RC4190
PRODUCT SPECIFICATION
When the switch is the down position, the capacitor charges
up to the battery voltage. The, when the switch is changed to
the up position, the capacitor is put in series connection with
the battery, and the doubled voltage is applied directly to the
positive power supply lead of the RC4190. This voltage is
enough to bias the junctions internal to the RC4190 and gets
it started. Then, when the stepped up output voltage reaches
a high enough value, diode D1 is forward biased and the out-
put voltage takes over supplying power to the RC4190. The
circuit is shown with component values for +5V output, but
the circuit can be set up for other voltages.
Question: What happens if too small a core is used?
First, one must understand how the inductor's magnetic field
works. The magnetic circuit in the inductor is very similar to
a simple resistive electrical circuit (see Figure 20). There is a
magnetizing force (H, in oersteds), a flow of magnetism, or
flux density (B, in Gauss), and resistance to the flux, called
permeability (U, in Gauss per oersted). H is equivalent to
voltage in the electrical model, flux density is like current
flow, and permeability is like resistance (except for two
important differences discussed on the following page).
First Difference: Permeability, instead of being analogous
to resistance, is actually more like conductance (1/R). As
permeability increases, flux increases.
Electricity Versus Magnetism
Electrically the inductor must meet just one requirement, but
that requirement can be hard to satisfy. The inductor must
exhibit the correct value of inductance (L, in Henrys) as the
Second Difference: Resistance is a linear function. As volt-
age increases, current increases proportionally, and the resis-
tance value stays the same. In a magnetic circuit the value of
permeability varies as the applied magnetic force varies.
This nonlinear characteristic is usually shown in graph form
in ferrite core manufacturer's data sheets. See Figure 26.
inductor current rises to its highest operating value (I
).
MAX
This requirement can be met most simply by choosing a very
large core and winding it until it reaches the correct induc-
tance value, but that brute force technique wastes size,
weight and money. A more efficient design technique must
be used.
Electrical Circuit
Magentic Circuit
I
E = I * R
1
H =B •
U
R
E
North
South
Flux
65-3464-07
Figure 25. Electricity Versus Magnetism
6000
+25°C
5000
+85°C
4000
+125°C
3000
2000
1000
0
Stackpole Ceramag 24B
Hysteresis Loop vs. Temperature
-0.5 0 0.5 1
2
2.5 3
5
7
9
H Oersteds
Figure 26. Typical Manufacturer’s Curve Showing Saturation Effect
19
RAYTHEON [ RAYTHEON COMPANY ]
