Difference Between LED Driver Circuit and Bipolar LED Driver Circuit Explained

Hi!

I have recently read the following 2 posts:

1. "*LED Driver*(LED Driver Circuit)":http://www.electronicshub.org/230v-led-driver-circuit/

2. "*Bipolar LED Driver*(Bipolar LED Driver Circuit
)":http://www.electronicshub.org/bipolar-led-driver-circuit/

What is the main difference between these 2? Is it not possible to use Bipolar LED Driver circuit in place of normal LED Driver circuit?

What is the difference between Bipolar LED Driver and Bicolor LED Driver?

Can anybody give detailed explanation about it???

What Colin said!

I would only add that the *LED Driver* circuit [#1] is a terrible circuit! The final stage should be a current regulator, not a voltage regulator. Also, there is a vulnerability in that if, for some reason, the LED string suffers an open, or if the series resistance (R4) isn't set properly, the voltage at the input of the voltage regulator could exceed the max input voltage (35V for a TI part) and destroy the regulator.

In place of the 78L12 I would use something like the CL2N3-G -- a 20ma current regulator designed to drive LEDs. And it can withstand up to 90V across the device, so it is a lot less vulnerable to tolerances and instabilities, and, in fact, if there are enough LEDs in the string, you could drive them with just the bridge rectifier, the CL2N3-G and a filter capacitor [and you can eliminate the filter capacitor if flicker is not a problem].

So, in other words, if a CL2N3-G [or similar] is used in place of the 78L12, then, R1, C1, U1, C3, C4 and R4 could all be eliminated (as long as there are enough LEDs in the series string), and with just two LEDs (as shown), the following parts can be eliminated: U1, C3, C4 and R4. And, in both cases, if flicker is not an issue, C2 can also be eliminated.

Here's another good one (but, it's really meant to be used with a long string of LEDs since it's minimum supply voltage is 20V, so the sum of the forward voltages in the LED string should exceed 20V):

* HV9921N3-G [www.mouser.com/ds/2/391/HV9921-26434.pdf]

Also, check out my Blog all about linear solutions for driving low to medium current LEDs:

* www.sinistercircuits.com/Blog/LEDs_LightemWithoutSmokinem/index.php

The configuration used to drive a bipolar LED is an H-bridge, where the half-bridges are two push-pull outputs of one or more digital devices. While it is possible to drive a unipolar LED with an H-bridge, there is no benefit to having the voltage reversed on it and so one can save an output by tying the other end of the LED to either VCC or to ground, depending on which terminal is connected to the output.