Anyone familiar with a high voltage charge pump designed as a step down power supply? The voltage is between 175 & 200. Numerous high voltage versions exist using inductors, (Onsemi has one that is "self supplied" which is attractive) but not a one that works with just a capacitor. Are there any out there I've missed?
Hul
Most charge pump designs will multiply voltages (invert or step up), not divide.
While a step down configuration is possible, I think it requires much more careful choices of values and control law to keep the output from getting too high of a voltage.
Also, all charge pumps that I know use MULTIPLE capacitors, they generally work moving charge in a controlled way, so generally require at least one 'moving' capacitor to transfer with and one fixed output capacitor to store the output charge.
One reason you don't generally use a charge pump for step down is that charge pumps are best used at very low current. For very low current steo down, the simple linear regulator is normally a perfect solution and often is as efficient or even better than a switched capacitor step down system.
Richard - what I'm looking for is an ic similar in results to Microchips tc7662 with an input voltage limit above 200 volts. The output current needed is only 60 ma. which is in the range of charge pump ic that I've seen so far.
Hul
Richard Dam> > Anyone familiar with a high voltage charge pump designed as a step down
Yes, a doubler configuration can be reversed to become a halfer, if that is the voltage you need. 60 mA is also on the high range of what these supplies are considered good for, due to the somewhat high output impedance of a charge pump.
I am not familiar with devices in that range, so can't suggest what might work up there. One issue that you may run into is that a lot of things likely need to scale in the wrong directions. Higher voltages means more charge transferred for equivalent percentage ripple, which up the energy involved, so you may need to reduce the capacitance, or the switching frequency which drops the current capacity of the system.
There is nothing to stop you from creating your own design. The switches a re just FETs and need some drive circuitry to make them do their job. I ha ven't looked at the details, but you might be able to use H-drivers. I exp ect you can find them in high voltages.
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