Answer 1—Yes, it does would make a difference. The following figure shows the equivalent circuit for the 5 to 10-V doubler in both of its states: a) shows the charging of C1; b) shows the discharging.

a)

b)

First of all, note that C3 gets bootstrapped to 5 V by the 5-VDC input supply. This saves a small amount of time when the circuit starts up. Secondly, note that in the second half of the diagram, the load current flows through the parallel combination of C1 and C3.

The equivalent circuit for the alternate configuration (C3 connected to ground) is shown below.

a)

b)

In this configuration, not only does start-up take longer because C3 must be charged all the way up to 10 V, but also the current through C1 is doubled overall because the load current flows through C1 alone. This reduces the transient performance of the supply, especially when you consider nonlinear effects in the switches (transistors) such as saturation current.

Contributor: David Tweed

Published July 2003