Advertisement
The output capacitors are included to give some protection
against low impedance loads at low frequencies, and to ensure that
a n y s l i g h t D C i m b a l a n c e d o e s n o t c a u s e c u r r e n t t h r o u g h t h e
speaker. Note that if the bridge's gain is to be increased, only the
gain of the first 260 should be altered.
DB 9.2.3 Full bridge mounting
Fig D89.2.3 shows how two Z60s are mounted on one heatsink
block, with a
'floating
earth point' between them. Wires go from
this point to power supply, chassis, preamp, etc. lf two bridges
are used with a common power supply, the inset earthing is best.
T e r m i n a l s 1 - 1 , 2 - 2 , 3 - 3 a r e c o n n e c t e d w i t h o n e w i r e f r o m e a c h p a i r t o
the common earth point for all four amplifiers.
D89.4. DC Amplifier
This application is not suggested for the less experienced con-
structor.
DB 9.4.1 DC amplifier
The figure shows the basic connections for using the 260 as a dc
amplifier. Note that a split power supply voltage is used. This supply
must be symmetrical but can varv between 5-0-5 and 25-0-25.
However, use at high voltages can result in excessive current if the
load is of low resistance and this could destroy the amplifier
R 1 a n d R 3 , D 1 a n d D 2 a n d R V 1 a r e i n c l u d e d a s a ' s e t z e r o ' c i r c u i t
to adjust the zero voltage level on the output. The setting will be
somewhat dependant upon the source impedance connected be-
t w e e n t e r m i n a l s 5 S 6 .
Inputs
Fig. DB9.4.2. a & b show two input circuits -
a is a virtual earth
inverting mode input and the gain will be approximately
'
Zf)
100K
R 4 .
b is a non-inverting input, which should be used from a low source
impedance to minimise offset voltaEe. R5 (2K7) can be added if
necessarv.
D89.4.2 a + binputcircuits
Absolute maximum ratings Assuming the amplifier is well heat-
sinked, so that the transistor case temperature does not rise above
50 C, the transistor maximum dissipation is 50w. This heatsinking
will be difficult in practice because of thermal resistance from case
through transistor insulating mica and heat fin to the heatsink
proper, so the specifications are for guidance only and are not
c o n t i n u o u s m a x i m a .
Supply voltage maximum 23-0-23v.
L o a d c u r r e n t m a x i m u m 4 4 .
Load resistance maximum must alwavs be less than
Vs2 and Vs, which ever is the smaller.
200
6
Thus
with a 23v supply, Vs2 gives 2.6 and Vs gives 3.8.
200
6
I n p r a c t i c e l o a d i m p e d a n c e s h o u l d b e g r e a t e r t h a n 4 O
Inductive loads lf the load is highly reactive a series resistor is
n e c e s s a r y . W i t h m o t o r s u s i n g b r u s h e s a v e r y ' s p i k y ' b a c k E M F i s
given and the circuit below is suggested.
l o u
25V
Reversible
DB 9.4.3 Motor drive circuit
E Power Supplies
E4
Specif ications
The power supply chosen will determine the power output obtained
from the whole system so that, it a PZ5 is chosen, this will limit the
output to around 12w total output into 40.
With the PZ6 the output will be 25w total into SQor 4O(e.9. 12w +
1 2 w i n t o 8 0 , 1 1 w * 1 1 w i n t o 4 O b u t a b o u t 2 0 w i n t o 4 O w i t h o n l v
o n e c h a n n e l d r i v e n ) .
Advertisement
