Eight switching circuits to power wide VIN applications - brought to you by Vijay Choudhary and presented by Santa’s reindeer


We all know that Santa has eight reindeer pulling his sleigh (read technical details publishing in Behind the Wheel on Saturday).  In the spirit of the holiday, I bring you eight wide VIN circuits recommended by each reindeer as his favorite.

1.  Dasher

In figure 1, we present the first wide VIN switching circuit, a 75V simple buck converter based on TI’s LM5007 constant-on-time (COT) buck regulator. A favorite of Dasher, who demands direct, no-nonsense gift delivery, it is one of the simplest wide VIN non-synchronous circuits there is. For 100V input ratings, he also recommends the LM5008A and LM5009A.

Figure 1 - Dasher’s favorite is a wide VIN non-synchronous circuit based on TI’s LM5007.

2.  Prancer

Up second and pictured in figure 2, is a 10V/600 mA synchronous buck regulator circuit with a wide input voltage range of up to 100V. Much like Prancer, who likes to change direction on a whim, the programmable UVLO feature allows the user to select a minimum input voltage at which the converter starts up.

Figure 2 – Prancer likes a wide VIN synchronous circuit based on TI’s LM5017.

3.  Vixen

In figure 3, Vixen brings us an inverting buck-boost circuit that generates a negative output voltage from a positive input voltage. Vixen is always riling things up, and he (she?) recommends TI’s LM5009A with its 100V input rating for converting wide VIN rails to negative voltages. The input output relationship is given by: 

For higher output currents, Vixen likes the LM5008A.  And if you really want to live on the edge, you can try a synchronous version without an external diode. See the hoof-by-hoof instructions here.

Figure 3 - Vixen likes the wide VIN inverting buck-boost circuit based on TI’s LM5009A.

4.  Comet

Figure 4 is brought to you by Comet. The 5V/4.5A buck converter is based on TI’s LM5085 COT PFET controller. A PFET controller has the unique advantage that it allows 100% duty cycle operation because there is no bootstrap capacitor needed to drive the PFET gate, and you know Comet is all about 100% delivery efficiency.  This feature is really useful for low drop-out conditions or for battery/supercap charging applications.

Figure 4 - Comet operates at 100% much like this circuit based on TI’s LM5085.

5.  Donner

Next up – figure 5’s wide VIN dual output buck with tapped inductor, a personal favorite of Donner because, well he is a buck.  He’s all about an easy and cost-effective way to generate lower non-isolated output voltages. Because of the synchronous FETs, the regulation can be better for lower output voltages than flybuck topology, favored by Blitzen, but we’ll talk about that later. The second output voltage is related to the main output (VOUT1) by the inductor turns ratio:

VOUT2=VOUT1  N2/(N1+N2 )

Figure 5 - Donner’s nemesis, this dual output buck with tapped inductor features TI’s LM5006.

6.  Cupid

Figure 6 is passionately beloved by Cupid, because Cupid is passionate about everything.  In this circuit, a small bias solution with a 5V/500mA isolated output based on TI’s 100V synchronous buck regulator. If the inductor windings are rated appropriately, the total load current can be divided between primary and secondary outputs as long as the total does not exceed 500mA (spread the love). Further, the isolated output can be configured as an inverting output to create a dual bipolar supply.

Figure 6 - Cupid loves, loves, LOVES this wide VIN small bias solution featuring TI’s LM5017.

7 - Blitzen

Figure 7 features TI’s LM5017 based 3-output flybuck converter. This one is brought to you by Blitzen, because, well there is always one Blitzen in the group and he truly personifies “FlyBuck.”  In this circuit, VOUT1 is the non-isolated output.  VOUT2 and VOUT3 are isolated 10V and 5V outputs respectively. The isolated output voltages and currents can be changed by using an appropriate transformer, or an abundance of reindeer juice - at which time Blitzen should be isolated.

Figure 7 – Blitzen likes the 3-output flybuck converter based on TI’s LM5017, but may not remember it in the morning.

8.  Dancer

Last but not least is figure 8, brought to you by Dancer. This non-inverting buck-boost (ZETA) converter uses TI’s LM5085 PFET controller IC. A zeta converter (a dance move) also called inverse SEPIC is a non-inverting buck-boost converter. It can produce outputs above or below the input voltage, much like the luau dance game, limbo. The input and output are related by the PFET duty cycle by the following relationship.

Figure 8 – Dancer is the star of the party with his zeta converter to buck and boost based on TI’s LM5085.

Happy holidays everyone!  Anybody have one for Rudolph?

  • Hi everybody,

    I am looking for a switched application for some time: It should power a tube-amp. So it had to feature at least 3 outputs -> 450VDC@150mA, 6,3VDC@5A and 30V@100mA. Regulation should be coupled with the 6,3VDC. Preferably switching at the primary and input 230VAC 50Hz, showing input to output isolation. Can anybody give an opinion?

  • I would like to see DC-DC converter circuit that provides power from a single 1.5 alkaline or 1.2 volt rechargeable battery for applications such as the Fenix flashlights, audio devices, etc.  Highest efficiency possible, and ability to milk the most out of a discharging alkaline (low input voltage capability) -- what are some really good circuits.

  • Thanks for the feedback and we are looking into this now.  In the meantime, feel free to subscribe to Power House so you will receive our response.