International Rectifier Control ICs are monolithic power integrated circuits
suitable for operating low-side and high-side MOSFETs or lGBTs through logic level,
referenced to ground input leads.
They feature balanced out voltage
functionality as much as 600 VDC and, contrary to ordinary driver transformers,
can bring super-clean wave-forms with virtually any duty-cycle from 0 to 99%.
IR215X sequence is actually a recently available accessory to the Control IC
family and, besides the previously mentioned characteristics, the product employ
a top end comparable in performance to the LM 555 timer IC.
These types of
driver chips give you the developer with self oscillatory or coordinated
vacillation capabilities purely with the help of alternative RT and CT
components See figure below
They likewise have in-built circuitry which offers a
moderate 1.2 microsecond dead-time between outputs and switching high side and
low side components for driving half-bridge power devices.
Whenever included in
the self oscillatory form the frequency of oscillation is calculated simply by:
f = 1/1.4 x (Rt + 75ohm) x Ct
The three accessible self-oscillating devices are
IR2151, IR2152 and IR2155. IR2I55 seems to have more substantial output buffers
that will turn a 1000 pF capacitive load with tr = 80 ns and tf = 40 ns.
includes minuscule power start-up and 150 ohm RT supply. IR2151 possesses tr and
tf of 100 ns and 50 ns and performs much like IR2l55. IR2152 will be
indistinguishable to IR2151 although with phase cambio from Rt to Lo. IR2l5l and
2152 include 75 ohm Rt source (Equation l.)
These types of drivers usually are
meant to be furnished with the rectified AC input voltage and consequently these
are intended for minimal quiescent-current and still have a l5V in-built shunt
regulator to ensure that just one limitting resistor works extremely well
through the DC rectified bus voltage.
Looking yet again to Figure 2, be aware
the synchronizing potential of the driver. Both back-to-back diodes in line
together with the lamp circuit are efficiently configured as a zero crossing
detector for the lamp current. Ahead of the lamp strike, the resonant circuit
involves L, Cl and C2 all in a string.
Cl is a DC blocking capacitor having a
low reactance, in order that the resonant circuit is successfully L and C2. The
voltage around C2 is amplified by way of the Q factor of L and C2 at resonance
and hits the lamp.
As soon as the lamp strikes, C, is appropriately short
circuited by the lamp potential drop, and the frequency of the resonant circuit
at this point is determined by L and Cl.
This leads to a change to some lower
resonant frequency in the course of standard operations, just as before
coordinated through sensing the zero-crossing of the AC current and taking
advantage of the resulting voltage to regulate the driver oscillator.
As well as
the driver quiescent current, you will find a couple of additional elements on
DC supply current which are a functionality of the very application circuit:
current as a result of charging the input capacitance of the power FETs 2)
current resulting from charging and discharging the junction isolation
capacitance of the International Rectifier gate driver devices. Each components
of current arc charge-relatcd and for that reason stick to the rules:
Q = CV
It could conveniently be observed, consequently, that to be able to charge and
discharge the power device input capacitances, the expected charge can be a
product of the gate drive voltage and the true input capacitances and also the
input power recommended will be specifically proportionate to the product of
charge and frequency and voltage squared:
Power = QV^2 x F / f
mentioned associations propose the below factors when making a real ballast
1) pick the smallest working frequency according to decreasing inductor
2) opt for the most compact die volume for the power devices
dependable with reduced conduction deficits (that minimizes the charge
3) DC bus voltage is normally selected, however , if there
exists a alternative, make use of the minimum voltage.
NOTICE: Charge is simply
not a functionality of switching rate. The charge transmitted is the very same
with regard to I0 ns or 10 microsecond transition times.
We will at this point
take into account a few useful ballast circuits which can be achievable using
the self-oscillating drivers. Probably the most well-liked fluorescent light
fixture may be the so called ‘Double 40’ type which often employs a couple of
typical Tl2 or TS lamps within a common reflectante.
A pair of recommended
ballast circuits are demonstrated in the following figures. The first is the minimal
power factor circuit, along with the other works with a novel diode/capacitor
settings to accomplish a power factor > 0.95. The lower power factor circuit
proven in figure 3 welcomes 115 VAC or 230 VAC 50/60/400 Hz inputs to generate a
moderate DC bus of 320 VDC.
Considering that the input rectifiers carry out just
close to the peaks of the AC input voltage, the input power factor is around 0.6
lagging with a non-sinusoidal current wave-form.
Such type of rectifier is
simply not advised for anything at all apart from an assessment circuit or
reduced power compact fluorescent and without a doubt could become unwanted as
harmonic currents in power supply devices are additionally lessened by power
Observe that the International Rectifier IR2l51 Control IC
performs dircctly off thc DC bus by way of a limiting resistor and pivots at
close to 45 kHz in conformity with the given relationship:
f = 1/1.4 x (Rt + 75ohm) x Ct
Power for the high side switch gate drive arises from a bootstrap
capacitor of 0.1 pF and that is charged to roughly 14V anytime V5 (lead 6) is
dragged low within the low side power switch conduction.
The bootstrap diode l
IDF4 prevents the DC bus voltage as soon as the high side change conducts.
fast recovery diode ( <100 ns) is necessary to be certain that the bootstrap
capacitor will not be moderately discharged since the diode comes back and
obstructs the high voltage bus.
The high frequency output in the half-bridge is
actually a square wave with extremely fast changeover periods (around 50 ns). To
avoid abnormal extended noises through the fast wave fronts, a 0.5W snubber of 10 ohm and 0.001 pF is employed to minimize the switch periods to just about 0.5
Observe that we have a built-in dead time of 1.2 ps in the IR2l 5I driver to
stop shoot-through currents in the half-bridge. The fluorescent lamps are
controlled in parallel, each using its own L-C resonant circuit. Approximately
four tube circuits could be operated from a single set of two MOSFETs measured
to match the power level.
The reactance valuations for the lamp circuit are
picked from L-C reactance tables or through the formula for series resonance:
f = 1/2pi x square-root of LC
The Q of the lamp circuits is pretty small simply because of the
advantages of functioning from a fixed rate of recurrence which usually,
obviously, may differ due to RT and CT tolerances.
Fluorescent lights tend not
to generally need extremely high striking voltages therefore a Q of 2 or 3 is
enough. ‘Flat Q` curves often originate from bigger inductors and small
capacitor ratios in which:
Q = 2pi x fL / R, wherein R is often greater because a lot more
turns are employed.
Soft-starting during tube filament pre-heating may be
inexpensively contained by utilizing PTC. thermistors around each lamp.
manner, the voltage along the lamp steadily boosts as the RTC. self-heats right
up until eventually the striking voltage together with hot filaments is achieved
and the lamp illuminates.