Charge Pump Question - Page 1
Forum section: electronics / projects

author: void_error
author_rank: Frequent Contributor
timestamp: March 24, 2015, 09:31:03 am
content: Just wondering if it's possible to add 10V on top of a 30V rail using a charge pump with both sharing a common ground. Can it be done using jellybean parts? The current supplied doesn't exceed a few mA.

author: Richard Head
author_rank: Frequent Contributor
timestamp: March 24, 2015, 11:14:00 am
content: Absolutely possible. And you can do it with a 555 timer, a few diodes and capacitors.

author: cellularmitosis
author_rank: Unknown
timestamp: March 24, 2015, 01:16:43 pm
content: You can also use the ICL7660, which is fairly jellybean. The 555 will accept a wider input voltage though.Also, switched capacitor ICs are noisy, if that's important for your design.https://www.eevblog.com/forum/projects/an-evening-with-the-icl7660/

author: cellularmitosis
author_rank: Unknown
timestamp: March 24, 2015, 01:18:46 pm
content: And if you need to simulate the 7660 in LTSpice, you can use the LTC1044 and get a rough idea.

author: calexanian
author_rank: Super Contributor
timestamp: March 24, 2015, 08:14:25 pm
content: To add a 10 volt rail above a 30 volt rail with a 7660 you will need a pseudo ground 10 volts below the top of the rail you are boosting from. I would use a negative adjustable regulator with its ground reference from the 30 volt rail and use the output of that as your 7660 ground and the 30 volt rail as the Vdd of the 7660 and the output will be 30 volt rail + whatever that adjustable regulator is set to.

author: void_error
author_rank: Frequent Contributor
timestamp: March 26, 2015, 02:18:17 pm
content: What if the 30 V rail can be anywhere between 3V & 30V? Hint: tracking pre-regulator. I will still have access to 30V.

author: void_error
author_rank: Frequent Contributor
timestamp: March 27, 2015, 06:17:40 am
content: Hmm... how do i slap a 5V rail on top of a rail that goes from 0 to 20V using a charge pump?

author: void_error
author_rank: Frequent Contributor
timestamp: April 26, 2015, 09:31:12 am
content: Sorry about the dodgy posts but I was posting from my old crappy tablet lying in bed in hospital three days after surgery.I've figured out how to do what I was asking about and I ended up with this:

author: prasimix
author_rank: Unknown
timestamp: April 26, 2015, 10:34:59 pm
content: Hi Void_Error as first I wish you a fast and painless recovery. I'm playing with charge pump with TLC555 which LTspice model can be find in the attachment.Check also Figure 17a in IRApplication Note AN-937and Figure 16 in IRApplication Note AN-937.Edit 2015-05-02: Revised version can be foundhere.

author: void_error
author_rank: Frequent Contributor
timestamp: April 27, 2015, 02:03:05 pm
content: Quote from: prasimix on April 26, 2015, 10:34:59 pmThanks Prasimix. I was actually looking to stick a 5V rail on top of another rail with variable voltage in order to drive a N-MOSFET in its linear region and not need an extra isolated DC supply. However a P-MOSFET is easier to drive in my case. This is obviously for the power supply I'm working on. Just looking for ways to avoid extra transformer winding requirements for various bias voltages.

author: prasimix
author_rank: Unknown
timestamp: April 27, 2015, 03:21:27 pm
content: Yes, that is also my intention.Vout+will become a gate bias for n-ch power mosfet in linear post-regulator whileVout-is connected to theVpregthat is variable (approx. 2-52V) and feed power mosfet. So idea is to have at least 5V overVpregvalue. It's made floatable that TLC555 can survive voltages higher that max. allowed (18V).

author: void_error
author_rank: Frequent Contributor
timestamp: April 27, 2015, 03:31:54 pm
content: Not sure how well the TLC555 will do in a charge pump given the fact that the maximum source and sink currents are unequal. I'd personally go with aMC14584or74HC04with one inverter used as an oscillator and the others paralleled up.

author: prasimix
author_rank: Unknown
timestamp: April 27, 2015, 03:56:47 pm
content: Basic testing was done for biasing IRFP250N (Q4) gate in circuit presentedhere. A minor issue is with lowVpregvoltage but I derived 10V from +15V that is used for op amps to cover that range.

