LED LED Tester, LED Tester
Keywords: LED LED Tester
A simple circuit described herein can quickly test the light emitting diode. And distinguish whether its type is low current or high power. The low current light emitting diode only uses a current of 1-2 mA, but only provides a relatively dark light: and high-power light-emitting diodes produce higher brightness with 10 mA or greater current.
also. When a circuit in which a plurality of light emitting diodes are simultaneously, these light-emitting diodes are required to emit the same brightness when a particular current. This requirement can also be checked by this test circuit: two or more LEDs are connected in series to facilitate comparison and select them.
In this circuit (see Figure 1), start with an adjustable current source. The current passing through a light emitting diode (or two tandem light emitting diodes) from O to 20 mA, depending on the brightness of the light-emitting diode, when the voltage meter changes from 0 to the highest volt value, you can judge your light-emitting diode. Which type is. A low current light emitting diode will make normal illumination when a smaller current, and does not become brighter when the voltage meter reading continues to increase; the opposite, high power light emitting diode will slowly Continue to increase brightness.
If you want to select the same brightness, you can connect two or more light emitting diodes. E.g. Checking the red light-emitting diode, when the voltage is 9V, you can even connect 4 light emitting diodes. It is easier to see the selection results. If necessary, you can increase the power supply voltage to the maximum value of 15 V (but not the two-section 9V battery series!). The maximum supply voltage allowed here is 16V here. At this voltage. You can compare 6 to 8 light emitting diodes (green, yellow and red). The maximum number of actual tests depends on the forward voltage drop of the test light emitting diode, the pressure drop in the white light emitting diode is approximately 3.6V, so you can only measure 3 at the same time when the power supply voltage is 15V.
Circuit Figure 1 consists of a classic current source (this current source is composed of a transistor and an op amp). The op amp IC1 sets the voltage drop of T1's emitter resistor R5 and the slider varistor P1 set a voltage comparison. The output voltage of the op amp drives the base of T1 after the R3 and the R4 voltage divider. The reason for choosing this divider is to reduce the risk of a potential failure: For example, when the output of IC1 exceeds the supply range, the current through T1 cannot be too high (up to more than 20mA a little bit). But pay attention to it! If you increase the supply voltage of the entire circuit, the maximum current through T1 will also increase the destructive.
Apply a voltage regulator diode D1 to obtain a reference voltage such that the voltage of P1 does not depend on the supply voltage. By controlling the current of D1 at about 1 mA, the stable voltage of D1 is only 4.2 V, rather than the nominal value of 4.7V. Now the voltage of P1 is about 1V.
Before assembling this resistor, you should pay attention to the actual value of the potentiometer P1. This type of potentiometer often has an ± 20% error. If your potentiometer deviation exceeds 5% of the nominal value, you can adjust the value of R2 in the same scale.
4.7V voltage regulatory diode (D2 and D3) is parallel with each of the measured light emitting diodes. These regulatory diodes are dual. On the one hand, when a light emitting diode is removed, a current passage flowing through other light emitting diodes can be maintained. On the one hand, when a light emitting diode is reversed. The regulator diode prevents the voltage of the light-emitting diode more than the maximum reverse cutoff voltage. This voltage is typically 5V, but sometimes it may be lower than this value.
Note: The best way to build this circuit is to use a small piece of energy circuit board because fewer components and the connection between them are easy to install. For convenience, the light-emitting diode is quickly inserted and removed, it is preferable to use two double-hole sockets as a connector.
The maximum current consumption of the circuit prototype is less than 23mA, and the current through R1 is 1 mA. Operation By connecting 8 foots to the voltage positive (set to a low power mode): The current is now consumed is only a micro-level.
If you want to use more light-emitting diodes while you can safely test, you can use a single, higher voltage to supply power, but please note that the pressure resistance of the transistor T1 cannot be exceeded. If necessary, when the T1 voltage is high, the power triode can be used and the heat sink is installed. However, don't forget to connect a regulated diode for each LED. This will be much safe.
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