Nuts and Volts - November 2008

■ FIGURE 6

Last month, Figures 6 and 7 (solar power supply) were inadvertently left out of the layout. They are reprinted here for your convenience and are also available at www.nutsvolts.com.

90 VOLT SUPPLY PARTS LIST

■ FIGURE 7; October ’08 issue

PART ■ IC1 ■ IC2 ■ Q1 ■ D1 ■ LED1 ■ R1 ■ R2 ■ R3 ■ R4 ■ R5 ■ R6 ■ R7 ■ R8 ■ C1, C2 ■ C3 ■ C4 ■ T1 Core ■ T1 Bobbin ■ Battery ■ Solar Panel

DESCRIPTION P/N NE556 dual timer 595-NE556N LM393 dual comparator 511-LM393N NMOS, 100V, 0.45A, logic level 522-ZVN4210A 400V, 1A, 50 ns, DO- 41 821-1N4936 Red 156954 13.3K, 1/8W, 1% 270-13.3K-RC 1.0K, 1/8W, 1% 270-1K-RC 6.81K, 1/8W, 1% 270-6.81K-RC 100Ω, 1/8W, 1% 270-100-RC 10Ω, 1/8W, 5% 270-10-RC 1M, 1/8W, 1% 270-1.0M-RC 10K, 1/8W, 1% 270-10K-RC 10K trimpot 652-3296Y-1-103LF 1,000 pF, 50V, NPO 81-RPE5C1H102J2P1A03 0.1 µF, 50V, X7R 81RPER71H104K2P1A03 0.1 µF, 200V, film 80-R821C3100DQ60J F-42510-EC B2510-10 6V gel cell, 1.3 Ah 4.5V/90 mA, 2 3/8” square

SUPPLIER Mouser Mouser Mouser Mouser Jameco Mouser Mouser Mouser Mouser Mouser Mouser Mouser Mouser Mouser Mouser Mouser Magnetics Magnetics Mouser BG Micro

type with two 15 volt windings to give a 1:1 ratio. A 240/24 volt transformer should work also. It is all in a securely fastened plastic box. Also, because the mains voltage in the US is 120 VAC, the resistor R4 is 620 ohms, 5W.

Dimmer for 12 VDC Lamps

QI have a small pop-up camper with two sets of dual lamp light

fixtures in it. There is only a single on/off switch. I would like to build a couple of dimmers for these fixtures. I think I can do this the easiest with a circuit similar to a switching power supply. What are your thoughts and ideas for a circuit?

— Tom Bohacek

632-GH613 PWR1241

AIt is only necessary to chop the 12 volts; 12 volt lamps are normally 40 watts and there are two of them so the current to be chopped is: I = P/E = 80/12 = 6. 7 amps. A 556 IC driving a MOSFET is the circuit; see Figure 6. The frequency only needs to be high enough that you don’t see the flicker, so 100 Hz will work. The first 555 is an astable and provides the frequency. The second 555 is a one