high voltage charge pump

   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

On 12/30/19 8:53 AM, Hul Tytus wrote:
>     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 Damon <Richard@damon-family.org> wrote:
> On 12/30/19 8:53 AM, Hul Tytus wrote:
> >     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.

On 12/31/19 11:35 AM, Hul Tytus wrote:
> 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

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.

On Tuesday, December 31, 2019 at 11:36:01 AM UTC-5, Hul Tytus wrote:
> 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.

There is nothing to stop you from creating your own design.  The switches are just FETs and need some drive circuitry to make them do their job.  I haven't looked at the details, but you might be able to use H-drivers.  I expect you can find them in high voltages. 

-- 

  Rick C.

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