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104 Threads found on edaboard.com: Across Led
The peak current is only 2mA if there are no voltage spikes on the AC. Voltage spikes will also arc across a little resistor that has a 250V absolute maximum voltage rating causing very high current in the led. I think you should rectify the AC, it feeds a series resistor with a capacitor to ground as a filter then another series resistor to feed
Hi, This solution doesn't use a PIR, but I can't think of any solution for what you describe... If the room only has one entry point, maybe an ir led across the doorframe could be used to latch on for entry and off for exit from the room.
Don't you think that when a transistor turns on then the current in the led attached to it is determined by the voltage across the resistor in series? The resistor is R1 and R4. You did not say your battery voltage. The kit says 3V to 15V. If you use a 9v battery then it is small so it will not last long. You need to look on the datasheet for yo
A narrow beam led is important. I sent signals from one to a photodiode across the room, several feet. I also mounted a magnifying glass in front of the photodiode. The setup worked fine.
Hi, 5V and 122 Ohms means 40mA. Find a PNP transistor with about >=100mA current rating and >=20 V voltage rating. And use a diode with about the same ratings. Use the relay and connect the diode across the coil. Cathode to + of coil, anode to - of coil. Connect - of relay coil additionally to gnd of your circuit. Disconnect the led. Connect the
A circuit diagram would avoid misunderstanding regarding to the depicted above, as for instance if you are using capacitors for softening the current pulses across the leds.
The losses due to light emission should be negligible, and the power consumption of the led can be took solely on the current across its terminals against its drop voltage. Even assuming that the OP is referring to a continuous operation ( not pulsed ), the power density over this sufrace size seems feasible to operate at the standard FR4 PCB i
This is basically a continuous Buck regulator switching oscillator than regulates the pulse width for an average DC voltage across Vbe controlled by D1 zener voltage , Vbe and Ie*Re and duty cycle. Offline buck designs have improved over this and work in principle like active PFC to provide a sinusoidal current fluctuating aro
What do you mean by "My circuit works on 5V. Controller works on 3.3V"? if you mean the leds are powered from 5V, consider that even if the PIC port pins are high (~3.3V) there is still 1.7V across the led which might be enough to light it. Brian.
I think any expectations for bright, long hours of storage and fit into a small space are not realistic. Even the smallest I would consider is too big for your application and too short a runtime. A CR-123A Primary Lithium 3.0V directly across 20mA = 60mW approx with compatible white led with only 65h expected life. using[URL="www.batte
Cool! Thanks to both! I was wondering whether it was safe to spike a little over max rating in a strobe application. Yes - these are 5W 700ma emitters. They don't have a lm rating, but I suspect it's ~ 200. That's good info about the human eye capability. As you say, each flash will be "on" for about a 6th of a second. My initial con
IS YOUR INDUCTOR CURRENT smooth? Have a look at the voltage across the sense it a regular triangle wave? If not then maybe you have instability. Sometimes, surface mount inductors cam make noise esp if the inductor current is not smooth.....also maybe the 1khz pwm may be making the inductor coils vibrate and make noise...maybe yo
You just have to check for the output current only. The voltage doesn't care, as the led will self adjust the voltage across its terminals. By using a PWM signal and using the output current as feedback signal you could accomplish your task (led dimming). Think about led as a simple diode - you don't have to set the (...)
I assume that your car is a small toy car because the leds will be VERY dim. You have 5 White(?) leds in parallel. A white led has a forward voltage of about 3.2V so the current limiting resistor will have 12V - 3.2V= 8.8V across it when the battery is 12V. Then Ohm's Law calculates the total current in the 1k resistor and (...)
As explained the voltage across a led is a crude way of controlling the current through it. Put a small resistor in series with the earthy end of the led and monitor the voltage across it, this will be proportional to your led current, which you want to stabilise. Frank
My question is related to thread . but since the thread is old i am starting a new one. I want to build a sensor using led so i need a constant brightness and temperature compensating driver (so no drift in wavelength with T) with a good precision. I have come across the CL2 series from Microchip (pre
I think a schematic would help but I'm guessing the issue here is the 12V relay and leds being mixed. For the relay to be used safely, the catch diodes in the ULN2003 should be connected to the relay supply (12V) so when connected to leds fed from 5V they forward conduct and leave 7V (12V- 5V) across the leds. The cure is (...)
Short answer: no. 5V (less the led drop) across 100K would only give you about 30 microamps. Unless you have an optocoupler that can work with this low current, you'll need to find another method. I'm not sure what you mean by "My scope is need to check the voltages". If you are using a scope, what do you need optos and rectifiers for?
It depends on whether your led shares a common anode or common cathode. The simplest scenario is you connect the leds to spare contacts on the relay. If the led is common anode, you could connect the common pin to the relay supply, one cathode through it's resistor to the collector of the transistor (so it is across the (...)
The only ways to do it are: 1. to pick up the original remote control codes on an IR receiver and use a logic analyzer to see what they are 2. open the remote control and connect the logic analyzer across the IR led. Each manufacturer and each equipment they make uses a different code system so trying to guess it when there are millions of combina