How do I reduce EMI radiation?
Slowing down the switching decreases edge rates, which helps to reduce high frequency energy blasts, especially relevant to radiated emissions. Try increasing the gate resistor, often called R13 in JST schematics. Also, try putting a snubbing network around the main diode, often called D5 in JST schematics. Line input filter networks also help to reduce both common-mode and differential-mode conducted noise. Please refer to JST reference schematics for examples.
Improve the layout. Tightening high-frequency current loops helps to reduce radiation, but also helps to reduce noise that interferes with circuit operation.
Use a magnetically shielded main power inductor and place noisier components away from sensitive circuit nodes.
How do I adjust the output current level?
The sense resistor (R7) is the coarse adjustment for current level.
- Lower R7 to lower the power.
- Increase R7 to raise the power.
The SNS divider pulldown resistor (R25) provides a fine adjustment.
- Lower R25 to adjust the power upwards.
- Increase R25 to adjust the current downwards.
Increasing the ITH divider pulldown resistor (R17) will also increase the output current. Please note, however, that as ITH approaches 1.5V (associated with the clamping limit on SNS ~150mV), the degree of clamping changes strongly with changes in R17. With more clamping, the line regulation is better, but the power factor is worse.
Once R17 is set for the right level of clamping, we generally use R7 or R25/R27 to scale Po in order not to affect the relative amount of clamping.
Jade Sky Technologies provides a software tool to help simulate the effects of these changes before trying in the lab.
Are any external short circuit protection (SCP) circuits required for the JST301?
No, SCP is already built into JST products. A supplemental SCP circuit (available in application note AN-10-21-SCP) helps to reduce' short circuit input current further in applications that demand very tight levels of protection.
How do I adjust my JST301 driver circuit to work with my triac dimmer?
Depending on the driver topology, input voltage, power level, and LED configuration, adjustments to the JST301 circuit may be needed to maximize dimmer compatibility. Application note AN-10-32 explains in detail the typical driver circuit adjustments that can be made, depending on the observed issues.
Where do I measure power factor?
Please measure power factor at the input of the LED driver board. Power factor at the input of a dimmer will include effects of LED driver and dimmer. Measurement after the dimmer, at the input of the driver board provides the definitive, unambiguous quantitative effect of the Jade Sky driver. Please see application note AN-1-9 for more information.
What inductor or transformer do I use?
Jade Sky provides a spreadsheet-based tool that allows entry of typical application parameters such as input and output voltage, power, current, etc. This spreadsheet tool offers estimation of current levels both RMS and peak for inductor (or transformer), diode, and switching MOSFET. Calculations include inductance value (buck, buck-boost, boost), and primary inductance and turns ratio (transformer). The resulting output from this spreadsheet directly leads to choice of commercially available magnetics component, or in other cases to customized manufacture.
Does Jade Sky offer an isolated solution?
Yes. Jade Sky's drivers operate in all common topologies, including
- isolated flyback
- non-isolated buck
- non-isolated buck-boost
- non-isolated boost