Maplin auto electronics projects P8

Maplin auto electronics projects

T C w i r e

Figure 8.13 Extending leadouts of axial resistors

2 x 2 / 2 t u r n s o f 1 6 S W G

E C w i r e w o u n d b i f i l a r

o n F X 4 - 0 5 4 t o r r o i d

S m e a r s i l i c o n

r u b b e r s e a l a n t

o v e r w i r e s a n d

t o r r o i d t o h o l d

i n p l a c e

R e m o v e e n a m e l f r o m

w i r e e n d s u s i n g

e m e r y p a p e r t o

f a c i l i t a t e s o l d e r i n g

Figure 8.14 Li winding information

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Photo 8.3 Close-up of the toroid inductor fitted into the PCB

Next insert the power relay

Insert the large SMPS e l e c t r o l y t i c c a p a c i t o r s , ensuring that the c o r r e c t voltage rating c a p a c i t o r s are fitted in

t h e c o r r e c t l o c a t i o n s and are c o r r e c t l y o r i e n t a t e d as previously d e s c r i b e d

Referring to Figure 8.15 wind t h e t r a n s f o r m e r , this is

p r o b a b l y the most difficult part of the c o n s t r u c t i o n pro-cedure and should not be rushed Note that the diagrams

do not figuratively show the required number of turns per layer When winding t h e transformer take c a r e not

to o v e r s t r e s s t h e b o b b i n o t h e r w i s e pins may b r e a k

1 7 3

r Q^

t En

Star

Photo 8.4 The component parts of the ferrite transformer

Cover e a c h layer with a single layer of masking tape Starting at pins 13 and 11, wind bifilar two 9 turn windings

of 1 8 S W G EC wire first, finish at pins 3 and 5 r e s p e c -tively, as shown in Figure 8 1 5 ( a )

S t a r t i n g at pins 16 and 15, wind bifilar two 26 turn windings of 20 SWG EC wire in two l a y e r s ; first wind bifilar 13 turns, as in Figure 8 1 5 ( b ) Wind bifilar a fur-ther 13 turns and finish at pins 10 and 9 respectively, as

in Figure 8 1 5 ( c ) , note the wires c r o s s over Check for continuity between pins 16 and 10, and 15 and 9

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off — use pliers to carefully bend the wire around the pins It will be n e c e s s a r y to r e m o v e t h e enamel coating from the wire to allow soldering, e m e r y paper is ideal for this P h o t o 8.4 shows an exploded view of t h e com-ponent parts of the transformer

Starting at pins 1 and 2, wind bifilar two 15 turn windings

of 20 SWG EC wire in two layers; first wind bifilar 13 turns,

as shown in Figure 8 1 5 ( d ) Wind bifilar a further 2 turns and finish at pins 7 and 8 r e s p e c t i v e l y , as in Figure

8 1 5 ( e ) , note the wires c r o s s over Check for continuity between pins 1 and 7, and 2 and 8

Solder all of the leadouts to the transformer bobbin pins, fit the c o r e s and clip into place the sprung steel c o r e

r e t a i n e r s

Insert the transformer into the PCB, ensuring that pin 1 aligns with the number 1 on the PCB

Referring to Figure 8.11 and using the 32/0.2 power

con-nection wire, link Wnumber holes; W l to W l , W2 to W2,

W3 to W3

Finally tin the e x p o s e d lengths of PCB t r a c k s with a thick

layer of solder Take c a r e not to splash solder e l s e w h e r e which may c a u s e s h o r t c i r c u i t s

Double-check your work and remove e x c e s s flux from the underside of the PCB using PCB c l e a n e r Photo 8.5 shows the a s s e m b l e d PCB

Connect the two LEDs to the PCB via lengths of insulated wire as shown in Figures 8.11 and 8.16

