DIY Audio Projects documents several DIY HiFi audio projects for Audiophiles. Projects include vacuum tube amplifiers, gainclones (chip amps), mosfet amps, preamplifiers, loudspeakers and audio cables. This is Constant current circuit using LED. Normally the voltage drop across LED while forward bias will be about 1.2 to 1.4 volts depend on type of LED. An explanation of what constant current sources are, and how to use an LM317 to build a constant current source that can power strings of LEDs and laser diod. LM3. 34 Constant Current Circuits Tutorialby Lewis Loflin. A constant current source (CCS) in electronics is a device/circuit that produces a constant value of current regardless of source voltage or load resistance. CCS circuit using a PNP bipolar transistor. The values of the Ic = Ib * hfe (Beta) of the transistor. A constant current circuit can also be used as a current limiter. Maxim Semiconductor notes the following on why we need to use a constant current source. Ib is controlled by a 1. K resistor and a 5. K potentiometer. With a Vcc of 1. Q1. We adjust the potentiometer for a base current of 3m. A (. 0. 03 Amps.) If Q1 has a hfe of 5. I came up with this idea, tested it and implemented it a while back, but I never got around to writing the article. So here’s the first new circuit article I’ve posted in well over a year. The basic idea is very similar to. The Safe constant current source. Figure 1 the below is a Safe constant-current source circuit, how it works? A cmos op-amp (number ICL 7611) controls the input current through a P-channel Hexfet power transistor (No. Hello, in this project i want to show you how to make a constant-current source which gives 20mA at the output. Its also known as LEd driver, because many leds need 20 mA to light up. The input of the constant-current source. Ic = . 0. 03 * 5. A or 0. 1. 5A. These circuits are a must for operating high- power light emitting diode (LED) arrays. The circuit above is simple, can be a little unstable due to temperature drifts with Q1 causing current drift. That problem is minor compared to power supply drift can cause far greater instability. Fig. 2 shows a more stable constant current source using a LM7. OP- AMP. The collector current Ic = (Vcc - Vref) / RE. In the example above with Vref = 1. V and RE= 1. 0 Ohms; (1. V - 1. 0. 5. V) / 1. A. This design is more stable due to feedback to pin 2 on the LM7. Q1. The 2. 0K pot can be replaced by fixed resistors. Big plus is Ic is not dependant on Q2 hfe - hfe is DC current gain. This was tested and worked well even down to 5- volts driving a white power LED at 1. A at 3. 2. V. The only weakness is current swings due to power supply changes. Constant current source circuits with a LM317 variable voltage regulator. These circuits are easy to build and inexpensive. I think these lamps come with a constant current driver of some kind already built in to them. In the data sheet I found here: http:// there is a somewhat cryptic blurb which reads. The world of electronics, which is driven by the needs of digital devices, generally requires its power in the form of regulated voltages, making voltage regulators both cheap and readily available. LEDs, however, are current. After reading the answers of two questions regarding the LM317, the answers made me think about whether I realy understand current source and current limiter. In this answer it says: The LM317.Fig 3 uses a LM3. A to 1. 0m. A as set by an external resistor Rset. The device operates as . Rset is the R1 and R2 combination adjusted for 1. Iset = Ib = 6. 7. V / Rset = 6. 77u. A. Ic = Ib * hfe; Ic = 6. A * 1. 80 = 1. 20m. A. See LM3. 34 Spec sheet. This is far superior to the two earlier circuits because power supply swings produced little measurable change in Ic. But the LM3. 34 suffers from a maximum drive current of only 1. A and there are many applications where far higher currents are need. In our next section we explore using the LM3. See LM3. 17 Constant Current Circuits.
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January 2017
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