Dimming of no dimming led driver - Page 1
Forum section: electronics / beginners

author: Miha
author_rank: Contributor
timestamp: May 25, 2023, 09:16:39 am
content: Hello.I have 230V 200W led driver for led lamp.The driver has no control (dimming) wire, but I need to dimming the lamp.Can the schematic in the picture works good?Can there be problems with the driver?Are there any other options for dimming besides replacing the driver?

author: tszaboo
author_rank: Super Contributor
timestamp: May 25, 2023, 10:20:34 am
content: LED driver is a current source. So if you disconnect the output, the voltage will rise, in theory. I don't think the driver or your dimming circuit will like that.

author: Miha
author_rank: Contributor
timestamp: May 25, 2023, 10:52:23 am
content: The driver, like this:https://www.inventronics-co.com/wp-content/uploads/2021/03/DS-EAM-200SxxxSB_Rev.A.pdfYes, when disconnect the output of driver, voltage will be rise, like in DS (page 2). There is limit of output voltage. So, MOSFEET should be high voltage (300 V, or more).Proposed output dimming is not usual driver mode of operation. I do not know, can this dimming method reduce lifetime of driver or lamp?

author: Doctorandus_P
author_rank: Super Contributor
timestamp: May 25, 2023, 03:47:48 pm
content: It does not look like a good Idea to make that.The result will be somewhere between "it works", and "it smokes", depending on how that driver is made.I suggest you use this driver for some other light, and get another driver that is suited for dimming for this application.

author: Zero999
author_rank: Super Contributor
timestamp: May 25, 2023, 09:31:49 pm
content: It's generally a bad idea to hot plug, i.e. disconnect and reconnect an LED to a constant current driver, whilst it's on, which is why your circuit does. The output voltage will rise, when the LED is disconnected and a large current spike will occur, when it's reconnected. You could try shorting instead, but then you have a high current spike through the MOSFET and the supply in question is only designed to work properly over a certain output voltage range.This isn't the answer you're looking for, but there's no way to reliably get this LED driver to dim the LED, without breaking into it and that's not recommended. The easiest solution is to buy an LED driver which can be dimmed.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: May 25, 2023, 09:47:13 pm
content: terrible idea. get a proper dimmable driver.

author: Zero999
author_rank: Super Contributor
timestamp: May 26, 2023, 10:08:58 pm
content: Quote from: mikeselectricstuff on May 25, 2023, 09:47:13 pmAgreed. The original poster needs something like this.https://www.mouser.co.uk/ProductDetail/MEAN-WELL/XLG-200-L-AB?qs=sGAEpiMZZMvV8Y9YugmIggXPjVR9iwOZ%2Fse8APZhuLj48O7SpkT3wQ%3D%3DIt can be dimmed with 10V PWM, a 100k variable resistor or 0 to 10V.I've used the following circuit to dim it using 5V PWM. The opto-coupler is a APV1121, which has a photovoltaic output of 8.7 to drive a J-FET. The J-FET is normally open device. It has a negative gate voltage threshold i.e. it's normally on and turned off, when the gate voltage is taken negative, with respect to the source. This inverts the 5V PWM signal, giving -8.7V, when input is 5V and 0V, when it's off. The LED driver has an internal 100µA current source. When the J-FET is on, its resistance will be tens of Ohms, so the volt drop will be near zero. When the J-FET is off, the 100µA source will see 100k and generate 10V. The LED driver internally filters the PWM to generate a smooth current for the LED drive.https://docs.rs-online.com/0444/A700000009081197.pdf

author: Miha
author_rank: Contributor
timestamp: May 29, 2023, 06:16:46 am
content: Zero999Control schematic is very interesting.But, for what using of so difficult schematic, if led driver already have opto-decoupling?

author: Zero999
author_rank: Super Contributor
timestamp: May 29, 2023, 09:17:10 am
content: Quote from: Miha on May 29, 2023, 06:16:46 amThe purpose of the opto-coupler is to generate a negative voltage from the PWM, to bias the J-FET off. I wouldn't say it's difficult, just four parts. PC1 looks complicated because I drew models of the internal circuitry, so I could simulate it.

author: Miha
author_rank: Contributor
timestamp: May 29, 2023, 10:05:17 am
content: Quote from: Zero999 on May 29, 2023, 09:17:10 amThe question was, why even use additional opto-isolation (4 extra components), if the LED driver already has opto isolation at the dimming inputs?The driver you specified requires to dimming 10V PWM.Is your control circuit not have a 10V source?

author: Zero999
author_rank: Super Contributor
timestamp: May 29, 2023, 07:01:13 pm
content: Quote from: Miha on May 29, 2023, 10:05:17 amThe opto-coupler isn't used for isolation. The control circuit doesn't have a 10V source. It's just 5V PWM from the microcontroller. The opto-coupler is purely there to drive the J-FET, which requires the gate voltage to be below the source, to turn off. It is possible to use an enhancement MOSFET, such as the 2N7002 and no opto-isolator, which would simplify the circuit, but the downside is it would reverse the logic and if the microcontroller were turned off, it would default to full brightness. This might not be a problem for your application, but I wanted the LED to be off, when the control signal is lost.