Charge pump "Voltage Quadrupler"- data sheet error?

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pmd34

Joined Feb 22, 2014
507
I was just checking a data sheet for the MIC1555 (an IC similar to the NE555 timer), and came across the following circuit:
charge pump.jpgI confess I find following such switching circuits a bit mind mending, but as far as I can see, surely this is at best about a voltage doubler:
As the output on pin 5 only switches between 0 and 5V (and not -5V like an AC voltage doubler), the maximum voltage that C2 can charge to is then only about 5V (minus a diode drop). C2 is then able to charge C3.. so the result should the C4 sees about 10V minus 2 diode drops. Or am I missing something?!
 

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LesJones

Joined Jan 8, 2017
2,671
The schematic in post #1 is only a voltage doubler. The output of the MIC1557 is a 0 to + 5 volt square wave. So if you allow for the forwards volt drop of 4 diodes Albert's simulation makes sense.

Les.
 

DickCappels

Joined Aug 21, 2008
6,463
Take note long time taken for the gate voltage to build up and then to bleed down through the resistor to ground. This would greatly increased switching losses resulting in transient power dissipation during the switching transition because the MOSFET will be in its active state as to the low dissipation on state (saturated) and the even lower off state. This might mean a higher power MOSFET might be needed. This certainly be investigated as part of implementing this circuit.
 

AnalogKid

Joined Aug 1, 2013
8,493
I confess I find following such switching circuits a bit mind mending, but as far as I can see, surely this is at best about a voltage doubler:
As the output on pin 5 only switches between 0 and 5V (and not -5V like an AC voltage doubler), the maximum voltage that C2 can charge to is then only about 5V (minus a diode drop). C2 is then able to charge C3.. so the result should the C4 sees about 10V minus 2 diode drops. Or am I missing something?!
The D1 anode should be connected to Vcc, not GND. This will put *approx* 2Vcc at the anode of C2, and the C4 voltage will be stacked on top of that. Not 4x, but more than 2x.

Both C1 and C3 should be reversed.

ak
 

jpanhalt

Joined Jan 18, 2008
9,784
The D1 anode should be connected to Vcc, not GND. This will put *approx* 2Vcc at the anode of C2, and the C4 voltage will be stacked on top of that. Not 4x, but more than 2x.

Both C1 and C3 should be reversed.

ak
If you are referring to post #8 D1's anode is connected to VCC.
 

AnalogKid

Joined Aug 1, 2013
8,493
Nope, #1, the one I quoted. His question was about his analysis of that circuit, and I didn't see a response that addressed that. Turns out, his analysis was correct.

ak
 
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