Testing

Figure 8.11 shows the location of the input and output

c o n n e c t i o n s referred to in this s e c t i o n

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Photo 8.5 The assembled PCB

Fit ICI, IC2 and the fuses

Using a multimeter on a suitable r e s i s t a n c e range, meas-ure the r e s i s t a n c e between FS7 and P2, the r e s i s t a n c e

should be greater than 2 kQ Check also the r e s i s t a n c e

between FS2 and P2, the r e s i s t a n c e should be greater

than 2 kQ If significantly lower readings than stated are

measured, r e c h e c k all of your work as t h e r e is likely to

be a short circuit or a misplaced c o m p o n e n t

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F l a t o n p a c k a g e

S h o r t l e a d

C a t h o d e A n o d e

C P 3 2 H e a t - s h r i n k

s l e e v i n g

\

S l i d e o v e r c o n n e c t i o n s

a n d s h r i n k

R e s i s t o r

T w i s t a n d s o l d e r Λ

c o n n e c t i o n s

C a t h o d e

A n o d e

Figure 8.16 LED leadout identification and connections

Connect a 12 V supply c a p a b l e of delivering 5 A to the input pins PI (+V) and P2 (0 V ) via a 5 A fuse (for F S 1 ) and a multimeter on 5 A or higher range T h e q u i e s c e n t current should be less than 1 mA

Link P3 and PI with light duty wire, whereupon the relay should e n e r g i s e and the power-on LED (LD1) should illu-minate T h e current indicated on the m e t e r should be

a p p r o x i m a t e l y 4 0 0 mA If an o s c i l l o s c o p e a n d / o r

fre-q u e n c y c o u n t e r are available, then t h e s e may be used to confirm that a 50 kHz ( a p p r o x i m a t e l y ) s a w t o o t h wave-form is available on P24 Avoid undue c a p a c i t i v e loading

o t h e r w i s e the frequency of t h e o s c i l l a t o r will b e shifted

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Unlink P3 and P I , d i s c o n n e c t the supply and d i s c o n n e c t the multimeter

R e c o n n e c t the supply and relink P3 and P I Measure the voltage on the output pins, using a suitable voltage range P4 to P7 should read +30 V with r e s p e c t to P8 Pins P12

to P15 should read - 3 0 V with r e s p e c t to P8 P16 should read +12 V with r e s p e c t to P17 and P 1 8 s h o u l d read

- 1 2 V with r e s p e c t to P17

T h e thermal shutdown circuit may be t e s t e d by carefully

h e a t i n g t h e t h e r m i s t o r with a h a i r d r y e r W h e n t h e

t h e r m i s t o r r e a c h e s a t e m p e r a t u r e of approximately 80°C the thermal shutdown LED (LD2) will illuminate and the power supply will shutdown, this can be confirmed by measuring one of the supply voltage outputs When the

t h e r m i s t o r t e m p e r a t u r e drops to approximately 60°C the power supply will r e s t a r t and the thermal shutdown LED will extinguish

This c o m p l e t e s testing of the power supply

As previously stated, the power supply is specifically intended for use with two Maplin 50 W bipolar power amplifiers In most applications the audio output power attainable from t h e s e amplifiers when used in c o n j u n c

-t i o n wi-th -t h i s p o w e r s u p p l y s h o u l d b e m o r e -t h a n sufficient for in-car use However the purist may wish to use s e p a r a t e power supplies for e a c h amplifier to

in-c r e a s e the power available per in-c h a n n e l Similarly, if a single c h a n n e l subwoofer amplifier is required, a single amplifier may be driven from one power supply

It is strongly r e c o m m e n d e d that the power supply is fully

c a s e d and provided with an additional external heatsink, type 2E is suggested Metal c a s e s are ideal for this

pur-1 8 0

pose, and also provide a degree of shielding against ra-diated radio frequency e m i s s i o n s T h e audio amplifiers may also be housed in the s a m e c a s e , which could be

c o n v e n i e n t l y mounted in t h e c a r b o o t or under a seat

T h e audio amplifiers should also be heatsinked, again type 2E is suggested

To c o n n e c t the 50 W bipolar amplifiers to the power sup-ply, t r e a t t h e s w i t c h e d - m o d e p o w e r s u p p l y a s a conventional power supply (as shown in the amplifier

c o n s t r u c t i o n a l d e t a i l s ) and c o n n e c t a c c o r d i n g l y (HT1 and HT2 are positive, HT3 and HT4 are negative) Refer

to Figure 8.11 for c o n n e c t i o n s to the power supply T h e amplifier set-up p r o c e d u r e s should be followed in the

s a m e way as for the conventional power supply Connec-tions from the power supply to the amplifiers should be made using 32/0.2 wire

