Gheorghe Plasoianu
EDN
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).
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| 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.
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| 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).
