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I have an LED backlight driver with 2 current sinks. Each current sink does not sink enough current to reach the max LED backlight current, so I want to combine them. Is it okay to drive a load, in my case an LED backlight, with parallel current sources? The circuit would look like something this -

schematic

simulate this circuit – Schematic created using CircuitLab

In reality the LED backlight is a bunch of LEDs in series and parallel, but for the sake of simplicity we can treat it as a single LED since the connector to the LED backlight consists of an anode and cathode pin. Are there any issues with this approach, such as unbalance or what not? To me I pretty much equate this approach to paralleling load resistors and it is pretty much just an application of the parallel current source concept, so I think it's fine, but I want to see if I am missing something.

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  • \$\begingroup\$ I don't see any problem. Unballance may be caused in LED matrix itself because of LEDs inequality. As I understand this backlight comes to you ready assembled and is not your problem. Another unballance may occur if current sinks are not equal, but as long as they can withstand supply's maximum voltage and power (voltage * sink current) you will be fine. \$\endgroup\$ – Todor Simeonov Jun 8 '17 at 16:11
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Yes, you can parallel current sources to get a combined current source that is the sum of the two. This is analogous to putting voltage sources in series to get a combined source that is the sum of the two voltages.

There is no issue of balancing the current sources. Each will sink the current it is set to sink. There is nothing wrong, for example, with combining 5 mA and 20 mA current sources to make a 25 mA current source.

One issue to watch out for is the compliance range of each current source. That is the voltage over which a current source still works like a current source. The voltage the two current sources settle at must be within the compliance range of both sources. If it's not, then at least one of them isn't a current source anymore.

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If the current sources employ a closed loop or have poor matching then you will need to add a small resistor on the high side of the current source to limit the current offset from the other supply. Check the datasheet or analyze the current source circuit and find how well matched the current source circuits are. If its just a transistor mirror it should be fine.

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