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Programmable Simple Switcher

Ben Satkiewicz
Prodigy 10 points

Other Parts Discussed in Thread: LMZ23610, LMZ14203H, TL783, LM3481

I have built fixed simple switcher circuits in the past. They are nice, efficient units that dissipate little heat.


As part of a circuit that powers a vacuum tube tester (for the audiophiles), I need a reasonably efficient system that can power the heaters for the almost seemingly infinite kinds produced.

This means a power supply that can supply the following voltage ranges along with their currents:

Range 1 - 1 to 6 @ volts 5 amps. An LMZ23610 switcher is what I am eying for this job.

Range 2 - 6 to 24 @ volts 3 amps. An LMZ14203H switcher is what I am eying for this job.

Range 3 - 24 to 117 volts @ 200mA. This range is for the low current, high voltage tubes like the 35WC, 50C5, etc.

A linear regulator for ranges 1 and 2 can dissipate up to 40 watts, according to my calculations in some cases. Range 2 with a switcher is more tricky, but the heat should be manageable with TL783 regulators in conjunction with a multi-tapped transformer. If there is a relatively simple switcher solution for this, feel free to discuss it.

The unit will be computer controlled. Therefore, a SPI interface will need to program a DAC that sets the voltage level for the LMZ regulators. The enable pins can be used to select each range. This problem is easy enough with op-amps and linear regulators. How do you recommend I digitally program the LMZ simple switchers with DACs and the feedback pins?

  • 0
    TI__Genius 10145 points

    Hi Ben,

    I am going to answer the adjustable output voltage first. 

    The easiest way is to use a DAC with a SPI interface.  You can take a look at this article (beware there are typos in some of the equations).  THe DAC through a resistor to the feedback node can control the output voltageu u u

    5241.Programmable_Power_Supply.pdf

    Remember if the power supply starts up with a zero output from the DAC it will output its highest output voltage so yo

  • 0
    TI__Genius 10145 points

    For the Range 3,  you would want to use a boost converter that is configured as a voltage doubler or tripler depending.

    Here is an example circuit using the LM3481. For the power level you require because you need something with about a 2 amp switch current limit from 12Vin. It is basically a boost, to get Vout.  You then add the 2 caps and the diode to make a charge pump doubler circuit.  This would allow you to get an output voltage of twice the rating of the base device nI  .