One solution of zillions. Another advantage is that the power loss in the sense resistor can be reduced for both heating and power efficiency gains in higher power applications. Resistors One options I looked at is using 3 switching dc-dc converters, adjustable, one for each colour of LED chip, and adjusting them to just above the highest Vfwd of the 12 LEDs, and using resistors to limit the current. Boost converter current source for LEDs More than one reply has a recommendation to add an external mosfet. The only thing that is not quite nice with this solution that it might violate the maximum conditions of the ZXCT

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Oct 19, 4.

Boost supply to 2. Russell McMahon k 9 Check input voltage of the switchregulator feedback.

Not sure I’m experienced enough to diagnose any problems with it. I know this works on other constant current chips but they actually say in the data sheet that you can do it.

LED Driver Circuits

Does that make sense? The present is theirs; the future, for which I have really worked, is mine. Mar 1, Driving a 3W, 1. If you can select your supply voltage to be close to the forward voltage of the LEDs, then you can include a very small current limiting resistor, much smaller than you’d cutrent use. Annoyingly, I got home and tried my led driver out and my “1w led curgent is only putting out ma at 3v. As an example, consider driving a series of high intensity starleds at 1W each.


Dimming a 3W led using mc34063

There are other linear current source designs that require less drop over the current sensing resistor, as well. It is on the internet in a couple of places, and I’m not sure who to credit.

The resistor and the capacitor at the gate will determine the time it takes for switching just as above. I can not really figure out why the regulator does not limit the excessive current if you start with high current values.

Choosing a npn type would have been the wiser choice. So that kinda sucks. This one is intended to supply anything digital, using a voltage like 3. Minimum cost isn’t as important for this as efficiency, size and simplicity in that order.

From reading the datasheet, it looks like they should be able to operate with a supply voltage only 0. Oscilloscope readings show the comparator input node voltage just reaching 1. It’s a little more complex than a simple soft-start, but should give you some wiggle room to optimize for your application.


During start-up, the inductor is being charged with a current to ground and currdnt current is not going through your sense resistor.

Efficient constant-current regulator for ma LEDs – Electrical Engineering Stack Exchange

My benchtop power supply has a maximum current limit of 2A. Decreasing gain while the circuit is operating leads to an increasing in gain, and the output stays stable. In any case, would you possibly be able to elaborate why the latching occurs due to this?

Two suggestions have been made by other designers:. Oct 18, 2. During this time the feedback of the current sensor will slowly take over. I have modified the circuit to run current mode, using a ZXCT current sense amplifier and sense resistor.

Post as a guest Name. I independently arrived at a similar version – works reasonably well. Let’s get serial UT