Transformless Transformers

The 232 uses the 5V input to a generate a 5V charge stored on top of the 5V input ie 10V, and then -10V from the +10V. In each case it's an independant single flying cap in use.

RL

So far so good, but ...

Er, yeah, right ;) That part only holds if C2 starts out fully discharged, which isn't going to be the case for a practical regulator.

So what would be the advantages over a linear regulator? The fact that you can use a fixed resistor for the dissipative element instead of a BJT/FET?

My first thought was that C-R-C wouldn't be significantly simpler than C-L-C, and less efficient to boot. OTOH, it doesn't have the issue of overshoot with variable loads (e.g. PWM). Anything else I'm still missing?

The thread wasn't about a regulator, it was about an isolator. My particular interest is in providing sort-of-isolated power to a measurement circuit with a minimum of noise and hassle, so a low-freq switched-cap isolator is interesting. As just a regulator, this is silly... the power is dissipated in expensive clocked analog switches instead of simple transistors.

The important thing is that the cap is continuously switched between the input and the output at some relatively high rate, so the flying cap voltage is always close to the input voltage.

The isolation, such as it is. Or the ability to boost, divide, or invert a supply without inductors.

This is cute:

John

Given that the power dissipation rating of the TPS package is 550mW @

25C, there must be some hairy calculations to be made, or performance vetting going on as the efficiency swings between 50 and 90% with source variations over some pretty small ranges. With the recommended capacitors, losses within the IC will dominate.

There are plenty of practical applications for charge pumps as energy scavenging elements, particularly where losses in lower powered circuits can significantly improve the efficiency or performance of higher-powered sections. Often the switches of the higher powered circuitry will easily serve a dual purpose.

I'm not saying you shouldn't use the charge pump methods - it's just important to go into the exercise with your eyes open. Using the term transformer, in reference to them, is misleading.

RL