JPS596231Y2 - Defrost control circuit - Google Patents

Description

[Detailed description of the invention] This invention detects and compares the temperature of a heat exchanger using a refrigerant and the air temperature, determines the amount of frost formation based on the results, and performs defrosting control by the ON/OFF output of a relay. Regarding circuits.

A conventional control circuit of this type is shown in FIG.

In Fig. 1, 10 is an operational amplifier having input terminals on the (→ side and
) side input voltage<(-) side input voltage, it is set to be L level.

1, 4, 6 and 7 are voltage dividing resistors, 3 and 8 are thermistors, 5 is a semi-fixed resistor for adjustment, and 2 and 9 are thermistors 3 and 8 in order to obtain linearity of resistance change with respect to temperature. A voltage dividing circuit including the thermistor 3 is connected to the (1) side input terminal of the operational amplifier 10 with the thermistor 8
is connected to the (→ side input terminal of the operational amplifier 10).

26 is an output relay, 25 is its protection diode, 27
are transistors for driving the output relay 26, 22, 23
and 24 are voltage dividing resistors for setting the base voltage of the transistor 27, and the output terminal of the operational amplifier 10 is connected to the base of the transistor 27 via the protective diode 12, the resistor 17, and the voltage dividing resistor 23. .

14 is an IC timer; 15 and 16 are capacitors and resistors for setting the oscillation frequency; 18 and 19 are capacitors and resistors of a differentiating circuit for generating trigger pulses to the timer 14; 11 and 21 and 13 and 20 are:
The output side of the timer 14 is connected to the (1) side input terminal of the operational amplifier 10 via the protective diode 20 and the resistor 21, respectively.

Next, the operation will be explained.

The (g) input voltage of operational amplifier 10 is It is indicated by.

The resistance value R3 of the thermistor 3 is inversely proportional to the temperature.

Therefore, (g) the input voltage changes inversely proportional to the temperature.

Similarly, the (-) input voltage of the operational amplifier 10 is also shown as (
-) The input voltage also changes in inverse proportion to the temperature. If the detected temperatures of thermistors 3 and 8 are the same temperature, (g) Input voltage < (-) Set the constant of each resistance value so that the input voltage becomes Then, the output level of the operational amplifier 10 becomes L.

Therefore, since the base voltage of the transistor 27 is L, no current flows through the coil of the output relay 26.
The switch of output relay 26 is not ON.

Therefore, the defrost circuit is not turned on either.

Here, the thermistor 3 is used to detect the heat exchanger temperature, and the thermistor 8 is used to detect the air temperature.

In a heat exchange cycle, when a refrigerant transfers heat from air through a heat exchanger, the temperature of the heat exchanger decreases and frost forms on the heat exchanger.

As the frost builds up for a long time, the heat exchange efficiency decreases, so defrosting is necessary.

Frost formation is detected based on the difference between the air temperature and the heat exchanger temperature.

When the temperature of the thermistor 3 for detecting heat exchanger temperature decreases, the resistance value R3 of the thermistor 3 increases.

Therefore, the condition that (→input voltage>(-) input voltage) is satisfied.

However, the IC timer 14 waits until a certain period of time is reached.
Since the T terminal is at L level, (1) the input voltage does not go to H level.

When the IC timer 14 reaches a certain time, the OUT terminal becomes H.
When the input voltage reaches the level (1) input voltage>(-) input voltage, the output terminal of the operational amplifier 10 becomes H level.

Therefore, the base voltage of the transistor 27 becomes H level, and the transistor 27 is turned on, so that current flows through the coil of the output relay 26, and the switch of the output relay 26 is turned on.

Therefore, the defrost circuit is also turned on.

In the conventional defrost control circuit, if the IC timer 14 is malfunctioning and is at L level, if the thermistor 8 is disconnected, or if the IC timer has not reached the predetermined time, (1) of the operational amplifier 10 Since the input voltage was at L level, the defrost control circuit could not be turned on even if defrosting was desired.

The purpose of this invention is to eliminate the drawbacks of the conventional ones as described above and to provide a circuit that can forcibly turn on the defrost control circuit in any state that requires defrosting.

An embodiment of this invention is shown in FIG.

This invention is characterized in that a resistor 28, a capacitor 29, and a control switch 30 are added to the (-) input voltage terminal side of the operational amplifier 10.

The resistor 28 is a current limiting resistor, and the capacitor 29 is a noise absorbing capacitor.5 The control switch 30 is connected to ground only when the switch is pressed.When the control switch 30 is pressed and connected to ground, (→The input voltage becomes L level.

On the other hand, the control switch 31 is connected in parallel to the oscillation frequency setting resistor 16 of the IC timer 14.

When the control switch 31 on the timer side is pressed, the resistor 16 is short-circuited and the oscillation frequency becomes extremely high, and the OUT terminal voltage of the IC timer 14 drops from the L level within a few seconds.
Changes to H level.

When the control switches 30 and 31 are pressed in synchronization, the (1) input voltage of the operational amplifier 10 becomes H level, and (
-) Since the input voltage is at L level, the operational amplifier 10
The output level of is H.

Therefore, the base voltage of the transistor 27 becomes H, so the transistor 27 is turned on, and the coil current flows through the output relay 26, so that the defrost control circuit is turned on.
do.

Note that the control switch 30 is connected to (1) of the operational amplifier 10.
It may be connected in parallel with the resistor 1 on the input voltage side.

Also, switches 30 and 31 do not have to be synchronized.

Furthermore, the control switch may be a push button type or a switch for other functions.

As described above, according to this invention, by providing the operational amplifier 10 and the timer 14 with the control switches 30 and 31, it is possible to forcibly start defrosting by controlling the switches under arbitrary conditions. be.

[Brief explanation of the drawing]

FIG. 1 shows a conventional control circuit, and FIG. 2 shows a control circuit according to an embodiment of this invention. In the figure, 3 and 8 are thermistors, 10 is an operational amplifier, 14 is an IC timer, 26 is an output relay, 30, 31
is a control switch. Note that the same reference numerals in the figures indicate the same corresponding parts.

Claims (1)

[Scope of utility model registration request] Thermistor 3 for detecting the heat exchanger temperature and thermistor 8 for detecting the air temperature are operated manually by a defrosting circuit operated by an operational amplifier, and a timer for restraining the defrosting circuit for a predetermined period of time after the defrosting of the defrosting circuit is completed. 1. A defrost control circuit comprising: a control switch for forcing the operational amplifier and the timer to defrost.