Switcher regulates HV in novel way

Linear Technology LTC1625

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).

Switcher regulates HV in novel way
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.

Switcher regulates HV in novel way
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).

Materials on the topic

  1. Datasheet Linear Technology LTC1625
  2. Datasheet Vishay GBPC6
  3. Datasheet Vishay SiR846DP

EDN

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