400 Hot Springs Road, Carson City NV 89706 · (775) 883-0820 · Fax (775) 883-0827 · www.hytek.com · 1

HY5640

TEC Controller

Subminiature Controller for

Thermoelectric Coolers

The HY5640

is a subminiature temperature controller for

thermoelectric coolers (TEC). This device is intended for "heat
or cool" fixed temperature applications where front panel con-
trols and digital readouts are not required. The HY5640 uses
a thermistor bridge to precisely measure and regulate the
temperature of a device affixed to a TEC. With proper heat
sinking, the power stage of this device will deliver up to +/- 2
Amperes of current to a TEC. This controller was designed for
single power suppply operation down to +5V. In addition, the
device can be operated with dual supplies where V

can be as

low as +3V and V

as low as +5V.

Features:

Proportional/Integral (PI) control

Small size

Drive current to +/2 amps

Operation to 12 volts

Control above/below ambient

Temperature stability of 0.01°C

Single supply operation

Thru-hole or surface-mount packaging option

Maximum ratings:

Rating

Symbol

Value

Unit

Supply Voltage 1 (Voltage on Pin 8)

+20

Volts DC

Supply Voltage 2 (Voltage on Pin 10)

+12

Volts DC

Current Sink (Heat and Cool Cycle)

2.5

Amperes

Maximum Power Dissipation

MAX

Watts

Operating Temperature (Case)

MAX/MIN

100/20

°C

Storage Temperature

STG

65 to +150

°C

Figure 1

TEC

Controllers

Laser

Diode

Drivers

M
icro-heaters

2 · 400 Hot Springs Road, Carson City NV 89706 · (775) 883-0820 · Fax (775) 883-0827 · www.hytek.com

HY5640

TEC Controller

Temperature Set Resistor Rs (Pin 1 to Pin 7)

The temperature set resistor for the HY5640 controls the
temperature at which the TEC will operate. When the cir-
cuit has stabilized, the resistance of the thermistor will
be equal to that of the set resistor Rs. For example, if a
Dale 10k

thermistor is used as the temperature sens-

ing device, a set resistor of approximately 56K

will set

an operating temperature of 10°C. A graph of Rs vs. set
temperature is shown in figure 4 when using a Dale
1M1002 thermistor.

· Thermistor, R

(Pin 6 to Pin 7)

The thermistor should be located in close proximity to
the device being temperature controlled by the TEC. It
should be in good thermal contact to avoid stability prob-
lems.

The HY5640 has been designed for a negative tem-

perature coefficient thermistor. A thermistor with a posi-
tive temperature coefficient can also be used if the
position of the temperature set resistor and temperature
sensing resistor are changed. The same result can also
be achieved by reversing the leads of the TEC in which
case Rcc and R

must be interchanged.

· Gain Set Resistor, R

(Pin 5 to Pin 6)

The ratio of the gain set resistor R

to R

controls the

response time of the servo loop. A ratio that is too large
can cause slow response and a ratio that is too small
can cause loop instability. In most applications R

may

not be needed since a 10M

resistor is internal to the

HY5640 and generally provides enough gain for good op-
eration.

· Loop Stability Network, R

and C

(Pin 3 to Pin 5)

The R

time constant of these two components is a first

approximation of the thermal time constant of the servo
loop. The thermal time constant of the combination of the
device being cooled, the thermistor, and the TEC can be
approximated by applying constant power to the TEC
and measuring the length of time it takes to reach 66%
of its final temperature.

For example, if the thermal time constant was ob-

served to be 5 seconds, then a 1

F capacitor and a

4.7M

could be chosen as the loop stabilizing compo-

nents. Typical values for loop compensation components
are shown in Table 1.

Note:

The values of R

, R

, and C

are generally selected

by experiment. C

should be a low leakage

nonpolarized capacitor.

· Current Limit Resistors, Rcc & R

(Pin 1 to Pin 3, and Pin 1 to Pin 2)

These resistors limit the maximum current that the
HY5640 can supply to the TEC when in the cooling
cycle and in the heating cycle. Rcc limits the maximum
current for the cooling cycle and R

limits the maxi-

mum current in the heating cycle. This feature prevents
damage to the TEC during turn on. It is often desirable
to limit the maximum value of heating current as much
as 30% less than the maximum cooling current. This is
because TECs are much more efficient heating than
cooling. Figure 5 shows the approximate values for Rcc
and R

required to program a desired turn on current.

For example, an Rcc value of 17K

will limit the maxi-

mum cooling current to 1.5 Amperes and an R

value

of 13.5K

will limit the maximum heating current to 0.5

Amperes.

· V

(Pin 8 to Pins 11 & 12) +5 < V

< +20 Volts

This input supplies the voltage to the internal circuitry of
the HY5640. The maximum current drain at this terminal
is 5mA.

· Vs (Pin 10 to Pins 11 & 12) +3 < Vs < +12 Volts

This input supplies the voltage to the HY5640 power drive
circuitry. The maximum current drain at this terminal
should not exceed 2 Amperes. Note that V

and V

can

be driven with the same power supply in the range of +5V
< V

= V

<+12V.

Ideally V

is no more than 1.5V higher than the V

MAX

of the selected TEC. Setting V

higher than this can

cause excessive heating of the controller.

· Thermoelectric Cooler, TEC (Pin 9 to Pin 13)

The cooling lead of the TEC should be connected to Pin
9 and the heating lead should be connected to Pin 13 of
the HY5640. If the temperature of the thermistor is
greater than the set temperature at turn on, maximum
cooling current will flow into Pin 9 and out of Pin 13. Con-
versely, maximum heating current will flow into Pin 13
and out of Pin 9 if the temperature of the thermistor is
less than the set temperature at turn on. The maximum
turn on current is limited by Rcc and R

. Once the TEC

reaches its set temperature, the current through the TEC
will decrease to exactly the value required to maintain
the correct set temperature.

Description of the HY5640 Pin Outs

400 Hot Springs Road, Carson City NV 89706 · (775) 883-0820 · Fax (775) 883-0827 · www.hytek.com · 3

HY5640

TEC Controller

Figure 2 illustrates the characteristics of
the HY5640 power drive section. It also
illustrates the unsafe operating area
where the power dissipated in the device
exceeds the maximum 6 Watt rating.
This curve applies for both heating and
cooling operation.

Note that the resistance of the power
drive section is approximately one ohm
when the HY5640 is fully turned on.

Figure 3 illustrates the locus of operating
current and voltage for two different TECs.

Example 1:
A supply voltage of 5 Volts was chosen for
use with the ITI Ferro Tek Model
6300/018/018A TEC. This device is rated for
a maximum current of 1.8 Amperes at a
maximum allowable voltage of 2.7 Volts.
This is a load resistance of approximately
1.5 ohms. The intersection of the 1.5 ohm
load line and the HY5640 current source
characteristics defines the locus of operation
voltage and current for both the HY5640
and the TEC. In this application the current
was limited to 1.8 Amperes when cooling and
to 0.6 Amperes when heating by proper
selection of R

and R

Example 2:
A supply voltage of 12 Volts was chosen for
the Melcor FC 0.45-66-05 TEC. This device
has a maximum rated voltage of 7.98 Volts
at a current of 0.8 Amperes. A load line for
this device is also shown on the plot. Once
again maximum turn on current is set by
proper selection of R

and R

Note that the power dissipated in the HY5640
never exceeds the 6 Watt maximum
power dissipation in both of these examples.

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