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 (Fig. 1).
|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 switched-mode power supply 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 switched-mode power supply output reaches its upper limit (Fig. 2).