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Arbitrary Voltage boost circuit???

I know the basics of charge pumps but they seem to be limited to providing integer multiples of the input voltage.

I'm looking for a circuit that given a single available input voltage, Vin, provides an output voltage, Vout, such that Vout = Vin+10.0volts. (nice if the circuit actually was tweakable... Vout = Vin + Vadd)

Current requirements for Vout are small. 10-20ma would be sufficient I think.

Vin should be relatively wide, 12v - 170v would be ideal, 12-48v would be ok too.

Efficiency doesn't have to be good and output ripple can be pretty insane. I want to use it to drive high side mosfets on indefinitely. The gate charge is very tolerant so ripple voltages of a couple of volts could be handled.

My basic question is: Is such a circuit feasible and simple? Where should I look for such a beast?

My first thought is since Vin > 10v (or basically Vin > Vadd) you could use a simple doubling charge pump with the flying capacitor connected to a current limited zener diode with a breakdown voltage of 10V (or Vadd). But at higher voltages this doesn't seem to work well since the flying capacitor could only be charged with about 10mA without exceeding the power rating of common zeners. And of course efficiency would be ultra terrible.

Is there a better way given a Vin to charge a capacitor to Vadd where Vadd < Vin?

I'm not an electrical engineer so am I missing something relatively simple?

Reply to
druberego
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No. The step-up per section is equal to the P-P clock voltage.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.
Reply to
Jim Thompson

Do you have a source of more-or-less steady voltage? If you do you should be able to drive a transformer primary with a square wave, reference the secondary to your Vin, and rectify the output to be above Vin.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google?  See http://cfaj.freeshell.org/google/

"Applied Control Theory for Embedded Systems" came out in April.
See details at http://www.wescottdesign.com/actfes/actfes.html
Reply to
Tim Wescott

This am quite simple stuff unless you am stupid.

All you am need is volt reg thing and make reference voltage Vin + Vadd.

Ov course if you am stupid then education am not wurf bovring wiv.

Not problim EBAY.

DNA

Reply to
Genome

See, so now I have solved your problim what's this stuff about bacon in a fring pan along wiv toasty rolls and delicatlye tosted bunt cheese wiv crispy stuff plus softlee frid egg.

DNA

Reply to
Genome

There you go. YOU ABSOLUTE BASTARD YOU.

Come along and nance about with your nancy bollocks s**te from Google and then you bugger off.

FUCKING SCUM PIECE OF SCUM FUCK.

YOU SELL LOANS TO YOUR MATES AND THEN FUCK THEM OVER FOR A JOB AT HAMBURGERS R US TO APPEAR ON JUDGE JUDY.

Noncy boi.

DNA

Reply to
Genome

I think what you are looking for is a bootstrap charge pump doubler, often used to drive high-side IGBTs in motor controllers. Here is a good app note:

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A rough sketch of the circuit is:

ZD1 / +-->|----+ | / | Vin-----------+---------+---)|---+------Vout | | C2 | +---+ | | |Q1 | V D1 | +---+ --- | | | | +----)|---+-->|----+ | C1 +---+ |Q2 | +---+ | GND-----------+--------

The idea is that C1 is pumped to Vin when Q2 conducts. When Q1 conducts, you get nearly 2*Vin at Vout, except it is limited by ZD1. You may need a resistor across Q1 to get the pump primed. Choose C1 and C2 according to switching frequency and output current requirements. It is not highly efficient, but it only loses perhaps one or two watts out of a motor control that could be thousands of watts.

BTW, the schematic in the link from IXYS shows ZD1 connected to GND, which I believe is incorrect. I think it must go to Vin to get Vin + VZD1 on Vout.

Paul

Reply to
Paul E. Schoen

This does not seem that hard. Generate a variable regulated voltage (i.e same as your 10V or whatever you want to add to Vin) with an LDO or op-amp. Power a clock or squarewave generator, about 100kHz (freq not important but higher f means smaller caps can be used) from that. Some CMOS gates should do (in parallel if you need more current) for the clock output. From the clock output connect a cap (maybe 0.1uF and rated at the max Vout). Connect the other side of the cap to the center of 2 series-connected diodes (also rated for max Vout). The diodes point in the same direction. Connect the cathode (diode arrow pointing) end of the diode pair to another 0.1uF cap (that is your output). Connect the anode end of diode pair to your Vin. Vout will now be Vin + variable reg output - two diodes. You may have to mess with the freq and cap values to get output current and ripple to your liking.

snipped-for-privacy@gmail.com wrote:

Reply to
lens

Yes. The high side rail of the high side mosfets is a stable source. The problem is that it is not fixed from application to application.

With some motors, 24V is connected to the high side while others require 48V and so on. So even though the step-up is not a multiple but rather fixed this strikes me as not working. Whatever I build to add 10V ontop of 24V will add 20V on top of 48V when different motors are used and this will eventually lead to a gate to drain voltage that exceeds maximum and breaks down the insulation layer.

The trick I think is to get a wide range DC-DC power supply that given some input 10 - 180V (180V let's me use a very simple rectifier bridge and large cap. as an AC-DC power supply. Ripple in the motors isn't much of a problem.)

Anyhow. I would think if I had such a DC-DC converter (none of the simple switcher national parts go this high though) then I could repeatedly charge a cap from the 10V regulated source and pump it on top of the high rail to get a constant step-up of 10V regardless of the available power supply.

Thanks,

Tim Wescott wrote:

Reply to
druberego

Fantastic!!! Tie ground to the high rail primary voltage that I already have, tie the output (which will be Vcc+Vadd) to the gate logic like I want and tie the voltage regulator's input to... what?

If I had a secondary voltage high enough to drive a voltage regulator then I wouldn't need the voltage regulator would I? The problem is getting the secondary voltage in the first place and also a secondary voltage that is of a fix value relative to Vcc and not proportional.

Was your account highjacked and abused or are you just naturally this unfriendly?

Genome wrote:

Reply to
druberego

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