Download Preliminary Specifications

Preliminary Specifications
DynaOhm - Model D619
FEATURES:
●Constant
current over a wide voltage range
●Can be connected as a two-terminal device
●Easy to use
●Inexpensive
●On/off control and strobe capability
●Wide range of user options
●Small size - SOT23-6 package
1
6
2
5
3
4
PINS 1&4 - IB/EN (TIE TOGETHER
PIN 2 - GROUND
PIN3 - LED ANODE
PINS5&6 - VS (TIE TOGETHER)
The DynaOhm, D619, is an active device which functions as a dynamic resistor,
changing its value to maintain a constant current flow. Unlike a fixed resistor
which will provide the proper current at a single voltage, the DynaOhm will
maintain a fixed current over a wide voltage range.
Designed primarily for use with low current LEDs (5mm, 30 mA) where the
expense and size of a switching regulator cannot be justified, the DynaOhm can
also be used to drive some of the new high power LEDs.
An additional feature is the ability of the DynaOhm to provide on/off control and
strobing using a standard logic level input.
LEDdynamics also offers a pcb, Model 04006, measuring 0.2 inches x 0.32
inches which will accommodate the D619 configured in accordance with many of
the applications shown. The D619 maybe ordered separately, mounted on the
pcb alone, or with the pcb fully populated to meet your operating requirements.
Absolute Maximum Ratings
Parameter
Symbol
Limit
Unit
Input Voltage
Bias Current
Power Dissipation (a)
Linear Derating(b)
Temp. Range, Operating
Temp. Range, Storage
50
200
0.9 @ 25oC
7.2
-50 to +85
-50 t0 +150
Vdc
mA
W
mW/oC
o
C
o
C
VIN
IB
PD
TO
TS
(a) D619 mounted to D619B pcb
(b) The D619 compensates for this derating by decreasing the output current at
elevated temperatures.
Operating Characteristics
The following symbols are used throughout this section and the Applications
Notes. All characteristic curves are based on the circuit shown in the Test Circuit
below.
Parameter
Symbol
Units
Input Voltage (nominal)
Input Voltage (minimum)
Input Voltage (maximum)
LED Current
LED Forward Voltage Drop
Sense Voltage
Bias Current
Bias Resistor
Sense Resistor
Shunt Resistor*
Bias Resistor Power Rating
Sense Resistor Power Rating
Shunt Resistor Power Rating
VIN
VMIN
VMAX
ILED
VLED
VS
IB
RB
RS
RH
W RB
W RS
W RH
Vdc
Vdc
Vdc
mA
Vdc
Vdc
mA
Ohms
Ohms
Ohms
Watts
Watts
Watts
V IN
W H IT E L E D
5 MM
RB
3
LED ANO DE
1
4
IB /E N
VS
IB /E N
VS
6
5
GND
2
Test Circuit
Rs
ILED = 25 mA
VMIN = 6 Vdc
RS = 22 ohm
RB = 10 kohm
VLED = 3.5 Vdc
Graph 1 shows a comparison of ILED vs VIN for the DynaOhm and a fixed 100 ohm
resistor. Note that above 9 Vdc in, with the fixed resistor the LED will be driven
at higher than its maximum rated current.
40
35
30
25
OUTPUT
CURRENT 20
mA
15
Dynaohm
100 Ohm
10
5
0
0
2
4
6
8
10
12
INPUT VOLTS VDC
14
18
20
Graph 1
Graph 2 shows the current decrease with operating temperature to maintain a
safe level of power dissipation of the D619
25
20
15
OUTPUT
CURRENT 10
mA
Current
5
0
20
25
30 35
40
45 50 55 60 65
TEMPERATURE oC
70 75 80 85
Graph 2
Application Notes
The D619 is capable of being configured to drive a wide variety of LED types and
arrays at appropriate current levels. The following are typical examples of how
the D619 may be used. Note that pins 1and 4 must be tied together externally
as shown. Likewise pins 5 and 6 must be tied together externally.
For all configurations shown in the following applications, the minimum operating
voltage can be calculated from:
Eq. 1
Minimum VIN = VLED + VS + 0.75
Where multiple LEDs are connected in a series string, VLED would equal the sum
of the individual values of VLED.
