This Design Idea regulates high voltage without using high-voltage switching components.
Designing a high-voltage regulator can pose difficulties associated with component stress, reliability, and costs.
This Design Idea offers a solution: a simple unregulated high-voltage supply in series with a low-voltage switched-mode power supply (SMPS).
Figure 1 The LTC1625 regulates the combined HV output.
The sum of VHigh and VLow is fed back for regulation.
At minimum load, when VHigh is maximum, the SMPS outputs a small voltage. As the load increases and VHigh drops, the SMPS outputs an increasing voltage, and also compensates for ripple.
D6 and the fuse offer some short-circuit protection, and can be adjusted to suit your application. Without them, an output short will force C1 to discharge into the switcher’s output, possibly destroying it.
Figure 2 VReg and VHigh (Y-axis) vs. load in milliamps (X-axis).
At around 200 mA, the circuit ceases to regulate, as the SMPS output reaches its upper limit.
—Gheorghe Plasoianu has a Masters degree in electrical engineering from the Polytechnics Institute of Bucharest.