quick n dirty boost

That circuit does not produce a regulated output voltage.

At a few milliamperes output, a charge pump might be a simpler open loop supply:

See figure 4-6.

LC oscillator. Single transistor.

Tim

-- Deep Fryer: a very philosophical monk. Website:

Do you have a link or something I can see?

Bottom of:

Part of "Floating Supply Inverter".

Q14, C27 (L2 optional), C28, R77, C28, erm, huh, I put two C28's on that schematic, and T4.

Q14 was a ZTX651 but for your current requirement, a 2N3904, 2222, 4401 or anything else rated for the voltage will work.

On the transformer, instead of a secondary winding, you can use a highspeed diode from the transistor collector to get the doubled voltage. In this schematic, I needed an isolated supply, so I needed a secondary.

The primary winding (labelled 20uH) should come to around 20-40 turns of fine wire on a ferrite transformer core. The capacitor across it should be smaller, more like 0.01uF. The feedback winding (going to the transistor base) should be 1-5 turns, depending on supply voltage and primary turns.

It's pretty fool-proof.

Tim

-- Deep Fryer: a very philosophical monk. Website:

You can add regulation by using a TL431 as a feedback element. it should shunt the gate of the nmos when the output reaches the appropriate voltage... use a voltage divider to feed the R input. You could also use a zener and an NPN transistor to do this.

JP mentioned the TC7662, which is also a nice solution, will probably require fewer parts, and will be less likely to stall or fail. For a small current requirement, it works well (although it won't give you 2x voltage, due to the diode drops required.)

--
Regards,
  Bob Monsen

The unleashed power of the atom has changed everything save our modes
of thinking and we thus drift toward unparalleled catastrophe.
    Albert Einstein, Telegram, 24 May 1946

Okay, I think I will try it. Instead of winding my own inductor, I'll just take one of those little chokes that looks like a two-watt resistor and wrap a few turns of fine wire around it; if it doesn't work I'll wrap it in the other direction.

Depending on load and inductor value, the output voltage of that circuit could climb until something (MOSFET, diode or capacitor) breaks down.

I suggested using a feedback element to regulate it. He can do it like this:

12v | +-------, | | | )|| | )|| | )|| ,------,--,------+ )|| | | | | | 1K R R 1K +->|-+---+----OUT | | | | __| | | | | | | | | | +--||--+ +--||--+-o-||nmos --- | | \\/ | | |__ --- | \\c /\\ c/ | | | | |----' '----| B | | load /e e\\ | | | | | | | | '----------------+-------'----'---' | gnd

B OUT | | | [150k] --- | /x\\------- + --- | | [17.4k] | | GND-+---------'

x is a TL431A

He can also do this:

B | / c |\\| b---| |--[100]---OUT e |/| | / | 23V Zener GND-'

However, just using the TC7662 is the easiest, and it probably won't fail to start in 2 years due to a decreased beta in Q1 and smoke...

-- Regards, Bob Monsen

Science is a wonderful thing if one does not have to earn one's living at it. Albert Einstein (1879 - 1955)

Right. Probably less board space as well.