DC DC boost giving high voltage , minimum quiescent current

Question

My dc-dc gives 25 V on load instead of 5 V, Arduino calculator shows similar values for 3 V supply.
Supply is 3 V 2 AA batteries.

Led blinking ON for 100 msec OFF 900 msec, current 150mA

The intended load is 5V, to run 5 LED in parallel at 150 mA total current.

Base resistor is 3.3 kΩ, inductor 47 µH.

Square wave oscillator uses 470 kΩ and 100 nF capacitor running on 74HC14. Also used SMD values 1 kΩ & 4.7 nF, giving 110 kHz.

How to get 5 V and 150 mA output?
Transistor should go into saturation, need minimum quiescent current required to save battery current. Ripple can be 0.3 V.

Update: I tried 10 nF, 100 nF, the cap at HC14 osc, still voltage is above 18 V.

Update: 2 smd pcb boards were assembled. Board 1 gives 5V , board 2 gives 25 V.

Board1 has SS14 diode, base resistor 1k , 22mH inductor.

Board2 has BAT65 diode, base resistor 2k2 , 47mH inductor.
Transistor used is 2n2222.
Load and no load has little change in voltage around 3.5 V

Answer 1

This circuit works well.
It's not pretty, but it works superbly.

You could adapt the shown regulator to suit your own system, or could create a simpler one based on the same principle.
Example only: A zener diode fronm the output to the oscillator gate input would pull up the oscillator input when Vout exceeded the zener voltage "plus a little". This turns off the transistor.

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Here is a related post from "The PICList in 2010"

I did something extremely similar* some years ago - even extending to the LDO with one Vbe drop which I used to drive the SMPS feedback.

I guess in retrospect that I expected the drive clamp to work on whole cycles when regulation was reached BUT what actually happened was that it adjusted the length of the drive pulses to maintain very smooth cycle by cycle regulation. Intuitive in hindsight but a pleasant discovery at the time.

... It was used to provide a stable local supply for the logic core in the face of widely varying battery voltage** and sudden very large and noisy electromechanical battery loads. AFAIR the CD40106 smps and 2 x LDOs quiescent current loads and some logic idled "in regulation" at slightly under 100 microamps. (** 4 x C cells and some logic rated at nominal 5 volts. Not a marvellous design initially).

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Here we are. Seemed worth digging up. Y' don't buy no ugly SMPS! I hacked this out of the middle of a jpg with other irrelevant stuff in it and cut and pasted it into left to right alignment using Irfanview so the result is even less beautiful than the ugly original.

LH inverter is an oscillator with 2 x R + diode providing asymmetric mark/space.
RH inverter (RHI) drives transistor to provide drive to L21 which "rings" to > Vbattery when Q21 is turned off.
When voltage on C22 at input of LDO regulator rises a Vbe drop =about 0.5 Volt above regulator output then Q22 starts to turn on.
If Q22 is turned partially on it will pull input of RHI high thereby stopping drive to Q21.
The squeamish may wish to put a resistor betwixt Q22c and RHI pin 3.
If Q22 was turn hard on the drive would cease suddenly until C22 voltage fell far enough to turn Q22 off.
In practice Q22 turns on enough to be "modulated" by rising V_C22 to reduce the effective length of the drive pulses to Q21. Look at it too too hard and the logic begins to fail, but in practice this is what happens.

The arrangement with Q22 and IC22 means that the LDO regulator is always supplied with a voltage about 0.5 volt above its output. As long as the LDO does not drop out with this delta-V it works well.

I show an LM2950, which is good enough for this, but the final version used a superb and approx zero cost Taiwanese sourced LDO.
Frequency, mark space ratio and inductor values can be arranged to suit. This would work well enough at milliWatts to Watts.

The 40106 allows very low Iq with no load.
I left R26 in, although its purpose is obscure - presumably it snubbed a slight transient. Inductor value is high, reflecting low power level here.
Note that the oscillator is loaded by the modulation but not stopped and that right hand inverter only needs a sniff of signal SO this system could 'borrow" a clock from anywhere available and us only a single inverter. OR replace RH inverter with a MOSFET and pullup and get a discrete parts add on smps.
1 x MOSFET, 2 x bipolar, L, C, LDO.

Answer 2

Working off your design:

^{simulate this circuit – Schematic created using CircuitLab}

You're going to have to modify R1 and/or R2 to adjust the frequency and duty cycle. Bigger R1 will give you lower frequency and lower duty cycle which will amount to lower voltage. I don't have any useful formulas for frequency and duty cycle; the ones I know won't be very precise for this. It's best you optimize this with an equivalent load resistor, tweak R1 and R2 until you get the desired operating point, then put the LED load back in circuit. That's what I would do in real life. Also, this isn't a regulator. So the output will be affected by input voltage and output loading to some degree. Fortunately, your load is constant and tolerant to poor regulation.

Answer 3

How to get 5 V and 150 mA?

Some modifications could be made, adding an equal "load" (5 / 0.15 = ~ 35 Ohm).
Changing also resistor base.

Simulated with microcap v12.

Note that without the "load", voltage output may be much "higher".