Is this ~150W 12V dc-dc supply realistic?

I don't think this is a half/full bridge or forward converter. All three of those types of converters typically employ at least two magnetic devices (one transformer and at least one inductor). This device only appears to have one magnetic device (which appears to only have 2 wires on it, so only a simple inductor, although that isn't 100% guaranteed given the low resolution of the images). Additionally a full bridge takes more than four semiconductor power devices (four MOSFETs + typically two output rectifiers), but the board only appears to have four on it.

Exactly what topology this is isn't fully clear to me given the resolution of the images.

However, given the modern design approach that appears to employ synchronous rectifiers, the output power and size specifications are quite possibly realistic. The efficiency claim seems awfully high, but on the other hand not totally unrealistic using synchronous rectifiers and modern MOSFETs.

It looks legit to me.

I am not so sure Jim. I didn't mention but when I was trying to accomplish this myself I looked into the SEPIC configuration, particularly with the LM3488 chip from national and to be able to manage the ripple to the ATX spec (

On Thu, 31 Mar 2005 07:48:21 -0700, "Fritz Schlunder" wroth:

There is a solder pad visible between the "inductor" and the caps. My guess is that it's for a center-tap on the inductor. I seem to recall a CUK or SEPIC topology that uses a center tapped inductor for a buck/boost converter.

My guess is that the converter is legit too.

Jim

If you are interested in buoilding your own, see

Ted

I'd guess that the efficiency is probably a bit off. It's not hard to get measurement errors, and a 97% efficiency is moderately hard to obtain.

I think it is a bridge converter with two of the fets being used in reverse current.

Based on the Linear Technology LTC3780. It operates as boost, buck-boost, or buck depending on Vout - Vin.

They show a 60W example on the front page, although they don't give any critical part values. One surprising thing, I couldn't find a FET gate-current drive-capability spec anywhere in LTC's datasheet. This is an important parameter for a converter running at 400kHz. They do mention you'll need to use logic-level FETs, due to the low internal Vcc = 6V drive voltage. The VCC regulator is spec'd with a 20mA load (5mA per FET), and the absolute maximum rating is 40mA, which implies rather modest average FET gate-drive currents. Their worked-out 36W example uses Vishay Si7884 MOSFETs, which feature a low 10-milli-ohm Ron, have a fairly-high 2000pF gate capacitance, and a 22nC gate charge at 6V. Note, 22nC * 4 * 400kHz = 35mA, oops! Hmm, wonder why they didn't tie PLLFLTR low and run at 200kHz.

Apparently the LTC3780 is capable of driving moderately-serious, but not too serious, power FETs.

It may be possible to scale up the 36W design example, but be aware that higher operating currents mean higher dI/dt, which means larger V = L dI/dt voltage spikes from fast FET switching and high-current slew rates, which means blown out stuff, if you don't know exactly what you're doing. Suggestion: Build the 36W and 60W versions first.