Power Electronics and
Here are power supply, inverter
drives, chargers and high current equipment diagrams and links.
There are Mosfet and Thyristor circuits too.
Power Supplies, Inverters, UPS
Chargers, Electro Plating, Precision Welding-erosion, Coating
Metals and many other Processes are made of high current
circuits. Even in measurement of parameters like Micro-Ohm
high currents are involved. Electronic Circuits are
required in such products to give control to time, current,
frequency and voltage in order to accomplish with the required
precision a process or job.
Solid State Relays or Thyristor Contacters
In any power equipment, efficiency and reduction of bulk is
crucial so SMPS and high frequency control is an important part
of this domain. These products also generate EMI-RFI
Product Safety Study is also vital.
EMI RFI Filters and Electrical Noise Control
(These are notes jotted down of my experience in the 90s,
it may have spelling and other errors)
SMPS designs should have clear line or patch of isolation for
product safety and long term reliability. If you use
opto-couplers they need to have 5kV or better isolation and
10mm between pins. The Live circuitry and the output circuitry
should not overlap on PCB, tracks should not stray to the
opposite side, The Transformers can be split bobbin if
possible. A 10 to 20 mm desert (means no tracks) running from
end to end of PCB under Transformer and under optos etc., Even
ground tracks and ground planes should not stray.
Related Pages in delabs
The high voltage side must have layer to layer (mylar)
insulation, means wind a layer and then put the yellow mylar
tape, make tape concave so no strands should slip over to next
layer, use split bobbin if possible. have terminations far
away and enclosed for safety. vacuum impregnate with natural
resin or epoxy depending on voltage and environment. product
safety is very important.
- If in your power supply you have a varistor, then you
should have a fast acting fuse in series, as varistor fail
as a short.
- Wire and crimping of wires for supporting the high
currents and high voltages must be carefully chosen. The
copper cross section area gives its ability to carry
current, the quality, thickness and flexibility of the
insulation gives its voltage capability. The Tightness of
the crimped contact will ensure long term reliability.
Mechanical Stress prevention for all wiring is very
important and guarded termination for user-operator safety.
- BTA16600 and triacs of this series from ST have the metal
TO220 tab electrically insulated from the device.
and others, switch triacs at zero crossover which reduces
EMI-RFI and spikes. It means when the sine wave is close to
zero volts the triac is turned on.
- You have to ensure proper air circulation and fix proper
heat-sinks with thermally conductive heat-sink compound or
silicone grease with alumina. Anodized Aluminum heat-sinks
with large surface areas and small fans are used in power
electronic products for this purpose. If a component works
very hot the specs will get derated, precision is lost and
undesirable and unpredictable results will happen.
- A thermistor must be used in series with huge power
electrolytic capacitors to limit the enormous current inrush
on start, or spikes may stress components, cap or EMI-RFI.
- A freewheeling diode should be used across a relay,
solenoid coil or motor because inductive kickback will
damage transistor or mosfet. High current loads like relays
can reset logic circuits if ground is not connected well, It
also produces more ripple in supply, so it is better to have
a separate supply for such parts.
- EMI-RFI causes-Switching Loads Simultaneously (inductive
loads). Power factor correction capacitors and devices.
Lightning strikes (enhanced by earth faults). Line
Inductance (inductive kickback, resonance). DC and AC Drives
for Motors. Rectifiers with large filters and stray
- Small battery
operated gadgets when turned on after a very long time may
not work properly due to a thin oxide layer at the battery
connector, replace cells if required, scratch and clean
battery and connector surface, the reason is some gadgets
consume so low power that the current cannot break a
micronic oxide layer. Keep using regularly.
- Loose Contacts may have a resistance like 100mE
(milliohm). A bit of corrosion and 10A of current will make
that dissipate 100 * 102 = 10,000mW = 10W , if the contact
area is 1 sqmm the heat will cause the resistance to
increase, then the dissipation becomes more, sparking and
welding may happen, it can even cause fire.
Supplies and SMPS,
Transformers, Drive circuits for Motors, Heaters and Solenoids
are all Power Electronics. Thyristors, Mosfets and High Power
Transistors are important components used in these circuits.
Stability and Supply Regulation
- Foldback circuits in the form of constant current or
voltage can protect a Power Circuit from overload. eg.
- Air gap in inductor core prevents saturation of the
Magnetics, it must be made like that when required. eg.
- High power equipment should have a soft start, so that
fuses dont blow on start, inrush can cause damage to parts.
- Caps can be put in series to double voltage withstand
capability, when we put el-caps in series they have to be
identical in value. put caps in parallel to increase the cap
uF value and it also lowers ESR which is equivalent series
resistance, this is good when filtering in SMPS. Two el-caps
with the negatives of both connected and the positive
terminals serving as the two terminals will give a non-polar
cap, used in crossover networks.
- When smps has to work at 100Khz or more, the primary of
transformer must have multiple strands, and secondary can be
a copper flat ribbon. this is due to skin effect, as high
frequency current flows on surface of conductor.
needs a turn on pulse and a turn off pulse as gate
capacitance is huge.
- Do not club Heatsinks unless the heatsink is very big or
the clubbed components form a part of a current sharing set.
If you club say two TO220 devices one dissipating 10W with a
2 Watt heating device, you may reduce reliability of the 2W
device. Then clubbing parallel current sharing devices on
one heatsink may be a good idea as it may reduce thermal
runaway, also parallel power transistors should each have
0.1E in emitter path, this also can force load sharing on
- Test a mosfet, charge the gate with the DMM in diode mode,
then there is a short between source and drain.
- Snubbers consisting of R-C should be used across switches,
relay contacts, MOSFETS when switching inductive loads, this
will absorb the spike and save the device.
- Transformers used in SMPS could be split bobbin for
product safety, and transformers should be resin
impregnated, hazard may arise when using a badly made
- In a SMPS which is not earthed the floating (unconnected)
earth terminal will give a slight shock due to the two Y
caps connected to earth from phase and neutral.
- Power mosfets, transistors or IGBT's should be
electrically isolated very well from heatsink with alumina,
mica or silpad. It could withstand 2KV -5KV DC, related to
product safety. Also these heatsinks should not be earthed
but floating, do not fix to the metal chassis for maximum