Summary of 5V/400V DC/DC converter
Small, inexpensive 5V→400V DC/DC converter using the MC34063 in boost configuration is presented, suitable for low-power projects like Geiger–Müller counters. It has limited output power and temperature stability but can be improved by component selection. Key components include a coil-based step-up stage (Q1, L1, D2), rectification/filtering (D2, C4), and feedback network (R3–R11, C3) with selectable output via S1. Safety cautions emphasized due to high voltage; converter can drive GM tubes for radiation detection using three STS-5 lamps for increased sensitivity.
Parts used in the 5V/400V DC/DC converter:
- MC34063 IC
- Q1 power MOSFET (rated above output voltage)
- L1 coil (inductor for step-up)
- D2 rectifier diode (Schottky recommended)
- C1 timing/stability capacitor
- C3 feedback/stability capacitor
- C4 output filter capacitor (high voltage rated)
- R3 through R11 resistors (feedback network)
- S1 output voltage selector switch
- Geiger–Müller tubes: three STS-5 lamps (for detector application)
A small and cheap 5V/400V DC/DC converter can be useful in many DIY projects, e.g Geiger–Müller counters. I will present here one of such DC/DC converter based on popular MC34063 chip in step-up configuration.One big limitation of this device is little output power, but for many applications this won’t be a problem.
Another problem is poor temperature stability, but this could probably be improved by using low tolerance C1, R7-R11.Q1, L1, D2 are coil-based step-up converter. Q1 should be a power MOSFET rated a bit more than the output voltage. Empirical tests have shown that Q1 didn’t heat up, so I didn’t mount it on a radiator. D2 and C4 rectifie output voltage, they also should be rated for bigger voltage than the output. To improve performance, D2 can be replaced by a Schottky diode, capacitance C4 can be increased. R3-R11, C3 provide output feedback to the MC34063. S1 is used to select output voltage if needed.Such high output voltage can be dangerous (even while the maximum curent iof this converter s small), so if you make the same or similar device, please be careful. If you are interested in higher voltage, you ma take a look on The Geiger–Müller counter is a relatively simple tool to measure ionizing radiation. To increase sensitivity, construction presented here contains three (instead of one as usually) soviet STS-5 lamps. This is important for measurements of natural sources of (low) radiation like soil, rocks (an article about my trip with Geiger–Müller counter on Śnieżka mountain).When high voltage (typically 380-420V) is applied to the Geiger–Müller tube, the tube doesn’t conducts electricity, but it does conducts for a short period, when radiation particle is observed. Those pulses are observed by the detector. The level of ionizing radiation is proportional to the amount of pulses detected in a constant interval of time (typically from 20s to 2,5min).
For more detail: 5V/400V DC/DC converter
- What IC is used in the step-up converter?
The MC34063 chip is used in step-up configuration. - Can this converter power a Geiger–Müller counter?
Yes, it is suitable for low-power projects like Geiger–Müller counters. - What limits the device performance?
Limited output power and poor temperature stability are the main limitations. - How can temperature stability be improved?
Using low tolerance C1 and resistors R7 through R11 can probably improve temperature stability. - Which parts form the step-up stage?
Q1, L1, and D2 form the coil-based step-up converter. - What should Q1 be rated for?
Q1 should be a power MOSFET rated a bit more than the output voltage. - How is the output rectified and filtered?
D2 and C4 rectify and filter the output; D2 can be replaced by a Schottky and C4 increased to improve performance. - How is output voltage feedback provided?
Resistors R3 through R11 and capacitor C3 provide output feedback to the MC34063. - Is the high output voltage dangerous?
Yes, the high output voltage can be dangerous even though the maximum current is small, so caution is advised. - Why use three STS-5 lamps in the detector?
Using three STS-5 lamps increases sensitivity for measuring low natural radiation sources.
