I need a circuit to indicate if the DC voltage across two points is exceeded a certain High value (350 V) by using LED as an indicator. For example if the voltage is 355 V then the LED will light,but if the voltage is 345 the LED won't light. thank you for helping me.
your sincerely Moad Nassar
Electronic – High voltage led detector
controldetectorindicatorled
Related Solutions
Sorry, Geremy, but you've misunderstood. The module you're looking at will simply not work well with the dimmer turned down. It will ALWAYS try to drive 1400 mA through your LEDs. If the input voltage is too low (because of your dimmer) it will get very unhappy and may do strange things.
The 17 to 29 volt range just means that it will successfully drive 1400 mA through an LED string when the voltage needed to produce that current varies between 17 and 29 volts. This voltage difference could be produced by differing numbers of LEDs in a string, or using the same number of LEDs, but of different colors.
As the earlier comments and answer pointed out, if you want an accurate indication of voltage level, you need an accurate reference.
The more normal method is to use a voltage reference and multiple comparitors or op-amps to compare your input voltages to the reference. The output of the comparitors or op-amps would then drive the LEDs.
However, there is a simple trick that is inexpensive and very simple. It works best with positive voltages but can be made to work with negative voltages with some effort. Because you want to measure only two positive voltages, I'll offer it as a solution for you.
It uses only 3 resistors, a LED, and a TL431 adjustable shunt regulator per voltage rail to be monitored. Very simple and quite accurate.
simulate this circuit – Schematic created using CircuitLab
The TL431 is normally intended to be an adjustable shunt regulator - sort of an adjustable zener diode. It contains an accurate 2.5V reference and is normally configured so that the cathode connects to the voltage to be regulated.
But it will happily run open-loop. In that case, the TL431 has a high impedance from the cathode to the anode so long as the adjust pin voltage is less than the internal 2.5V reference. When the adjust pin voltage is more than the internal 2.5V reference, the cathode has a low impedance between itself and the anode.
It is that low impedance that turns the LED ON.
You will need to set the voltage divider ratio on the adjust pin so that the TL431 conducts when the input voltage is above your desired value.
Duplicate the circuit for each voltage rail to be monitored.
Best Answer
What you want is a simple comparator. However, neither LEDs nor comparators run at 350 V. You therefore need to divide down the input voltage to something in the range of what a comparator can handle.
Let's say you use a 9 V battery to power your detector. You can make a 3.3 V reference from the 9 V battery with a single cheap chip and use that as the threshold voltage.
A simple resistor divider can scale 350 V down to 3.3 V. The top resistor needs to ideally be 105.1 times the bottom. If you make the top 10 MΩ, for example, then the bottom resistor must be 9.52 kΩ.
Many comparators are available with open collector outputs. Arrange the output to go low when input voltage is above the threshold. Connect the LED in series with a resistor between the 9 V battery and the comparator output. Let's say you are using a red LED and want to run it at 20 mA. That will drop about 1.8 V, leaving up to 7.2 V across the resistor. By Ohm's law, the resistor should be (7.2 V)/(20 mA) = 360 Ω. Just be safe, I'd use the next higher common value of 390 Ω.