The following schematic diagram of basic flash memory programming voltage supply is taken from the Linear Technology Application Note. LT1072 IC is used in this circuit. This integrated circuit is a switching regulator to generate high voltage by driving the L1. R2 and R1 provide DC feedback. The SC roll-off is controlled by the R3-C2. 12V or 12.75V supply can be generated depend on the R1 values. Here is the circuit :
If 4.5V minimum output is acceptable, the zener diode can be removed. It does not have trimming requirement because it is erased by the combination of LT1072′s tight internal reference and resistor. The memory will not damaged during the power up or power down. It is because this circuit will not overshoot. Synchronous switch option can remove the power dissipation of this circuit.