Wednesday, August 31, 2016

High Voltage Switching Regulator Circuit using LM5008 IC

Electronic Kit School. - This is electronic circuit for you who want to build high voltage regulator that can switch from 26V - 95V to 24V with 230mA. We think that this circuit when do you have maximum input voltage = 90V and /or linear regulator has unreasonable power dissipation.

In here beside we give you circuit of High Voltage Switching Regulator Circuit using LM5008 IC, we also will show the component parts of this circuit and describe about this circuit after it.


Figure 1. High Voltage Switching Regulator Circuit using LM5008 IC

Component Parts
  1. IC1: LM5008
  2. Resistors
  3. Capacitors
  4. Inductor
  5. Diode
  6. Fuse

Circuit like in Figure 1 above show you about the High Voltage Switching Regulator Circuit using LM5008 IC that can produce 24V voltage output from 26V to 90V voltage in input. The main component used in this circuit is LM5008 IC is served as step-down switching regulator.

The LM5008 is available in only SMD (Surface Mount Device) or SMT (Surface Mount Technology). It is further complicated in that the VSSOP package has a 0.025” lead pitch. As a result, this is in no way suited for breadboard testing –the best thing to do is to ‘bite the bullet’ and design a circuit board. You may also prefer to use 0805 size resistors and capacitors to make hand assembly easier –0603 is difficult, and the 0402 size is simply an electronic dust particle.

How it works

According Electroschematics site describe that to provide heat sinking to the tiny IC, I put copper blocks on all 4 corner leads –you will see how I did it when you poke around the expresspcb file. At the time, I had to create the IC footprint symbol –now expresspcb supports this device –both are present on the layout.

Scaling the voltage

I scaled the feedback for 24V output –you may desire a different voltage –output voltage = 2.5V * the ratio of R1:R1 + R2. Output capacitor voltage may be selected accordingly.

Electrolytic capacitors

Low ESR (Effective Series Resistance) capacitors required for both input and output –the input capacitor takes the worst beating to the low duty cycle rectangular discharge waveform –I do not recommend GP (General Purpose) capacitors.


The schematic indicates 500kHZ. I do not know where this figure came from –all I know is that the frequency is relatively high. The switching regulator uses the constant off-time topology –off-time is 300nS –this makes the max frequency approach 3mHZ –frequency is variable, depending input voltage.

Free wheeling diode

The free-wheeling or back diode (D1) is an ultra-high speed 1A, 150V rectifier –the voltage rating of schottky rectifiers is too low for this application.

Input protection

To prevent catastrophic failure from accidents or IC failure, I used a Raychem PTC resettable fuse –the one selected has a 240V interrupting rating.