SMPS

BITD hybrid bridge rectifiers were used occasionally. SCR pre-regulators on the primary side of a bog-standard transformer-rectifier supply also work, sorta.

Cheers

Phil Hobbs

I’ve never designed one, but I recall seeing SCR bridges as the HV preregulator in an argon laser supply.

For regulating medium amounts of AC, the regular way was a ferroresonant transformer (Sola).

Cheers

Phil Hobbs

There are some situations where the 'chopper' and 'bridge' are placed in series with the AC line and load. Rectification still present in most practical circuits, unless simple phase angle controls or saturable reactor distortion (and weight) is permissible.

There's not much point in high frequency conversion, unless it avoids the size and weight of lower frequency components at the regulator, isolation barrier or the load itself.

Topologies, as such, don't necessarily require real components or practical circuits - they are conceptual.

RL

Yes. Some so called true sine stage dimmers and smart solar PV immersion heater controls build a kind of all silicon variac. Think a buck switcher but where the series switch transistor and catch diode are replaced by inverse series mosfets. Buck inductor and smoothing capacitor are sized for kHz pwm switch rate but output is 50/60Hz reduced amplitude version of the input supply.

piglet

Grid tie chargers connected to the line synchronize to the grid and turn into a boost converter to PFC charge batteries in the opposite direction using full wave bridge switchers and inductors tied to the AC line itself.

There is more circuitry of course.

Full wave diode bridges work pretty well too. Just not PFC corrected.

boB

Does "bridgeless PFC" meet the requirements?

This replaces two or all four of the diodes in a rectifier bridge with transistors, and places an inductor between line input and the bridge, thus integrating bridge rectifier and step-up switcher in one block.

cu Michael

Replacing the remaining 2 diodes with FETs is an options. I believe the term "bridgeless" is supposed to mean "no separate bridge in front of the PFC stage".

Figure 3 in the TI Appnote has a breakdown of losses for both topologies - the bridgeless version seems to improve efficiency. Figure 9 shows the resulting efficiency. For compact designs where cooling is the limit (think laptop chargers etc.), this may be significant.

cu Michael

Only up to 75W (?) - above that, PFC is mandatory, at least in the EU.

cu Michael

Sorry for the generalization. Yes, there are exceptions, but most devices above a certain power limit nowadays *do* require PFC.

The exceptions are getting fewer with every new version of the standard.

There are different classes which have different limits, but few exceptions remain (see chapter 7). Above 75W (or 5W for lighting), those are basically phase control dimmers, heating elements and professional equipment >1kW.

There is a clause for "professional equipment" that does not comply to the limits, but that includes "requirement to ask the supply utility for permission to connect", so that is no easy way out.

I have not looked at the exact limits for each class, but I assume it is not possible to meet them without some kind of PFC - correct me if I am wrong.

cu Michael

Ok, I see - *that* extends the range of the exceptions quite a bit, thanks.

cu Michael

Testing at lower current levels will pro-rate the 16A values as a ratio.

What it avoids is phase displacement characteristic of motors.

That's why Power Factor isn't in the actual standards.

RL