Heatsink overheating indicator. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Ham Radio Technologies
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Powerful transistors of most designs, say, laboratory power supplies, voltage converters, 3H amplifiers, are installed on heat sinks. Under severe operating conditions, transistor cases are heated to a temperature close to critical - 125...150°C. This increases the likelihood of their thermal and electrical breakdown. It can be prevented by controlling, for example, the temperature of the heat sink (it heats up to 80...100°C) using a sensor installed on it, since it is not always possible to place such a sensor directly on transistors.
One of the options for the indicator of heat sink overheating is shown in fig. one.
Germanium transistors are used as a temperature sensor - they are rigidly attached to the heat sink through thin insulating gaskets made of mica or fluoroplastic. Transistors are included in the power circuit of the light indicator - LED HL1. The current through the LED and transistors limits the resistor R2. The indicator is powered from the source of the controlled node through the parametric stabilizer R1VD1. The resistance of the resistor in kiloohms is calculated by the formula R1 \u10d (Un - 8) / 50. If the supply voltage reaches 0,5 V, the resistor must be at least 16 W. At a voltage of less than XNUMX V, it is permissible to exclude the stabilizer parts.
The LED begins to noticeably glow when the temperature of the transistor cases exceeds 70 ° C.
In another version of the indicator (Fig. 2), transistor VT2 is used as a temperature sensor.
On the transistor VT1, the LED current amplifier HL1 is made. Trimmer resistor R4 adjust the sensitivity of the device. Resistor R1 is calculated according to the above formula.
If the corresponding optocoupler or optoelectronic relay is connected in series with the LED in this indicator, it will be possible to automatically disconnect the controlled node from the power source in case of an emergency.
Indicator sensors can be any germanium transistors of the MP25, MP26, MP40, GT402, GT403 series. Instead of the KT361B transistor, any of the KT361, KT502, KT3107 series is suitable. In addition to the LED indicated in the diagram, KIPD21P-K can be used. Zener diode D814V is completely replaceable by D814B, D814G, D814D, KS510A. Trimmer resistor - any type with a resistance of 10 ... 15 kOhm, constant - MLT, S2-23.
Author: A.Butov, village of Kurba, Yaroslavl region
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