RC4190M datasheet(19/25 Pages) RAYTHEON

19 / 25 page

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.

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

inductor current rises to its highest operating value (IMAX).

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.

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.

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.

Figure 25. Electricity Versus Magnetism

Figure 26. Typical Manufacturer’s Curve Showing Saturation Effect

E = I * R

65-3464-07

North

Electrical Circuit

Magentic Circuit

South

Flux

H =B •

6000

5000

4000

3000

2000

1000

-0.5 0 0.5 1

2 2.5 3

H Oersteds

+25

°C

+85

°C

+125

°C

Stackpole Ceramag 24B

Hysteresis Loop vs. Temperature

RC4190M Datasheet(PDF) 19 Page - Raytheon Company

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