author: prasimix
author_rank: Unknown
timestamp: April 27, 2015, 04:39:14 pm
content: Quote from: void_error on April 27, 2015, 03:31:54 pmHave you seen this article:Comparing the NE555 Timer and LM386 Amplifier as Inductorless DC-DC Converters?

author: rx8pilot
author_rank: Super Contributor
timestamp: April 27, 2015, 04:50:59 pm
content: I have used a few high side gate driver devices to do this. If you are trying to learn more about charge pumps and gate drivers, ignore this comment. If you just want to drive a high-side N-CH MOSFET gate, consider a gate driver IC? They avoid needing an iso supply, easy to use, and cheap.

author: prasimix
author_rank: Unknown
timestamp: April 27, 2015, 04:54:15 pm
content: Quote from: rx8pilot on April 27, 2015, 04:50:59 pmAny suggestion for one that survive up to 60V without need to make it "floating"?

author: rx8pilot
author_rank: Super Contributor
timestamp: April 27, 2015, 05:01:33 pm
content: 60v on the input side or the gate drive side?

author: rx8pilot
author_rank: Super Contributor
timestamp: April 27, 2015, 05:13:38 pm
content: I have been using the Linear LT1910 for years to drive N-FET's. It has some other current monitoring features that may not be useful to you. It will so a simple logic level to gate drive about 15v above the supply voltage.There are others that are just a pure driver without the fancy stuff.This Micrel part is good to 36v on the supply side.http://www.digikey.com/product-detail/en/MIC5021YM%20TR/576-1239-1-ND/771878

author: prasimix
author_rank: Unknown
timestamp: April 27, 2015, 05:54:17 pm
content: Quote from: rx8pilot on April 27, 2015, 05:01:33 pmOn the input/supply side.

author: rx8pilot
author_rank: Super Contributor
timestamp: April 27, 2015, 06:13:18 pm
content: There are far fewer options at 60v for high-side applications. I have never needed anything above 48v so do not have any specific device to suggest. If your supply is 30v nominal and you are simply protecting for a 60v transient - that is a different story. You can use a TVS or other scheme to level transients to a safe point. If you expect to see a constant 60v, your discreet charge pump concept may be the choice.

author: void_error
author_rank: Frequent Contributor
timestamp: April 27, 2015, 06:24:47 pm
content: Hmm... I have yet another charge pump related question...It sounds like this:I have a 5V and another rail that goes from 0 to whatever. How can I get that "another" rail to have -5V added to it?Or should I stick with just a shunt reg + current sink to -5V?

author: prasimix
author_rank: Unknown
timestamp: April 28, 2015, 01:40:49 pm
content: Quote from: rx8pilot on April 27, 2015, 05:13:38 pmI'm afraid that gate drivers cannot help here a lot. As far as I know (not so much) they are mostly intended to be used for switching application where frequency, rise and fall time are critical. Where Cboost is present that presume that duty has to be below 100% but continuous bias voltage presence is exactly what I need. Currently I only succeed to have 5-10V over Vin with 555 based floating charge pump over the whole range (Vin=2-52VDC).

author: rx8pilot
author_rank: Super Contributor
timestamp: April 28, 2015, 05:29:39 pm
content: The LT1910 is particularly terrible at high-frequency switching and primarily intended for static load routing. It cannot drive the gate very hard although it can turn it off very fast. There is no reason that any of the typical gate drivers cannot be used at 100% even if they are optimized for fast on/off. Once a gate is charged on a FET it takes nothing to hold it in that state - no current flows through a gate. It is essentially a small capacitor. Charge it and the FET passes current, discharge it and the FET blocks current.My primary design interests are in power electronics. I am relatively new to the field and still learning but have used many of the of the shelf gate drivers in 100% applications for power routing and control. For high-side applications, they reduce the part count and complexity.

author: prasimix
author_rank: Unknown
timestamp: April 29, 2015, 11:20:36 am
content: Thanks for this suggestion. LT1910 looks like an another class of device (high-side switch rather then just driver) but I still don't have a clue how to use it in circuit like one from the attachment where it should provide Vbias (~7mA).

author: prasimix
author_rank: Unknown
timestamp: May 17, 2015, 11:05:56 am
content: Just to confirm what I mentioned in some of previous posts in this thread: if preregulator is used, if I simply use rectified input from main transformer as a bias I can drive mosfet in whole range, full load. I don't know is that a right way to proceed and maybe that can announce a minor 100Hz noise inVout. I need to test that further.