how to lower PWM frequency using external circuit?

I heard that WS2801(led driver) can also driver servo motor, but can't google it anywhere. I learn from WS2801 datasheet that its PWM frequency is about 2.5Khz. I also measured it using my oscilloscope and got approximately 2.07Khz but servo motors need 50Hz PWM. So the question is how to get a lower frequency but the same duty cycle. I have a idea using counter(maybe 74HC590) to lower the frequency, but I shortly realized I can't get the same duty cycle. Any suggestion is appreciated, thx!

You might be better off with something like the Adafruit 16-channel 12-bit PWM/Servo Shield:

http://www.adafruit.com/products/1411

It uses the NXP PCA9685: http://www.adafruit.com/datasheets/PCA9685.pdf

johnwasser: You might be better off with something like the Adafruit 16-channel 12-bit PWM/Servo Shield:

http://www.adafruit.com/products/1411

It uses the NXP PCA9685: http://www.adafruit.com/datasheets/PCA9685.pdf

Thanks John, I should open the door and turn right to PCA9685 like you said!