SMPS problems

[5321488]

Hi everyone,

I built an SMPS from an article I found online, schematic attached (the one Dave used for his nixie sub counter, https://threeneurons.wordpress.com/nixie-power-supply/hv-supply-kit/). I'm not getting the desired output voltage at all, and Q2 and L1 are becoming very hot. I've checked and checked and checked the circuit and it seems fine, and Q2 is still testing ok. I added a resistor in series with L1 but while it solved the heat it didn't produce any decent output voltage.

If someone was able to have a look and spot any issues I'd really appreciate it.

[Circlotron]

The IRF630 looks like it is drawn upside down. Big problems if it is actually connected this way.

[tautech]

https://www.onsemi.com/pub/Collateral/MC34063A-D.PDF

Look where the inductor is on P8.

[Circlotron]

No, the OPs cct is basically the same as the one in fig 9.

[eblc1388]

The connection of the IRF630 is wrong in the original circuit. See the correct one below.

[T3sl4co1l]

Holey moley, a TIFF disguised as a JPG!

Fixed:



Yeah, that's upside-down.  Note the diode (which is redundant, because note the arrow into the MOSFET junction indicating the body diode too!) shorting the inductor to GND.

Q1 is backwards, too.

Tim

[eblc1388]

Good catch on Q1, missed that.

[5321488]

Ah thanks so much!! Just switched both, Q2 and L1 are working perfectly, but Q1 is now hot after switching it around. I would agree now that it seems backwards, but should I switch it back?

EDIT: forget that, its actually D1 now super hot. Any ideas?

[eblc1388]

You can try place in series a 22 ohm resistor between the cathode of 1N914 and the emitter of MPSA55.

[T3sl4co1l]

Might be worth checking if you've shorted any components at this point.  Check the transistors, diode, controller sure why not?

Tim