Take note — Take note — Take note — Take note Loudspeakers should be suitably rated for high power use Beware — many car loudspeakers are given misleadingly high power ratings, so try and find out what the true r.m.s ratings are before you use any loudspeaker Often car loud-speaker ratings are given in peak power or total peak power, so be prepared to divide the rating

by 1.414 or even 2.828! Loudspeaker wiring should also be sufficiently rated for the pur-pose

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Connections from the power supply to the car electrical system should be made using very heavy duty cable It

is advisable to c o n n e c t the power supply directly to the car battery via its own in-line fuse at the car battery end Assuming a negative earth car, the c h a s s i s may be used

to provide the 0 V c o n n e c t i o n , which saves on wire

Take note — Take note - Take note - Take note

It should be pointed out that excessive sound pressure levels may lead to long term, irrevers-ible hearing problems · High levels of sound may also blot out other external sounds, which could

be dangerous when on the move · Please use common sense when using a high power in-car entertain-ment system

Input:

Input current (P 0 = 116 W ) :

Output power:

Outputs

Main:

Auxiliary:

Continuous output current

±30 V

±12 V

Efficiency:

Thermal shut-down temperature:

Thermal shut-down hysteresis:

Standby input:

Remote switch-on input:

Thermal shut-down output:

Input noise ( P 0 = 120 W ) :

Output noise ( P 0 = 120 W )

Main:

Auxiliary:

Switching frequency:

Converter mode:

11 to 15 V d.o, nominally 13.8 V 10.7 A (V s = 11.3 V)

120 W continuous, see note below

±30 V

±12 V

2 + 2 A

50 mA + 50 mA

>90%

80°C 20°C Active low Active high Active low

140 mV

60 mV

40 mV

25 kHz Push-pull Table 8.1 Specification of Prototype

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Car audio switched-mode PSU parts list

Resistors — All 0.6 W 1% metal film (unless specified)

R13,17,22,

23,26,27,

R 1 4 , 1 9 , 2 1 ,

R16,20,

Capacitors

C l , 5 , 1 5 ,

16,25,26,

28,30 100 nF p o l y e s t e r

C2.13.14 220 μ Ρ 5 0 ν 8 Μ Ρ δ

C3,4,l 1,12 1000 μΡ 50 V SMPS

C6.31 2n2F 1% p o l y s t y r e n e

C7,8,9,10,17,

18,19,20 560 pF c e r a m i c

8

3

4

2

(BX76H) ( J L 5 1 F ) ( J L 5 7 M ) ( B X 6 0 Q )

8 (WX65V)

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C21.22 1000 μΡ 25 V SMPS 2

D3.4.13,

14,15,16,

D9.10,

TR6,7,8,

Miscellaneous

( J L 5 6 L ) (WW69A) (FF11M) (FF06G) (WW68Y) ( B X 2 9 G ) (QL73Q)

( Q L 8 0 B ) (UK63T)

(UK65V) (QF67X) ( Q B 6 8 Y ) (UJ33L)

(QQ18U) (WL27E) (QL32K) (WQ93B) (RA85G) (QY09K)

( J R 8 4 F ) (HW06G) ( J R 8 1 C ) ( J R 8 2 D ) ( J R 8 3 E ) (YX99H)

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FSl

FS2.7

FS3,4,5,6

174·η c h a s s i s fuse holder 1 (RX50E)

0.9 mm 20 SWG TC wire 1 ( B L 1 3 P )

1.25 mm 18 SWG EC wire 1 (BL25C) 0.71 mm 22 SWG EC wire 1 ( B L 2 7 E )

All of t h e a b o v e are available as a kit

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Optional (not in kit)

car fuse holder

HC wire b l a c k

HC wire red 32/0.2 wire red 32/0.2 wire b l a c k 32/0.2 wire blue zip wire

50 W power amp 2E heatsink

1 (RX51F)

1 (UK13P)

as r e q ( X R 5 7 M )

as req ( X R 5 9 P )

as req ( X R 3 6 P )

as req (XR32K)

as req (XR33L)

as req (XR39N)

2 (LW35Q)

2 (HQ70M)

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