Hello!!
Our R&D Dep. is in the designing process of a power supply for traffic lights.
This PS is supposed to drive a LED disc consisting of 120 LEDs (10 strings,12 LEDs per string).
We have 3 LED discs one of each colour.
Red: 90mA@23.5V
Amber: 120mA@26V
Green :100mA@35V
So, we want a universal PS that, with the help of a microprocessor, can select the appropriate output current controlling Iadj and Pdim pins of TPS92512 IC.
Design Requirements for TPS92512 :
- Vin min :42V
- Vout max :36V
- Iout max :120mA
- Switching Freq :300kHz
- Iled ripple p-p :36mA or less
Output Control Operation
With the help of a dip-switch we select the appropriate disc.
The MC reads the status of the dip-switch and then controls the voltage of Iadj pin to achieve the desired output current.
If a certain number of led-strings go off (open string) the output voltage will increase because the tps92512 provides constant current.
The MC will sense this increase of the output voltage and properly controls the PDIM pin to reduce the output current to prevent stressing of the remaining leds. If the number of strings that will be off exceeds a certain number, the MC will put the TPS92512 at off-state.
Input Control Operation
The operating voltage of the power supply comes from an external controller, and it is 230VAC. However, the external controller can supply our device with three voltage levels which will determine how the device will work. More specifically, for voltages <90 VAC the power supply will be in the off-state. For voltages 90VAC <Vin <170VAC output should be in a the low-state (70% of normal operation). Finally, for voltages 170VAC <Vin <230VAC power supply will operate normally.
In a same way as in the output, MC will sense the input voltage and will control the PDIM pin so as the tps29512 will provide the desirable output current.
What I want is to ask if this is the proper way of using the tps92512 and if you have any further suggestions that will help me complete my project.
Thank you very much in advance
Nick
