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Part Number: TPS61086
Tool/software: TINA-TI or Spice Models
I am trying to use the TPS61086 configured as a charge pump doubler. The boost converter is deisgned to boost voltage from 3.3V to 7V (Vout_boost net in the schematic attached). This voltage is then doubled and stored in a bank of three 820uF capacitors. (2Vout_boost net in the schematic attached). The working is as follows
When switch node SW = 0V i.e., the device is ON, the flying capacitor C3 is charged to Vout_boost – SD3
When device is off, i.e., the switch is open then SW = Vout_boost + SD1.
Now voltage on C10, C11, C12 becomes Vout_boost + SD1 + Vout_boost –SD3 = 2Vout_boost + SD1– SD3 and ignoring the diode voltage drops , this voltage of 2Vout_boost is transferred to the output capacitors C10, C11,C12
I am trying to simulate the output waveforms using TINA. The output waveform for Vout_boost net is correct - at approximately 7.2V but the waveform for the 2Vout_boost net shows as 7V.
What is wrong with the way I am trying to simulate and how can I get it work? I should be able to see Vout_boost as 7V and Vout_boost as aprroximately 12V considering diode voltage drops.
Nikhil Gupta | Product Folder Modeling
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In reply to Nikhil Gupta (Online Design Tools):
In reply to user4376413:
Can the flying capacitor C3 be modelled as a voltage source?
The flying capacitor should be typically between 100nF to 1uF.
The storage capacitors are too high for a frequency of 1.2MHz.
I have modified the capacitors and its working now. PFA the same.
In reply to K Prasad:
Thanks for the corrected schematic. It seems to work fine now.
I really appreciate the quick response. :)
Just another quick question -
The reason I put three 820uF capacitors for the storage caps in my schematic is because I wanted them to provide 100mA for 200ms which is like 0.02 couloumbs of charge. The caps will be charged to only about 10V considering the drops across the diodes and the ESR losses and can only be discharged down to 3.2V so this will be (10V-3.2V) = 6.8V. Since Q = C * V => 0.02 Coulombs of charge = C * 6.8V so C = 2.9 mF so putting three 820uF caps in parallel (2.46mF) which is somewhat close to 2.9mF.
Is there any way that the schematic can be modified to achieve this?
The circuit does not work with high value of storage caps as you rightly pointed out. What is the maximum value that I can use?
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