I'd like to use this thread to list all the known constant-current buck converters suitable for 12V use currently available. Personally, I keep looking and finding new ones and have never seen a central resource. Please respond with any that you find and I'll keep updating the list at the top.
Higher frequency lowers the required inductor size and seeing as this is the largest/most expensive part this is very significant. Constant Freq is for (Vin/Vled)>0.5. Typically Constant-Toff is needed for (Vin/Vled)>0.5 to avoid stability/harmonics problems. Constant Freq and Constant-Toff use different inductor selection methods (check the part's datasheet and/or appnotes). Lower feedback voltage reduces the wattage requirement on the feedback resistor- 250mV @ 2.8V for a P7 is 0.7W, a BIG SMD resistor! Internal transistor devices may present additional thermal limits on the current, the pkgs are small and the rds-on significant. The external transistor may place additional limits on max freq of external transistor parts, check the part's driving current vs the ext transistor's gate charge.
If I can't find singles off-the-shelf at Digikey or Mouser I'm calling it "limited distribution". You do your own shopping.
External Transistors
HV9910B: Supertex. 8V-450V Vin. External transistor, constant freq or constant-Toff, freq programmable up to 100KHz, 250mV feedback, linear or PWM dimming. This is a slightly improved version of the HV9910.
MXHV9910: IXYS clone of HV9910 (Future Electronics). Limited to 400V Vin. Spec seems to suggest max freq of 64KHz.
QX9910: QXMD version of 9910 (limited distribution). 2.5V-450V Vin. 2MHz max freq.
Internal Transistors
ZXLD1360: Zetex. 7V to 30V (transient 40V) Vin. 1A internal transistor rds-on .5ohm typ 1 ohm max. Freq 280KHz recommended/1 MHz max. 100mV feedback. linear dimming.
ZXLD1362: Zetex. 6v-60V Vin, 1A internal transistor rds-on .5ohm typ 1 ohm max, freq 300KHz recommended/500KHz max, 100mV feedback, linear dimming.
ZXLD1350: Zetex, 350mA version.
PT4105: Micro Bridge Technology (limited distribution). 5v-18v, 20V ab max. Internal transistor, Iled >600mA @5v Vin, >1A @12V Vin, 200mV feedback voltage. 500KHz, internally fixed. PWM dimming.
NCP/NCV3065. ON Semiconductor. 3v-40V. 1.5A internal bipolar darlington transistor (check dropout voltage and thermal limit issues), 235mV feedback, 250KHz, linear/PWM dimming.
ZD850: Zywyn (currently very limited distribution). AC/DC capability (internal rectifier): • 4~16VAC on VAC1 and VAC2 with current up to 350mA • 5~27VDC on VAC1 and VAC2 or on HVCC and PGND with current up to 800mA • 5~16VDC on HVCC and PGND with current up to 1.5A. 30VDC absolute max. 200mV feedback. 500KHz.
Higher frequency lowers the required inductor size and seeing as this is the largest/most expensive part this is very significant. Constant Freq is for (Vin/Vled)>0.5. Typically Constant-Toff is needed for (Vin/Vled)>0.5 to avoid stability/harmonics problems. Constant Freq and Constant-Toff use different inductor selection methods (check the part's datasheet and/or appnotes). Lower feedback voltage reduces the wattage requirement on the feedback resistor- 250mV @ 2.8V for a P7 is 0.7W, a BIG SMD resistor! Internal transistor devices may present additional thermal limits on the current, the pkgs are small and the rds-on significant. The external transistor may place additional limits on max freq of external transistor parts, check the part's driving current vs the ext transistor's gate charge.
If I can't find singles off-the-shelf at Digikey or Mouser I'm calling it "limited distribution". You do your own shopping.
External Transistors
HV9910B: Supertex. 8V-450V Vin. External transistor, constant freq or constant-Toff, freq programmable up to 100KHz, 250mV feedback, linear or PWM dimming. This is a slightly improved version of the HV9910.
MXHV9910: IXYS clone of HV9910 (Future Electronics). Limited to 400V Vin. Spec seems to suggest max freq of 64KHz.
QX9910: QXMD version of 9910 (limited distribution). 2.5V-450V Vin. 2MHz max freq.
Internal Transistors
ZXLD1360: Zetex. 7V to 30V (transient 40V) Vin. 1A internal transistor rds-on .5ohm typ 1 ohm max. Freq 280KHz recommended/1 MHz max. 100mV feedback. linear dimming.
ZXLD1362: Zetex. 6v-60V Vin, 1A internal transistor rds-on .5ohm typ 1 ohm max, freq 300KHz recommended/500KHz max, 100mV feedback, linear dimming.
ZXLD1350: Zetex, 350mA version.
PT4105: Micro Bridge Technology (limited distribution). 5v-18v, 20V ab max. Internal transistor, Iled >600mA @5v Vin, >1A @12V Vin, 200mV feedback voltage. 500KHz, internally fixed. PWM dimming.
NCP/NCV3065. ON Semiconductor. 3v-40V. 1.5A internal bipolar darlington transistor (check dropout voltage and thermal limit issues), 235mV feedback, 250KHz, linear/PWM dimming.
ZD850: Zywyn (currently very limited distribution). AC/DC capability (internal rectifier): • 4~16VAC on VAC1 and VAC2 with current up to 350mA • 5~27VDC on VAC1 and VAC2 or on HVCC and PGND with current up to 800mA • 5~16VDC on HVCC and PGND with current up to 1.5A. 30VDC absolute max. 200mV feedback. 500KHz.
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