I'm toying with the idea of putting together a switching power supply (my first), using something like the LT1076-5 or the LM2576 controller ICs. These ICs have low external parts counts, and a relatively low switching frequency (56kHz-100kHz). Having spent some time reading datasheets for controller ICs, it's clear to me that some component placements are critical to the design. I'm wondering, then, if it's advisable or even possible to create and test the power supply on a breadboard, and later move it to a breadboard-layout protoboard.
If I'm not requiring ultra-high efficiency (any switcher's gotta be better than a linear when dropping ~35V, right?), does that make a difference? Or is it more likely to simply not work at all?
Best Answer
If built carefully and sensibly with shortest minimum lead lengths, short paths to power rails and proper decoupling and filtering then a breadboard can be not too much different than a PCB based supply. Good results can be expected and noise should not be vastly worse than a typical PCB based circuit.
If built as roughly as breadboard circuits often are then bad results can be expected. However, the low frequency (50 - 100 kHz MAY even save you in those cases.
Switches have a certain amount of magic in them. In some cases/locations a few pF of stray capacitance can make things go very wrong. BUT
I have successfully built numerous switchers on breadboards (plug in style).
LT1076 Datasheet:
LM2576 datasheet
Spec sheets say these operate at 100 kHz and 52 kHz so both are relatively "breadboard friendly".
The fixed voltage LM2575 has a slight edge in lashup-proofness as it has the critical feedback divider internally, but I'd recommend going with a variable output voltage version as being more useful and flexible and being able to teach you more. The LT part looks somewhat more capable overall.
Lower than higher frequency is liable to be more successful on a breadboard, so around 100 kHz is a good starting frequency. Old tech for most ICs. Even 1 MHz may be OK but capacitive coupling increases by 10X wrt 100 kHz. A 1 pF is 10 pF equiv. A 10 pF is 100 pF equiv. A few pF seldom hurt too much at 100 kHz.
Keep leads short. Group components together that share common heavy current paths. Bypass well. Do the best breadboard job you can. Avoid long loopy wires such as usually don't matter at all. Think ahead and plan it at least a little bit. Odds are it will work.
A trap is the feedback divider network (R1 & R2 in each case on datasheet page 1 diagram, but upper/lower swapped). Here yu have a feedback input pin and a divider from output to regulate voltage. Neither datasheet shows it, but a small capacitor across top resistor of divider (feedback ping to Vout) usually helps impulse response. A small cap from the centre point = Feedback pin to anywhere else is often a disaster. Ask me how I know :-). That MAY be most sensitive spot in many circuits.
Think about current paths. Inductor /switch/diode/filter caps (in and out), Ground and power sides.
If driving an external transistor (not relevant here) keep leads short. USe reverse zener across gate-source if using a FET.
The IC's chosen make life easy at the cost of some flexibility. For "playing" look at MC34063 - I recommend them to one and all. Old. Some defects. Cheap. capable and flexible and fun and low parts count. Built in high side current limit. Can do about ANY topology (boost, buck, buck boost, CUK, SEPIC, ... .
MC34063 datasheet
See figs 15, 20, 21 in datasheet for step down examples.
Fig 15 is with internal switch. Up to 0.5A out - maybe more.
Fig 20 uses NPN external but I'd use an N Channel FET.
Fig 21 uses PNP external - I'd use a P Channel FET.
I'd prefer Fig 20, with N-Channel FET.
This will do 36V + direct (40 V rated) BUT start at say 12V to 5V to play. MUCH more energy and things to go wrong at 36V in.
Ask more questions if of interest.
ADDED: 20 July (NZT)
The example ICs which have all pins in a straight line give every prospect of good results if used following the guidelines above and data sheet guidelines.
The IC can be positioned so that power rails are fed from breadboard strips only a few tenths of an inch away and decoupled with minimal lead lengths. There are few other components and these may be placed with very short leads.
However, this is such a simple circuit that use of "vectorboard"/ veroboard / ... etc copper strip board would allow a tidy and easy implementation with slightly less to go wrong.
When using plug in bread boards some component leads are so thick that they will either not fit or will permanently "set" the breadboard springs if inserted. These can be dealt with by soldering SHORT lengths of wire to them as lead extensions and plugging these into the board. Properly done and with leds trimmed the result looks OK and is liable to be effective.
Too thin wire may also have contact problems.