Question about the current generated by charge pump in LED driver circuit

[lhlbluesky]

in LED driver circuit,a charge pump is normally contained;i want to ask,what's the current generated in charge pump(in the output end of charge pump)?is it an average current or a pulse current?if it is a pulse current,what's the amplitude and period?and how to model the current when simulation?

 

[020170]

Re: LED driver problem

Typically, Cahrge Pump output current was sustained during normal operation.

Charge pump can generate higher voltage more than input voltage.

Charge pump charge the voltage you want into load "in a half cycle" and discharge the other half cycle.

Because discharge duty period was too short, charge pump can sustain the output voltage.

Because charge pump sustain the output voltage, output current of charge pump was not fluctuant. (if not change load condition)

 

[rfzheng]

LED driver problem

it is a pulse current at the charge pump output end,this pulse current is used to sustain the output capacitor voltage which is decided by the feedback loop. the pulse current width is decided by the flying capacitor discharging with the power switch on resistance . normally we use average current model to analysis the charge and discharge in the charge pump, but actually it does not indicate the transient state of the current and voltage.

 

[flatulent]

Re: LED driver problem

If the frequency is high enough, your eye will not notice the flicker in the LED if the current is not continuous.