# HV9910B Driver

A offline LED constant-current driver and matching LED array / fixtures, based on HV9910B.

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## Notes

This is an **offline / mains** design. Do not work on the board while it is powered.

If you are not experienced with mains circuitry, **do not build this**.

**R6** is the current-sense resistor. Use a dedicated sense resistor with a low temperature coefficient. By changing **R6**, you can set the driver’s maximum current; the resistor value is inversely proportional to the maximum current. A practical range is 500mOhm < R6 < 2Ohm. If **R6** is too large, it may dissipate excessive power and run hot.

**R7** sets the driver’s off-time. Increasing **R7** increases the off-time (i.e., the off-time is proportional to the resistor value). A practical range is 200kOhm < R7 < 600kOhm. If **R7** is too small, the switching frequency may become too high and cause severe heating; if **R7** is too large, the frequency may drop into the audible range.

By tuning **R6** and **R7** together, you can adjust the LED’s maximum average current. In general, increasing the maximum current will increase the average current, while increasing the off-time will reduce the average current. Then use **VR1** for fine adjustment to match the LED’s recommended maximum current.

With the BOM configuration, the average current is about **225 mA** when **VR1** is fully counter-clockwise; after turning **VR1** clockwise by **10 turns**, the average current is about **150 mA**.