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G8MNY > TECHNI 05.03.21 11:05l 106 Lines 4716 Bytes #999 (0) @ WW
BID : 25863_GB7CIP
Read: GAST
Subj: Car 12V Switch Mode Adaptors
Path: DB0FFL<OE5XBL<DB0RBS<DB0ERF<DB0RES<ON0AR<OZ5BBS<CX2SA<N3HYM<AL0Y<
KD8FMR<PY2BIL<OK2PEN<GB7CIP
Sent: 210305/0952Z @:GB7CIP.#32.GBR.EURO #:25863 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Update Jan 08)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
12V adapters for your Walkman, Mobile Phone, PDA, GPS, Digital Camera etc. are
often based on the many versions of the 1.5A 34063 8 pin DIL switch mode
regulator IC in this circuit using several PCB layouts in different sized plugs
adaptors.
I have seen what happed to a GPS (not mine) when the 12V to 5V adaptor failed!
There was no worthwhile fusing/zener to protected the kit & hence the whole
thing is a right off, after the GPS internal 3.3V regulator then failed
(overheated), fusing the CPU to a short circuit with 12V!
12V Fuse
CarÄÄo-oÄÂÄÄÄÄÄÄÄÄÄÄÂÄÄ¿ ÚÄÄÄÄÄÄÄÄÄÂÄÄÄÄÂÄÄÄÄÂÄÄÄÄÄ>+ to gadget
Plug ³ R1 ³ R2 ||( ³ ³
³ ³ ³ ³ ||( L1 ³ _³_
³ ÚÄÄÄÄÂÄÄ´ ³ ÃÄÄÄÄ¿ ||( ³ \_/==
³ ³ 8ÚÁÄÄÁÄÄÁÄÄÁ¿5 R3 ³ ³+ ³LED
³ ³ ) K34063 ³ ³ ³ === ³
³ ³ 1ÀÂÄÄÂÄÄÂÄÄÂÙ4 ³ ³ ³C3 ³
³ ÀÄÄÄÄÙ ÀÄÄ)ÄÄ)ÄÄÄÄ>ÄÄÄÄ´ ³ R4
³+ ³ ³ ³ _³_ ³ ³
C1===C1 C2=== ³ ³ /_\D1 ³ ³
gnd- ³47uF ³ ³ ³ ³ ³ ³
gndÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÁÄÄÄÄÁÄÄÄÄÁÄÄÄÄÁÄÄÄÄÁÄÄÄÄÄ>- to gadget
Typical values
R C D Fuse IC PIN Function
1 1 - 4.7R 47uF 1N4001 2A 178 Current drain & sense-
2 1 - 4k7 n47 - 1n 2 Switched Output
3 560 - 1k 4u7 - 220u 3 Osc Timing C
4 330 - 1k 4 Ground
5 Voltage NFB
6 Current limit +ref
R2/3 sets the output voltage.
R1 sets the switching current limit.
Output cap C3 has ripple on it due to pulse currents. These give this sort of
spiky ripple..
³³ ³
³³_ ³_ Due to the small capacitor value. its self inductance,
Mean DC´ ~-_³ ~-_ & ESR, you always get this waveform with the sharp rise
³ QRM edge on the gadget lead of these adaptors.
³
³
ÁÄÄÄÄÄÄÄÄÄÄ>Time
Problems with this simple circuit are:-
1/ No output over voltage protection. (important on costly gadgets!)
2/ No input idiot diode.
3/ High output ripple & QRM?
4/ High input ripple & QRM?
5/ Direct QRM magnetic radiation from L1 if bobbin type.
6/ Too high a fuse rating?
7/ Only 1 ground spring connected in car plug earth.
IMPROVEMENTS
If you have space in the plug, try some of these embellishments...
12V Fuse __
CarÄÄo-oÄÂÄ((()ÄÂÄÄÄÄÄÄÄÄÄÂÄÄ¿ ÚÄÄÄÄÄÄÄÄÂÄÄÄÂÄÄÂÄÄ(((()ÄÂÄÄÂÄÄÄÄ>+ to gadget
Plug ³ ==== ³ R1 ³ R2 ||( ³ ³ ===== ³ ³ ~~
³ L2 ³ ³ ³ ³ ||(L1 ³ _³_ L3 ³ ³ FB
³ ³ ÚÄÄÄÂÄÄ´ ³ ÃÄÄÄÄ¿ ||( ³ \_/== ³ ³
_³_ ³ ³ 8ÚÁÄÄÁÄÄÁÄÄÁ¿5 R3 ³ +³ ³LED +³ ³
/_\ ³ ³ ) K34063 ³ ³ ³ === ³ C4=== ³
D2³ ³ ³ 1ÀÂÄÄÂÄÄÂÄÄÂÙ4 ³ ³ C3³ ³ ³ ³D3
³ ³ ÀÄÄÄÙ ÀÄÄ)ÄÄ)ÄÄÄÄ)ÄÄÄ´ ³ R4 ³ _³_
³ ³+ ³ ³ ³ _³_ ³ ³ ³ /_\'
³ ===C1 C2=== ³ ³ /_\ ³ ³ ³ ³ FB
gndÄÄ¿ ³ ³47uF ³ ³ ³ ³ ³ ³ ³ ³ __
gndÄÄÁÄÄÄÁÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÁÄÄÄÄÁÄÄÄÁÄÄÄÁÄÄÁÄÄÄÄÄÄÄÄÁÄÄÁÄÄÄÄ>- to gadget
~~
Typical values
No. R C D L Fuse
1 1 - 4R7 47uF 1N4001 1A
2 1 - 4k7 n47 - 1n 1N4001 5 turns
3 560 - 1k 220uF Zener 3 turns
4 560 - 1k 100uF
MODS
1/ Add an output zener just a bit higher than the no load voltage.
2/ Add input idiot & back EMF diode D2.
3a/ Add series L3 of a few turns on a 6mm ferrite bead feeding new C4.
3b/ Add ferrite beads on both output leads.
4/ Add series input L2, several turns on a 6mm ferrite bead.
5/ If L1 is bobbin, try a ferrite ring & listern to MW QRM for comparison.
6/ Change the fuse to one just higher than the maximum drain.
7/ Tin & wire up the 2nd plug ground earth spring.
After you have done these mods, & carefully put it back together, tested it
(not on your gadget at first!). If it is working OK, you should find the
adaptor is much safer than before on your precious gadget. And any nearby QRM
is much reduced, as is the possibility of malfunction, in an RFI environment.
Why don't U send an interesting bul?
73 de John G8MNY @ GB7CIP
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