Programming old EPROM devices needs high voltage, and this is a circuit of high repetition rate Vpp programming supplies. This circuit is used for memory programming that need higher repetition rate. This circuit produces the Vpp continuously by the switching regulator that runs continuously. To preclude any possibility of inadvertent Vpp output, the switching regulator mus t be turned of by driving the Vpp lock line. This is the figure of the circuit;
The LT1072 loop comes on if the Vpp lock goes low, stabilizing at about 17V. This circuit has a clean rise time because of the two pole compensation. The LT1004 reference is biased by the 74C04 when the Vpp command line is low. The A2 and A1 give a scaled output and the LT1004 clamps at 1.23V. To control loop slewing, this circuit uses 680pF that also erase the overshoots. [Circuit diagram source: Linear Technology Application Note]
