. Since I'm using a linear regulator I want to know if this apply to me. ?Will it stop dropping if I fix the voltage of LM317?
?Will I have to recalculate the resistors for the adjustable current regulator?
?Will the leds still reach full brightness?

■ If the pot position is change the lights instantly changes.
● Is it possible the have them fade from A to B slower than to movement on the pot?
● If yes, what are my options?
? Bigger capacitance or the parrallel resistor higher value.
? Having the capacitor discharge after a delay and fade is complete.
? Adding new stuff to improve the circuit.

Thanks!