High-V DC-DC Converter Is Ideal for MEMS (Warning: High-Voltage Circuit)
Figure 1. A high-voltage DC-DC converter (U1) converts a typical 5V input to 36V, and a 2-stage charge pump boosts that voltage to more than 100V.
U1 is a step-up DC-DC converter capable of output voltages to +36V, and a 2-stage charge-pump converter (D2-D5 and C1-C4) nearly triples the U1 output. The R1/R2 divider provides feedback for regulating the circuit's output voltage. Use these equations to calculate the resistor values:
For lower output voltages (< 70V), remove D4, D5, C3, and C4 to produce a single-stage charge pump. Similarly, you can add another stage to produce voltages higher than 100V. An optional post filter (R3 and C5) reduces the output ripple to < 10mVP-P. Figure 2 illustrates the variation of output voltage with output current.
Figure 2. The output voltage in Figure 1 is well regulated for load currents up to 0.7mA.
A similar version of this article appeared in the August 18, 2002 issue of EET magazine.