Figure 1 shows the most common configuration of the D619 - driving a single 5
mm LED with a constant current. This circuit can be used for indicator lights with
a VIN ranging from 5 to 24 Vdc.
V IN
W H IT E L E D
5 MM
RB
3
LED ANO DE
1
4
IB /E N
VS
IB /E N
VS
6
5
GND
2
Rs
Figure 1
RS is selected by the relationship:
Eq. 2
RS = 0.55/ILED
where ILED is the current at 25 oC.
The minimum power rating for RS would be:
Eq. 3
W RS = 0.55 X ILED
RB is given by:
Eq. 4
RB = (VMIN X 100)/ILED
As an example, if VMIN is 6 Vdc and an ILED of 25 mA is chosen, RS will be 22
ohms and RB will be 10Kohms. This value of RB will provide sufficient drive at 6
volts in and will be well below the maximum IB at 24 volts in.
Figure 2 shows the D619 driving several LEDs in series. The values for RB and
RS are calculated from Eqs. 2, 3, and 4 above. When driving series strings,
check that the Minimum VIN meets the conditions of Eq. 1.
V IN
V IN
W H IT E L E D S
5 MM
W H IT E L E D S
5 MM
RB
RB
3
3
LED ANO DE
1
4
LED ANO DE
IB /E N
VS
IB /E N
VS
6
1
5
4
G ND
2
IB /E N
VS
IB /E N
VS
6
5
GND
Rs
Figure 2
2
Rs
Figure 3
Figure 3 shows the D619 driving two 5 mm LEDs connected in parallel. In this
case, ILED would be the sum of the currents through each of the LEDs. For
example, if each LED were driven at 25 mA, ILED would be 50 mA and the values
for RB and RS, given a 6 Vdc value for VIN would be:
RS = 11 ohms
RB = 5 kohms
Figure 4 shows an array of four 5 mm LEDs being driven. Again, ILED is the sum
of the currents in each LED string. Calculate RB and RS as above.
Figure 5 illustrates connection of the D619 as a two terminal device. This
configuration requires a slightly higher value of VIN in order for current regulation
to occur. In this case, RS would be calculated per Eq. 2. RB, however would now
be:
Eq. 5
RB = (VMIN - VLED X 100)/ILED
V IN
V IN
W H IT E L E D S
5 MM
W H IT E L E D
5 MM
RB
RB
3
3
LED ANO DE
LED ANO DE
1
4
IB /E N
VS
IB /E N
VS
6
1
5
4
IB /E N
VS
IB /E N
VS
6
5
GND
GND
Rs
2
Rs
2
Figure 4
Figure 5
Where remote on/off control or strobing is desired, the D619 can be connected
as shown on Figure 6. RS would be calculated as above. The value of the
strobe or on/off voltage, typically 5 V for a standard TTL logic signal, would be
substituted for VMIN in Eq. 4.
V IN
V IN
O N /O F F
STRO BE
W H IT E L E D
5 MM
W H IT E L E D
5 MM
RB
RB
3
3
LED ANO DE
1
4
IB /E N
VS
IB /E N
VS
6
1
5
4
Figure 6
IB /E N
VS
IB /E N
VS
6
5
GND
GND
2
RH
LED ANO DE
Rs
2
Figure 7
Rs
Figure 7 illustrates how a high current, high power LED may be driven by the
D619. Use of resistor RH reduces the dissipation in the D619. It is used for high
current LED applications as shown, or where several parallel strings of 5 mm
LEDs are to be driven. The value of RH is obtained from:
Eq. 6
RH = (VMAX - VLED)/ILED
The minimum power rating for RH is:
Eq. 7
W RH = ILED2 X RH
Accessories
To make the use of the D619 easier, LEDdynamics offers the D619B printed
circuit board. On the front side, it will accommodate the D619 i.c. as well as RS
and RB. The patterns for the resistors are sized so the RB may be either a
standard 0603 or 0805 surface mount resistor, and RS may be either an 0805 0r
1206 surface mount device. Two additional pads are provide on the rear for RH
which may be either an 0805 or 1206 device.