High efficiency 24V to 80V 25W Boost converter

Lot of power to deliver around your system and too much cabling weight? HV might be the way to go.

24V to 80V Step Up Boost converter DC-DC

High voltage power transmission is used all around the world: in our grid system to power  homes and charge electric cars, and in airplanes to save weight, thus why don’t we take advantage of a low power loss along our cables and save some mass with more volts?

This little (see my 42M3 personal standard) boost converter, based on the LT1082 chip from Linear, can handle a low voltage input, between 19V and 35V, and boost it up to 80V (with 60mVpp ripple ca.).

Maximum DC-DC boost converter current at 80V output, LTSPICE simulation
Maximum Load SPICE simulation, 321 mA at 80V

A wide input voltage range can be achieved only by not using all the power this converter can deliver: at 25W RMS output, any input voltage lower than 22/23V will result in Vout oscillations and an improper regulation.

SPICE simulation of a DC-DC boost converter from 24V to 80V with LTSPICE
Maximum load waveforms of the LT1082: LEFT Voltage scale, Right Current scale. I(L1) = RED, I(R5)= light blue, Vout = blue

At maximum power output, 320mA @80V ca., I(L1) (RED LINE) ranges from 1 to 1.3Amp, thus the inductor was selected to have a very big footprint, heavy mass and low ESR (213mOhm ca.) with a maximum current of 2.5 Amp.

SPICE DC-DC boost converter step-up simulation circuit schematic
LT1082 Simulated circuit

High efficiency (90%+) is achieved thanks to a low ESR inductor (we gain 3% of efficiency ca. by selecting a 215mOhm one instead of a 960mOhm one [from 90% to 93%]), and by using a LOW ESR output capacitor (C4).

ESR calculation from Tangent loss - dissipation factor
ESR calculation from Tangent Loss data (DF) and Regulator switching Frequency

An interesting calculation for newcomers might be the ESR “guess-estimation ” by deriving it from the tangent loss (from the datasheet). Here an interesting document from Illinois Capacitor.

If you know the DF and switching frequency (derived from the SPICE simulation) you can actually estimate it, but be aware that this is only an estimation and that here I’m writing 90%+ efficiency instead of the actual calculated 93-94% one because of that (and the complete absence of any PCB trace resistance consideration in the simulation model).

DC-DC converter BOOSTER step-up power output spectrum analysis with SPICE 24V to 80V
LT1082 Vout power spectrum(SPICE Simulation) shows a strong peak around 58Khz, exactly at the switching frequency

Last but not least, this module is protected by a fuse and Metal Oxide Varistor (MOV), thus Vin cannot exceed 35V or the MOV will shunt Vin to GND and blow up the FUSE.

Vout power spectrum is shown in the last image: a strong component at 58Khz and multiples can be seen quite nicely (-40dB peak at 58Khz with 20dB/div), but for most applications, it should be low enough.

And for those who really want to see something more about high voltage DC transmission, here an interesting (and funny) video about this topic.

Feel free to write a comment and tell me your opinion about these 42M3 modules and articles!

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