Kangaroo pet - Circuit Description; Charger Base; AC to DC Conversion; Supply Voltage Output

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3.

circuit

description

charger

base

AC

to

DC

Conversion

Fuses

F1

and

F2

protect

the

user,

charging

base.

and

pump

in

case

of

a

short

circuit.

MOV1

and

MOV2

clamp

voltage

spikes

above

their

rated

voltages,

protecting

internal

circuits

from

large

voltage

spikes

present

on

the

AC

input.

Transformer

TX1

converts

the

115/230

VAC

input

to

approximately

17

VAC,

which

is

fed

into

diode

bridge

BR1.

BR1

is

a

full

wave

rectifier

that

converts

AC

to

pulsating

DC,

which

is

subsequently

filtered

by

electrolytic

capacitors

:C1

and

C2.

U1

is

a

switching

voltage

regulator

that

reduces

an

unregulated

DC

input

into

a

regulated

7.3

VDC

output.

Further

filtering

is

done

with

C3.

Supply

Voltage

Output

U2

further

regulates

the

output

of

U1

to

5

VDC;

this

output

is

then

filtered

by

C5

and

protected

by

diode

D2.

The

5.

VDC

is

terminated

at

pin

2

of

connector

J1A.

Charge

Current

Output

Current

regulator

U3

supplies

a

constant

85

mA

fo

a

load

connected

to

pin

1

of

connector

J1A.

This

is

used

by

the

pump

for

trickle

charging

the

internal

NiCd

batteries.

The

output

of

U3

is

filtered by

C6

and

protected

by

D3.

Current

regulator

U4

supplies

a

constant

255

mA

to

a

load

connected

to

pin

1

of

connector

J1A.

This

output

only

occurs

when

FET

Q1

is

turned

on.

The

output

of

U4

is

filtered

by

C7 and

protected

by

D4.

The

combined

outputs

of

U3

and U4

are

used

to

quick

charge

the

internal

NiCd

batteries

of

the

pump

with

a

combined

current

of

340

mA.

Quick

Charge

Control

The

pump

generates

a

TTL-level

signal

received

by

the

charger

base

at

pin

4

of

J1A.

If

no

pump

is

connected

to

the

charge

base

or

if

a

pump

is

connected

and

the

control

signal

is

high,

transistor

Q3

is

turned

off,

and

the

signal

at

U5B

pin

5

is

low.

This

low

causes

the

output

of

this

gate

at

pin

4

to

go high,

turning

on

FET

Q2.

This

in

turn

allows

drain

to

source

conduction,

allowing

current

to

flow

through

LD1 and

light

to

be

emitted.

This

state

will

last

as

long

as

the

charger

base

is

powered

and

no

pump

is

connected

or

the

control

signal

from

the

pump

is

high.

if

the

control

signal

from

the

pump

goes

low,

transistor

Q3

is

turned

on,

resulting

in

a

high

signal

at

USB

pin

5.

Because

USB

pin

6

will

normally

float

to

a

high

level

when

the

charger

base

is

powered,

the

combination

of

inputs

to

U5B

will

cause

the

gate

to

output

a

low signal.

The

low

output

turns

off

FET

Q2

and

blocks

current

flow

through

LD1,

extinguishing

the

light

output.

The

low

output

of

U5B

also

discharges

capacitor

C8

through

R8.

After

about

3

seconds,

the

signal

at

U5B

pin

6

will

be

low,

and

the

output

of

U5B

will

then

go high.

This

again

turns

on

Q2

and

allows

current

flow

through

LD1.

This

cycle

repeats

itself

as

long

as

the

charger

base

is

powered

and

the

control

signal

from

the

pump

is

low.

The

flashing

of

LD1

is

the

visual

indication

that

quick

charging

is

occurring.

USA

simply

inverts

the

output

of

G3.

When

O3

is

turned

on

by

a

low

input

from

the

pump,

the

input

of

USA

(pins

1

and

2)

is

high;

this

high

results

in

the

output

of

U5A

(pin

3)

going

low.

This

turns

on

FET

G1,

allowing

current

to

flow

from

the

output

of

regulator

U1

to

quick

charge

current

regulator

U4.

U4

is

then

able

to

supply

the

current

required

to

quick

charge

the

pump

batteries.

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