Hi guys,
since we're talking charge pumps now here is my preliminary design for a charge pump for the iPod 6 nano reverse engineering project
Features:
- +5V / 50mA input, 15.2V/10.5mA constant current output, PWM capable
- Power off mode
- Made from very flat components (major feature!)
- Dirt cheap
It works by charging 3 caps to the +5V supply voltage, then reconnecting them in series with power supply to get "almost 20V".
Schematic tour:
JP1 on the left is power and control conenctor.
Then we have a 100kHz, roughly 50% duty cycle clock generator made from IC1A and IC1B.
Two pulse shorteners made from IC1C and IC1D delay rising edges of the two clock phases by roughly 100ns to make sure they never overlap.
Non-overlapping clocks are then distributed in the forms suitable for the switching transistors (pull ups, pull downs).
Next is a 3 stage charge pump. During parallel phase, caps are connected across power supply to charge (Q4,Q5 etc).
During serial phase supply rails are disconnected from the caps and Q1, Q6, Q9, Q12 connect the caps in series with power supply across C7, which is charged to sum of the voltages of the pumping caps and power supply.
On the right there is conenctor for the LED backlight and a PWM switch/constant current source Q13 that limits the output current to ~10.5mA as requited by the LCD.
Comments?